Anesthesia Final
How can you help?
1. Stay calm & alert DVM(s) 2. Stop any drugs & start compressions 3. Intubate trachea 4. Fluid bolus if needed 5. Appropriate PPV (watch clock) 6. Attach monitoring devices (ECG, ETCO2) 7. Start recording (time, values, drug doses) 8. 1st drug (outside reversal) usually vasopressor 9. Switch compressor q2 min: check ECG & pulse ±administer drug (≤10 sec)
Doxapram
"Analeptic" respiratory stimulant -promotes normal healthy activity of the respiratory system Respiratory "stimulant" -Increases myocardial and cerebral oxygen demand-> leads to higher mortality rate -Based on human literature no longer recommended -If must used - make sure first breath is with 100% oxygen
Other pre-anesthetic drugs to remember
"Chill protocol" (Costa et al. 2019 -Clinician's brief -May 2019): drugs owner will give to their animal at home prior to hospital visit • Gabapentin PO • Melatonin PO • AcepromazineOTM Oral pre-medication • Gabapentin- sedation, analgesia • Trazodone-sedation
AAHA/AAFP pain management guidelines 2015
"Due to their safety and significant benefit, local anesthetics (LA) should be used with every surgical procedure" The least used class of analgesics in small animal practice Only drug that completely blocks pain -cheap -cheap for you, cheap for client
"Propoflo"- "Rapinovet"- "Propoflo28"-
"Propoflo" • no preservative -discard unused at end of day "Rapinovet" • no preservative -discard unused at end of day "Propoflo28"- Abbott • Open bottle is OK for 28 days if using sterile technique • Contains benzyl alcohol • CRI & repeated dosing > 6hrs may cause adverse effects due to benzyl alcohol
Pain
'is an aversive sensory and emotional experience representing an awareness by the animal of damage or threat to the integrity of its tissues; it changed the animal's physiology and behaviour to reduce or avoid damage, to reduce the likelihood of recurrence, and the to promote recovery' - Molony and Kent (1997) Conscious experience of nociception Example: A patient is under general anesthesia and are mentally unresponsive. You make a skin incision and there is a physiologic reaction (increased heart rate, respiratory rate and blood pressure) Are they experiencing pain or nociception?
Stages of GA- 3
(3-4 planes) Light Eye position- central Palpebral reflex- + Jaw tone- ++++ Corneal reflex- reduced Nystagmus- ++ Medium Eye position- ventro-medial Palpebral reflex- reduced/absent Jaw tone- reduced/minimal Corneal reflex- reduced Nystagmus- N/A Deep Eye position- central Palpebral reflex- absent (horses may still have reflex) Jaw tone- lost Corneal reflex- reduced Nystagmus- +
Drugs that modulate spinal pathways
(inhibit central sensitization) Local anesthetics Opioids or a2 agonists NSAIDs NMDA antagonists (ketamine) Tricyclic antidepressants Anticonvulsants
Drugs that Inhibit Transmission
(inhibit impulse conduction) Local anesthetics a2 agonists
Drugs that inhibit transduction
(inhibit peripheral sensitization of nociceptors) NSAIDs Opioids Local anesthetics Corticosteroids
Infra-orbital NB Technique
- Palpate foramen - Insert needle to engage into the foramen itself (as ventral as possible) -Draw back -Inject LA (if no blood seen) *Use firm pressure over foramen after withdrawing needle to keep local in the canal
Toxic dose (TD50)
- dose necessary to induce toxic effects to 50% of animals it is administered to
What to ask yourself when selecting a dose:
- what effect do I need and what side effect can I tolerate? Some of this knowledge will come with experience If you are working with something unfamiliar and there is a large dose range, try low doses at first - you can always top up Go to the literature and look up what doses were used for certain cases
One lung intubation
-Chest radiography of a Gorilla under anesthesia -Cervical region: presence of an ET tube -Thoracic region: right lung well ventilated; left lung collapsed -ET tube is positioned passing the tracheal carina - NOT ideal
Why use a Pre-medication?
-Decrease stress, anxiety, fear-aggression -Facilitate catheter placement "chemical restraint" -Reduce induction dose, reduce inhalant required-> "balanced anesthesia" (small doses of different drugs for less side effects) -Improve recovery-> reduce excitement, provide analgesia -Provide analgesia
How do I confirm ET intubation?
-Direct auscultation of the ET tube during expiration -Visualization of condensation inside the ET tube during expiration -Fogging of class in front of the ET tube -BEST PRACTICE: Capnography (AKA: Capnometry, ETCO2, End- Tidal CO2) capngraph calculates the amount of CO2
Cholinergic receptors- Nicotinic
-Ion channel linked receptors -Ganglia (presynaptic neuron) of sympathetic and parasympathetic nervous systems -Adrenal medulla (norepi and epi) -Skeletal muscle (neuromuscular junction) -->Important is using neuromuscular blocking agents -Excitatory
Brachycephlalic extubation
-Keep ET tube in as long as possible -Have a laryngoscope available -Have anesthesia induction agent available -Have an ET tube available -Do not hesitate - reintubate if necessary If reintubation is necessary (obstructed airway) Plan B -Mannitol -Dexamethasone -Time -Sedatives
Monitoring a patient under sedation or general anesthesia includes:
-Keep track of vital parameters -Know if any unexpected or life-threatening changes happen or even be able to anticipate any complications -Act promptly to keep patient safe
Why is it Imperative to keep an anesthetic record?
-Legal document -use black or blue pen, don't make a mess -Protects staff, institution and/or practice
Agonist/antagonist- Butorphanol -useful for: -Not useful for:
-Mu antagonist (mu= increased threshold of nocciceptive neurons and decreased APs) -Kappa agonist (Sedation and analgesia) -Sedation, cough suppression, mild analgesia IM, IV, SC Lasts for approximately 1h; 45min in horses Useful for: Moderate sedation Partial reversal of pure agonists Not useful for: Painful procedures (unless very minimal pain)
Cuff inflation
-Mucosal capillary pressure is about 30 cm H2O (higher than 30 capillary bed will collapse) -Ideal intra cuff pressure is 20 cmH2O -Watch video regarding correct tube inflation technique to assure a seal against aspiration pneumonia and prevent over pressurization of tracheal mucosa and possible tracheal necrosis
Physiologic response is dependent on:
-Neurotransmitter (excitatory vs inhibitory) -Receptor type (Ionotropic vs metabotropic) -Class of receptor -Opioid, NMDA, GABA -Receptor location (brain, blood vessels) -species
Setting up a fluid bolus
-Press 'Run/Hold' to pause infusion -Press 'Select' until VTBI is highlighted and visible on the display screen Use the 'Up/Down' arrow buttons to adjust volume to 60mL Press 'Select' until Rate is highlighted and visible on the display screen -Use the 'Up/Down' arrow buttons to adjust rate to 360 mL/hr Press 'Select' until Time is highlighted and visible on the display screen - this should read 10 (minutes) if you have done your calculations correctly *Note - you cannot set the time to 10 minutes expecting it to calculate the rate. This will not work! *If you have a large dog and the rate is set to 999mL/hr which is lower than calculated to deliver the bolus in 10 minutes - it will display the amount of time to deliver the volume -Press 'Run/Hold' to start the fluid bolus -Once the fluid bolus has finished the pump will beep -Press 'Run/Hold' to pause infusion Using the original set up instructions, reset the pump to the VTBI and rate for the patient -Do NOT clear VI at any time during anesthesia, this is only to be cleared at the beginning
Inhibitory Neurotranmitters
-Prevents an action potential -Norepinephrine and epinephrine --> Sympathetic nervous system -γ-aminobutyric acid (GABA) - spinal cord, CNS (depression) -Glycine - spinal cord -Serotonin -Dopamine Usually propagate
Excitatory Neurotransmitters
-Promotes an action potential and progresses the signal -Acetylcholine (Ach) - peripheral nervous system -Glutamate - CNS - NMDA receptor -Norepinephrine and epinephrine -->Sympathetic nervous system -Substance P - NK 1 receptor -Dopamine Usually block
Goals of oxygen supplementation and airway management Examples:
-Protecting airway against aspiration of gastric contents (aspiration pneumonia) -Provide high FiO2 (>21%) to improve oxygen delivery Examples: -Anything causing hypoxemia (PaO2<60 mm Hg) -Respiratory distress -Anemia -Hemorrhage -Cardiac disease -Respiratory disease (diffusion abnormalities, V/Q mismatch & hypoventilation) -General anesthesia
Rabbit Intubation
-Two people, hold back and head -Head and nose in a straight line -small airway -mouth does not open widely -layrnx is not visible -mandible with restricted mobility -long incisors
What do we need for cardiac output and blood pressure to be maintained?
-volume (fill the heart) -vessels with an appropriate amount of tone -normal electrical impulse conduction (to contract) -adequate heart rate -contraction of the heart
Prolonged recovery morbidity data-
0.14-0.18% dogs and cats
Regurgitation morbidity data-
0.42 - 0.74% (previously 16-60%) very serious- can lead to aspiration pneumonia
Bradycardia morbidity data-
0.62% dogs and 0.14% cats
Calculate the milliliters (mL) needed for the following dose: Dog 9.7 kg Drug: Buprenorphine 0.3 mg/ml Dose: 20 mcg/kg
0.65
What physical exam status (or American Society of Anesthesiologist) would you classify a 6 month old cat presenting to the clinic for an ovariohysterectomy?
1
Local anesthetic drugs can be used:
1) Topically (i.e. EMLA cream -lidocaine/prilocaine) 2) Injection in the vicinity of peripheral nerve endings or major nerve trunks 3) Instillation within the epidural or subarachnoid spaces 4) Intravenousinfusions for acute pain management (lidocaine)
Anesthesia machines - basic components
1- Compressed Gas Sources (oxygen tank) 2- Pressure Regulators (for compressed gas) Oxygen will go through either: 3a- Flowmeters (Oxygen sent to vaporizer and then to fresh gas outlets) 3b- Oxygen Flush Valve (O2 bypasses vaporizer and ends up in fresh gas outlet) 4- Vaporizers 5- Fresh gas outlet 6- scavenger system
If Hypotensive:
1- Correct heart rate (based on physical exam) 2- Check depth of anesthesia/ optimize anesthesia with balanced anesthesia 3- Give a fluid bolus-> more fluids will expand heart and allows for more powerful contraction 4- Drugs A) Ionotropics - Dobutamine - Norepinephrine - Dopamine b) Vasoconstrictors - Vasopressin - Dopamine
Rule of thumb 6 things to assess depth of GA
1. Eye position -> 1.1 Horizontal nystagmus (horses) 2. Palpebral reflex 3. Jaw tone 4. Muscle tone -many times used to evaluate horses when no access to eye (sometimes anal tone) 5. HR and BP 6. RR and EtCO2
To select the safest agent possible:
1. Familiarity with drug, dose, side-effects, contraindications 2. Familiarity with the patient o History (signalment, co-morbidities, medications) o Previous known allergic reactions o Stabilize animal prior to anesthesia -give fluids if dehydrated for example
Rebreathing Systems The amount of rebreathing depends on:
1. Fresh gas flow into the system (rate of oxygen and gas going into the system -A low flow rate indicates high CO2 levels 2. Amount of dead space in the system -amount of space in resp system that is not making a contribution to the gas exchange 3. System design
5 causes of hypoxemia
1. Low fraction inspired O2 (FiO2) 2. hypoventilation 3. V/Q mismatch - Atelectasis 4. Diffusion impairment 5. Right to left shunt 1 & 2 related 3 & 4 related
Monitoring Equipment
1. Most important one is: YOU! -Evaluate the patient 2. Temperature -thermometer, esophageal probe 3. Pulse oximetry 4. Capnography-side-stream, main-stream 5. ECG 6. Blood pressure -non-invasive (oscillometric, Doppler), invasive
Monitoring equipment
1. Most important one is: YOU! -hands, stethoscope -Evaluate the patient 2. Temperature -thermometer, esophageal probe 3. Pulse oximetry 4. Capnography-side-stream, main-stream 5. Electrocardiogram (ECG) 6. Blood pressure -non-invasive (oscillometric, Doppler), invasive
Physical exam status classification from the American Society of Anesthesiologists (ASA)
1. Normal healthy patient -> ex: ovariohyserectomy 2. Mild systemic disease (or localized disease) -> fracture w/o shock, cryptochidectomy 3. Severe systemic disease -> fever, anemia, uncontrolled diabetes 4. Severe systemic disease that's a constant threat to life -> sepsis, uncompensated cardiac disease, anemia 5. not expected to live 1 day with or w/o operation -> severe trauma, GDV in respiratory arrest Allows you to assess the risk of anesthesia informed discussion w/ owner plan for anesthesia
Reassessment Campaign on Veterinary Resuscitation
1. Preparedness and prevention 2. Basic life support (BLS) 3. Advanced life support (ALS) 4. Monitoring 5. Post cardiac arrest (PCA) care
Hypoventilation morbidity data-
1.3% dogs; 0.1% cats in one study. In another study up to 60% of dogs Very common side effect
Ventilation
10 breaths per minute VT 10 mL/kg • Avoid hyperventilation - Hypocarbia (low CO2) = cerebral vasoconstriction, decreases cerebral blood flow - CO2 is already low due to CPA Peak pressure: 10-20 cmH2O • Increased intrathoracic pressure = decreased venous return -normally during CPR more towards 10 cmH2O Minute Ventilation = RR x VT (tidal volume = VT)
• You are performing CPR on a dog. How often should you breath for the dog? a) 20 breaths/min b) 5 breaths/min c) 15 breaths/min d) 10 breaths/min
10 breaths/min
Visual Analogue Scale
100mm line 0 = no pain 100 = worst imaginable pain Doubling the number does not necessarily double to pain Training required
15-20% and >20% blood loss-> what is your fluid plan for hemmorrhage?
15-20% blood loss: Administer 10 mL/kg crystalloid (LRS) fluid bolus over 10 minutes AND 3-5 mL/kg colloid bolus >20% blood loss: Start with crystalloid fluid bolus (10mL/kg) while preparing blood products Administer 10mL/kg whole blood - speed will depend on the stability of the patient
Triple drip (GG + xylazine+ ketamine) IV
1L of 5% GG + 500 mg Xylazine+ 1500 mg Ketamine Titrate to effect >1-2 h = rough recoveries -limit procedure times Used for stall drop and field anesthesia
Compressions -2min cycle- Stopping?
2 minute cycle non stop! Pauses during compression = negative outcome Do not stop compressions for: • IV catheter placement • Tracheal intubation • ECG placement • Drug administration blood work important
You are anesthetizing a normal health dog for an ovario-histerectomy (OHE) and the patient is apneic. Your technicians are asking you what is the maximum inspiratory pressure they should use while providing manual ventilation. Your answer is?
20 cm H2O
• What should be your maximum peak inspiratory pressure when ventilating a patient a) 10 cmH20 b) 20 cmH20 c) 2 cmH20 d) 30 cmH20
20 cmH2O but want to stay between 10-12 cmH2O
How pregnancy changes anesthesia Anesthetic Requirements:
25-40% decrease in anesthetic requirement: ○Progesterone and estrogen - natural occurring analgesic action -progesterone acts on the GABA receptors -both have analgesic effects Epidural space decreased by 30-50% ○Engorged vessels and fat -make sure to lower your volumes
Supplement oxygen for your patient via flow by or face mask at:
3 minutes at 100ml/kg/min of oxygen -flow by technique is a waste of time -no good -USE A MASK
Another study in 101 geriatric dogs demonstrated:
30 new diagnosis and cancellation rate of 10% Very important to do blood work for geriatric
Capnography- EtCO2(mmHg) differences
35-45mmHg: Normal 0 ETCO2: • Check patient, sensorand ETT; • Machinefailure • extubation • obstructed ETT • esophageal intubation • dead < 15 -20mmHg: • Aim to increase EtCO2 with more efficient CPR • Increase compressions pressure or frequency (should be 100-120 per min) • underlying disease(e.g. cardiac tamponade) -where no matter how much or hard you are pressing, it will not help < 10mmHg: • Low despite CPR efforts • If also no ECG activity, consider stopping CPR Ideally want an ETCO2 above 15mmHg with chest compressions
The pressure gauge for an oxygen H tank is showing 1000 psi. Approximately, how many liters of oxygen does the tank have left?
3750 L
When using the non-invasive blood pressure monitoring, the cuff width should be approximately what percentage of the limbs' circumference?
40%
How do you choose the cuff size?
40% of limb circumference -measure How do we measure? ○Look for a video in media files A-Diagram illustrating the arterial pulsations in relation to the cuff pressure. Doppler sounds reapear when cuff pressure reaches the SAP. SAP= Systolic arterial pressure; C= cuff deflation period; D= cuff pressure release.
What is the maximum body weight (in kg) for the Bain system?
5
What Causes Hypoxemia?
5 Classic Reasons • Low inspired oxygen -No, FiO2 is 95 -98% • Hypoventilation -No, we are ventilating • Diffusion in the lung -Lung disease in anesthetized horses not common (responsive to O2 supplementation) • V/Q mismatch -Yes, responsive to O2 • Shunt Low cardiac output worsens hypoxemia -Yes, but does not respond to O2 supplementation
It is dangerous to use the oxygen flush valve while the patient is connected to the breathing circuit because it delivers ______ liters/kg/min at _____psi
5 liters/Kg/min 50 psi
The percentage of inhalant anesthetic coming out of the vaporizer is constant when the flow rate is higher than _____________
500 ml/min
What is the mean arterial pressure (in mmHg) that is used for horses/dogs/cats to ensure renal perfusion during anesthesia?
60
Body water rule
60:40:20 Rule 60% of body weight is water 40% (2/3 of total body water) intracellular 20% (1/3 of total body water) extracellular -- >15% interstitial fluid (lymph and fluid between cells) --> 5% intravascular compartment (fluid within blood vessels - plasma) -this is typically for adults Changes with age, species and body fat content Pediatrics = 80% body weight
Hypotension morbidity data-
7% dogs and 8.5% cats
How about horses?
70mmHg Ensure muscle perfusion dogs- below 60 mmHg poor blood perfusion and muscle weakness, but have time to get that back up after surgery, able to lie down Horse- have to have good muscle tone to stand up after surgery, can't stand up = nerve damage -improves survival rate if kept above 70 mmHg
Reference ranges are for approximately ______of population
80% of population In a study of 102 horses, 55 animals had results out of the reference range from no correlation to complications of alteration in patient management
Hypothermia morbidity data-
85% dogs < 99.1°F and 51% cats < 95°F
Match the labels on the oxyhemoglobin dissociation curve with the appropriate options.
A SpO2 % B PaO2 (mmHg) C 100% D 60 mmHg
E tank: calculating volumes
A full cylinder will contain 700 liters of oxygen. When the cylinder is full, the pressure is approximately 2000 psi. When the tank is half full (350 liters), the pressure in the tank will be 1000 psi. If you know the pressure in an oxygen tank (from the pressure gauge), you will be able to calculate the amount of oxygen remaining. (how long the tank will last) Based on you flow of oxygen, you can calculate for how long a tank will provide oxygen for your patient.
Which first order neurons are responsible for the transmission of pain and their location in the pain pathway?
A-delta and C fibers that transmit a noxious stimulus from the nociceptor to the spinal cord Beta more proprioception and pressure
Hepatic system- Drugs that should be avoided: Why hypotension should be avoided:
ALL patients who are liver compromised Highly metabolized drugs should be avoided Acepromazine, thiopental, halothane, non-steroidal anti-inflammatory drugs (NSAIDS), propylene glycol Hypotension should be avoided -Further decrease in hepatic blood flow -Exacerbation of possible ischemic hepatic damage
Heart rate variation- most species vs horse, exotics
ALWAYS evaluate HR and BP Most species (e.g. dog, cat, pig) • Increase in HR or tachycardia = light/lighter plane of anesthesia Horse • HR not good indicator of anesthesia depth -tend not to increase if light -HR doesn't change much in horses • Increase in BP may be a more sensitive indicator of changes in depth Exotics (e.g. rabbits, birds) • Tachycardia = light plane • Acute decrease in HR = may also be light plane or pain; caution
Ventilation
ALWAYS evaluate RR and EtCO2 Normal EtCO2: 35 -45mmHg Too light May hyperventilate • Increased RR, • decreased EtCO2 Too deep May hypoventilate • Decreased RR, • increased EtCO2
3y old, male intact, Pointer, weighing 24kg. He requires general anesthesia for a 3cm superficial benign mass removal in his left forelimb. Blood work and physical examination are unremarkable and he is bright alert and responsive (BAR). What is this dog's ASA health status? *ASA = American Society of Anesthesiologists
ASA I
Opioids
AVOID use IV in an non-painful awake horse without prior sedation • Excitement will occur Butorphanol most common premed opioid • Has the fewest side effect • May not provide adequate analgesia -for some procedures Morphine administration (IV, IM, CRI) • Histamine release may occur with IV administration • Good for incremental dosing during inhalant anesthesia for very painful procedures (e.g. fracture repair)
IV top up doses
Able to achieve a reliable response given IV administration and absorption
MAC sparring
Able to use a lower dose of inhalant thus, lower risk of side effects from inhalant
Analgesia
Absence of pain in response to a normally painful stimulus Usually in conscious patients
ADME
Absorption - how does the drug get into the body Substance entering systemic circulation Distribution - where does the drug go Dispersion of substances through the body fluids and tissue Metabolism - what does the body do to the drug Biotransformation of parent compound to daughter compound Excretion - how does the body get rid of the drug Removal of substances from the body
Treatment of Adverse Reactions
Accidental overdose: 1st-->> STOP administration! Oxygenation and Ventilation -> reduce risk of hypercapnia, hypoxemia and acidosis (these promote toxicity and will make it worse) Anticonvulsant: benzodiazepine Cardiac arrhythmias:-->start CPR immediately; amiodarone- antiarhythmic (propofol would cause more vasodilation- don't give) Cardiac arrest: IV lipid emulsion
You are required to anesthetize a 5 year old English bulldog for airway surgery and he is currently regurgitating and has a history of vomiting and regurgitation at home. Which protocol would less likely worsened his GI signs? Acepromazine + methadone Dexmedetomidine + morphine Midazolam + hydromorphone Xylazine + hydromorphone
Acepromazine + methadone
Alternative Therapies
Acupuncture Rehabilitation Ice/hot therapy
Types of pain
Acute Chronic Inflammatory Neuropathic Visceral Wind up pain Somatic
Chronic Pain
Acute pain involved tissue injury and behavior to avoid the injury Involves assessment of these behavior and intensity of injury and associated pain Chronic pain is much more complex Examples: osteoarthritis, cancer pain In humans, chronic pain is associated with depression, anger and fear Becomes more of a quality of life assessment Tracked over longer periods of time Usually observation is made by the owner and information is analyzed by trained personnel like the veterinarian
Multidimensional Scales
Add questions to assess the emotional and sensory components of pain Psychological and behavioral Response to palpation Body tension Glasgow Composite Pain Scale 279 expressions/words associated with pain in dogs! Refined to 47 within seven behavior categories Equine orthopedic pain Heart rate, respiratory rate, bowel sounds etc. Reluctance to move, restlessness, agitation, sweating, kicking at abdomen etc. Most accurate indicators of orthopedic pain in horses was response to palpation, posture and pawing Equine visceral pain Post-abdominal surgery Reduced locomotion, elevated cortisol and heart rate were indicators of pain
Ketamine IM
Add to pre-med cocktail to increase chemical restraint Provides analgesia (somatic pain > visceral pain) Excessive salivation Does NOT provide muscle relaxation -never used alone for IM or IV Opioid + acepromazine+ ketamine IM Opioid + alpha 2 agonist+ ketamine IM Alpha 2 agonist + ketamine IM Commonly used for animals that are difficult to restrain
Preparedness and prevention
Adequate facilities Stocked crash carts - important drugs, emergency drugs, reversals Patient monitoring devices- incubation, capnograph, Be able to recognize the need for CPR • Rapid recognition of arrest • Early prompt and effective compressions as soon as CPA is seen
Preemptive analgesia
Administration of analgesic drug before noxious stimulus is applied to prevent sensitization of neurons Improves post-operative analgesia Reason for providing an analgesic in a premedication
Pulse ox -Sp02 Advantages and Limitations
Advantages: Non-invasive Easy to place Relatively easy to interpret Continuous data Correlation of SpO2 to partial pressure of O2 in arterial blood Limitations Affected by several variables- • Movement (movement artifacts) • Pigment • Hair • Vasoconstriction (can give no readings in patients with vasoconstriction) • Carboxyhemoglobin • Methemoglobin Late indicator of hypoxemia-> does not indicate early enough that there is a problem
Circle System (re-breathing) -Advantages: -Disadvantages:
Advantages: less environmental pollution conservation of heat and humidity less abrupt changes in anesthetic depth**** -harder to have an overdose, but can take longer control of PaCO2 depends on patient ventilation, not fresh gas flow Disadvantages: composed of many parts which may: - malfunction - be improperly assembled resistance is greater than in nonrebreathing systems: - relief valve - unidirectional valves - soda lime canister - *resistance increases with increases in respiratory rate and tidal volume Why these are not used in smaller patients-> do not have a large enough tidal volume to move the valves and end up rebreathing the CO2
Conclusion
Age is a multifactorial, all-encompassing process No "single ideal anesthetic plan" could be recommended for all patients based on age What the veterinarian should consider when designing anesthetic protocols? 1st: Specific co-existing diseases 2nd: Life stage
Age and anesthesia
Age is not a disease, however it is considered an important independent risk factor of anesthesia related morbidity and mortality and therefore is often used as a predictor of perioperative outcome for anesthetized patients.
Alfaxalone IM
Agent commonly used for IV induction of anesthesia More recently used as part of sedation/premedication protocols: • Approved for IM use in cats • Off label for IM use in dogs -Never given IM on its own; will always combine IM with something else Common IM protocols include: • Opioid (ie. butorphanol) and/or Alpha-2 agonist (dexmedetomidine) No analgesia Do not administer alfaxalone IM alone • Require higher doses • Large volume needed via IM • Higher risk of side-effects
Conclusion
Agonist, partial agonist and antagonist ADME IV administration = rapid and profound effects IM administration = absorption required, less profound effect and more time to peak effect Obesity may affect drug distribution and dosing Organ failure may affect metabolism or excretion Intermittent dosing vs CRI Intermittent dosing - no specialized equipment needed but peak and trough effect CRI - constant drug administration for consistent clinical effect; should administer a bolus dose to increase plasma concentration initially Potency vs efficacy Potency is related to drug dose; efficacy is related to clinical effect Therapeutic index Wide therapeutic index typically mean larger dose range and safe How to select a dose Patient physical exam, history, species, procedure etc. Understand drug effect and side effect Use multimodal approach
The following diagram is an example of:
Airway obstruction pattern on the capnography
Pharmacodynamics - Cardiovascular System Blood Pressure
All inhalants cause dose dependent decrease in BP Cardiac dysrhythmias - Sensitizing myocardium to catecholamines
Pulse Variation Index (PVI)
All pulsations have same maximum systolic pressures PVI = calculation of the percentage difference from max to minimum SpO2 gives idea on needs for fluids
Abnormal responses:
Allodynia Hyperalgesia Analgesia
Weight/Obesity
Allometric scaling and dosing on body surface area is not well proven to be effective Clinically, small dogs may require higher doses of some drugs (sedatives) than large dogs -Opioid doses usually remain the same Obesity: There are not accurate ways to estimate lean body weight Fat tissue has low blood flow but may affect distribution of some drugs Use clinical judgement, therapeutic index and degree of obesity to decide if doses should be adjusted to lean body weight -Low therapeutic index drugs (NSAIDs, antibiotics, chemotherapeutics) may consider dosing on lean body weight
What are adrenergic receptors?
Alpha (α) and beta (β) receptors They are involved with the sympathetic nervous system and are activated by the binding of catecholamine's (epinephrine and norepinephrine) G-protein coupled receptors -Binding starts a cascade of second messengers leading to a response -Response is dependent on the receptor, the cascade and the final product -Example: β1 receptors are involved with contractility - the final products including Ca++ production assist with the binding of actin/myosin and increase contractility
Adrenergic receptors- Functions-
Alpha 1 adrenergic receptors Post synaptic end plate Stimulated by norepinephrine Vasoconstriction Alpha 2 adrenergic receptors Presynaptic Extrajunctional - vasoconstriction -->On effector organ Stimulated by norepinephrine and epinephrine Vasoconstriction Beta 1 adrenergic receptors Heart Increases heart rate, contractility and conduction Beta 2 adrenergic receptors Blood vessels of muscular beds Vasodilation in face of stress M2 muscarinic Parasympathetic nervous system postganglionic neurons Stimulated by acetylcholine On atria and AV node -vagus node Decrease conduction and heart rate
Activation of which adrenergic receptor results in sedation and analgesia?
Alpha 2
Treating peri-op pain in horses- drugs
Alpha 2 agonists • Intraop dexmedetomidine CRI for orthopedic sx pain • Xylaxine or romifidinein recovery Ketamine CRI intraoperative (0.6mg/kg/h) Lidocaine CRI intra and postop -(esp. colics)
Sedative- Drug classes
Alpha 2 agonists (dexmedetomidine, xylazine) Benzodiazepines (midazolam, diazepam)
Sedation and analgesia using:
Alpha 2- agonist (dexmedetomidine) Reduce fetal blood flow, bradycardia, hypertension and hypoxemia Not recommended Phenothiazine (acepromazine) Prolonged sedation in neonate, hypotension Not reversible Not recommended Opioids Readily cross the placental barrier -Respiratory depression on fetus -Monitoring of neonates for opioid effects is recommended - Naloxone can be administered Use ultra short opioids
Low perfusion/low ventilation Bronchospasm/panting/ Dilution
Alpha and Beta angles are missing- low perfusion, low ventilation, low perfusion- less diffusion of CO2 check flow rate look at PB (if low fix) Then think about needing to bronchodilate patient
Sedation/chemical restraint -Alpha 2 agonists Mechanism of Action
Alpha-2 adrenergic receptor agonist Stimulate α-2 adrenoceptors resulting in CNS depression & decrease in catecholamines Dose dependent sedation Analgesic properties Excellent muscle relaxation Reversible: atipamezole-give IM -Given IV can cause a lot of vasodilation -Tolazolene- more specific reversal for xylazine
Reversal agents: Alpha-2 agonist- Opioid- Benzodiazepine-
Alpha-2 agonist (e.g. dexmedetomidine) o Atipamezole IM -acts fast enough -IV can cause hypotension Opioid (e.g. hydromorphone) o Naloxone IV -o.o4mL/kg Benzodiazepine (e.g. midazolam) o Flumazenil IV
Sedation -Alpha-2 agonist (xylazine and Detomidine IV, dexmedetomidine)
Alpha-2 agonists • IV loading dose (bolus) followed by constant rate infusion (CRI) • Detomidine, Dexmedetomidine Detomidine IV - Longer onset of action (5min) - Longer duration (40min) - Less ataxia than xylazine Xylazine IV - Fast onset of action (2-5min) - Short duration (15-30min) - Ataxia
Capnograph
Also known as an end-tidal CO2 monitor. A monitoring device that measures the amount of CO2 in the air that is breathed in and out by the patient, by sampling air passing between the endotracheal tube connector and the breathing circuit.
Geriatric central nervous system
Also require lower doses decreased cognitive, sensory, motor and autonomic functions Decreased requirement for anesthetic drugs: -Inhalants, benzodiazepines, opioids, barbiturates -Prolonged recovery time -Consider reversing drugs -->Opioids, benzodiazepines
Inhalant- cardiovascular system
Altered distribution of blood flow to tissues -Depression of the vasomotor center causing global vasodilation Reduced cardiac output Decreased stroke volume from decrease myocardial contractility and systemic vascular resistance
Important factors in cesarean sections
Altered physiology of the mother induced by pregnancy and labor can affect anesthesia Impact of selected drugs on the mother and fetus Carryover effects on the neonate following separation from the mother Risk of anesthetic‐related complications Goal= Anesthetize mother without adversely affecting the fetus
IV Catheter placement
Always make sure that you are fully prepared before starting IV catheter placement - have all the materials ready, T-port flushed etc Must wear gloves for the placement of an IV catheter Do not need gloves to administer an injection into a port on a catheter that is already placed Do NOT use needles in the blue microclave port Depress syringe into port and twist to tighten luer lock syringe If using a non-luer lock syringe, depress tip into blue port, ¼ turn and it should stay in place If blue port if visibly contaminated, wipe with alcohol Use needle to inject into injection port only Do NOT place caps, needles, syringes or anything in your mouth
Pre-anesthetics
An agent given before anesthesia is induced • Pre-anesthetic or Pre-medication An agent or technique that limits or prevents harmful effects of other drugs & procedures Agents that improve the quality of anesthesia Some agents provide analgesia(pain relief) and/or tranquilization or sedation
Insufflation
An insufflation system is a system in which gases are delivered directly to patient's airways in the absence of valves, reservoir bag, or carbon dioxide absorption Significant amount of pollution if anesthesia gases are used. Not commonly used for anesthesia. a.Only used to supplement oxygen b.Equipment •Nasal canula (A, B) •Face mask (C) •O2 line connected to large bore IV catheter going through trachea (for emergencies only) - "trivial"
The ideal anesthetic protocol
Analgesia Muscle relaxation Without sedation for the fetus- don't want to endanger fetus or mom Anesthesia Without endangering either mother or fetus
Temperature Hypothermia
Anesthesia causes delay or lower homeostatic set points in temperature In most species < 97 °F • Hot dog to prevent conductive losses • Bair-hugger to prevent convective losses • Reduce the amount of alcohol when scrubbing to reduce evaporative losses • Use lower O2 flow to reduce respiratory losses (but monitor EtCO2) - Rebreathing circuit usually 40-50ml/kg/min, can try lower flow: 10 -30 mL/kg/min - Non-rebreathing circuit: 150 mL/kg/min, cam try to reduce • Reduce anesthesia time
Preparation of Horses
Anesthesia workup (same as small animals) • Physical exam and full history • Blood chemistry, hematology • Listen to heart and lungs • Body weight (day of) (cardiorespiratory and hydration status) Patient preparation (mostly the same as SA but a few differences) • IM premed optional • Place IV catheter in jugular vein w/o premed • Catheter must stay capped! - can get air embolism • Pick out feet (dirty) and wash out mouth (food may get dragged with ETT)
Pharmacodynamics - Liver
Anesthetic & % of Anesthetic metabolized Halothane 20 - 46 -> gives headaches Sevoflurane 2 - 5 Isoflurane 0.2 Desflurane 0.02 Nitrous Oxide 0.004
Variables to monitor
Anesthetic depth- Insensible to pain & no movement during procedure Temperature- Physiologic range to sustain life and minimize possible complications Circulation-Adequate tissue perfusion Oxygenation-Adequate oxygen content in arterial blood (PaO2) Ventilation-Adequate ventilation (respiratory rate, end tidal CO2) Recovery-Smooth with pain and stress reduced or eliminated
Drugs that inhibit perception
Anesthetics Opioids a2 agonists Benzodiazopines Phenothiazines
Others- (used as adjunct analgesics)
Anesthetics, benzodiazepines, phenothiazines Tricyclic antidepressants Anticonvulsants Corticosteroids NK-1 receptors antagonist
Step 3 includes:
Anesthetist uses a laryngoscope to help visualize the arytenoids • Pull tongue forward • Laryngoscope -press down at the base of the tongue • With the other hand, insert the endotracheal tube (ETT) between the arytenoids • Use a tie: tie around the ETT and then around the muzzle or behind the ears
Positive pressure ventilation
Animal is breathing under anesthesia with an endotrachial tube and we physically give them a breath Unlike a normal breath, PPV does not draw diaphragm down and intercostals do not contract to bring the ribcage up and out -pushing air into lungs and expanding it which pushes against the rib cage and thus compressing the vessels in the chest which decreases venous return -healthy animals- effect is minimal
When you are making ECG diagnosis, the purple arrow is a representation of a ______ , the green arrow is the representation of a _______ and the red arrow is the representation of a ______
Answer 1: P wave Answer 2: Ventricular depolarization Answer 3: repolarization
Using the available diagram of the heart, what is A, B, C?
Answer 1: Sinus node Answer 2: Atrio ventricular node Answer 3: Bundle of His
How do you calculate the size of a reservoir bag (also called rebreathing bag) [ Select ] ["kilos", "pounds", "ml"] x [ Select ] ["15", "5", "50"] x [ Select ] ["1", "6", "3"]
Answer 1: kilos Answer 2: 15 Answer 3: 6
What is the function of a modern vaporizer? The isoflurane vaporizer is designed to [ Select ] ["slow down", "speed up"] the vaporization of isoflurane liquid to [ Select ] ["dilute", "concentrate"] it to clinically safe concentrations
Answer 1: slow down Answer 2: dilute
Corticosteroids
Anti-inflammatory in the arachidonic acid pathway Not to be used with NSAIDs
Anesthetic adjuncts -sometimes used
Antihistamines (benadryl) • risk of allergic reactions (mast-cell tumor) -give 30 mins before pre-meds GI protectants/antacids • brachycephalic dogs -history of vomiting or regurge Anti-emetics (maropitant "cerenia", metoclopramide) • brachycephalic dogs -cerenia only helps with vomiting not regurge or vomiting -metoclopramide- both anti-emetics and gastric issues Anti-arrhythmics (beta blockers)
Acepromazine- Other useful effects
Antihistaminic Antiemetic -decreased occurance of vomiting Anti-arrhythmic Post-op anxiety • Smooth recovery • Low dose (0.01mg/kg IV) very useful for recovery
Factors increasing MAC
Anything that stimulates CNS will increase MAC Hyperthermia (up to 42 ºC) Hypernatremia CNS stimulants - a1-adrenoreceptor agonists (ephedrine, amphetamine) Hyperthyroidism -speeds up metabolism which will increase MAC Research has been demonstrated that hair color effects MAC with red-haired people requiring about 20% more than others.
Apnea Bradypnea Tachypnea Hypoventilation Hyperventilation End tidal CO2 -
Apnea - no respiratory rate Bradypnea - slow respiratory rate Tachypnea - fast respiratory rate Hypoventilation - increase CO2 Often is related with bradypnea but not always! Hyperventilation - decrease CO2 Often is related with tachypnea but not always! End tidal CO2 - amount of CO2 that is exhaled Normal is 35-45 mmHg Measured non-invasively using the capnograph
Cardiac pump model
Apply pressure to area over the heart Direct compression of ventricles ↑ ventricular pressure, opens pulmonic and aortic valves 1. Hand placed over heart Lock elbows 2. Fingers on 1 side & thumb on other
Bronchial C Fibers
As above but in bronchial circulation Rapid, shallow breathing, bronchoconstriction and mucous secretion
Step 2 includes:
Assess depth of anesthesia to see if able to intubate the trachea • Jaw tone -loose enough that is safe to intubate the trachea? • Palpebral reflex -may still be present but reduced • Eye position -may be ventrally rotated Assistant when open the animal's mouth
Physical exam- assess hydration status
Assess hydration status: oTent skin over the dorsal shoulder/caudal neck (dehydrated- skin turger lasts longer) oAssess eyes and mucous membranes (capillary refill time -CRT) >2 seconds If PCV is high (along with other signs)- can indicate patient is dehydrated- should dehydrate before
Numerical Rating Scale (NRS)
Assess individual behaviors Assessment in horses have included the use of multiple NRS May have unequal weighting of categories
Simple Descriptive Pain Scales
Assess intensity of pain Basic and highly subjective Not accurate for detecting small changes in pain intensity Not validated Commonalities of pain scores Psychological and behavioral Response to palpation Body tension
Goal Directed Therapy
Assess what is being lost or needing to be maintained Healthy patient under anesthesia for elective procedure - maintenance IV fluids Lost whole blood - ruptured splenic tumor: be careful not to administer fluids too rapidly or you may dislodge clot formation Lost red blood cells that are lysing - immune mediated hemolytic anemia: you should replace the red blood cells only Vasodilatory shock - sepsis: crystalloid and colloid fluids (synthetic or natural) may be required Repeated physical exams, physiologic parameters assessed Set goals to reach: -MAP 60 mmHg -Targeted heart rate -CRT < 2 seconds Additional, more advanced monitoring techniques using invasive lines
Step 5 includes
Assistant will press the rebreathing bag (give a breath to the patient) • Anesthetist listens for any leaks around the ETT and inflate the ETT cuff if needed
What drug increases heart rate and how?
Atropine (anticholinergic)
Anticholinergics
Atropine and Glycopyrrolate • Agents able to increase the heart rate Mechanism of action • Antimuscarinic • Competitively antagonize acetylcholine
First order Neurons
Aδ - thin myelinated, rapid transmission Chemical and mechanical C - unmyelinated, slow transmission Chemical, thermal and mechanical Aβ - large myelinated, very rapid transmission Non-noxious stimulus Pressure, proprioception
Ultrasound Doppler flow detector
B-Diagram illustrating the arterial pulsations in relation to the cuff pressure. Doppler sounds reapear when cuff pressure reaches the SAP. SAP= Systolic arterial pressure; MAP= mean arterial pressure; DAP= diastolic arterial pressure; A= cuff inflation period; B= cuff pressure equilibration period; C= cuff deflation period; D= cuff pressure release. Automated oscillometric MAP = DAP + 1/3 (SAP-DAP) Cannot use doppler for cats
The most important basic skill
BE ABLE TO RECOGNIZE CPA!
6yr old draft mare is under inhalant anesthesia. HR is 32 bpm, SBP 80, MAP 63, RR 7, ETCO2 45. What is abnormal with these parameters?
BP is low (hypotensive)
Non-Rebreathing systems
Bain circuit Ambu bag Modified Jackson-Ress system Other Mapleson systems Used for smaller patients Absence of unidirectional valves Carbon dioxide removal depends on fresh gas flow (fresh gas removes CO2) Used for smaller patients
Which system requires higher fresh gas flow rate for the maintenance of anesthesia?
Bain system
CalculatingVolumes (cont.)
Bain system (150ml/kg/min) -flow rate of O2 Dog 10kg 150*10kg*60min=90.000ml per hour or 90 liters per hour 350 liters/90 liters = 3.8 hours
Renin-angiotensin system:
Balance fluid volume and electrolytes
How do we provide safe and effective anesthesia and analgesia?
Balanced anesthesia or multimodal anesthesia Use of multiple drugs in smaller doses than a single drug Reduced the side effects of a single drug Manipulate multiple receptors in an advantageous way Be prepared Know patient history and physical exam findings Obtain appropriate preoperative blood work Understand physiology, pathophysiology and pharmacology
Acepromazine -caution
Be cautious giving ACE to patients who have: Anemia, or blood loss anticipated (transient decrease in PCV and vasodilation) Liver disease or shunt (non reversible) Some cardiac disease (relative contraindication) Abdominal surgery Avoid Unstable Compromised Critically ill patients
Prevention of fetal complications
Be prepared for resuscitation Oxygen- preoxygenate Warm towels Staff- one person per puppy Reversals for drugs Emergency drugs Suture/iodine Bradycardia in neonates = hypoxemia! Provide oxygen
Body core temperature - below ___ = risk of _______
Below 92F - risk of ventricular fibrillation
Benzocaine vs Lidocaine
Benzocaine Brand names: Cetacaine, Hurricaine Causes: Methemoglobinemia Use lidocaine Benzocaine is toxic to cats
Benzodiazepine/ketamine combo
Benzodiazepine with Ketamine IV: -Great and safe combo for healthy patients -Commonly used for small, large and exotic animals -Often used for sick patients -->Example: GDV surgery -combo less likely to cause hypotension than propofol -when used in combination, does not cause disinhibition
Mortality data: compared to morbidity data- Sources-
Better reporting than morbidity University and teaching hospitals typically have higher mortality rates due to the types of cases seen Reduced mortality rates over the last 50 years Limited accuracy because variation in case definition, study populations, procedures performed etc. Assessing the mortality risk over all versus ASA 1-2 and ASA 3-5 separately will often yield different % Confidential Enquiry into Perioperative Small Animal Fatalities (CEPSAF) Confidential Enquiry into Perioperative Equine Fatalities (CEPEF)
Irritant receptors
Between epithelial cells of airway Noxious gases, smoke, dust, cold air Afferent via vagus nerve Reflex bronchoconstriction -> important for diagnostic procedures or aspiration
Anesthetic Complication: Vasodilation Big cause= other causes- treatment-
Big cause= inhalational anesthesia (isoflurane, sevoflurane) -sm relaxation Others- -Alpha 1 antagonists (acepromazine) -GABA agonists (propofol and alfaxalone) --> direct action on vascular sm, inhibition of symp activity; NOT all GABA agonists cause vasodilation -Disease (sepsis) Treatment- -reduce dose of drug causing side effect -IV fluids = fill the vessels -vasoconstriction = drugs (norepi, phynylephrine) -treat underlying disease if present
GABA Receptor Mudulation- Propofol, Alfaxalone, Benzodiazepines, Etomidate
Binding of the GABA receptor (to come in the next lecture) inhibits the pathway for arousal and awareness CNS depression and hypnosis Propofol blunts the baroreceptor reflex but causes vasodilation HR should increase but propfol inhibits this so HR stays lower Alfaxalone maintains the baroreceptor reflex and causes vasodilation What will this do to the blood pressure? -HR will increase so BP will remain maintained
Metabolism -most common type:
Biotransformation is a slightly more accurate term Drugs are transformed from a parent compound into other less active compounds* *Ketamine in cats is not metabolized to an inactive compound Most common type is hepatic metabolism Liver failure or severe restriction of blood flow to the liver may affect metabolism of drugs Some drugs are also metabolized by: Plasma Remifentanil Lung Propofol
Alpha 2 agonists -side effects
Biphasic blood pressure effect Phase I • 1st Vasoconstriction (hypertension) • Reflex bradycardia -compensatory Phase II ~ about 1 hour • Vasodilation (hypotension) • Can become normal or can see Bradycardia or low normal HR Decreased cardiac output - do not give to patients who cannot handle decreased CO!! Cardiac arrhythmias
Why the use of un-cuffed endo tracheal tubes?
Birds do not have the trachealis muscle therefore we only use uncuffed ET tubes Very small animals need very small ET tubes -The smallest commercially available cuffed ET tube is 3.0 mm OD (some animals need something smaller, so we use un-cuffed) -For rats, mice and other smaller animals an intravenous catheter or a red rubber tube can be used as an ET tube
Disadvantages/side effects
Bleeding (hit a vessel) Infection Nerve damage (ex sciatic nerve -anesthetic into the nerve can cause nerve damagez0 Duration of action • May not be enough for post-op analgesia • May need to repeat nerve block or give other analgesics • *Nocita (bupivacaine liposome) -up to 72h Motor blockade • May affect ability to evaluate patient in the immediate post-op period • Usually up to 18h with bupivacaine -proprioceptive deficits possible
Distribution- Four major compartments Bound and unbound drugs- How are drug doses calculated?
Blood (plasma) Fat Extracellular fluid Intracellular fluid Other minor compartments - cerebral spinal fluid, peritoneum, synovial fluid Drugs are unbound (free) and bound to proteins (like albumin) Unbound drugs are the pharmacologically active form Drugs distribute throughout the compartments and form equilibriums of bound and unbound fractions Drug dosages are calculated by parameters involving absorption, distribution and excretion of drugs
Monitoring anesthetized patients
Blood pressure MAP= CO x SVR -CO = HR x SV -->MAP = HR x SV x SVR Gold standard for monitoring= invasive
Autoregulation
Blood vessels adjust blood flow to match metabolic and blood flow requirements of tissues in order to makes sure it is getting enough oxygen and getting rid of waste Capillary blood flow influenced by perfusion pressure, blood flow rate, metabolic rate of tissue, oxygen tension, viscosity Oxygen delivery and uptake balance critical Within a certain pressure range, the body self regulates to get appropriate amounts of blood flow to the organs The relationship between blood flow and perfusion pressure in peripheral vascular beds is characterized by the pressure range over which blood flow changes very little.
Dog blood volume (9%) = 90ml/kg Example: 20kg dog -Blood volume= -Tolerated blood loss= -Acute blood loss=
Blood volume = 1800ml (1.8L) Tolerated Blood loss (<20%) Acute blood loss (15%) = 270ml Monitor blood loss, if getting close to 270ml blood loss, act fast • Fluids, blood sample (PCV, TS, lactate), blood products
Bolus dose and continuous rate infusion
Bolus dose is administered to achieve a plasma concentration that will produce clinical effect The continuous rate infusion is started using a syringe pump to deliver the drug at a constant rate It takes 5 half lives to reach peak plasma concentration Example: Fentanyl: half life approximately 20 minutes in dogs Time needed to reach peak plasma concentration of CRI = 5 * 20 minutes = 100 minutes Your dog is painful now and need analgesia, so give a loading dose to rapidly increase the concentration of fentanyl in the blood stream while the CRI starts
You are anesthetizing a 3 year old domestic short hair cat for an elective ovariohysterectomy. The cat received midazolam, buprenorphine, alfaxalone and isoflurane. The mean arterial blood pressure is 55 mmHg and heart rate is 90 beats per minute. The depth of anesthesia in appropriate and you cannot decrease the isoflurane. What is the likely cause of hypotension AND what is the most appropriate treatment option?
Bradycardia and administer an anticholinergic (atropine) MAP is low - want at least 60mmHg HR low- min in cat is 100 BPM -> these both are the cause of hypotension -we know depth is appropriate so HR is the problem HR is low so-> bradycardia Best to treat bradycardia first before giving fluid bolus because if HR is too low to generate CO, fluid is not going to help
Anticholinergics -when to use
Bradycardia, AV block (2nd degree) • Can be inherent to patient, drugs, or procedure • Reflex increases in vagal tone (laryngeal, ocular stimulation and vasovagal reflexes) Ocular surgery (oculocardiacreflex) - press too hard on eyeball decreases BP Brachycephalic breeds- have ECG hooked up to watch if heart rate decreases-> give anticholinergic Pediatric patients Myelograms, neck or back surgery Intraoperative bradycardia and hypotension
Sodium Channel Blocker- Local Anesthetics Examples-
Bupivacaine - longer onset, longer duration of action Lidocaine - shorter onset, shorter duration of action Can combine with an opioid or alpha 2 agonist for synergistic effects
Newerdrug: Nocita
Bupivacaine liposome injectable • Slow release of bupivacaine • Long-acting LA Onset of action • Approximately 20 - 30 min Duration of action • Analgesia for up to 72h -make sure to pain score patient! Labeled only for • Dogs following cranial cruciate ligament surgery (local infiltration - closing layers only) • Cats undergoing onychectomy (peripheral NB only)
Amide-Linked LA- Bupivacaine Concentration: Toxic Dose: Recommended Dose: Indication: Onset of action: Duration of action: Comments: Notes:
Bupivacaine- High potency & long duration Concentration: 0.5% Toxic Dose: 5mg/kg (potency related to dose) Recommended Dose: Dog- 2mg/kg; Cat- 1mg/kg Indication: Infiltration; Epidural Onset of action: 10-30 min Duration of action: 4-6 hours Comments: Intermediate onset, prolonged analgesia Notes: Never IV; most cardiotoxic
Partial Mu-agonist opioid- Buprenorphine
Buprenorphine Partial mu agonist Kappa agonist? Moderate analgesia, minimal sedation Minimal respiratory and cardiovascular depression Longer Duration of action: 6h -8h- good for post op analgesic Useful for: -Mild to moderate painful procedures -post-op analgesic, stable patients -Good post-op choice for cats (IM, IV, SC, OTM) Not as useful for: - pre-med -slow onset, minimal sedation --> very painful patients or invasive procedures= do not give this drug!! Blocks effects of full mu agonists for pain Hard to reverse!- can still try with nalaxone -avoid using in critically ill patient Not useful for: -sedation -intra-op (if decide now you need full mu agonist- wont work)- Slow onset, not tritratable, hard to reverse) -Severe pain 30 mins to 1hr to get analgesic effects
How long does buprenorphine analgesia last for? Methadone?
Buprenorphine= 6-8 hrs Methadone= 2-4 hrs
• These are some of the reasons you pre-medicate a patient prior to anesthesia? EXCEPT: a) Facilitate intravenous catheterization b) Decrease stress c) Increase induction agent dose required d) Provide analgesia
C- want to use lower induction agent for less side effects
Rapid induction of anesthesia by administration of an inhalant anesthetic is primarily caused by which of the following? • A. The low potency of the gas. • B. The low partial pressure of the gas in the central nervous system. • C. The low solubility of the gas in the blood. • D. The low rate of metabolism of the gas. • E. The low respiratory rate.
C. The low solubility of the gas in the blood.
Which one of these pre-anesthetic drugs is known to cause pain on IM injection? a. methadone b. midazolam c. diazepam d. dexmedetomidine
C. diazepam -is not water soluble; viscous and may cause pain on injection
Muscarinic Receptors- M3 location and effects when activated
CNS Salivary glands- salivation Airway smooth muscle- bronchoconstriction
Benzodiazepines effects
CNS • Tranquilization and sedation (at higher doses) • Anticonvulsant • Skeletal muscle relaxant Cardiovascular • Minimal to no depression (even at higher doses) Respiratory • Minimal respiratory depression No analgesia!
Muscarinic Receptors- M4 and M5 location
CNS and heart- unknown effect
GABA agonists cause what central nervous system response?
CNS depression and hypnosis
Muscarinic Receptors- M1 location and effects when activated
CNS- Neuron depolarization Stomach- H+ secretion
Oxygen delivery=
CO x Oxygen content Oxygen content= hemoglobin, O2 saturation of hemoglobin, and partial pressure of O2
Physiology
CO2 out and O2 in Partial pressure of venous CO2 Partial pressure of alveolar CO2 Partial pressure of arterial CO2 All relatively the same - 30-45 mmHg Partial pressure of inspired CO2 = 30mmHg Anesthesia- 0 partial pressure of inspired CO2
What is CPA, CPR and ROSC?
CPA = Cardiopulmonary Arrest -Sudden cessation of spontaneous and effective circulation and ventilation CPR=Cardiopulmonary cerebral resuscitation -Treatment to re-establish perfusion to the heart and brain ROSC=Return of spontaneous circulation; have heart beat, pulse is back and perfusion to the body
CPR survival rates
CPR -small animals • > 6% of dogs and cats survive to hospital discharge ^1-3 • Higher in some cohorts of patients CPR -people • 15 -20% (patients in hospital) CPR -anesthesia related arrest • 47% survived to discharge^1 • 36.4% in cats^4
Acepromazine
Calms/tranquilizes animal -Long onset (~30 min) and duration (~4-6 h) of action Smooth recovery • 0.005-0.02 mg/kg IV, 10 min before end of surgery • Avoid with excessive blood loss, shock, colic -due to hypotension and vasodilation Hypotension and affects temperature regulation No analgesia Risk of paraphimosis (paralysis of muscles assoc. w/ penis retraction) -Avoid in breeding stallions
Recovery
Can administer acepromazine Apply intranasal phenylephrine Remove the arterial catheter and hold off the artery for several minutes Turn off the vaporizer Disconnect the fluids and ECG leads Turn off the ventilator Move the animal to recovery area Use demand valve to provide O2 (gives a big breath) • or run O2 into trach tube at 15 L/min Remove ETT after horse is breathing spontaneously • or tie ETT tube to jaw till horse stands or place nasal or nasotracheal tube • Assure adequate air movement during spontaneous ventilation
Devices- Nasal Cannula
Can be connected via Y piece to one bubble tubing Naso Gastric (NG) tubes in horses placed in the nasopharynx to insufflate O2 during recovery Apply lidocaine for application in conscious patients (pts) -30-70% FiO2 (depending on proximity to carina & flow) ->In horses: ~15L/min optimal (Muir et al) ~Feeding bubble tubing into trachea, even better -->In dogs (measured @ carina): ~50 ml/kg/min = 28% FiO2 ~100 ml/kg/min = 37% FiO2 ~150 ml/kg/min = 40% FiO2 ~200 ml/kg/min = 47% FiO2 ~Up to 80% with bilateral insufflation (less room air entrainment) sometimes is not best plan, may need to anesthetize patient to put it in
Causes of Hypoxemia
Can be due to; and think about in this order: 1. Low FiO2 -% of inspired O2 (100% under anesthesia) 2. Hypoventilation -measure CO2 not O2 for ventilation -low CO2 = hyperventilating -High CO2 = hypoventilating 3. Diffusion impairment (pneumonia, pulmonary edema) -something not allowing gas exchange 4. V/Q mismatch -ventilation/cardiac output -collapsed alveoli- good perfusion, but no ventilation -obstruction- good ventilation but no perfusion -horses have a lot of v/q mismatch 5. Shunt -good perfusion but blood is not going to certain areas -another type of v/q mismatch
Opioids- Can be given in what ways: Provide:
Can be given IM, IV or SC -Commonly with a sedative or tranquilizer Provide analgesia -hydromorphone/methadone (excellent analgesia) > buprenorphine (moderate analgesia) > butorphanol (mild) Provide sedation - hydromorphone/butorphanol> methadone > buprenorphine (does not provide much sedation; sometimes not at all)
Assessment of Pain in Small Animals- Problems
Can't communicate directly Species variation - Prey vs predator species - Protective mechanisms Individual behavior variation - Guarding, aggression, decreased appetite, less energy - ADR - 'Ain't doing right' Behavior at home compared to at the hospital - Aggression in cats especially - Exotics species and pigs become quite stressed Variation in physiologic response
Monitoring during CPR- Most important monitoring tools for CPR :
Capnography - good indicator of CPA Electrocardiogram (ECG)- tells you rhythms- so if you can defibrillate Remember: CO2 reflects perfusion not ventilation During CPR: Think Capnography& ECG! ETCO2-> perfusion
Capnography and Capnometry
Capnography and Capnometry are not the same thing. Just like ECG and HR are not the same. Capnography (graphy) implies you have a graph to be visualized with which you can make clinical interpretations. Capnometry (metry) implies you are measuring the concentration of CO2 in the gas.
Capnography vs. Capnometry
Capnometry is referring to the ETCO2 number -measurement -Diagnosis of ventilation status -Normal ETCO2 = 35-45 mmHg ○If ETCO2 is lower than 35 = hyperventilation ○If ETCO2 is higher than 45 = hypoventilation Capnography is referring to the ETCO2 graph -Useful tool for the tracheally intubated patient
Ventilation monitoring
Carbon dioxide level is dependent on ventilation, so CO2 is used as a measure of adequate ventilation Ventilation is a function of: -Tidal volume -Respiratory rate Tidal volume (Vt): volume of air in one breath -10 - 15 ml/kg Minute volume (Vm)= Vt x RR -150 - 200 mL/kg/min Bradypnea = Decreased Vt and/or RR
Alfaxalone -side-effects
Cardiovascular -Hypotension and tachycardia (at therapeutic doses) -->compensation (unlike propofol) -Hypotension follows peripheral vasodilation Respiratory -Dose-related respiratory depression -Post-induction apnea -minimize this with slow IV injection CNS -Appear to be cerebral protective similar to propofol -Does not seem to increase ICP *Similar to Propofol- maintains barroreceptor reflex
Etomidate effects -cardio -resp -muscle -endo
Cardiovascular • Minimal changes in HR, BP, SV and CO • Safe for healthy and sick patients • Often the drug of choice for cardiac procedures or patients with cardiac disease undergoing minimally invasive Respiratory • Minimal effects Muscle • Myoclonus, tremor --Usually IV induction with a benzodiazepine Endocrine • Adrenocortical suppression: dose-dependent inhibition of the conversion of cholesterol to cortisol • Not ideal for invasive surgeries, septic patients -may not be able to recover; septic patients- need cortisol to fight infection
Ketamine -possible side effects -Cardiovascular -Respiratory -Other side effects
Cardiovascular • Tachycardia and hypertension • Increased risk of tachyarrhythmias • Hypotension in critically ill patients with depleted catecholamines -May see the direct effect of ketamine on the heart Respiratory • Minimal respiratory effects • Retain pharyngeal and laryngeal reflexes Other side effects • Muscle rigidity/spasms (poor muscle relaxant) • Increase salivation • Pupils remain dilated with present corneal reflexes; remains central rather than going off ventrally
Propofol -side effects
Cardiovascular depression -Hypotension due to vasodilation (decreased PVR) -->Magnitude related to rate of administration -->Avoid use in hypovolemic, hypotensive patients Respiratory depression -Decreased responsiveness to elevations in CO2 (typical of most anesthetics) Post-induction apnea = more likely if injected fast Slow IV injection over 40-60 seconds Myoclonus • treat with diazepam or low dose ketamine Methemoglobinemia (Hb unable to release O2) Heinz bodies in red blood cells- anemia Greyhounds may have a slightly longer recovery than other breeds
How pregnancy changes anesthesia- Cardiovascular System:
Cardiovascular: Relative anemia -Plasma volume increase more than RBC count -PCV would look anemic (should expect, or else patient may be dehydrated) Decreased compensatory mechanisms Hypovolemia -Dehydration -Hemorrhage Hypotension -drugs that cause hypotension should be avoided -Anesthetic drugs -Dehydration -Positioning into dorsal recumbency (worst position, pressure on aorta-> may see a larger decrease in CO in pregnant animals in this position than non-pregnant animals)
Physical Exam- Cardiovascular
Cardiovascular: Normal heart rate and rhythm Presence of murmurs Synchronous pulses Do the distal pulses match the auscultated heart rate? • Pulse quality o Strong o Weak confirm with ECG
Receptors and Breathing- Peripheral chemoreceptors
Carotid and aortic bodies Efferent nerves are the CN IX and X Sense CO2, H+, PO2 and pH
Peripheral Chemoreceptors
Carotid body Located at the bifurcation of the carotid artery Detects alterations in blood pH, pO2 and pCO2 Modulates cardiovascular and respiratory function via sympathetic nervous system Innervated by a branch of the CN IX Low pH, high PCO2, low pO2 - increase blood pressure, heart rate and respiratory rate -> caused from hypoventilation
Baroreceptor Location- Function-
Carotid sinus and aortic arch Parasympathetic nervous system is activated - Detects changes in blood pressure - Related with the carotid body (to follow) - Innervated by a branch of CN X and IX
Which patient would you be cautious with the use of an induction dose of ketamine? cat with unknown respiratory depression cat with unknown heart murmur cat with unknown vaccination
Cat with unknown heart murmur tachycardia and tachyarhythmias
Dissociative Anesthetics- Ketamine
Cataleptic state -Not responsive to external stimulus but does not appear to be asleep Antagonism of the NMDA receptor dissociates the limbic and thalamocortical systems Central sympathetic nervous system stimulant -Causes release of endogenous catecholamines -Increases heart rate, blood pressure, cardiac output, myocardial oxygen requirements -BUT if the catecholamine stores are depleted (septic animals) then there is a negative ionotropic (contractility) effects -no increase in HR and BP (such as when sick) Commonly combined with other drugs Become eurphoric-like; stiff for awhile then relaxes
Benzodiazepines Cause excitement when given to: Good in: Provides: Avoid in:
Cause excitement if given alone to an adult horse • Good when used with other drugs for induction of anesthesia Good alone in very young foals • no excitement, just sedation Provides good muscle relaxation Avoid midazolam in horses getting fluconazole • lengthens recovery time
Anesthetic Complication: Decrease venous return causes- treatment-
Causes- -dehydration -PPV -positioning -hemmorrhage -disease: gastric dilation and volvulus; pregnancy Treatment- -treat the cause -stabilize before anesthetizing -dehydration- give IV fluids -positive pressure ventilation (PPV)- reduce volume and pressure -Positioning (dorsal recumbency)- unavoidable usually; slow purposeful position changes -Hemmorhage- give IV fluids and blood products -Disease- usually the procedure is to treat the disease
Anesthetic Complication: Contractility
Causes- -drugs: inhalational anesthesia (isofluorane, sevofluorane); ketamine in sympathetically depleted patients -heart disease -arrhythmias -disease- sepsis, electrolyte imbalance-> hypocalcemia -volume depletion -frank starling (if you don't have enough volume, your heart doesn't stretch an appropriate length -actin and myosin don't stretch fully and then they don't contract fully) Treatment- -reduce the dose of drug causing the side effect -drugs to increase contraction ->dobutamine, dobmine
Hypothalamus and pituitary gland
Central neural control ex: Antidiuretic hormone
Inhalation Anesthesia- cognition and movement
Cerebral cortex, amygdala and hippocampus - site of action for hypnosis (sleep) Spinal cord - suppression of movement Decrease cerebral metabolic rate
Rhythm check- Change person doing compressions every____min AND:
Change person doing compressions every 2min AND Check patient at the same time • Limit checks to <10 sec • Check ECG for any change (e.g. shockable rhythm) • Check for a pulse
Unresponsive, apneic patient - what do you do?
Check for pulse, if nothing->> CPR (1 cycle = 2 minutes) • Compressions: 100 -120/min, 1/3 -1/2 chest width • Ventilate: 10/min, Vt= 10ml/kg, Inspiratory time = 1sec • Initiate Monitoring: ECG and ETCO2 -> Evaluate patient; check ECG -> ROSC; Asystole/PEA; Ventricular fibrillation
Maintenance of anesthesia Choose a Maintenance plan: Based on:
Choose a Maintenance plan • Total intravenous anesthesia (TIVA) • Inhalant Isoflurane Sevoflurane Desflurane Based on: • Duration of procedure • Location of procedure • Need for sterile environment
Rebreathing systems
Circle system To-and-fro system (rarely used) Used for larger patients
Pharmacodynamics - Cardiovascular System
Clinically: HYPOTENSION - Indirect blood pressure measurement - Direct blood pressure measurement Treatment: - Decrease inhalant concentration - IV fluid therapy All inhalants depress cardiovascular system -in a dose dependent manner Titratable to effect: give enough to observe ventrally rotated eye position but not too much that it causes hypotension Desflurane > Sevoflurane > Isoflurane
What supplies are required?
Clippers bandage scissors tape vetwrap gloves prep dry gauze catheters flush t-port
Indicators of hypoventilation
Color membranes Chest movement - very subjective Apnea monitors Measurement of Vt or Vm with respirometer Capnography and blood gases - more accurate
Compressed gas tanks - come in different colors, why?
Come in different colors - code to prevent mistakes and improve safety Green- O2 Blue- N2O Gray- N May see liquid oxygen in large tanks
Tonicity
Comparison of concentrations of two solutions It determines how water moves across a semipermeable membrane Most fluids are described with tonicity compared to plasma (which is 300 mOsm/kg) Hypertonic: >300 mOsm/L Isotonic: 300 mOsm/L Hypotonic: <300 mOsm/L
Main information obtained in pre-anesthetic blood work
Complete blood count Red and white blood cell count and morphology and platelet count Chemistry Electrolyte, total protein, kidney and liver values Urinalysis Urine concentrating ability Urinary tract infections The Big Four, Emergency Panel
Injectable Analgesia- Continuous rate infusion
Consistent plasma concentration and efficacy Accumulation in some drugs possible If infusion line occludes or IV catheter is not patent the patient will receive no analgesics Usually used with potent, short acting drugs like fentanyl Requires special equipment and continuous monitoring May be more than needed for minor procedure
Autonomic Nervous System and Respiration
Control of respiration is a complex topic There are more voluntary influences to control respiration than blood pressure and heart rate The following slides include some of the receptors and reflexes that can be associated with the autonomic nervous system include- peripheral chemoreceptors, irritant receptors, bronchial C fibers
Flowmeters
Control the amount of gas entering the low-pressure portion of the anesthetic machine (flow) There is a separate flowmeter for each gas The floats should be read at the top, unless they are round, in which case they are read in the middle. -Ball float- read in the middle of the ball
Aim of chest compressions
Coronary (myocardial) perfusion pressure (CoPP) • Difference between aortic diastolic pressure and right atrium diastolic pressure CoPP= P ao-D - P RA-D
Atropine
Crosses BBB and placenta Rapid onset -if patient is about to die THINK ATROPINE! Duration of action: 15 -20min Drug of choice for CPR * Pregnant animals when fetus is bradycardic * -drug to use for pregnant animals Dilates pupil (photosensitivity for up to 24h) Some species have atropinases (rabbits, camelids, ruminants)- destroys atropine fast
Ketamine
Crosses the placenta and enters fetal circulation Neurologic reflexes in puppies born via cesarean section ketamine and midazolam- good combo usually but in pregnant animals: -The most depression of neurologic reflexes when compared with propofol and alfaxalone.
Fluid Requirements for hypotension
Crystalloid fluid bolus = 5-10 mL/kg over 10 minutes Example 1: Dog weighs 6 kg Total volume to infuse = 6 kg * 10 mL/kg = 60 mL 60mL/10 min * 60min/1 hr = 360 mL/hr More simply put: there are six 10 minute intervals in 1 hour So, multiple the total volume to infuse by 6 to get the mL/hr 60mL * 6 = 360mL/hr On the fluid pump, set the VTBI (volume to be infused) to 60 mL and rate to 360 mL/hr
Types of Fluids
Crystalloids : Aqueous solutions with mineral salts and water-soluble molecules Classified by their tonicity -Hypotonic -Isotonic -> most consistent one that is used -Hypertonic Replacement fluids for maintenance - usually what is used in anesthetic procedures (LRS or normosol R) Maintenance fluids are usually hypotonic- lower in sodium and higher in potassium - *semantics
Diazepam vs. Midazolam
D- propylene glycol vehicle -may cause hemolysis and result in anemia -Avoid rapid IV injection (may cause hypotension and bradycardia) -pain on IM administration (not water soluble) M- preferred for IM use
What is the normal systolic and diastolic pressures? The mean is closer to which one?
D= 80 S= 120 Mean is closer to diastolic pressure
Conclusion
DELIVER oxygen to patient REMOVE exhaled carbon dioxide CONTROL the deliver of volatile anesthetic agent to patient Provide a mechanism to ASSIST patients ventilation Provide a mechanism for the SCAVENGING of waste gases, thereby reducing environmental pollution
Anesthetics, Benzodiazepines, phenothiazines
DO NOT PROVIDE ANALGESIA Alter the conscious state which may alter the perception of pain but they are NOT analgesics
Epidural- dog vs cat
DOGS: Spinal cord (red) finishes around L6-L7 CATS: spinal cord finishes more caudally • Easier to do a true epidural or spinal nerve block • Insert the needle more caudally than in dogs
NSAIDs Mechanism of action
Damage to the cell membrane releases inflammatory mediators (prostaglandins) NSAIDs reduce the production of the inflammatory mediators for the cyclooxygenase (COX) pathways Prostaglandins are cytoprotective in the gastrointestinal (GI) tract and regulate blood vessel tone of kidney, regulation of salt and water balance Inhibition of these can be detrimental in patients with hypotensive insults, GI or renal disease and GI surgeries COX-1 is the constitutive enzyme (over simplification) Also involved with central mediation of pain COX-2 is the inducible enzyme (over simplification) With GI damage COX-2 is required for healing COX-2 selective drugs are used commonly to reduce the negative effects of COX-1 NSAIDs
Damage to the glycocalyx
Damaged EGL results in increased permeability, compromised coagulation, altered inflammatory response -intravascular fluids leak into the interstitium -tissue edema Damage is caused by hypervolemia, rapid administration of IV fluids, inflammatory mediators, sepsis, trauma, endotoxins, hyperglycemia etc
Pre-anesthetic blood work- what is done previously with the blood work? What other things should you consider?
Day of PCV/TP, blood glucose and BUN and/or lactate (Big 4, Emergency panel etc) for healthy patients or patients with blood work gives you day of hydration status Blood work requirements should be patient specific Pre-operative panels vary depending on exactly what values you are looking for (This information is directed by your physical exam and history)
Respiratory side effects
Decrease ventilatory response to both CO2 and hypoxemia. -central nervous system is able to respond with increase respiratory rate and tidal volume if CO2 goes up or O2 goes down -inhalants will suppress that reflex and so patient can die from hypoxemia while anesthetized Tidal volume and minute ventilation decrease -so alveolar ventilation will decrease as well Respiratory Rates rises Inefficient ventilation: increased ratio of dead space to tidal volume. -with higher resp. rate and lower tidal volume you have inefficient ventilation Expiratory muscle recoil→ promotes atelectasis -muscles might relax too much
Peripheral sensitization
Decreased threshold and increased responsiveness of nociceptors Injury, infection can cause tissue inflammation and change the chemical environment around the nociceptor
If blood pressure is low (vasodilation) deep- light/adequate-
Deep- reduce dose of inhalant, if no response check heart rate light/adequate- check heart rate HEART RATE- low- give anticholinergic (atropine) or reversal; if no response- IV fluids- if no response-> adjunct medications normal/high- give IV fluids
Defibrillator -external defibrillation
Deliver an electric current from defibrillator paddles to the myocardium • The entire myocardium is depolarized simultaneously • Disrupt aberrant conduction = terminate fibrillatory rhythm Shockable rhythms: Vfib, pulseless SVT, pulseless Vtach Internal defibrillator= open chest CPR If you shock and see asystole now, that;s okay because at least you stopped the uncoordinated electrical currents -but immediately start chest compressions again
Function of the breathing circuit (or system):
Deliver the fresh gas to the patient, Remove exhaled carbon dioxide, Reduce pollution (scavenging waste gases).
How do you convert % to mmHg?
Dependent on the atmospheric pressure Sea level is 760mmHg Multiple % * atmospheric pressure = Partial pressure Example at sea level: 21% * 760 mmHg = 160mmHg
Which port to use, why?
Depress syringe into port and twist to tighten luer lock syringe If using a non-luer lock syringe, depress into blue port, ¼ turn and it should stay in place If blue port if visible contaminated, wipe with alcohol Do NOT use needles in the blue microclave port
Airway irritation
Desflurane and isoflurane are "pungent"- they make people cough and can cause bronchospasm Sevoflurane and halothane are well tolerated for inhalation induction (mask/box) Dose dependent bronchodilation
Non-Rebreathing Systems- Bain System
Designed for smaller patients For patients with body weight smaller than 5 kg ******* Most used non-rebreathing circuit in veterinary anesthesia. Its features include: A. Valveless coaxial system B. Low resistance due to the absence of valves C. Some warming of inspired gases due to coaxial design POP-OFF valve-> very important (most moralities) When using the Bain circuit: - Flow rate of oxygen: 150 ml/kg/min during induction, maintenance and recovery is associated with no rebreathing of expired gases.
Large animal circle system
Designed for the 150 kg to 2 Ton Flow rates are lower than small animal 10-30 ml/kg/min **** If it was the same rate as for small animals- that would be way too much
Drugs that activate alpha2 receptors
Dexmedetomidine Xylazine Detomidine Romifine Dopamine Ephedrine Epinephrine
Examples of Alpha 2 Agonists
Dexmedetomidine - small animals, exotics, pigs, CRI's in horses Xylazine, detomidine, romifidine - large animal
Hypotension Dexmedetomidine = _____BP Acepromazine = _____BP Hydromorphone = _____BP Propofol = _____BP Isoflurane = _____BP
Dexmedetomidine = __increase___BP Acepromazine = __decrease___BP Hydromorphone = __no change___BP Propofol = ___decrease__BP Isoflurane = __decrease___BP
Sedation/chemical restraint -Alpha 2 agonists
Dexmedetomidine • IM, IV, SC, intranasal (IN), oral transmucosal(OTM) -most used for small animals Xylazine • mainly for large animals, shelters may still use for cats Detomidine • large animals Romifidine • large animals - recovery for crazy horses (know will have hard recovery) Medetomidine • no longer in US
3y old, male intact, Pointer, weighing 24kg. He requires general anesthesia for a 3cm superficial benign mass removal in his left forelimb. Blood work and physical examination are unremarkable and he is bright alert and responsive (BAR). Choose an appropriate analgesic (with the correct justification) to provide neuroleptoanalgesia
Dexmedetomidine. Good and reliable sedative and has analgesic properties
Decision for C-section
Diagnosis Dog: pregnant >70 days Cat: pregnant >71 days Continuous straining for > 1 hour Black or green discharge before the first puppy 3 or more hours between puppies Dam is ill or distressed Puppy is stuck or malposition Calcium level Fetal heart rate < 180 = distress Fetal heart rate < 160 = emergency intervention required Ultrasound X rays Doppler
Which drug can only be drawn up immediately prior to administration?
Diazepam -adheres to plastic -cannot to CRIs
Causes of CPA - dogs/cats vs people
Different causes of death -dogs/cats - usually respiratory arrest, systemic disease -people- usually cardia arrest, stroke, systemic disease animals can have completely different body conformation -barrel vs long chest -brachicephalic- harder to incubate need for our own CPR approach
Causes of CPA -dogs/cats vs people
Different causes of death • Dogs/cats -usually respiratory arrest, systemic disease • People -usually cardiac arrest, stroke, systemic disease
Brachycephalic
Difficult airways need to be managed with intubation
Local infiltration
Diffuse infiltration of operative area Uses: • Incisional line block • Wound repair • Mass removal • Testicular block
How do we monitor blood pressure?
Direct- Invasive-> gold standard Indirect Non-invasive blood pressure monitors -Dopper -Oscillometric
Informed consent
Discussion with the risk of anesthesia is crucial In veterinary medicine, the degree of workup if often dependent on the owners compliance and ability to afford it Need to be mindful of an informed, complete conversation regarding the option for work up and anesthetic procedures The more you understand, the more the owners will the willing to do and comfortable with the situation Anesthesia is often one of the biggest worries when undergoing a procedure
Injectable anesthetics
Dissociative (cyclohexamines) anesthetics • Ketamine Propofol Alfaxalone Etomidate
Ketamine Type MOA
Dissociative anesthetic agent Mechanism of action NMDA receptor antagonist NMDA receptor is present throughout the CNS • Dissociative effects in the thalamocortical and limbic CNS • Analgesic properties • Better analgesia for somatic pain (less for visceral pain)
Distribution of Electrolytes is important for:
Distribution of electrolytes is important for normal physiologic function, generation of action potentials, acid-base balance, fluid balance
Drugs that activate Beta 1 receptor
Dobutamine -& dopamine are common for hypotensive and compromised patients Dopamine Ephedrine Norepinephrine Epinephrine
Glycopyrrolate
Does not cross blood brain barrier or placenta Slower onset, more gentle, drug of choice for most peri-anesthetic uses -less dramatic increase on HR Duration of action: approximately 1h Not affected by atropinases (can use on bunnies, etc) No effect on pupil More potent than atropine (= lower dose needed)
Ketamine is a dissociative anesthetic commonly used in small and large animals. However, ketamine is not administered alone due to:
Does not provide muscle relaxation
CPA under GA: also consider blood loss and drug overdose
Dog blood volume (9%) = 90ml/kg Example: 20kg dog Blood volume = 1800ml (1.8L) Tolerated Blood loss (<20%) Acute blood loss (15%) = 270ml Monitor blood loss, if getting close to 270ml blood loss, act fast • Fluids, blood sample (PCV, TS, lactate), blood products
Mortality data: Dog, cat, and rabbit % risk of anesthetic-related deaths
Dog- 0.17% Cat- 0.24% Rabbit- 1.39% These sick animals are ASA 3-5
Mortality data: % risk of anesthetic on sick dogs, cats, rabits
Dog- 1.33% Cat- 1.40% Rabbit- 7.37% These sick animals are ASA 3-5
FYI Alfaxan IV induction doses cat- dog-
Dogs 1-2 mg/kg if premed 2.5 mg/kg if not premed Cats 2-3 mg/kg if premed 4 mg/kg if not premed May be part of IM combo for sedation Example: Cat: Butorphanol 0.2mg/kg + Alfaxan 2mg/kg IM
Total Blood Volume and Acceptable blood loss
Dogs 90 mL/kg Example: Dog weighs 10 kg Total blood volume = 10kg * 90 mL/kg = 900 mL Acceptable blood loss (10%): 900mL * 10% = 90 mL Cats 60 mL/kg Example: Cat weighs 3 kg Total blood volume = 3 kg * 60 mL/kg = 180 mL Acceptable blood loss (10%): 180mL * 10% = 18 mL *Another method to calculate total blood volume is an estimate of body weight but this may overestimate total blood volume Dogs 10% of body weight Cats 8% of body weight
diazepam/midazolam premedication
Dogs and cats : GERIATRIC PEDIATRIC, NEONATE SICK, DEBILITATED, DEPRESSED Pigs, rabbits, birds : Good, more reliable sedation Commonly combined with butorphanol, alpha-2 agonist and/or ketamine IM Good pre-med for pigs- medazolam, butorphanol and dexmedetorphine
Drugs that activate Beta 2 receptors
Dopamine Ephedrine Epinephrine
Intermittent Dosing- Peak and trough effect- Repeat injections either IV or IM
Dose administered at intervals based on the duration of effect If IV often profound effect (analgesia) and side effect (sedation) at first -But rapid response, good if patient needs immediate intervention -Repeat injections of drugs like propofol allow miniatous of anesthesia for minor procedures IM takes time to absorb and repeated painful experience for the animal -But good to allow anxiolysis and sedation to take effect for stressful or painful procedures like handling and restraint (especially cats)
Effective dose or concentration
Dose require to achieve a desired response EC50 or ED50 is the effective concentration or dose that will elicit a desired response in 50% of the animals it is administered to
Lethal dose
Dose require to achieve lethal toxicity LD50 is the dose to induce death in 50% of the animals it is administered to
Propofol -pharmacodynamics
Dose-dependent depression of CNS GABA agonist Modulates GABA A receptor • Depression of the CNS through enhancement of the actions of the inhibitory neurotransmitter GABA
Benzodiazepines effects
Drug of choice for sick, unstable patients Minimal/unreliable sedation in healthy dogs, cats or horses More reliable sedation in human and pigs* Centrally acting muscle relaxants Anti-convulsants Minimal cardiorespiratory depression Reversible: specific antagonist -flumazenil (can be given IV)
Treatment types
Drugs Regional and local anesthesia Alternative Therapies
Induction of anesthesia Drugs- How CV stable is the patient?-
Drugs Ketamine + Benzodiazepines Ketamine + Guaifenesin (muscle relaxant) Ketamine + Propofol How CV stable is the patient? Unstable: GG and ketamine Relatively stable: Ketamine and Benzo Healthy horse: whatever I want (Ketamine + benzo commonly used)
Premedication Drugs and Goals of Premed:
Drugs • Acepromazine • Alpha 2 agonists -xylazine, detomidine, romifidine -->Opioids optional (likely used, butorphanol) Goals of premed Minimize stress Keep humans safe Decrease additional drug requirements Decrease drug side-effects
The endotracheal tube
ET tube I will intubate the trachea We don't say we will intubate the dog We identify the internal diameter (ID) And the outside diameter (OD) Cuff designed to seal the airway
End tidal carbon dioxide
ETCO2
End tidal carbon dioxide
ETCO2 increases as you expire The amount of carbon dioxide present at the end of an exhaled breath.
Monitoring anesthesia importance
Early detection of anesthesia related cardiovascular and pulmonary complications is key to reduce anesthesia-related mortality rates
3- The following ETCO2 diagram is an example of a
Effective CPR
Local anesthesia
Effective in all ages Same techniques Dose requirements are lower for neonatal and pediatric patients Castrations are the most common elective surgery for the pediatric patient effective and inexpensive
Efficacy
Efficacy - therapeutic effectiveness of a drug Emax is the maximal response possible
Common arrest rhythms- Pulseless electrical activity (PEA)
Electro-mechanical uncoupling- heart cells have some electrical potential but they do not result in contraction also very common- no pulse, no blood being pumped out of heart Never shock!! Resume chest compressions
Fluid Movement Theories- Endothelial Glycocalyx Layer
Endothelian glycocalyx layer (EGL): glycoprotein and proteoglycan layer that covers the endothelium of the vasculature Acts as a sieve/trap for proteins -which helps regulate vascular permeability Involved with coagulation, inflammatory response, cholesterol deposition on vascular endothelium etc. arterial end of capillary has higher pressure than the venous end Most return of fluid from the interstitial space to the vasculature is actually through the lymphatic system
How does alfaxalone work?
Enhance the action of inhibitory neurotransmitter GABA
Equine Morbidity data-
Equine - Have intraoperative morbidities including hypotension and respiratory depression but more post-operative complications including fractures, neuropathy, myopathy, colic leading to euthanasia
5- The following ETCO2 diagram is an example of a
Esophageal intubation
Body core temperature monitoring
Esophageal temperature probe: Temperature probe (Thermistor) The tip of the probe at the level of the 8th-9th intercostal space - NOT in the stomach
Anesthetic depth -monitoring
Evaluate your patient every 5 minutes -avoid making decisions on one variable May see settle signs first • Spontaneous movement • Eye position • Palpebral reflex • Jaw tone • Corneal reflex • Withdrawal reflex • Heart rate and/or blood pressure • Respiratory rate, effort and EtC02
Anesthesia -safe approach
Evaluate- • History • Blood work if present • Physical exam Choose appropriate- • premedication • induction agent • maintenance agents Determine- • Appropriate equipment • What to have ready to go • What to connect before induction Think- Why monitoring becomes even more important when I administer drugs to an animal?
Anesthesia recovery- important for:
Even more important in neonatal, pediatric and geriatric patients Provide: -Oxygen -Heat -Continuous cardio-respiratory monitoring
Hyperalgesia
Exaggerated response to normally painful stimulus
Sedation - Example of a protocol: Local anesthesia technique:
Example of a protocol: 1. AcepromazineIM 30min prior to procedure 2. Detomidine IV just prior 3. Local anesthesia technique (local block) Local anesthesia technique • analgesia (blocks beginning of pain pathway- transduction) so no AP • local or regional effects • reduce need of systemic drugs
Tricyclic Antidepressants
Example: amitriptyline Alter the serotonin and norepinephrine reuptake Serotonin is an inhibitory neurotransmitter
Anticonvulsants
Example: gabapentin Unclear mechanism of action Neuropathic pain, decrease development of chronic pain
Ventilation settings: Excess ventilation
Excess ventilation -hyperventilation •Reduces CPR success rate in humans and animals oDecreases CoPP (coronary perfusion pressure) oDecreases venous return, preload and CO oIncreases intrathoracic pressure -puts pressure on larger vessels and decreases venous return to the heart
Anesthesia machines - Improper use
Excessive RESISTANCE to ventilation Hypoxia Hypercapnia Excessive PRESSURE transmitted to lungs Anesthetic overdose and DEATH
Mask induction with inhalant
Excitement phase May regurgitate - risk of aspiration pneumonia Acceptable for small dogs and cats if don't have propofol or hydromorphone, but not best choice
What is the cause of emergence delirium?
Excitement phase of inhalant anesthetics Rapid, explosive recover related to inhalants -emergent, excitement= inhalant
STEP 2: Recognize changes
Expected SpO2 during anesthesia with 97%+ O2 and good ventilation • 98 -100% SpO2 < 95% could indicate some degree of hypoxemia • make sure it is true! Determine if there is a plausible reason for that animal to be hypoxemic • e.g. procedure, co-morbidity, machine Remember: many variables can affect the readings
Level of anesthesia: Too deep
Eye position -Central Palpebral reflexes -Non present Muscle tone -Relaxed probably hypotensive -Lower isoflurane
Level of anesthesia: Too light
Eye position -Central Palpebral reflexes -Only medial present Muscle tone -Relaxed to strong
Level of anesthesia: Too light
Eye position - Central Palpebral reflexes - Only medial present Muscle tone - Relaxed to strong
Level of anesthesia: Surgical plane
Eye position -Ventrally rotated Palpebral reflexes -Not present Muscle tone - Relaxed jaw
Level of anesthesia: Too deep
Eye position - Central Palpebral reflexes - Non present Muscle tone - Relaxed
Stages of GA- 1 (awake)
Eye position- normal Palpebral reflex- ++++ Jaw tone- ++++ Corneal reflex- normal Nystagmus- ++++
You should stop chest compressions to gain IV access a) True b) False
False
Alpha-2 agonists are the drug of choice for sick patients- true or false?
False- one of the drugs of choice for healthy patients
Isoflurane and inhalant anesthetics distribute into
Fat During the recovery phase they must exhale the inhalants because they are minimally metabolized They will have to redistribute the equilibrium during the recovery phase as the inhalant concentration decreases
Checking the animal:
Feel the pulse -facial, metatarsal (lateral), palatine artery as well Check the breathing -rate, pattern Check the palpebral reflex Apply eye lubricant to both eyes Always protect the lower eye Start the anesthesia record Adjust padding if necessary Start fluids
The dose of hydromorphone 0.1 mg/kg will produce an equivalent level of analgesia as fentanyl 0.005 mg/kg. Which drug is more potent?
Fentanyl
Opioids:
Fentanyl Short acting (15 minutes) Acceptable for premedication if needed Reversal for neonate - naloxone sublingually Hydromorphone Acceptable for dam AFTER fetus is removed and for post operative analgesia May cause sedation in recover (4 hours) Buprenorphine Acceptable for dam AFTER fetus is removed and for post operative analgesia Less sedation than hydromorphone and longer acting (6 hours) Remifentanil Half life = 1-2 min Ultra short acting Acceptable for premedication if needed (as a CRI) No need of reversal for neonate since its ½ life is 1 minute long Expensive -if don't have fentynal, best option is to administer hydromorphone after delivery
Morphine and fentanyl are both full mu opioid agonists Dose to achieve clinically relevant analgesia using morphine is 0.5 mg/kg Dose to achieve clinically relevant analgesia using fentanyl is 0.005 mg/kg Given they achieve the same level of analgesia at these doses: which drug is more potent?
Fentanyl- takes less for same response
Causes of hyperthermia
Fever Increased hypothalamic set point Infection, inflammation, septicemia, endotoxemia -Common caused of anesthesia cancelation Hyperthermia Increased heat generation, increased basal metabolic rate, increased muscle activity, increased thyroid hormone, increased sympathetic activity Adverse drug reaction, serotonin syndrome, seizures, pheochromocytoma, malignant hyperthermia Increased ambient temperature Decreased heat dissipation
Cardiovascular system
Fingers on the pulse (HR and quality) Auscultate the heart (feel pulse at same time) Esophageal stethoscope Blood pressure -dopler ECG -diagnose arrhythmias Pulse oximeter = pulse rate ± quality
Patient evaluation for fluid administration; consider:
Fluids should be considered a drug! Fluid administration should be patient, breed, age specific. co-morbidities Complete physical exam (skin tent, mucous membrane, capillary refill time) and blood work (PCV, TP, USG) will indicate if the patient is dehydrated, anemic, in shock -TP and PCV helps determine hydration status -USG determines concentration of urine; indication of hydration as well In higher ASA patients also consider the condition they are presenting for (GI disease, sepsis, trauma), look for compensatory mechanisms like tachycardia, additional blood work including electrolytes and lactate
Negative Effects of Crystalloids and Colloids
Fluids should be treated as drugs Side effects: Fluid overload especially in small patients, normovolemic patients Coagulopathies Dilutional - If you get massive amounts of fluids, you can dilute out the clotting proteins in the blood Dislodge blood clots With rapid infusion of fluids Disruption of the glycocalyx Especially with septic patients and rapid administration of high-volume fluids Kidney failure Some colloids in human medicine with long-term infusions in septic patients This is not well proven in veterinary medicine Informed decision to use colloids should be made
TIVA for short duration anesthesia Protocol ex:
For 20 minutes to 1 hour Xylazine IV Ketamine + Diazepam IV Triple drip (guaifenesin 5% + ketamine + xylazine) CRI -to maintain for shorter procedure
Inhalant for longer duration anesthesia
For delicate procedures or those lasting 1 or more hours (e.g. colic, arthroscopy, conj graft) Xylazine IV Ketamine + Diazepam IV Inhalant Anesthesia
Pin Index Safety System
For each gas type, a unique configuration of pins on the hanger yolk conforms to the configuration of the cylinder head. -yolk holds oxygen tank in place This aids in the prevention of attaching the wrong type of gas cylinder to the anesthetic machine.
Oxygen Flush Valve
For emergencies: Not safe- delivers a very high flow Located between the regulator and the fresh gas outlet Delivers oxygen at 35-75 L/min (avg. 50 L/min) Bypasses the vaporizer - diluting the anesthetic gas-> patient will wake up High pressures - Transmitted to the thorax of a patient connected to the breathing circuit.-> leading to possible pneumothorax - Should not be used with a non-rebreathing system - Should not be used with patient connected to breathing system Dilute the anesthetic gas Used to reduce the concentration of anesthetic in the circuit quickly
Treatment of HYPOTHERMIA
Forced air heat blankets warm blankets heat-moisture exchanger warm towels
Alveolar fraction of anesthetic - FA MAIN DETERMINANT OF BRAIN Pp How it works:
Fraction of inhaled isoflurane- 16mmHg ▪Vaporizer setting (0-5%) ▪Fresh gas flow (o2 going through machine to patient) ▪Absorption and volume of machine and breathing system (absorption from the machine can occur and the amount of the vaporizer will be less (output less than input); concentration will rise which influences inspired concentration of isoflurane) -meaning even though you are giving a higher concentration, does not neccessarily mean that the patient will be inspiring that concentration FA- alveolar concentration Alveolar concentration of anesthetic- -Concentration from tube to alveolar drops significantly ▪Fi -inspired concentration ▪Functional Residual Capacity (amount of air you have in your lung) ▪Alveolar ventilation (determined by alveolar rate and tidal volume) Inhaled anesthetic is removed from alveolar to blood: -Venous blood = 0mmHg concentration of isoflurane -arteriole blood= now has 8mmHg concentration of isoflurane ▪Blood/gas solubility ▪Alveolar perfusion (cardiac output) ▪(Arterial concentration - venous concentration) At some point, inspired (Fi), Arteriole (PA), Alveolar (FA), and Venous (PV) concentration of the inhalant are all the same mm Hg: -Equilibrium-> uptake stops Tissues are saturated - the total time a patient is under anesthesia is too short to allow saturation of all tissues
What is the greatest cause of recovery-associated mortality in horse?
Fractures -tend to stand up faster than they should sedate
Circle System - Components
Fresh gas outlet Inhalation one-way valve Inhalation breathing tube Y-piece (patient end- connect endotracheal tube here) Exhalation Breathing Tube Exhalation one-way valve Reservoir or Rebreathing bag (adds compliance to the system) Pop-off valve-most dangerous part of anesthesia machine (also referred to as the Overflow or Adjustable Pressure Relief Valve) Carbon Dioxide Absorbent Canister Pressure gauge (manometer)
Describe how the electrical impulse travels in the heart:
From the sa node to av node-> delivered through the atrium (coordinates the contraction of the atrium) Then travels down the bundle of his and the perkinje fibers which depolarizes the ventricles (which will contract) After depolarization, there is repolarization, which occurs in opposite direction depolarzation of atrium correlated with P wave ventricles= QRS repolarization of ventricles= T wave
Examples of Opioids
Full Mu agonists - hydromorphone, morphine, fentanyl Partial Mu agonist - buprenorphine Mu antagonist, kappa agonist - butorphanol Tramadol - weak mu opioid agonist, norepinephrine and serotonin reuptake inhibitor -Questionable evidence of efficacy
Morphine
Full Mu-agonist opioid May cause histamine release, especially IV Lasts for 2-4h when given IM Given IV = 2 h Good sedation and excellent analgesia Most associated with histamine release -especially when given IV and high doses -less likely seen with IM but still happens
Methadone
Full Mu-agonist opioid Lasts for 2 -4h Only mild sedation (dose-related); excellent analgesia * Usually no vomiting in comparison to morphine and hydromorphine it causes less regurge and gastric reflex
Hydromorphone
Full Mu-agonist opioid Lasts for 2 -4h given as IV IM last 4 hrs aprox Good sedation; excellent analgesia
Fentanyl, sulfentanil
Full Mu-agonist opioid Short acting -IV last approx 15 mins Usually as a constant rate infusion (CRI)
Which type of opioid is hydromorphine
Full mu opioid agonist
What is the mechanism of action of Propofol and Alfaxalone?
GABA agonist
Etomidate
GABA-agonist Modulates GABA receptor • Depression of the CNS through enhancement of the actions of the inhibitory neurotransmitter GABA Route of administration: IV Available product • High osmolality • Potential for RBC damage (hemolysis) -can dilute to decrease this side effect Usually administered with an opioid and/or a benzodiazepine Hepatic metabolism
NK 1 Receptor- what is it, location, physiological effect, modulation
GPCR Endogenous ligand: Substance P (excitatory) Location: diffuse throughout body Physiologic effect: excitatory potential leading to vomiting and the facilitation of pain and hyperalgesia Modulation: clinically inhibition of this receptor may be beneficial in providing analgesia and antiemetic NK-1 receptor ANTAGONIST CERENIA
Opioid receptors
GPCR on nociceptive neurons - inhibition of cAMP, inhibition of Ca2+ channels in presynaptic membrane reducing glutamate and substance P (excitatory NT), increase K+ outflow Hyperpolarization of nociceptive neurons and increased activation threshold Receptor subtypes and variants explain different responses to opioids including different side effects (mu, kappa, delta) Location: brain, spinal cord, chemoreceptor trigger zone, gastrointestinal tract, synovium, urinary tract, leukocytes, cough center etc. Physiologic response: activation of the opioid receptor ultimately inhibits the action potential generation on neurons that normally transmit pain enhancing the activity of this receptor will provide analgesia, sedation etc.
7 Inhibitory Neurotransmitters
Gamma-amino-butyric acid (GABA) Enkephalin Glycine Serotonin Dopamine Opioids Cannabinoids
Factors not influencing MAC
Gender Duration of anesthesia PaCO2 (from 10 - 90 mmHg) PaO2 (from 40 - 500 mmHg) Metabolic alkalosis or acidosis Moderate anemia Moderate hypotension Potassium
Types of Anesthetic Complications
General - hypotension, bradycardia, pain, hypoxemia, etc Patient specific- aggressive, renal disease, murmur, pediatric/neonatal, etc. Procedure specific- difficult access to patient, expected blood loss, ocular surgery- vagal response
Assessment of Acute Pain- Behavior
General Appearance Behavior: Pre- and post surgery - Always look at the animal before it is an elective procedure Aggression - If the animal is not aggressive before surgery - assess pain carefully - If it is a genuinely aggressive animal - this can make things a bit more difficult Purring, tail flicking (cats) -Purring can be a sign of affection or stress Interaction with humans and environment Sleeping, crying, whimpering - Study before the routine use of opioids postoperatively for ovariohysterectomies shows very little sleep in dogs Appetite -Variable with individuals and species
Renal system- general anesthesia can lead to: key:
General anesthesia -Can lead to 40% reduction in renal blood flow and glomerular filtration. That is not a good combination! Key is to keep normal blood pressure
Balanced anesthesia should be the goal using:
General anesthesia Opioids Alpha-2 agonists Benzodiazepines Local anesthesia
Eye position - farm animals
Globe turned ventrally or ventromedially • animal is in surgical plane of anesthesia Globe in a central position • too deep (or too light) Palpebral reflex not best in judging depth of anesthesia • camelids (like horses) may retain palpebral
4 excitatory neurotransmitters
Glutamate Substance P Nerve growth factor Cholecystokinin
Conclusion
Glycocalyx is the protein layer important for the maintenance of oncotic support and vascular volume Total blood volume dog: 90 mL/kg; cat 60 mL/kg Acceptable blood loss is 10-15% of total blood volume Crystalloids are used to replace losses and maintain blood pressure during anesthesia. Only 25% remains in vascular space after 30-60 minutes Fluids during anesthesia: use 'replacement' crystalloid fluids (LRS): dog: 5mL/kg/hr and cat 3 mL/kg/hr Crystalloid bolus can be administered in the treatment of hypotension: 5-10 mL/kg over 10 minutes. Know how to calculate and what to set at VTBI and rate on the fluid pump Colloids are used for treating more profound hypotension and colloid support. Peak effect lasts approximately 4-6 hours, total effect 24 hours. Blood products are used to replace blood loss. Whole blood for hemorrhage, packed cells for RBC loss and plasma for natural colloid support (not replacement of albumin) Calculate a fluid plan for hemorrhage. 15-20% blood loss: crystalloids and colloids; >20% blood loss: crystalloids and blood products Describe the negative effects of fluid administration
Some patients may require administration of an anticholinergic as part of the premedication or during the intraoperative period. Which of the following drug is an anticholinergic and why do we use it? Glycopyrrolate. Increase heart rate Guaifenesin. Increase heart rate Atropine. Increase myocardial contractility Acepromazine. Increase myocardial contractility
Glycopyrrolate. Increase heart rate
Epidural -which drug? -why use?
Gold standard Lidocaine - lasts shorter than bupivacaine and will recover faster No respiratory depression, Good analgesia No side effect on fetus Long side effects; nursing may be compromised if can't feel hindlimbs or mammary glands Good time investment -can take time so epidural is good as it can be done quickly Should be performed by well trained personnel to save time
Alpha2 receptors- location and effects when activated
Good analgesics in large animals Vascular smooth muscle- vasoconstriction Presynaptic neurons- decrease NE release Pancrease- decrease insulin release Platelets- platelet aggregation CNS- decrease sympathetic discharge- sedation Spinal cord, CNS- analgesia Kidneys- vasoconstiction
Propofol Good in combo with ___ in adult horses Duration- Recovery-
Good in combination with Ketamine for induction of anesthesia in adult horses • Replaces benzodiazepines (for muscle relaxation) • Allows lower dose of ketamine to be used • If used alone, volume needed for induction is almost 100ml in an average size horse! Shorter time after induction until horse wakes up so must move quickly Recovery will be quicker and smoother
Cesarean section protocol
Good physical exam Pre-clip the abdomen Cardiovascular monitoring Have a mechanical ventilator ready Place an IV line without sedation Have your teams ready -Surgery -Anesthesia -Resuscitation -Communication is key for success
Chronic Pain
Greater than 1 - 3 months May outlast tissue injury Usually involves changes in central processing Usually a pathologic state Example: Osteoarthritis
Client communication/expectations
Guide owners to make the best choice for the animal (be realistic) Manage expectations (yours and the owner's) • Known success rate of CPR and discharge from the hospital • If no drugs/facilities/experienced team = success rate is even lower Can be quite expensive • May require long hospitalization = post-arrest stabilization and care • No facilities or experience = REFER the animal as soon as possible
Benzodiazepines effects
Healthy dogs, cats, horses: IM benzodiazepines • Minimal or unreliable sedation IM or IV benzodiazepines • May cause disinhibition • "Disinhibit" inhibited behaviors -healhy nice dog-> benzo may make patient become excited/aggressive (disinhibition) --> not drug of choice for healthy patients -Horses usually get IM or IV alpha 2 agonists
What to remember for the cardiovascular system when selecting drugs:
Heart rate vasculature contractility what receptors are modulated
What to consider with Equine neonates
Heart rate (HR ) has a primary function in controlling cardiac output (CO) and blood pressure (BP) Prudent to minimize the use of alpha-2 agonists in neonates &compromised older foals • Think young animal = consider benzodiazepine Equine neonates and foals - -Assisted foal recovery until 5 - 6 months of age
What is the impact of rebreathing?
Heat and humidity from expired gases -when expired gas comes out, inspired gas (O2) coming through the center tube is being warmed by the expired gas (CO2) increased Rebreathing, decreased concentration of anesthetic gas within the system. Rebreathing dilutes the anesthetic gases Induction = higher flow rates - not for Bain system Recovery, rebreathing can delay recovery - Increased flow rates -eliminating some isoflurane back to breathing system and getting re-anesthetized over time
Hyperthermia -less common
Heating pad too high -Animal with heavy fur coat can become hot quickly -When temp starts rising, may rise fast Response to drugs -Opioids in some cats (often slowly over several hours) -Check temperature q1h in recovery -Acepromazine can cause hyperthermia in a hot environment (poor temp regulation) Heavily muscled/furry dogs -Occasionally develop hyperthermia -giant breeds -can become hot easier Malignant hyperthermia -Some pig breeds -Reports in small animals but unclear (e.g. greyhounds) -high fast increase in CO2, muscle tremors, acidosis, death
Post-cardiac care
Hemodynamic optimization -Central venous O2 saturation (ScvO2) or lactate -Arterial blood pressure, central venous pressure, PCV, and arterial oxygen saturation (PaO2)-> 80-100mmHg Always remember to think about your patients blood! check PCV and TP for blood loss
Propofol -pharmacokinetics
Hepatic and Extra-hepatic metabolism • metabolism by cytochrome P450 enzymes • extra-hepatic sites: skin, GIT, etc. -many ways to metabolize the drug Repeated administration or CRIs • does not prolong recovery in most species = used for total IV anesthesia (TIVA) • occasional prolonged recoveries in cats - Inability to conjugate phenols -Cumulative effects -avoid doing repeated injections and giving to cats
You patient is under general anesthesia. It has an endotracheal tube in place and is maintained with inhalant anesthesia with 100% oxygen. You notice the patient is very deep and is actually apneic (not breathing). But the pulse oximeter is reading 98%. How is this possible?
High FiO2 You still want to correct the apnea and hypoventilation In healthy patients even with severe hypoventilation, if administering 100% oxygen by an endotracheal tube during general anesthesia it is unlikely they will become hypoxemic.
Alpha 2 agonists - Higher doses may- May cause- Have profound ______ effects
Higher doses may be needed in excited patients -instead of giving more and more for crazy patient Better in these patients if combined with other drugs Can be less effective if overly excited animal Very useful in combination with other agents (synergy) May cause vomiting -Especially higher doses (e.g. xlazinein cats) ** Have profound cardiovascular effects
Duration and intensity of effect- Drugs with large dose ranges
Higher doses will have greater effect and more side effects usually
Hind-limb NBs Pelvic/perineum NB
Hind-limb NBs: -Epidural -Sciatic and femoral NB • Nerve stimulator and/or • Ultrasound-guided Pelvic/perineum NB: -Coccygeal/sacrococcygeal
In what species when assessed consciously can heart rate be associated with the presence of pain?
Horse
Horizontal nystagmus
Horses -Horizontal nystagmus Good indicator of light plane
Question Healthy mixed-breed dog, 1y old female, weighing 20kg is undergoing general anesthesia for an abdominal explore (foreign body). Which drug will best provide the appropriate level of analgesia for this painful surgery? a) Butorphanol b) Buprenorphine c) Hydromorphone d) Midazolam
Hydromorphone -full mu opioid agonist
4- The following ETCO2 diagram is an example of a
Hyperventilation
Geriatric hepatic systems- Main clinical effects of liver failure
Hypoproteinemia Coagulopathies Hypoglycemia Always do comprehensive panel
Be careful with fluids! why? -hyptension: -fluid overload:
Hypotension -Adequate venous return -Fluid balance -Minimize the risk of anesthesia Fluid overload- not all patients can handle it ○Congestive heart failure ○Pulmonary edema Fluid rate should be prescribed based on the individual need, hydration and physical status
Common perioperative complications
Hypotension (SBP < 100mmHg, MAP < 70mmHg) 1. Check depth of anesthesia -decrease inhalant % if possible 2. Check hydration status (MM, HR, BW) -fluid bolus or increase fluid rate? 3. Start vasopressor i.e. dobutamine CRI Dobutamine CRI -Short acting Beta-1 adrenergic agonist -Positive inotrope (increase myocardial contractility) -Improves cardiac output and BP
What is the main cardiovascular effect of Acepromazine?
Hypotension (low blood pressure)
4 year old, male castrated, mixed breed dog, 40kg undergoing a complicated femur fracture repair. You premedicated him with IM hydromorphone and dexmedetomidine at 8am, induced anesthesia with IV propofol and anesthesia is being maintained with isoflurane in 100% oxygen. Surgery started at 11:30am and 20min later he developed a mild palpebral reflex and increased jaw tone. Heart rate went from 98 to 124bpm.You increased your isoflurane% and achieved an adequate plane of anesthesia. Blood pressure went from a mean arterial BP of 75mmHg to 58mmHg, respiratory rate from 20 to 10 breaths per min and the EtCO2 from 32 to 44mmHg. You cannot decrease the inhalant dose because the dog becomes light. What is your concern, what should you do next and why?
Hypotension. Administer an analgesic; MAC sparing effect
A healthy 2 year old cat under general anesthesia has a refractory bradycardia. The bradycardia is starting to affect his blood pressure and he is now mildly hypotensive. You administered glycopyrrolate with no response; the patient was not fluid responsive and you cannot decrease your isoflurane further. What could be the cause for this persistent bradycardia?
Hypothermia
The most common anesthesia related complication: Preventable via: Leads to what in cats?
Hypothermia! Preventable: Metal cages, gurneys, surgical tables ... -Conduction Air conditioning -Convection Open abdomen/alcohol scrub -Evaporation/convection/radiation Hypothermia leads to hyperthermia in cats
STEP 3: Address the issue (examples)- -hypoventilation -V/Q mismatch
Hypoventilation • Improve technique (e.g. IPPV), start mechanical ventilation - make sure getting enough breaths V/Q mismatch (e.g. atelectasis) • Recruitment maneuver? - works for small patients -give breath, hold bag for a little longer Low Fi02 • Under GA, normally 97%+ O2 Shunt • Improving CO and BP may help -deoxy blood going to left side Diffusion impairment • Treat underlying disease if possible
Hypoventilation -main causes: -consequences:
Hypoventilation is an increase in CO2 What are the main causes of hypoventilation? Deep plane of anesthesia -Causing bradypnea or apnea Obesity Some lung disease Why is this harmful? CO2 + H2O <-> H2CO3 <-> HCO3- + H+ What happens to your pH with excess H+? As a reminder the pH is a measure of hydrogen ion concentration Measure of acidity More hydrogen ions, more acidic, lower pH Respiratory acidosis Obtunded mentation
Hypoxemia vs Hypoxia
Hypoxemia Low level of oxygen in the blood Hypoxia Low oxygen to tissue Clinical signs Muddy mucous membrane color Tachycardia (possibly) Equipment used to assess: Pulse oximetry (normal is 95% or higher)
Common perioperative complications- Hypoxemia
Hypoxemia (abnormally low oxygen in the blood) • Could be due to Anatomy + anesthesia drugs • Hypoventilation if not mechanically ventilated less than 60mmHg
You have heavily sedated a cat, who is unresponsive and breathing shallow and few breaths per minute. You notice the cats mucous membranes are a muddy/purple color. You still need to perform a mass removal which is affecting the cats quality of life. What is the respiratory complication AND how can you treat it?
Hypoxemia and supplemental oxygen cat is hypoventilating as well but the significant finding is the muddy/purple colored mucous membranes which suggests hypoxemia -this needs to be treated right away with supplemental oxygen -do not reverse since in the middle of important procedure
Dental nerve blocks (NB)
I. Mental NB II. Infra-orbital NB III. Inferior-alveolar (mandibular) NB IV. Maxillary NB
Importance of IV fluids
IV fluids can be used for: Resuscitation to replace losses (urine, sweat, diarrhea, vomiting, hemorrhage) Maintenance during anesthesia fluid to compensate for lack of intake perioperatively, compensate for vasodilation from anesthetic drugs Promote perfusion and oxygen delivery to vital organs during vasodilatory states Compensate for potential dehydration from fasting Supplementation/resuscitation of electrolytes As a carrier for IV drugs Consider the route of administration For anesthesia fluids are typically given intravenous or intraosseous
Sedation using alpha-2 agonists:
IV loading does (bolus) followed by constant rate infusion (CRI) Detomidine Dexmedetomidine
Monitoring CO2- Goals
Identify the ventilatory status Identify the partial pressure of arterial CO2 (PaCO2) Assessment of partial pressure of alveolar CO2 Assessment of partial pressure of inspired CO2 Provide some information of the cardiovascular status
If hypotensive Check depth of anesthesia:
If deep- can turn down iso If light- check HR, if low, atropine! if HR normal or high, fluid bolus: NO RESPONSE = DRUGS
Peripheral stretch and irritant receptors
If fluid or stomach contents enter the lungs these are activated and respond with bronchospasm, cough, pain, increase/decrease respiration
IV fluids- -If hypovolemic: shock doses= -If euvolemic: excess fluids is deleterious=
If hypovolemic: shock doses • Dog: bolus 20 ml/kg (pressure bag), reassess • Cats: bolus 10 ml/kg (pressure bag), reassess If euvolemic: excess fluids is deleterious • ↑ right atrial (RA) pressure • ↓coronary perfusion pressure (CoPP) • Increase Central Venous Pressure - Opposes blood flow to the heart/brain
Low FiO2 and Hypoventilation
If the animal is hypoventilating AND has a low FiO2 for that scenario than they can become hypoxemic You can prevent or treat hypoxemia in these cases by correcting one of these factors
Time lag between turning vaporizer ON and brain going to sleep.
If the patient is waking up, cannot simply turn up the inhalant due to it taking time. Time lag-> the whole process takes time to work
IM top up
If you are repeatedly sedating an animal IM, small top up doses may not as effective as one injection of a larger dose initially Consider if you sedate an animal with a low dose of dexmedetomidine, wait 15 minutes, decide your animal needs more and give another small dose By the time of administration of the second dose, the minimal effect of the first dose is waning
Pediatric central nervous system
Immature CNS and neuromuscular junctions Less drugs to produce effective general, local anesthesia when compared to adults. doses adjustment should be performed
Common causes of low Sp02
Immediately after inducting of anesthesia: apnea +-decreased CO -Endobronchial intubation • Only one lung is ventilated = can lead to hypoxemia. • ETT should be past the larynx and not further than the thoracic inlet -measure from tip of nose to thoracic inlet
Mechanism of action Action on nervous system- Spinal cord
Immobilization → Ventral horn Decreased supraspinal (brain) arousal by decreased transmission of noxious information from spinal cord to brain -meaning that the transmission from spinal cord to brain is compromised -Ascending signals from spinal cord affect hypnotic actions of anesthetics in the brain - Descending signals modify immobilizing actions of anesthetics in the spinal cord
Adverse effects of peri anesthetic hypothermia
Impaired cardiovascular function Hypoventilation Decreased metabolism of drugs Decreased elimination of drugs Muscle weakness during recovery from anesthesia Decreased resistance to infection Increased incidence of surgical wound infection Increased postop protein catabolism Increased oxygen consumption
Without coordinated depolarization what happens?
Improper contraction - ventricle to atria for example
Esophageal intubation
Improper placement of an advanced airway device into the esophagus rather than into the trachea -short waves
Congenital heart defects -percentage diagnosed with congenital heart disease: -most common:
In a veterinary teaching hospital setting, approximately 17% of dogs and 5% of cats examined during a 10 years period were diagnosed with congenital heart disease Most common congenital diseases: Subaortic stenosis in dogs Patent ductus arteriosus in dogs Tricuspid valve dysplasia and ventricular septal defect in cats
Guaifenesin (GG) Used as ___ in human medicine What does it do? In horses? Issues? Administration-
In human medicine used commonly PO as expectorant Centrally acting muscle relaxant • spinal cord level Large safety margin In horses: • Good muscle relaxation • Some sedation • No analgesia Irritant to tissues (if extra concentrated)--> give IV at 5% • Max 10% concentration • Higher concentrations cause hemolysis Large volume required (1 ml/kg) Not commercially available • Must compound Administration • Infuse until relaxed, then bolus ketamine • Or combine with ketamine and infuse until horse falls
Palpebral reflex
In order to make a correct assessment you should always look at other variables 1. Make sure to check: jaw tone, HR, BP, RR, EtCO2 2. Be gentle when checking palpebral reflex but not too gentle 3. Don't keep poking
How to avoid complications (Inferior Alveolar NB)
Incomplete block or damage to other structures: -Needle next to the mandible, bevel towards the bony surface Self-mutilation (tongue) -lingual nerve desensitization: - Rare -Avoid bilateral inferior alveolar NB
Vasoconstriction will have what effect on the workload of the heart?
Increase narrow vessel makes it hard to push blood through decreases CO but increases workload
Under general anesthesia in horses, what cardiovascular response occurs in response to noxious stimulus?
Increase blood pressure under anesthsia, dogs and cats usually increase HR and BP Horses when conscious and awake can indicate pain in relation to HR; under anesthesia, HR does not increase, BP does
Common Sympathetic effects on the body:
Increase heart rate, coronary artery dilation Bronchodilation Secretion of epinephrine and norepinephrine Smooth muscle contraction of blood vessels
Inhalation- Respiratory system
Increase intracranial pressure, minimal change or mild increase in cerebral blood flow Decrease alveolar ventilation in a dose dependent manner Normal stimulation of ventilation depressed by inhalants from direct action on the chemoreceptors not as responsive to chemoreceptors -> respiratory depression
Hypoventilation
Increased expiratory CO2 Common side effect of many anesthetic agents
Central Sensitization
Increased pain signal transmission of nociceptive pathways May persist after cessation of signalling Change membrane excitability or reduced inhibition Uncoupling of stimulus - response relationship Activation and recruitment of NMDA receptors Aβ fibres that are not usually involved with pain transmission but can be recruited Results in an increase the perceptive field Example: Exaggerated response to handling or nonpainful procedures Osteoarthritis
BLS -interposed abdominal compressions
Increased pressures due to abdominal compression • Larger increase in Aortic Pressure during systole and diastole o Increased venous return • Larger increase in Right heart pressure during diastole • Increase in Caudal vena cava pressure o Increases filling back to heart Chest + abdominal compressions: Higher pressure difference between Aortic and Right atrium pressure People (few studies) o Improved ROSC o Indication of improved survival to discharge
Hypothermia -side effects
Increased risk of anesthetic overdose (decrease MAC) -decreased metabolism, same level of inhalant may overdose Bradycardia: *unresponsive to anticholinergics -<95 Myocardial depression (decreased contractility) -affects BP Increase in post-op wound infections -wound, blood flow decreased, decreases wound healing and prone to infection Possible coagulation impairment Recovery • Prolonged (long time to wake up) • Increased shivering and discomfort -- shivering: increase oxygen demand, provide O2 supplementation
What would you see after baroreceptors detect increased blood pressure?
Increased stretch from increased blood pressure Increased firing of baroreceptors Action potential to cardiovascular center via CN IX and X Increased parasympathetic and decreased sympathetic stimulation (increased vagal tone to decrease HR and vasodilate blood vessels; decreased input to cardiac accelerator nerves) Reduced HR and blood pressure
Oxygen cage Indications- Pros- Cons-
Indications: -same as any other insufflation of O2 -Patients who will not tolerate cannulas Pros: -pts behavior -free mobility within cage -can control humidity and temp -convenient for hsort term, then switch to cannulas Cons: -up to 30-60% FiO2 -expensive -Long filling time -Difficult to control humidity and temp with large dogs -FiO2 will decrease everytime cage is opened -Not practical for LA
Physiological Assessment of Pain- Plasma cortisol
Indicator of stress Not useful indicator of pain in dogs and cats Correlated with an increase in composite pain scale in horses
Injectable anesthetic drugs -What do they do?
Induce an unconscious state Adequate state that allows endotracheal intubation Reliable sedation and anesthesia
FYI Propofol -some common doses: -Induction -Dogs & cats -Continuous rate infusion
Induction -Dogs & cats -2 -4 mg/kg if premed -6 -10 mg/kg without premed Lower doses for "twilight anesthesia" (e.g. for radiographs)-> have to give very very very slow or will have to intubate Continuous rate infusion (CRI) 0.2 -0.4 mg/kg/min after initial induction dose Slow administration rate -calculated dose over 60 seconds to effect
Anatomy and behavior- Most critical moments during general anesthesia- Problems with recovery-
Induction of anesthesia • temperament and size Recovery • temperament, size and being nasal breathers • airway obstruction, rough recoveries (fractures or death), myopathy/neuropathy -normally due to pressure points, decrease to blood path
Circle System Fresh gas rate
Induction of anesthesia = 100-150 ml/kg/min for the first 15 minutes after Maintenance of anesthesia = 40-50 ml/kg/min for Recovery of anesthesia = 150ml/kg/min **Minimum fresh gas flow rate is 500ml/min -vaporizer requires 500ml/min to be efficient
When ETT in place:
Inflate the ETT cuff to seal Confirm correct placement: • Palpate trachea • Feel air leaving the ETT when horse takes a breath • Later on, capnograph
How do local anesthetics work?
Inhibit Na+ channels in the neuronal membrane: x Block the generation & conduction of nerve impulses x Sensory/motor blockade Main action- drug reversible binding to sodium channels preventing influx of sodium
The mechanism of action of a nonsteroidal anti-inflammatory is which of the following?
Inhibition of the cyclooxygenase pathway -decrease production of prostoglandins
Nonsteroidal anti-inflammatory (NSAID)- Side effects-
Inhibits formation of prostaglandins (COX-inhibitor) Can be administered pre or post-operatively Analgesic (multi-modal analgesia) + anti-inflammatory • Carprofen SC, PO (2.2 mg/kg q12h or 4.4 mg/kg q24h) -dogs • Meloxicam SC, PO (0.1 mg/kg q24h) -dogs, cats, pigs, cattle • Onsior SC -cats • Flunixin and phenylbutazone-large animals Side-effect/contra-indication: diarrhea, GI ulcers, liver injury and kidney damage
What if we don't have a validated score?
Interpretation from existing pain scores What are the commonalities between the scores? Must know the normal behavior Commonalities of pain scores Psychological and behavioral Response to palpation Body tension Intervention and re-score
Non-vascular access
Intra-osseous (IO) access: -Small patients (e.g. birds, rats, kittens) -Unable to place IV catheter • severe disease (e.g. hypovolemic shock) Intra-tracheal (drug administration via ETT) -Only used when no IV or IO access -Higher doses required (3 -10x normal IV dose) --> to make sure that it is actually reaching your patient -May need to add saline to increase volume
Route of administration- Pre-medication
Intramuscular (IM) • most commonly used route Subcutaneous (SC) • Slower onset of action • Potential for prolonged recovery times Intravenous (IV) • Safer if IV catheter present • May requires dose reduction • Majority of agents should be given slowly (avoid side effects- given slowly allows for side effects to be caught and medication stopped in time) Generally: pre-med using IM and place IV catheter
Propofol
Intravenous anesthetic • Predominantly used in dogs & cats -can use alone -or with benzo "Milk of Amnesia" -Lipid emulsion • Soy bean oil and egg lecithin base Sterile technique for drawing & administration -egg base prone to bacterial growth
Different modalities of G.A.
Intravenous: (induction) Propofol Ketamine Alphaxalone Etomidate Inhalation (maintenance) -Vapors -->Exposure to the pulmonary circulation allows a more rapid appearance of drug in arterial blood (fast absorption) -->Unique route of administration
Injectable anesthetic drug routes-
Intravenously (IV) • Most commonly route Intramuscular (IM) • Wild/zoo animals • Exotics • Shelters, large volume sx -need large volume Intermittent bolus, constant rate infusion (CRI) • Can be used to maintain anesthesia
BLS -airway and ventilation:
Intubate & ventilate 10 breaths per minute VT 10 mL/kg Peak pressure: 20 cmH2O -don't go over 20cmH2O!! (monometer shows you!) -trauma to the lungs -too much pressure also squeezes larger vessels 100% oxygen -can remove N from alveoli but for CPR this is fine -normal level is only 21% -can cause toxicity over long period of time
Injectable anesthetic -Induction Extremely important:
Intubate the trachea immediately after induction of anesthesia! Unable to protect airway Post-induction apnea and potential for hypoxemia Possibility of regurgitation and aspiration of gastric contents Many drugs have short duration of action, need to be fast
Injectable anesthetic -Induction Important:
Intubate the trachea immediately after induction of anesthesia! Unable to protect airway Post-induction apnea and potential for hypoxemia Possibility of regurgitation and aspiration of gastric contents Many drugs have short duration of action, need to be fast
Your patient is mildly sedated, breathing room air and you are going to induce anesthesia. You administer an induction agent that is known to cause respiratory depression leading to hypoventilation. You patient turns a very muddy/cyanotic color. What is the cause of the hypoxemia? How could you treat this situation? How could you prevent it from occurring in the future?
Intubate the trachea, provide 100% oxygen and ventilate Preoxygenate before giving the induction agent and causing hypoventilation. This will increase the FiO2 before causing hypoventilation and prevent hypoxemia from occurring
Once induced... what do you do first?
Intubate trachea -Endotracheal tube (ETT) • 500 kg horse, 26 -28mm • Blind intubation (don't use laryngescope) When induced and in lateral recumbency, Extend neck! • Open mouth, use a wood or PVC block to keep it opened • Insert lubed ETT inside mouth/trachea and gently advance • If any resistance noted, pull back slightly, rotate ETT 180 degrees and insert again -inflate ET tube cuff
When presented with a suspect of iatrogenic burn, what should you do?
Investigate sources of heat Remember the burn threshold (44ºC & > 6 hours) Assess duration of surgical procedure Review position of patient during procedure Review anesthetic record ○Looking for hypotension
Efferent respiratory
Involuntary efferent response Phrenic nerve to diaphragm Intercostal nerves to intercostal muscles Cranial nerves to airways and smooth muscle
Ion Channels
Ionotropic - ligand gated ion channels -When bound, ions are able to pass through the channel altering the resting membrane potential which will either promote or inhibit an action potential from being generated -Response is usually brief and localized compared to GPCR -Sodium and Calcium channels allowing passage into the neuron are usually excitatory -Chloride passage into neuron and potassium passage out of neuron via channels are usually inhibitory Ion
N-Methyl-D-Aspartate (NMDA) Receptors
Ionotropic receptor - ligand and voltage gated Allows entry of Na+ and Ca2+ into cell = excitatory Usually associate with the α-aminohydroxymethylisoxazolepropionic acid (AMPA) Endogenous ligand - glutamate, glycine Mg2+ keeps channel closed, when Mg2+ is released the channel will open
Na channels- what is it, physiological effects, location, modulation,
Ionotropic: voltage gated Na+ into cell generating an action potential Endogenous ligand: conformation change induced by increased membrane potential Physiologic effects: activation leads to propagation of action potential along nerve, which allows transmission of signal to the spinal cord and CNS Particularly important in the transmission of noxious stimulus Location: neurons Modulation: for anesthetic and analgesic purposes the receptor should be inhibited This is to prevent the transmission of the action potential along the neuron and therefore prevent transmission of noxious stimuli Sodium channel blockers --> Local anesthetics Lidocaine, bupivacaine, ropivacaine etc. Mechanism is not well understood
Excretion -Renal -Hepatic
Irreversible removal of drugs from the body Renal -Renal failure may affect clearance of the drug from the body -Especially ketamine in cats because it is renally excreted as an active metabolite Hepatic -Excreted into bile and then feces
Anesthetic Depth -determined by:
Is determined by partial pressure of the drug in the brain. Molecules of anesthetic must diffuse through a series of partial pressure gradients and equilibria: Inspired air -> Alveolar air -> Blood -> Brain
Maintenance of anesthesia
Isoflurane and sevoflurane are often prescribed for neonatal dogs and cats Desflurane is also an option (foals) Isoflurane, sevoflurane or desflurane is often used in geriatric patients ... - Intravenous CRI of lidocaine or fentanyl or ketamine or a combination of these agents -Local anesthesia
Saturated Vapor Pressure (SVP) and MAC
Isoflurane: Max [ ] = 31.5% (SVP=240 mmHg); MAC=1.28% (dogs) (what you want to deliver vs. max percent) Sevoflurane: Max [ ] = 20.6% (SVP = 157 mmHg/760) MAC = 2.36% (dogs) Desflurane: Max [ ] = 92.1% (SVP = 700 mmHg/760) MAC = 8% (dogs) This means a lethal concentration could be delivered if a vaporizer is not used properly.
From the following list of options, when you compare the cardio-respiratory side effects of isoflurane with sevoflurane, what is correct? Sevoflurane causes less cardiorespiratory side effects at 1 MAC Isoflurane causes less cardiorespiratory side effects at 1 MAC It is a dose dependent side effect
It is a dose dependent side effect
Regarding anesthesia vaporizer in the photo It is designed for isoflurane only You can use it with any inhaled anesthetic It is designed for sevoflurane only
It is designed for isoflurane only
Doses ---Ketamine + Benzo or Propofol Horse: -Commonly used drugs and doses (IV) -Ketamine and propofol (IV)
Ketamine 2.2 mg/kg Benzodiazepine0.08 mg/kg Ketamine 1.5 mg/kg Propofol 0.5 mg/kg
FYI Doses ---Ketamine + Benzo or Propofol Dog, sheep, pig, goat, cat: -Commonly used drugs and doses (IV) -Ketamine and propofol (IV)
Ketamine 5.5 mg/kg Benzodiazepine0.28 mg/kg Ketamine 2 mg/kg Propofol 2 mg/kg
You are required to anesthetized a cat with hypertrophic cardiomyopathy (HCM). Which anesthetic agent should you avoid in this animal? And for this cat, what is the main side effect you would be concerned with? Ketamine. Increase in HR Propofol. Vasodilation Alfaxalone. Increase in HR Etomidate. Vasodilation
Ketamine. Increase in HR
What you need to know about drugs:
Know why and when to use a drug as a premed • Class of drugs • How they work (*you have to know pharmacology to be a safe anesthetist) • Effects • Side effects • Contraindications
Therapeutic index = The higher the therapeutic index, the ____ the drug
LD50 : ED50 or TD50 : ED50 Generally, the higher the therapeutic index the safer the drug is considered This is true for most anesthetic drugs
Infra-orbital NB Trasmucosal Approach
Landmarks - Lateral side of the maxilla slightly rostroventral to the eye dorsal to 3rd premolar tooth Anesthetised structures- Ipsilateral premolar, canine and incisor teeth + associated soft tissues, skin of the muzzle and the upper lip
Simple Scales
Large inter- and intra- individual variability Training improves accuracy A single person performing all evaluations improves accuracy
Challengin intubations- Felines
Laryngeal hyper-responsiveness to mechanical stimulation (closes) Desensitize larynx with lidocaine spray before first attempt of intubation
Thoracic pump model
Lateral recumbency Apply pressure to the highest point of the chest Elbows locked (do not bend) A hand on top of the other Compressions ↑ intrathoracic pressure = blood to body Recoil of chest ↓ intrathoracic pressure = venous return occurs
Patient positioning
Lateral recumbency for most dogs and cats Dorsal recumbency for barrel-chested dogs may be required
Neuropathic Pain
Lesion or damage to the nervous system Peripheral nerve, spinal cord or dorsal root ganglia Example: Nerve sheath tumor Intervertebral disc disease
Amide-Linked LA- Lidocaine Toxic Dose: Recommended Dose: Indication: Onset of action: Duration of action: Comments: Notes:
Lidocaine- Intermediate potency & duration TOXIC dose- 10 mg/kg Recommended dose- Dog: 6 mg/kg Cat: 4 mg/kg, Large animals* Indication- Topical (lidocaine spray- intubating cats and pigs who are prone to laryngeal spasms when intubating); Infiltration; IV Onset of action: 2-5 mins Duration of action: 1-1.5 h Comments: Excellent penetration Notes: Avoid IV in cats (cats have problem metabolizing)
How does the pulse oximeter work?
Light source and light detector Calculates % of 02Hb in arterial blood (SO2) using spectrophotometry Probe passes light through the tissues at 2 different wavelengths: -Infrared light (940 nm) -Red light (660 nm) Oxyhemoglobin (carrying O2) absorbs more Infrared light Deoxyhemoglobin (no O2) absorbs more Red light Difference in light absorption of pulsatile arterial signal is calculated Final figure displayed as a % (SpO2%)
Loco-regional anesthesia Areas
Local infiltration- • Testicular • Incisional • Ring block Thoracic limb Pelvic limb- • Epidural Thorax- • Epidural Abdomen- • Epidural Facial- • Dental
Epidural- horse
Location- Sacrococcygeal or intercoccygeal injection Block - Loss of sensory and motor function to tail and perineum Indications • Surgical procedures • Prevent tenesmus • Pre-op or post-op analgesia
NMDA receptor location, physiological response, clinical effect, modulation
Location: postsynaptic neurons in many locations including CNS and spinal cord Physiologic response: postsynaptic excitatory action potential; recruitment of more AMPA and NMDA receptors Clinical effect: wind up pain, somatic pain Modulation: reduce the activation of these receptors using an exogenous ligand that will antagonize the receptor to reduce transmission of nociceptive input NMDA receptor ANTAGONIST --> KETAMINE (stops the response)
Sevoflurane renal toxicity
Loss of concentrating ability 2 mechanisms: 1. Inorganic fluoride nephrotoxicity - Fluoride peak short lived - Low blood/gas solubility (sevo removed fast) 2. Compound A production - Amount dependent on temperature (>50C) - KOH/ NaOH (sodalyme and baralyme) Sodasorb --> Isoflurane ans desflurane - carbon monoxide - Dissecated - Low FGF /High V%
Neonatal cardiovascular system -low-resistance - high-flow circuit: -Tissue perfusion (as compared with adult):
Low-resistance - High-flow circuit Low blood pressure Low blood volume Low systemic peripheral resistance Tissue perfusion (as compared with adult) High heart rate High cardiac output High plasma volume High central venous pressure Baroreceptors- non matured (cannot maintain homeostasis under anesthesia) The cardiovascular system of the neonate undergoes dramatic adjustment after birth to assume its own circulation and maintain homeostasis.
Sacrococcygeal Epidural
Lumbosacral junction
Compression atelectasis
Lungs are compressed by lesions in the thorax or abdomen Fluid or air in the pleural space Pregnant uterus or bloated stomach compressing diaphragm
Muscarinic Receptors- M2 location and effects when activated
Lungs- bronchoconstriction Myocardium and SA/AV- bradycardia, AV block, decrease contractility
Definition: MAP = _______________mmHg Cardiac output = _____ x ______ MAP = CO x ______ MAP = _____ x _____ x _______
MAP = less than 60 mmHg (70 for horse) -due to renal perfusion -horses- muscle perfusion important! CO= SV x HR MAP= HR x SV x SVR
Atropine
Main expected effect: Anticholinergic/antimuscarinic effect to increase HR • Most likely to be useful in asystole or PEA due to high vagal tone • Lack of clear detrimental effect • IV dose 0.04 mg/kg -or IO as well -would use 0.02 during anesthetized patient but in emergencies want higher dose increasing HR means you are also increasing O2 demand - could cause worsening myocardial ischemia
Vasopressin
Main expected effect: peripheral V1 receptor vasoconstriction (receptor located on vascular smooth muscle) -use if you tried epinephrine first but it didn't work (not available in many hospitals- very expensive) • No chronotropic or inotropic effects • Effective in acidic environment -may have metabolic acidosis-> will still work well • Shunts blood to CNS and heart • Increased use in dogs/cats due to effect noted in people during asystole • IV dose: 0.2 -0.8 U/kg every 3 -5 minutes • Intra-tracheal dose: 0.4 -1.20 U/kg • Really $$$ and not readily available
Extrajunctional Receptors
Main ones are alpha2 agonists located anywhere in the muscle membrane, inside or outside the neuromuscular junction.
Elimination
Main route is alveoli Factors that speed induction also speed recovery: elimination of rebreathing, high fresh gas flows- helps eliminate inhalant from the machine, low anesthetic-circuit volume- easier to remove, low absorption by the anesthetic circuit, decreased solubility, high CBF (cerebral blood flow)- faster inhalant gets out of the brain, increased ventilation
ETCO2 Technology Mainstream vs. Side stream
Mainstream -sensor on endotracheal tube (measurement on endotracheal tube side) -cheaper but only measures inspiration and expiration of CO2 Side stream- sensor on the machine (line brings air to the machine to read) -advantage= better measurements of multiple things
Blood pressure goals
Maintain adequate BP during anesthesia is essential • Maintain adequate muscle perfusion • Maintain adequate organ perfusion (e.g. gastrointestinal tract) VERY IMPORTANT MAP > 60 mmHg in foals MAP 70 -80 mmHg in adult horses depending on body size o horses > 500kg, keep higher MAP 80mmHg
Crystalloid Anesthetic Fluid Requirements
Maintenance crystalloid anesthetic fluid requirements for healthy patients Dog: 5 mL/kg/hr Cat: 3 mL/kg/hr *Patients with co-morbidities such as shock, renal disease or heart murmurs may require adjusted fluid rates Daily fluid requirements for healthy patients Dog 2-6 mL/kg/hr Cats 2-3 mL/kg/hr *many formula to calculate
Endotracheal Intubation
Maintenance of a patent airway -To provide positive-pressure ventilation -To deliver inhalant anesthetics -Species specific details -Oxygen administration Protection of the airway -To avoid aspiration pneumonia Suction- necessary to clean up the airway if they vomit
Pharmacodynamics - Skeletal Muscle
Malignant Hyperthermia: -Humans, swine (common), other species -Potentially triggered by all inhalants -Halothane most potent trigger -Rapid rise in body temperature and ETCO2 -Dantrolene prophylactic
NK-1 Receptors
Maropitant (Cerenia) Substance P is the endogenous ligand for this receptor Substance P is an excitatory neurotransmitter Inhibition will prevent the transmission of that signal
Induction of anesthesia
Mask induction is often prescribed for neonatal dogs and cats Propofol, alfaxalone, etomidate are often good choices for both peds and geri There is nothing such as a single induction protocol for the geriatric patients ...
Devices
Mask- some animals will not tolerate Oxygenation Nasal Cannulas Oxygen cage Endotracheal tube
Why do some drugs have to be administered a certain route?
May be tissue damage with drugs administered IM or SQ (thiopental) May be histamine release with rapid IV administration (meperidine and morphine) Example: NSAIDs are administered SQ Alfaxalone can be administered IM or IV (which is a great sedative in cats) Propofol is for IV injection only
Use of anticholinergics in horses
May cause ileus Horses are very sensitive DO NOT use unless specifically indicated: -AV block or severe bradycardia (<18 bpm) o depends on initial rate o racing thoroughbred may normally be at 18-20 bpm -Eye procedures rarely cause bradycardia -Cardiac arrest (atropine preferred)
Catheter placement- may require:
May require sedation (e.g. IV xylazine, acepromazine IM or IV) -make sure to suture secure the catheter placed without if bad temperment numb the area with lidocaine
Stages of GA- 2
May see uninhibited excitation, irregular breathing, agitation and delirium -may have to give a slight dose of the induction agent slightly faster Eye position- variable Palpebral reflex- +++ Jaw tone-++++ Corneal reflex- +++ Nystagmus- +++ (especially in horse/cow)- most reliable way to determine if a horse is too light; fast horizontal nystagmus-->> ACT FAST!
Finding how long the ET tube needs to be- Too long, what happens? Diameter too small? what happens?
Measure the distance (in centimeters) between the manubrium and the tip of the nose. Is the ET tube too long? Increased dead space will be observed Is the diameter of the ET tube too small? A leak and increased airway resistance will be observed
Hyperthermia - cats
Mechanism not well understood Stress, opioids and ketamine could be factors The more hypothermic the patients are during surgery, the more hyperthermic they will be during recovery Monitoring temperature As soon as possible Throughout recovery phase Provide heat when necessary
Tranquilizers and Sedatives- Phenothiazines-> Acepromazine
Mechanism of action: Alpha-1 antagonist Depression of CNS and catecholamines Anti-dopaminergic actions in CNS -Considered a tranquilizer Anxiolytic -reduce anxiety Sedative Chemical restraint when used with other drugs Onset of action IM: peak sedation 30 -45min Duration of action: up to 6h Route: IV, IM, SC, OTM (oral transmucosal) NO analgesic properties Slight/mild respiratory depression Vasodilation (α1 receptor antagonist) • Decrease blood pressure (hypotension) Depression of myocardium &vascular smooth muscle • Dose dependent
NSAID Examples
Meloxicam (Metacam) Carprofen (Rimadyl) Robenacoxib (Onsior) Phenylbutazone Flunixin meglumine
Amide-Linked LA- Mepivacaine Concentration: Toxic Dose: Recommended Dose: Indication: Onset of action: Duration of action: Comments: Notes:
Mepivacaine- Intermediate potency & duration Concentration: 1-2% Toxic Dose: 20mg/kg Recommended Dose: dog- 8 mg/kg; horse- 8mg/kg Indication: Infiltration; epidural Onset of action: 2 -5 min Duration of action: 1.5- 2h Comments: excellent penetration, less irritation Notes: <vasodilation than lidocaine; horse lameness exam
Sevoflurane- Metabolism and Toxicities
Metabolism: ➢ Considered minimally metabolized by the liver (2%) -More metabolized but at such a minimal effect it is not realized ➢ Isoflurane (0.2%) ➢ Desflurane (<0.02%) Toxicities: ➢ Increases intracranial pressure (↑ ICP). ➢ Small effect on cardiovascular and respiratory systems (same as Isoflurane). ➢ Generally safe for liver.
G Protein Coupled Receptors
Metabotropic - GPCR -When bound there is activation of a second messenger pathway -Response can be slower than ion channels, but effects may be larger because amplification via second messenger systems -Response may be brief or long -Second messenger can: -->Alter behavior of ion channels making them more or less active -->Change activity of proteins -->Change gene expression
3y old, male intact, Pointer, weighing 24kg. He requires general anesthesia for a 3cm superficial benign mass removal in his left forelimb. Blood work and physical examination are unremarkable and he is bright alert and responsive (BAR). Choose an appropriate analgesic (with the correct justification) to use as part of the premedication
Methadone. It has excellent analgesic properties and lasts for 2-4h
8y old, FS, Yorkshire terrier cross, weighing 6kg. She is sick and requires general anesthesia for an emergency splenectomy. Her health status is ASA III. Which sedative or tranquilizer is considered to be the safest for this patient due to its minimal cardiovascular effects?
Midazolam
If you pre-medicate your patient using IM, should you use Diazepam or midazolam?
Midazolam - diazepam may be used, but is more painful
Benzodiazepines Use- MOA-
Midazolam, Diazepam, Zolazepam Sedative agents Used IV as part of induction protocols such as: • Ketamine + Benzodiazepine • Propofol + Benzodiazepine MOA • GABA agonist
When Administering pre-medication- Minimize: For IM, give at least ____ minutes prior IV sedation:
Minimize patient excitement and stress -"Less is more" restraint For IM, give at least 20 minutes prior -Leave patient undisturbed while pre-med takes effect -Ace takes longer time-> 45 mins before full effect IV sedation -shorter time to effect dose reduction
Define MAC again
Minimum alveolar concentration (of a specific inhalant) Immobility- produce immobility in... 50% of tested population During a painful stimulation
Size
Minis and ponies can sometimes be uncooperative and bite and kick Draft breeds are docile -Need less drug per kg (due to size, metabolism and pharmacokinetics)
Air obstruction
Missing alpha angle- this is major; shark fins, problem with expiration leading to prolonged increase of expiration--> airway obstruction Endotracheal tube may be obstructed by mucous; use fresh clean endotracheal tube- don't want to add bacteria to the lungs
Air leakage
Missing beta angle- smaller portion of expired air; cuff not inflated completely
GABA receptor modulation Allosteric modulators means? types of drugs used?
Modulation: to produce sedation and anxiolysis the receptor activity should be enhanced Drugs we use are classified as allosteric modulators meaning when bound to the GABA receptor there is a conformational change resulting in hyperpolarization of the neuron Positive allosteric modulator (agonist) Benzodiazepine (diazepam and midazolam), propofol, alfaxalone Negative allosteric modulator (antagonist) Flumazenil (effect goes down)
What is a neurotransmitter?
Molecule that transmits messages between neurons or between neurons and muscles NT are excitatory or inhibitory depending on the receptor they bind to stops or propagates an action potential Important because we can manipulate these for desired result
Rescue Analgesia
More difficult to catch up with pain then to treat it from the beginning
Full Mu-agonist opioid -examples (5) -type -reversible= -Useful for:
Morphine Hydromorphone Methadone Fentanyl Sulfentanil, etc • Mu receptor agonists • *schedule II narcotics • Gold standard for analgesia • Reversible: Naloxone-> slowly IV diluted (only want to reverse side effects not the analgesic -good thing about opioids is that it can be reversed Useful for: Pre-op sedation Moderate to severe pain Fragile, critically-ill patient Balanced anesthesia techniques • Adjunctive analgesia • Minimum alveolar concentration (MAC) sparring • Fentanyl: short duration, good for sick patients. Only IV bolus or CRI Bolus last 15 mins
Replacement Fluids
Most are 'balanced' meaning their composition resembles extracellular fluid Only 25% remains in the intravascular space after approximately 30-60 minutes The remainder passes to the interstitium Examples: Lactated Ringers Solution Hartmann's Solution Normosol R Plasmalyte Normal saline Used most often in anesthesia Fluids used are similar to extracellular composition
Where to inject IM
Most common= epaxial -hamstring (not used as often due to chance of damaging sciatic nerve) -trapezius -triceps -quadricpes
Epinephrine (adrenaline)
Most important drug used during CPR Administer low dose during every other cycle of CPR Main expected effect: Alpha-1 vasoconstriction • Constriction of the vessels = increase peripheral resistance to increase coronary and cerebral perfusion pressures -increases myocardial demand -> which means the heart needs more O2 now -can worsen myocardial ischemia • IV dose: 0.01 mg/kg IV every 3 -5 minutes <---- • Intra-tracheal dose: 0.05-0.1 mg/kg (increased dose, dilated with some saline) • Higher doses of epinephrine did not improve outcome (only used if animal not responding to treatment) Also effects beta 1 and 2 receptors, so can effect the heart
Epidural Contraindications-
Motor and sympathetic blockade, Sensory interruption (if using LA) Contraindications- Infection at site, bacteremia, sepsis, coagulopathy, neurologic dysfunction Notes: Unable to palpate landmarks e.g. pelvic fracture or obese Reduce dose for older and pregnant animals (engorgement of vessels and space gets smaller) Sterile technique
What opioid receptor type produce the most profound analgesia?
Mu
Which class and drug can be used to reverse the negative dysphoric effects of pure mu opioid agonists and still provide mild analgesia?
Mu antagonist, kappa agonist; butorphanol don't want to completely reverse analgesia but reverse dysphoric buprenorphine- not kappa agonist; partial mu agonist butorphanol- it is a mu antagonist
Physical Exam- mucous membrane color
Mucous membrane color: Pink: adequate blood perfusion and oxygenation of peripheral tissues Pale (severe anemia or blood loss), Blue (low blood oxygen, lack of O2 being delivered to tissues (cyanotic), icteric, dark red: abnormal mucous membrane colors
Cholinergic receptors- Muscarinic
Muscarinic- -G protein couple receptor and second messenger -Located on all peripheral organs of the parasympathetic system -Excitatory and inhibitory
Geriatric cardiovascular system
Myocardial fibrosis- lose ability to stretch when filling with blood Valvular fibro calcification Ventricular thickening Compromised cardiac conduction system Arrhythmias Negative inotropy (heart not able to contract over time) Arrhythmogenics should be avoided in the geriatric patient -Avoid alpha2-agonists, thiopental, ketamine, halothane -cause cardiac arrhythmias and alike
Beta 1 Receptors- location and effect when activated
Myocardium- increase heart rate and contractility Sinoatrial and atrioventricular nodes- increase heart rate Kidney- renin release
Common perioperative complications -Myopathies, neuropathies
Myopathies, neuropathies -Hypotension: decreased perfusion to muscles -Weight/muscle mass: perfusion can be impaired during anesthesia = myositis* -Positioning during procedure: pressure point (i.e. inadequate padding) Usually noted during recovery *Myositis: inflammation and degeneration of muscle tissue
Ketamine -MOA
N-methyl D-aspartate (NMDA) receptor antagonist • NMDA receptor is present throughout the CNS Also acts on opioid, monoaminergic and muscarinic receptors Dissociation of the conscious and unconscious parts of the brain -Dissociation of the thalamocortical and limbic systems Block neurological impulses in the brain -Inhibits dopamine, noradrenaline and serotonin Change in awareness -looks awake but not really there Analgesic properties (somatic pain) - Somatic analgesia > visceral analgesia
Ketamine- When to use and not use
NEVER use in an awake horse without prior sedation • Dangerous excitement will occur • Muscle spasm -NO MUSCLE RELAXATION Good for induction of anesthesia if: • Used with an alpha 2 agonist and a muscle relaxant Ketamine + benzodiazepine, Ketamine + GG, Ketamine + Propofol Good for analgesia during inhalant anesthesia: • Add to LRS and use as an infusion (sub-anesthetic dose) • Intermittent boluses use in an awake horse without prior sedation
NMDA Antagonist
NMDA receptor activation will generate a post synaptic excitatory response and glutamate is an excitatory neurotransmitter NMDA receptors are upregulated in Wind Up pain states (consider this for case selection of drugs) NMDA receptors are also involved more with somatic than visceral pain Therefore, inhibition of this receptor will reduce the nociceptive transmission
Excitatory Receptors- types
NMDA- wind up pain Na channel- neuron transmission (pain) NK-1 receptor- pain and vomiting administration of antagonists will provide analgesia and antiemetic effects
Should you shock a patient with Asystole rhythm?
NO • ASYSTOLE = NOT SHOCKABLE RHYTHM • START CHEST COMPRESSIONS -and dose of epinephrine Asystole is associated with low survival rate and no meds are shown to be very effective heart has stopped and no electrical activity no pulse, contractions
Advantages of loco-regional anesthesia
NO Need for general anesthesia (patient awake) NO Inhalant use (eliminating environment contamination) NO Need for systemic drugs (e.g. opioid) INCREASED Cardiorespiratory stability INCREASED Sustained analgesia post-operatively Treatment of arrhythmias -lidocaine IV Not controlled drugs
Treating peri-op pain in horses
NSAIDs- most used analgesics to treat/prevent pain • Administered pre or post operatively • E.g. flunixinmeglumine, phenylbutazone Butorphanolis the most used opioid • During sedation for exam, painful procedures • As part of premed drugs or intraopanalgesia (esp. colics) • Postop for analgesia in more painful situations • Intermittent boluses • CRI's • May need morphine/fentanyl for extreme pain (fractures)
Local anesthetics (lidocaine) prevent the transmission of an action potential in the transmission of noxious stimulus by blocking what receptor?
Na channel
Colloids: Natural and Synthetic
Natural Plasma Synthetic Hydroxyethyl starch (Hetastarch, VetStarch), dextrans, gelatins High and low molecular weight proteins that increase intravascular colloid pressure This may draw water from the interstitium into the intravascular space increasing circulating volume Dogs and cats: 3-5 ml/kg over 15 minutes Total 24-hour dose: dogs 20 mL/kg; cats 10-15 mL/kg Excreted by the kidney- can have negative effects
Infra-alveolar NB (mandibular) Intra-oral Technique
Nerve enters the mandible on the medial side Mandibular foramen • Angular process of mandible • Caudal to the last molar Excellent analgesia of • Bone/soft tissue on ipsilateral side • Lower teeth extractions • Mandibulectomy Technique - Palpate mandibular foramen - Needle through the mucosa medial to the mandible, at the level of the last mandibular molar tooth - Direct it ventro-caudally towards the angular process to reach the mandibular foramen
Fluid Movement Theories - Starlings Forces
Net filtration Interaction between hydrostatic and osmotic (and oncotic) pressures to determine the direction of movement of water balancing of the two pressures help drive movement
Absorption atelectasis (collapse of lung)
Nitrogen acts as a scaffold to keep alveoli open When 100% oxygen is administered the oxygen molecules replace nitrogen molecules Oxygen is absorbed and volume in alveoli decreases resulting in collapse Remember room air= 78% nitrogen and 21% oxygen during anesthesia- 100% oxygen
Frequency and Duration of Pain Scoring
No defined amount of time to spend or frequency of pain scoring required May have to spend more time observing to see some behaviors especially depending on the species Consider video monitoring Consider time recovering from anesthesia Want to pain score at recovery and as the patient wakes up and metabolizes the drugs, becomes more conscious Know the intervention limit for any pain scale you are using If the intervention limit is met, provide analgesia and re-assess within 15-30 minutes
Mouth-to-snout
No evidence to provide specific guidelines Mouth-to-snout ventilation (30:2 ratio) 30 compressions 2 breaths Likely only beneficial to neonates where you can generate enough volume and pressure
Mechanism of action Action on nervous system- Brain
No specific region targeted by inhalants in the brain Amnesia (Amygdala, Hippocampus) -in people -not known in vet Unconsciousness - Hypothalamus, periaqueductal grey, locus coeruleus, cerebral cortex, parabrachial nucleus, ventral tegmentum Sleep states and anesthesia states share electroencephalographic and behavioral features - Suppression of sensory input - Inhibition of motor output
Physiological Assessment of Pain- Variable physiologic response in conscious animals
No studies have shown reliable correlation to changes in physiologic parameters to indicate acute pain accurately in conscious animals Affected by stress, fear, anxiety HR variability and gut sounds may be useful in conscious horses
US Department of Labor, Occupational Safety and Health Administration Guidelines: Exposure Concentrations
No worker should be exposed to concentrations of WAGs greater than 2 parts per million (ppm) of any halogenated anesthetic agent, based on the weight of the agent collected for a 45-liter air sample by charcoal adsorption over a sampling period not to exceed one hour.
Nociception
Nociception is detection of tissue damage by specialized receptors Nociceptors are globally distributed Skin, muscle, joints and viscera etc Noxious stimulus Thermal, mechanical, chemical Sufficient amplitude and duration will produce an action potential
Other drugs used for Local blocks
Nocita (long-lasting bupivacaine): -Duration- 72 h -safe dose- 5.3 mg.kg -$$$; limited approval -amputations Buprenorphine -duration- 6-12h -safe dose- 0.01 mg/kg -epidural (lasts longer when given as an epidural) Morphine -duration- 24h -safe dose- 0.1 mg/kg; 1mL/5-7kg; Max 6ml/dog -epidural, sacro-coccygeal; NB
Classification of Breathing Systems
Non-Rebreathing systems Rebreathing systems
S02 -PO2 relationship
Non-invasive pulse oximeter is able to correlate SpO2 % to the partial pressure of oxygen in arterial blood (PaO2) -based off the oxyhemoglobin (O2Hb) dissociation curve 100 % saturation = >100 mmHg of oxygen in blood 98 % saturation = 100 mmHg of oxygen in blood 95 % saturation = 80 mmHg of oxygen in blood, and on the downward slope! 90% saturation = 60 mmHg PaO2 A light change in pulse ox from 100 to 95 mmHg will also mean that PO2 has had a very large drop from 100 to 80 mm Hg which is already mild hypoxemia (sigmoid curve- larger drops) 90 means 60 PO2 Higher SPO2 also means that more hemoglobin is fully saturated with oxygen
What is a pulse oximeter?
Non-invasive, continuous • measures oxygen saturation of hemoglobin (SpO2) in arterial blood • common bedside test for evaluating oxygenation • may also help with cardiovascular system assessment -pulse rate, quality and fluid responsiveness Is it the gold standard? NO • Gold standard is arterial blood gas (ABG) • ABG invasive, more complex -reserved for critically ill patients, *horses (even healthy horses); easy to get, large arteries
NSAIDs
Non-steroidal anti-inflammatories (NSAIDs) Long acting, not controlled, oral or injectable formulations Standard use for inflammatory pain and acute pain unless contraindicated for medical reasons
What class of analgesic drug has a narrow therapeutic index and treats inflammatory pain?
Non-steroidal anti-inflammatory
Hyperthermia - treatment
Non-steroidal anti-inflammatory drugs Opioid reversal Patient may suffer from pain afterwards Butorphanol is a partial mu antagonist ○Partial analgesia reversal Use water instead of alcohol Peripheral vasoconstriction → prevents heat loss Fan helps to get the temperature down
Visceral pain scores
None validated for dogs and cats Nausea, praying position, hunched
When to do CPR?
Not all dying patients should receive CPR May pose an ethical dilemma I. Evaluate your patient II. Animal should not be in terminal stages of a malignant disease III. There should be some possibility of return to a functional existence
How pregnancy changes anesthesia Gastrointestinal:
Not fasted Regurgitation ○Longer gastric emptying time ○Less tone in lower esophageal sphincter ○Positioning Be ready for possible regurgitation and Aspiration pneumonia Rapid induction Keep in sternal until intubated and cuff inflated Have suction and flush ready Gastroprotectants once fetus removed -to reduce the acidity and gastric content in the stomach
Neonatal cardiovascular system- maturity
Not fully mature until around the 12 weeks of age, Decreased ability to vasoconstrict/vasodilate Heart rate - the drive for normal cardiac output Anticholinergics are used frequently (atropine to drive higher HR In the newborn, bradycardia is not vagally mediated and is often caused by hypoxemia -If HR is dropping- may be indicator that patient is hypoxemic
Breed sensitivities
Not well documented or proven Examples Greyhounds - hepatic metabolism leading to longer recoveries Boxers and acepromazine - could be related to other health concerns in the breed 'White feet don't treat'
Osmolality
Number of osmoles per kilogram of solvent - Sodium, potassium, chloride, bicarbonate, urea and glucose - Dog osmolality is approximately 300 mOsm/kg -cats approx 300 mOsm/kg but is a bit more variable
Recognizing CPA
Observe all patients, they are our responsibility: Is the animal breathing? Is the animal breathing normal? MMc normal? Is there a pulse? Pulse quality (strong, weak, thread pulses)? -no pulse, start chest compressions Is the EtCO2 normal? f already connected, can also check ECG -ECG only shows electrical ability of the heart- may show activity when actually dead->>> not reliable!!
Anesthesia recovery
Older patients more susceptible to aspiration pneumonia Aspiration pneumonia prevention -Create the habit of aspirating the esophagus and stomach before endotracheal extubation -Maintain an open airway via intubation until the animal is swallowing It is ok to wait for the pet to recover from anesthesia ○Rushing will not make it better Search for a quiet, warm and dim place for recovery Provide proper nursing care for recumbent animals ○Soft beds ○Frequent changing of decubitus ○Human touch ○Compassionate verbal encouragement Reversing the effects of drugs that are not analgesics Benzodiazepines Alpha2-agonists Check patient's glycemia
How to choose the drug dose
Once you've selected the drugs you would like to use, check the dose range Large dose range: Lower dose will have less effect and less side effects Smaller dose range: Either clinically proven effective dose OR Low therapeutic index meaning severe side effects with minor increase in dose Consider synergism and multimodal approach Using multiple drugs usually allows using reduced doses of each drug with greater effect This will also allow less side effects Comes with experience
Acceptable Blood Loss- hemmorrhage
One anesthetic complication that should be on your list for every invasive procedure is hemorrhage Every patient should have the acceptable blood loss calculated before anesthesia and monitored closely intraoperatively Acceptable blood loss -10-15% of total blood volume - can give fluids here as well -15-20% should be replaced with crystalloid and/or colloid fluids ->20% replace with blood products Dependent on: Rapidity of blood loss (acute vs chronic) Stability of patient before anesthesia (anemia, hydration status, co-morbidities) % dehydration Accuracy of blood loss estimate
Arterial Blood Pressure- what is used to determine? Minimum pressures= MAP=
One of the main things we look at when monitoring anesthesia Mean arterial blood (MAP) pressure is an indicator of perfusion to vital organs Use cuff on the legs Minimum pressures under anesthesia for healthy patients*: Systolic 80-90 mmHg Mean 60 mm Hg Diastolic 40-50 mmHg Remember 80, 60, 40 (FOR HEALTHY PATIENTS) MAP = 1/3 (SAP - DAP) + DAP DAP has more significant weight
FLUID ADMINISTRATION SET SET-UP
Open bag of IV fluids (LRS) Remove cover to the IV tubing port on the fluid bag Open fluid administration set Remove plastic cap for the tubing to expose the 'spike' but keep sterile Insert into insertion point 'Flush or prime' the fluid line with LRS to ensure there is NO air in the line Open door to IV fluid pump Feed line into the designated receptable Note the direction of the line -Close the door Turn on the pump with the 'On/Off' button -Use the 'Select' button to highlight and observe rate, VTBI, VI and time on display screen -Use 'Up/Down' arrow buttons to adjust the VTBI and rate Set the VTBI as the patients total blood volume (Dog: 90mL/kg; cat 60mL/kg) Round rate to the closest full number -Press 'Clear' button to clear VI (only do this at the beginning of anesthesia) Press 'Run/Hold' to start infusion
Types of Inhibitory Receptors
Opioid and GABA Administration of Agonist will augment sedation and analgesia Very species dependent
Opioids- what are they? What do they do?
Opioid receptors are g-protein coupled receptors that when activated they inhibit the action potential of the nociceptive neuron Reduce presynaptic neurotransmitter release Hyperpolarize post synaptic membrane Administration of exogenous opioids to inhibit the transmission of the nociceptive input Located in midbrain, spinal cord, periphery etc. Inhibitory receptors- Mu
Analgesic Drug class
Opioids -used primarily for analgesia BUT may also provide sedation GOLD STANDARD Alpha-2 agonists, dissociative agents -have analgesic properties -EX: dexmedetomidine = a2
Drugs
Opioids and non-steroidal anti-inflammatories are standard of care (if not contraindicated) Other adjunct analgesics
Post operative analgesia- use:
Opioids- -hydromorphone or buprenorphine -often the intraoperative dose will be in effect in the post operative time period NSAIDs- Meloxicam single dose both good options for post op
Commonly used pre-medications
Opioids- gold standard analgesia Tranquilizers and sedatives
Pharmacodynamics - CNS 3. Cerebral blood flow
Or Velocity Normocapnia No surgical stimulation To increase cerebral blood flow administer higher concentrations than .5 MAC up to 1 MAC > 0.6 MAC • Cerebral vasodilation Decreased cerebral vascular resistance • Dose-dependent increase in CBF
Chronic pain scale- osteoarthritis for cats and dogs
Osteoarthritis for dogs: Liverpool Osteoarthritis in Dogs Scale Helsinki Chronic Pain Index Canine Brief Pain Inventory Osteoarthritis in cats Feline Musculoskeletal Pain Index Cats should be assessed with both active and non-active terms
Sedation or general anesthesia? Risk- Preferred-
Overall risk associated with general anesthesia greater (1/100) than for small animals (1/1000) Prefer standing procedures and local blocks
Drug interactions- Synergy
Overall therapeutic effect of a combination of drugs is greater than the sum of each drug when used alone Most anesthetic drugs have synergistic effects Example: dexmedetomidine 5 mcg/kg IM as a sedative - moderate sedation hydromorphone 0.1 mg/kg IM as a sedative - mild sedation When combined together, they produce heavy sedation
Complications - fetus
Oxygen delivery -normally oxygen is delivered to the fetus from the mom via the placenta -so make sure you pre-oxygenate the mother before induction Hypotension Placental transfer of drugs Reduced metabolism- not mature Resuscitation- one person per fetus Assessment of vitality
Oxygen delivery= If there is low Oxygen content, How could the body compensate to maintain oxygen delivery?
Oxygen delivery = CO x oxygen content low oxygen content - body will have to do something to CO remember- CO = HR x SV -so body will increase HR (stimulation of the sympathetic nervous system- increases heart rate and vasoconstriction -increases SV which increases HR and deliver O2 Critical transfusion point where there is not enough O2 in blood
Monitoring equipment- Oxygenation- Ventilation-
Oxygenation: -Pulse oximetry • Measures oxyhemoglobin (O2Hb) saturation • Non-invasive -Arterial blood gas analysis • Measures arterial partial pressure of 02 (PaO2) --> more invasive: used for sicker patients Ventilation: -Capnography -Blood gas analysis • Measures partial pressure of CO2 (PCO2)
Oxyhemoglobin - absorbs more _______ light (940nm) Deoxyhemoglobin -absorbs more _____ light (660nm)
Oxyhemoglobin - absorbs more infrared light (940nm) Deoxyhemoglobin - no O2 - absorbs more red light (660nm)
Pediatric hepatic system
P-450 is immature at birth and develop during postnatal life33 Decreased drug metabolism Prolonged drug elimination Glucose levels Well maintained in normal neonatal patients -Avoid stress and fasting -May become hypoglycemic since glycogen stores are relatively low and they have low gluconeogenic ability
ANS- parasympathetic vs. sympathetic
P= homeostasis, vagus- HR S= stress response, ganglia of symp chain, vasomotor center in medulla oblongata, vasomotor tone
Post Operative Vocalization
Pain Dysphoria Emergence delirium Anxiety Need to urinate
Mechanism of action of LA
Pain Pathway (brief review) 1. Noxious stimuli (e.g. skin incision) • Exchange of sodium (Na+) ions • Na+ exchange occurs at the cell membrane • This series of exchanges generates an impulse 2. The impulse travels to the spinal cord then brain 3. In the brain = conscious perception of pain Local anesthetics work at the level of afferent nerve endings- transduction (conversion of noxious stimuli into chemical signal)
Visceral Pain
Pain associated with visceral organs Dull, not well localized pain sensations Often associated with feelings of nausea Les defined distribution of nociceptors compared to somatic pain May lead to referred pain Example: Bladder stones causing cystitis
Allodynia
Pain in response to innocuous (non-painful) stimulus
Somatic Pain
Pain of the skin, tissue and muscles Well localized pain sensation Defined distribution of nociceptors
Treatment of Post Operative Vocalization
Pain- analgesics Dysphoria -sedation -reversal (be careful of reversing opioids) Emergence delirium -sedation -proper preparation and handling -Be careful! Assessment anxiety before surgery -predict the level of anxiety after Express the urinary bladder before recovery -if unable or forget, take out for urination or defecation
Hydromorphine Induced-dysphoria
Panting Open mouth breathing Vocalizing Hyperthermic Butrophanol administered: -reverses side-effects of hydromorphine -is a mu antagonists
Knowing the vagal nerve is being stimulated in both these reflexes: Is the sympathetic or parasympathetic nervous system being stimulated and what will be the most prominent cardiovascular effect?
Parasympathetic; Bradycardia (low heart rate)
Multimodal anesthesia
Partial Intravenous anesthesia and Total intravenous anesthesia The term multimodal anesthesia refers to the use of multiple drugs for the anesthetic protocol The term partial or total intravenous anesthesia refers to the technique to keep the patient anesthetized. It usually requires multiple drugs.
How is the oxygen level assessed?
Partial pressure of oxygen in the blood As a reminder, partial pressure is the pressure exerted by one gas in a mixture of gases Usually measured in mmHg Hemoglobin saturation of oxygen Most oxygen sources are discussed in terms of %
Developing a pre-anesthetic plan Appropriate pre-anesthetic agents will depend on: Consider:
Patient evaluation History Physical exam Lab results Procedure required (painful?) Consider -species and breed-related problems -> can be harder to metabolize drugs for some breeds -relevant medical conditions (co-morbidities) -patient risk for surgery and anesthesia Boxers-> sensitive to ace; not reversible as well; use lower doses to be safe
When thinking about a case, in which ways should you approach it?
Patient history and physical exam findings Relevant blood work Anticipated anesthetic complications -General anesthesia, patient specific, procedure specific (may overlap) -This will help direct what protocol to use to help reduce risk and improve safety of the anesthesia Anesthetic drug selection -Sedative, analgesia, induction agent, maintenance, plan for recovery -Should be able to justify each drug with a reason for its use, effects and side effects
Creating an anesthetic and analgesic protocol -What to consider
Patient history, physical exam, blood work Decide how much affect you need -Mild, moderate or heavy sedation and analgesia Temperament of the animal -Calm, anxious, aggressive Age -Pediatric, adolescent, adult, geriatric Health status -Healthy, vs comorbidities ASA status Procedure being performed -Surgical vs noninvasive procedure Patient specific You should know the effects and side effects of all the drugs used Class of drugs used -Sedative -Analgesic -->Opioid, anti-inflammatory, other -Induction agent -Maintenance
10 yr old draft horse under inhalant anesthesia. HR is 32bpm, SBP 90, MAP 69, RR 6, ETCO2 40. You check the plane of anesthesia and it is adequate. She is receiving an adequate amount of fluids and there is no blood loss. Next step is to:
Patient is hypotensive Give dobutamine to increase BP Don't give anticholinergics!!
Small animal circle system
Pediatric - designed for patients with body weight between 5 and 10 kg Adult - designed for patients with body weight between 10 and 150 kg Maximum body weight is 150kg
Hypothermia; worse for pediatric and geriatric patients because:
Pediatric and geriatric patients have weak thermoregulatory center •More susceptible to anesthesia-induced hypothermia •Bradyarrhythmias- very cold patient with bradycardia will not respond to atropine •Reduced minimum alveolar concentration (MAC) of inhalants -> more side effects •Shivering -> Shivering increases tissue oxygen consumption by 400%
The marks on the vaporizer are in?
Percentage
Vascular access
Peripheral IV access • Cephalic vein, saphenous vein Central IV catheter • Jugular vein • Faster onset of action of drugs than peripheral access -easier to get blood sample and quicker for drugs When placing catheter, obtain a blood sample to be analyzed
Beta 2 Receptors- location and effects when activated
Peripheral blood vessels (muscle)- vasodilation Bronchial smooth muscle- bronchodilation Uterus- relaxation
Peripheral Pulse Palpation
Peripheral pulse is only the difference between systolic and diastolic BPs -cannot identify BP BP higher than 50 mmHg? incorrect Pulse palpation cannot substitute the real BP monitoring with non-invasive or invasive techniques UNRELIABLE- for monitoring of blood pressure; used for CPR (alive or dead?)
Vital signs monitoring during anesthesia
Personnel training to recognize any possible cardiovascular or respiratory complications Readiness for aggressive treatments of possible complications -safe analgesia during anesthesia and a better outcome for your patient
You have administered intramuscular dexmedetomidine to a dog 15 mins ago. What do you expect to see?
Phase 1- Hypertension (caused by vasoconstriction) and bradycardia (reflex)
Sedation - Phenothiazine
Phenothiazine (acepromazine) -Calming effects -Administered IM or IV at least 20min prior to procedure -Not enough on its own for sedation -used to calm the patient before
Tranquilizer- Drug class
Phenothiazines(acepromazine), Butyrophenones (pigs)
Drugs that activate Alpha1 receptors
Phenylephrine Epinephrine Norepinephrine Dopamine Ephedrine
What does hypoxemia look like?
Photo B- need to oxygenate
What's important in the pre-anesthetic period?
Physical exam, focusing on cardiac and respiratory auscultation Murmurs ->Locate which valve is affected ->Systole, diastole or both Palpation of peripheral pulses Strong Synchronous Mucous membrane color Pink Pale Muddy colored (purple- oxygentation ability) Capillary refill time Volume status Peripheral circulation
Temperature Anesthetic drugs affect/alter
Physiological responses & thermoregulatory threshold for compensatory response • Failure to shiver when mild hypothermic (won't be able to give same behavioral responses) • Core-temperature redistribution, heat loss -peripheral vasod. (e.g. acepromazine= vasodilation)
Acute Pain
Physiological, normal, adaptive or protective Occurs when noxious stimulus applied to the body Pain sensation ceases when stimulus is removed if no damage is done Example: IV catheter placement Ovariohysterectomy
Plethysmography Variability Index (PVI)
Pleth. variability index • Non-invasive method of measuring fluid responsiveness • Uses form of pulse pressure analysis to consider changes in peak and amplitude of the pleth. waveform (asses volume changes) small and weak -may be due to needing fluids (give fluid bolus) chaotic- mostly from motion artifact Normally the notch of the pulse wave form is lower during inspiration Normal- notch of pulse waveform lower during inspiration than expiration Abnormal- difference larger in hypovolemia, obstructive lung disease, intrathoracic pressure swings -can try giving fluid bolus (watch for change, if no change, problem is something else)
The following ETCO2 diagram is an example of a
Poor cardiac output
Most risky period for death during anesthesia
Postoperative death Dogs- 47% Cats- 61% Rabbits- 64%
Acepromazine -important things to know
Pre-operative sedation of a healthy patient -do not give to ill patients -high risk of hypotension -cannot reverse -last for long time Reduce the dose by ½ if using IV Reduce the dose for older patients Reduce the dose for Big floppy breeds • Newfoundlands, St. Bernards, Collies • If normal IM dose for a healthy dog: 0.03mg/kg --> For giant breeds reduce dose to ½ Boxers may be sensitive
Three types of analgesia-
Preemptive analgesia Multimodal analgesia Rescue analgesia
Factors decreasing MAC
Pregnancy Hypercapnia, paCO2 > 95mmHg (extreme) Hypoxemia, paO2 < 40mmHg (extreme) -extremes will influence CNS Hypotension MAP < 50mmHg Hyponatremia Systemic disease (hepatic failure, DKA, Sepsis etc.) Hypothermia Increasing age decreases MAC - Neonatal Halothane MAC: 1.1 - 70 y.o. MAC: 0.63 (geriatric patient- reduce anesthetic to maintain anesthesia) Drugs that depress the CNS - Opioids - Benzodiazepines, Acepromazine, propofol, alfaxalone Other volatile agents reduce MAC: - MACs are additive: 50% N2O + .5MAC Halothane = 1 MAC of anesthetic --> reduces the MAC of eachother -careful not to overdose
Summary for C-Sections
Premedication None Fentanyl or remifentanil Induction Propofol Have extra propofol!! I draw up at least 8 mg/kg - these are essentially unpremedicated, stressed out animals Maintenance- god monitorying Isoflurane or sevoflurane Intraoperative analgesia (after last puppy is removed) Hydromorphone Fentanyl (CRI) Post operative Things to consider with post op drugs - you are sending these animals home - how much pain, how long will the drug last? Hydromorphone or buprenorphine ○May be the intraoperative dose given NSAIDs ○Meloxicam single dose
Hydrostatic pressure
Pressure exerted by blood within the blood vessels On the arterial side of the capillary -pressure within the blood vessel by the blood -higher than oncotic pressure which drives fluids out of blood vessel into interstitium
Oxygen tank connects to: Must be secured to:
Pressure regulator Pressure gauge -indicates what pressure remaining in the tank and pressure being delivered to patient H tanks and E tanks (oxygen tanks)- Always must be secured to the wall H-huge E-emergency
ET tube cuff over inflation (30 cmH2O)
Pressure too high- causes necrosis of trachea
Major goal: minimize fetal depression- from:
Pre‐existing due to prolonged labor prior to fetal delivery Decreased placental perfusion -Fetal hypoxemia -Acidosis -Stress
Physiological Consequence of Pain
Produces a sympathetic response (reduced wound healing) -Tachycardia, increased CO, peripheral vasoconstriction (reduced sleep) -Cardiovascular instability in critical patients (Increased stress) Untreated pain can lead to immunosuppression -dysfunction of hypothalamic-pituitary Axis Release of proinflammatory cytokines
Propofol -effects
Produces short duration of anesthesia & rapid onset Smooth induction and recovery Decreases seizure activity - good for seizures Decreases ICP (intracranial pressure) No analgesia!
Oxyen Toxicity
Prolonged exposure to high O2 concentrations-> deterioration of pulmonary function EFFECTS Acute: -endotracheal damage, destruction of alveolar cells, increased microvascular permeability, edema, hemmorrhage, congestion Chronic: -alveolar type II proliferation, fibroblast proliferation = fibrosis Risk- more connected to time vs. FiO2 Endopoints of therapy: PaO2 = 70 mmHg (using lowest FiO2 as possible) DO NOT use FiO2 >0.6 for > 24 hr if possible
Isoflurane- Properties and pharmacodynamics
Properties: Widely used, colorless, less soluble than previous generation, nonflammable, stable, mild pungent odor, MAC 1.3%. Pharmacodynamics: Lungs: Mostly exhaled intact (metabolism <0.2%). Bronchodilation can be a beneficial side effect. Heart: Heart rate increases slightly, and cardiac output is maintained. Dose dependent decreased arterial BP due to a decrease in peripheral vascular resistance. -more isoflurane, more vasodilation, more hypotension Liver and Kidney: Not injurious. Skeletal muscle: Produces good muscle relaxation.
Anesthesia maintenance- best choices
Propofol and alfaxalone: -may accumulate in fetus if used as a continuous infusion-> can accumulate in plasma of fetus causing higher mortality rates -Recommended to use as a single bolus for induction Inhalant: -most commonly used -isoflurane -monitor depth -may cause hypotension (vasodilation) -best option for maintenance; very easy eliminated through the respiratory system
Propofol
Propofol readily crosses the placenta but it is rapidly cleared from the neonatal circulation It is considered the best choice for dogs undergoing cesarean section, as effects on healthy puppies are minimal
A patient recovering from anesthesia is shivering. What should you do and why?
Provide oxygen supplementation. Shivering increases oxygen consumption
Common arrest rhythms- Ventricular tachycardia
Pulseless Vtach: shockable rhythm -defibrillate! and resume compressions as well
Alfaxalone
Puppy vigor scores were higher in those dogs receiving alfaxalone when compared to those receiving propofol, Puppy survival rates 24h after birth were similar between groups 97% for alfaxalone and 98% for propofol Propafol seen as better drug for pregnant animals as it clears faster, has a lot of data studying it -not as much studies on alfaxalone
Scavenger systems
Purpose: Eliminate EXCESS volatile anesthetic gases FROM WORK AREA Components: Gas scavenging assembly (connected to pop-off valve) on machine Interface system to connect to disposal system - High pressure vacuum - Low pressure vacuum >> Elimination through outside wall >>Nonrecirculating air conditioner system >> Activated charcoal canister >>>> Not for N2O >>>> Must be changed frequently >>>> Exhaustion is detected by weight change
Temperature -Heat loss -radiation -convection -conduction -evaporation
Radiation: electromagnetic transfer of energy btw surfaces • most important mechanism of heat loss and anesthetic hypothermia Convection: direct heat transfer between 2 surfaces, via an intermediary (moving air or flowing liquid) • second most important mechanism of heat loss Conduction: direct transfer between 2 adjacent surfaces • Skin and cold metal table Evaporation: of liquids from skin or body surface -clip patients hair, prep with alcohol, abdominal surgery, examples of evaporation
Post Operative Vocalization- Emergence Delirium
Rapid, can be explosive recovery Immediately after turning inhalant anesthesia off or after extubation
BLS -Chest compressions Too slow: Too fast:
Rate 100 -120 compressions per minute Compress 1/3 to 1/2 chest width Allow full chest recoil • Allow adequate venous return 2 minutes of uninterrupted compressions Efficient compression still only generates: -20 -30% normal cardiac output Too slow: (<100/min) generates insufficient pressure Too fast: (>120/min) doesn't allow enough time for heart to fill INCOMPLETE chest wall recoil diminishes preload
Post Operative Vocalization- Pain
Reaction to palpation Pain score May become aggressive - especially consider if was not aggressive before surgery
Basic life support (BLS) consists of:
Recognition of CPA Chest compressions Ventilation & airway management
How to improve oxygenation
Reduce gut volume (pre-operative fasting 12h adult horses) Lateral position is best, dorsal worst Ventilate with an actual ventilator Blood gas analysis (pH, Pa02, PaCO2, HCO3, electrolytes, BE) In recovery do NOT switch sides "Good" lung will be moved underneath the horse and becomes congested more quickly than the "bad"lung clears
What are the goals of anesthesia and analgesia?
Reduce stress and response to pain, prevent awareness, provide immobility and muscle relaxation in order to complete a procedure Reduce risk to life and improve safety
How to treat hypoventilation
Reduce the dose of inhalant anesthesia to achieve a more appropriate depth Ventilate using a mechanical ventilator
What treatment of pain is considered gold standard?
Regional/local anesthetic -completely prevent transmission
The autonomic nervous system Major divisions:
Regulates 'involuntary' physiologic processes such as heart rate, blood pressure, temperature, metabolism, fluid and electrolyte balance, sweating, urination, defecation, gland secretions etc Consists of 2 major divisions: Sympathetic Fight or flight Allows body to function under stress Parasympathetic systems very direct Maintenance functions Counterbalance to sympathetic nervous system Organs may receive input from one or both systems
Temperature
Regulation of body temperature: Heat loss and heat production Behavioral + physiological mechanisms Heat loss • Radiation • Convection • Conduction • Evaporation Monitor continuously during anesthesia Every 10 -15min
Which of the following is considered an alternative therapy to the treatment of pain?
Rehabilitation
Hazards chronic anesthetic exposure
Reproduction disorders Abortion Malformations Malignancy Vital organ dysfunction - Hepatopathies - Renal pathologic changes Behavioral changes -depression Fatigue Decreased performance Nitrous oxide: (not on exam) - Direct toxic effects with > 10 hours exposure - Neutropenia - Megaloblastic anemia - Decreased vitamin B12 synthesis - Decreased methionine syntheses
Where to place it
Requires areas with no hair and no-pigment Essentially, any area with a pulsating arteriolar bed Commonly used places • tongue • toe • ear Other places • Vulva • prepuce
Injectable Analgesics- Repeat injection
Requires handling and noxious stimulus of injection which may lead to aversion behaviors and stress Peak and trough of plasma concentration and efficacy No specialized equipment needed More often used in private practice
Pharmacodynamics - Respiratory System Patient is experiencing respiratory side effects, what should you do?
Respiration depressed (decreased inhalant concentration) - Higher dose - Agent and species -Sedative and analgesic drugs Respiration increased (increased inhalant concentration) - Surgical stimulation - Central stimulating drugs
Prevention of complications
Respiratory Oxygen Ventilation -provide oxygenation and ventilation Cardiovascular Preoperative blood panel Stabilization (prior to induction with fluids usually) IV Fluids ○Crystalloids ○Colloids Maintain normal blood pressure
Full Mu-agonist opioid Adverse effects
Respiratory depression -dose related; highers doses cause more resp depression Bradycardia* -dose reduce and give very slowly Ileus, constipation Vomiting (non painful patients): morphine/hydromorphone > methadone Regurgitation & gastroesophageal reflux: hydromorphone > methadone Urinary retention Hyperthermia in some cats Excitement in some cats, horses
How pregnancy changes anesthesia- Respiratory System:
Respiratory system: Hypoventilation -Compression of the diaphragm -Decreased functional residual capacity (FRC) -pregnancy increases the intraabdominal pressure which leads to reduction of the ventilatory area of the lung Hypoxemia -Increased oxygen demand -preoxygenation to help avoid hypoxemia
Physical Exam- Respiratory
Respiratory: Auscultate dorsally and ventrally (all lung fields) and over trachea oBronchovesicular sounds oDepth oEffort Evidence of dyspnea? Respiratory rate • Rate • Effort Make sure to observe chest expanding When using alpha 2 agonists- because of the vasoconstriction, patient may look gray -> normal!!
Potential Complications - Cortical Blindness
Retrospective study Anesthetic protocol, mouth gag use, body position during procedure, visual + neurological status in recovery and outcome Anatomical dissection - maxillary artery DO NOT use mouth gags (spring loaded device to kee mouth open) on cats as it puts pressure on the maxillary artery- cause blindness 16/20 cats mouth gag 3/20 cats blind without other neurological signs 17/20 cats blind + circling, ataxia head tilt, weakness, opisthotonus, abnormal mentation 14/20 cats regained vision
Your patient is heavily sedated and unresponsive. They are hypoventilating because the level of sedation and drugs administered and breathing room air. How could we treat this?
Reverse some drugs and the effects causing hypoventilation Provide supplemental oxygen
Pharmacodynamics - CNS
Reversible dose-related unresponsiveness -the more inhalant administered, the more Immobility, unconsciousness Amnesia (0.3 x MAC in humans and animals) No analgesia effect
Inhalational anesthetics
Reversible, dose-dependent CNS and hemodynamic depression in response to noxious stimulus Mechanism remains unknown - multiple theories you will learn about later Isofluorine most commonly used
Post Operative Vocalization- Dysphoria
Rhythmic vocalization Associated with the use of pure mu opioid agonists and benzodiazepines in dogs and cats Usually get their attention for a moment and then they go back to it - Spaced out eyes - Not very responsive - BE CAREFUL to not over look pain
Respiratory System - PEDIATRIC considerations:
Ribcage is more compliable Intercostal muscles are weaker Work and pressure required to maintain tidal breathing is increased Respiratory chemoreceptors are immature -Less sensitive to increased CO2 and/or decreased O2 -CNS can't respond by increasing RR or TV to compensate -require manual or mechanical ventilation Higher resting respiratory rate, minute volume Tendency to develop atelectasis, oxygen demand and lower functional residual capacity (FRC). Maximum functional efficiency of the dog's lungs occurs around one year of age Decreased chest wall compliance Decreased elastic recoil of the lungs Decreased vital capacity Decreased and functional residual capacity Increased predisposition for atelectasis Reduced efficiency for expiration Gas exchange impairment
Equine Mortality data
Risk of death of 41 824 horses = 1.84% Reduced to 0.9% when emergency abdominal surgery and delivery of foals removed from statistics In general, overall anesthetic death risk is approximately 2.0% Anesthesia was sole cause of death - risk estimated to decrease to 0.1% Remember the high risk time for horses is in recovery and with emergency cases
Risk versus Benefit of anesthesia
Risk- inherent risk, Co-existing cardiovascular and respiratory disease greatly increase the risk, Most anesthetic drugs depress the cardiovascular and respiratory system, Facilities, staff and equipment Benefit- Allows life saving, necessary procedures, Provide analgesia, muscle relaxation and sedation, Improved quality of life Reduces stress from handling
Eye position
Rolls ventrally during surgical plane of anesthesia in most species • Eye central Too deep or Too light -must look at other variables to decide Dissociative agents (e.g. ketamine)-> Eye may be central ketamine- maintains the eye position central (so may not rotate central!)
Drugs dose depends on:
Route of administration Dexmedetomidine dose range 1 -10 mcg/kg Dexmedetomidine IM: 4 -10 mcg/kg Dexmedetomidine IV: 1 -3 mcg/kg
What are the systolic and diastolic blood pressure representative of?
S= contractility of the heart; ability to expulse the blood out of the heart D= volume, venous return and vasodilation Mean= slightly more dependent of diastolic for its measurement Inhalants cause vasodilation- diastolic pressure will be lower
Normal values
SAP- systolic arteriole pressure- 120 mmHg DAP- diastolic arteriole pressure- 40 mmHg MAP- mean arteriole pressure- 60 mmHg Horses: MAP 70mmHg to ensure muscle perfusion --important to increase survival rate
Steps to follow -example 1 -central eye position, no palpebral reflex, no jaw tone
STEP 1: Evaluate/monitor your patient -etco2, heart rate, etc STEP 2:Recognize changes Light plane of anesthesia • e.g. eye position central, palpebral reflex present, increased jaw tone, tachycardia (can see that patient is becoming too light) STEP 3:Address the issue • increase depth of anesthesia -Increase Inhalant dose (%) -if using rebreathing- can give oxygen -can give breaths to the patient, to make sure animal is receiving inhalant Give IV drug (induction, analgesic)
Steps to follow
STEP 1: Evaluate/monitor your patient STEP 2:Recognize changes Light, medium, deep plane of anesthesia STEP 3:Address the issue Increase or decrease depth of anesthesia Increase/decrease Inhalant dose (%) Give or stop IV drugs
Steps to follow -example 2 -CAT eye position central, no palpebral reflex, no jaw tone • decreased HR, blood pressure, respiratory rate/ high EtCO2 (hypoventilating)
STEP 1: Monitor your patient STEP 2:Recognize changes -Deep plane of anesthesia • eye position central, no palpebral reflex, no jaw tone • decreased HR, blood pressure, respiratory rate/ high EtCO2 STEP 3:Address the issue • decrease depth of anesthesia -Decrease Inhalant dose (%) and/or stop other drugs being administered --> cat is on central CRI and 2% isoflurane -decrease isoflurane wait 5-10 mins -may also have to decrease CRI
Steps to follow -example 3 -eye position central, no palpebral reflex, no jaw tone - normal HR, normal blood pressure, normal respiratory rate/ slightly increased EtCO2 (53 mmHg)
STEP 1: Monitor your patient STEP 2:Recognize changes -Deep plane of anesthesia • eye position central, no palpebral reflex, no jaw tone • normal HR, normal blood pressure, normal respiratory rate/ slightly increased EtCO2 (53 mmHg) STEP 3:Address the issue • decrease depth of anesthesia -Decrease Inhalant dose (%) and/or other drugs being administered- should ventilate better -monitor closely
Steps to follow -example 4 - DOG • eye position central, slight palpebral reflex, no jaw tone • HR from 90 to 115bpm, MAP from 75 to 108mmHg, RR from 7 to 22, EtCO2 from 45 to 34mmHg
STEP 1: Monitor your patient STEP 2:Recognize changes Light -becoming light • eye position central, slight palpebral reflex, no jaw tone • HR from 90 to 115bpm, MAP from 75 to 108mmHg, RR from 7 to 22, EtCO2 from 45 to 34mmHg STEP 3:Address the issue • increase depth of anesthesia -Give some breaths (IPPV) -Intermittent positive-pressure ventilation May need to increase Inhalant dose (%) May need to give a small dose of induction agent
Steps to follow -example 5 - HORSE • Eye position ventromedial, palpebral reflex present • HR (34bpm), MAP (85mmHg), normal RR and EtCO2
STEP 1: Monitor your patient STEP 2:Recognize changes Surgical plane • Eye position ventromedial, palpebral reflex present • HR (34bpm), MAP (85mmHg), normal RR and EtCO2 STEP 3:Address the issue • Nothing at the moment
Steps to follow
STEP 1: Monitor your patient STEP 2:Recognize changes STEP 3:Address the issue
Therapeutic index is considered a measure of what drug characteristic?
Safety
Pulse ox -Sp02
Saturation: % of hemoglobin in arterial blood that has oxygen attached Cannot go above 100% Pulse oximetry does not measure dissolved oxygen -98% O2 attached to hemoglobin; 2% dissolved pic 1: 50% oxygenated blood and 50% deoxygenated blood
Rationale for monitoring
Sedation- Central depression with drowsiness and some degree of centrally induced relaxation General anesthesia- Drug-induced unconsciousness characterized by reversible depression of the CNS and perception Critical systems affected by anesthesia & surgery - Blood loss, hemostasis Drugs affect the body's ability to control • Body temperature • Ventilation • Blood pressure • Reflexes (e.g. swallowing) Depth of anesthesia • Appropriate level for each specific procedure-not too deep, not too light Although these are reversible, patients are extremely vulnerable -drugs we give can cause profound problems
Clinical case 2 5y old, male, German Shepherd, 33kg Physical exam: lameness on right hind limb, suspicion of cranial cruciate ligament (CCL) rupture, mild pain All else unremarkable Presented for radiographs Choose your pre-anesthetic agents
Sedative Dexmedetomidine- analgesic properties, reversible, fast onset of action even when IM -BEST choice Benzodiazepine- healthy/young dog- may cause "disinhibition"; unreliable sedation Acepromazine- longer onset of action (30-45 mins IM for peak sedation), long duration of action (aprox 6 hrs), not reversible Opioid- Buprenorphine- minimal sedation, moderate analgesia, long onset of action (45 min up to 1 hr to take effect) lasts for 6-8 hr Butorphanol- good sedation, mild analgesia, rapid onset of action, short duration (1-2 hr)- Hydropormorphone- good sedation, excellent analgesia, rapid onset of action (aprox 4 hrs) -more side effects so go with butorphanol Methadone- mild sedation, excellent analgesia, rapid onset, duration of action (aprox 4hrs) SOOO... Dex + Butorphanol -> better (less side effects) OR Dex + hydro
Telazol(tiletamine+ zolazepam)
Sedative & anesthetic • dogs, cats, pigs and many exotic species At high doses = hypoxemia and cyanosis may occur Salivation frequently occurs Dogs may vocalize during recovery (recovery not as smooth as it is in cats) Come as a powder in multi-dose bottles Tiletamine • Produces analgesia, convulsive seizures and clonic muscular activity • To reduce seizures and improve muscle relaxation = zolazepam was added
Pharmacodynamics - CNS 1. Electrical activity of brain -
Seizure activity Isoflurane- -No seizure activity -Suppresses seizure activity Inhalant anesthetics suppress seizure activity Desflurane, Sevoflurane: -No evidence of convulsive activity -Seizure activity during sevoflurane anesthesia (humans)
Central chemoreceptors
Sensitive to the change in pH from conversion of CO2 to H+ CO2 + H2O <-> H2CO3 <-> HCO3- + H+ Fast response Ventilatory response is much more sensitive to CO2 than O2
Neonatal renal system
Serum phosphorous concentrations are usually elevated (aprox. 9 mg/dL) Lower serum creatinine levels (0.4 mg/dL) Blood urea nitrogen concentrations (10 mg/dL) are usually lower (when compated with normal health adult animals)
History inhalant anesthetic
Sevoflurane will dominate market in near future Isofluorane most common anesthetic currently
Cardiovascular side effects
Sevoflurane, desflurane and isoflurane reduce systemic vascular resistance (SVR) and maintain cardiac output (CO) (so these drugs are causing vasodilation) Isoflurane and desflurane can cause sympathetic stimulation and can increase Heart Rate and CO, with a low SVR Sevoflurane minimal effects on HR
Common arrest rhythms- Ventricular fibrillation
Shockable rhythm -defibrillate! commonly seen- both before or during CPR If you see V fib-> it is about to arrest, feel for pulse then start compressions and ask for help
Options for general anesthesia
Short duration anesthesia Longer duration anesthesia
Pharmacodynamics - Kidneys
Side effects in kidneys related to poor blood pressure and blood CO and poor perfusion output of kidneys Mild, reversible, and dose-related decrease in - Renal blood flow - GFR - Urine - output Effect is influenced by -Hydration status - Hemodynamics during anesthesia
Epidural Side-effects How to avoid/minimize
Side-effects may be seen: Vasodilation Hypotension Bradycardia Hypoventilation How to avoid/minimize Calculate an appropriate volume of drug Inject slowly Monitor patient carefully during/pos epidural injection
Monitoring the CNS made easy
Simple and reliable surgical plane= Palpebral reflexes- not present Eye position- medium Jaw tone- relaxed No need to check jaw tone if you have medial palpebral reflex
Monitoring the CNS made easy
Simple and reliable - Palpebral reflexes - Eye position - Jaw tone Palpebral reflexes -test the Lateral cantus of the eye only, then medial cantus of the eye- as the patient induces Eye position - Ventral -> Ideal/surgical Jaw tone-> relaxed
Cylinder Identification, size, capacity and pressure
Size Gas Gas symbol Color code Capacity Pressure psi at 70oF E Oxygen O2 Green 660 L 2000 psi E Nitrous oxide N2O Blue 1,600 L 750 psi H Oxygen O2 Green 7,000 L 2200 psi H Nitrous oxide N2O Blue 15,000 L 745 psi
Common Parasympathetic Effects on the Body
Slow heart rate Bronchoconstriction No release of catecholamine's
3y old, male intact, Pointer, weighing 24kg. He requires general anesthesia for a 3cm superficial benign mass removal in his left forelimb. Blood work and physical examination are unremarkable and he is bright alert and responsive (BAR). You decided to induce anesthesia with intravenous propofol. How should you administer this agent and why?
Slow, within 60sec to avoid post-induction apnea
Warming the patient:
Slowly Warm gloves - dangerous Palpation gloves with shavings in it Space blankets Bubble wrap
Physiological Assessment of Pain- Under general anesthesia
Small and exotic animals, pigs, goats: increased respiratory rate, heart rate and blood pressure Horses and cows: increased blood pressure +/- respiratory rate -Heart rate does not change as much
Reservoir bag (or Rebreathing bag)
Small animals: • 6 x patients' tidal volume • Tidal volume = 10-15 ml/kg • Available bag sizes include 0.5, 1, 3, 5 liter Adult horses (500kg): 20 or 30 L bag Young horses (< 300 Kg): 15 L bag
Carbon Dioxide Absorbent
Soda lime or barium lime Chemical absorption of CO2 coming out of the system Reaction: Co2 + h2o ↔h2co3 + 2naoh + ca(oh)2 ↔caco2 + na2co3 + 4h2o + heat Evidence of depletion of soda lime: Color change: usually white to blue Granules become hard Heat production stops (system is an exothermic reaction- not able to remove CO2, so heat production also stops)
Pulse ox and CVS
Some machines have a waveform (plethysmograph): • Quality of the peripheral pulse being measured • Amplitude of the wave corresponds directly to the pulse quality (or strength) -readjust probe vs low perfusion -->Make sure machine is assessing pulse (heart) rate correctly before using it to assess pulse quality Systolic- pulse Dicrotic notch- when aortic valve closes
STEP 3: Address the issue -SpO2 below 95% -If concern with patient saturation and oxygenation :
SpO2 below 95% ---make sure it is true! • Signal strength and readjust probe • Massage area (improve perfusion), place probe again • Place probe somewhere else • Check for obstruction (ETT/airway) • Check if patient connected to the anesthesia machine • Make sure O2 flowing and being delivered to the patient If concern with patient saturation and oxygenation • Manual breath -see if Sp02 % improves with IPPV • Arterial blood sample (blood gas analysis)
Things to consider when treating pain
Species Variable response to drugs Behavioral characteristics of the individual treated Friendly Labrador vs aggressive cat May change the frequency and degree of handling Pharmacology of the drugs available Onset, route of administration, duration of action Drug interactions Synergistic action of opioids, sedatives and anti-inflammatories Alternative therapies Cost
Species variation of effect- opiods and benzos as examples:
Species behavioral response to drugs is varied EX: Opioids: Cats and horses can become more dysphoric on pure mu opioids than dogs Cats are euphoric with buprenorphine Horses and some birds receive moderate analgesia from butorphanol vs mild analgesia in dogs Benzodiazepines: Good sedative in pigs, goats, calves and exotics Not reliable sedation +/- excitement in dogs, cats and horses
Anticholinergic effects & side effects
Speed heart rate Raise BP and CO ---- HR x SV = CO May cause tachycardia & tachyarrhythmias -increase in myocardial oxygen consumption May see transient paradoxical bradycardia -low heart rate for a few seconds- give drug a little time- DO NOT administer more right away if you see this Reduce salivary and respiratory secretions but make them thicker -thicker secretions may block tube Tighten lower esophageal sphincter Decrease GI motility ----Avoid in horse due to potential for colic If you don't need to use- don't - reserve
Acepromazine -other effects
Splenic enlargement • not usually a major issue • avoid for laparoscopic procedures - harder to find things if splenic is larger Transient decrease in PCV (red blood cells) Alters thermoregulation • E.g. patient becomes cold in a cold environment Paraphimosis • AVOID in stallions
Ventilation pattern- 4 stages Minute ventilation=
Stage I (awake): Irregular with panting or increased Stage II: Irregular with possible breath holding Stage III 1 (light): progressive decrease 2 (medium): decrease or shallow 3 (deep): slow irregular Stage IV: (way too deep) absent, may gasp terminally Don't evaluate respiratory alone: MV = RR x VT ALWAYS evaluate RR and capnography (EtCO2) -hyperventilating- increase in RR and decrease EtCO2 -hypoventilating- decrease RR and increase EtCO2
Neuroleptoanalgesia
State of CNS depression and analgesia: tranquilizer or sedative + analgesic drug This combination helps: Decrease doses of each individual drug Decrease its side effects Improve sedation or analgesic properties (synergistic effect) Examples: Acepromazine + opioid Alpha-2 agonist + opioid Benzodiazepine + opioid
Induction of anesthesia -small animals: Steps
Step 1: Induce anesthesia with injectable drugs or inhalant agents Step 2: Assess depth of anesthesia to see if able to intubate the trachea Step 3: Anesthetist uses a laryngoscope to help visualize the arytenoids Step 4: Connect patient to anesthetic machine Step 5: Assistant will press the rebreathing bag (give a breath to the patient)
Induction of anesthesia Steps-
Step 1: Premed (majority =IM) Step 2: Induce anesthesia with injectable drugs or inhalant agents Step 3: Assess depth of anesthesia to see if able to intubate the trachea • Jaw tone -loose enough that is safe to intubate the trachea? • Palpebral reflex -may still be present but reduced • Eye position -may be ventrally rotated Step 4: Intubate the trachea
Vagovagal reflex:
Stimulation of the vagus nerve (irritation of larynx, trachea, use of laryngoscope
Circulating blood volume- what happens with a hypovolemic patient?
Stroke volume decreases, less blood ejecting from the heart and less CO Need to give more volume
Peripheral Nervous System
Subdivided into the autonomic and somatic nervous systems Somatic nervous system is responsible for voluntary control of body movements
The ECG wave marked with an arrow represents an example of a _________ ?
Supra ventricular depolarization
Ring Block
Surgery or procedure distal to ring block • Dew claw removal • Toe amputation • Wound repair • Mass excision • Anesthesia of teat lift skin when injecting (similar to SQ) likely will do this four times when doing the foot to get all nerve
Eye position -horses
Surgical plane • Eyes roll towards medial canthus • Palpebral reflex may be present Dissociative agents (e.g. ketamine) -Eye may be central Light plane • Horizontal nystagmus -fast nystagmus
Choose the correct answer from the following list to describe which type of blood pressure the Doppler is designed to read
Systolic blood pressure
Physical exam
TPR (temperature, pulse, and respiration) on all patients Mucous membrane color: oPink: adequate blood perfusion and oxygenation of peripheral tissues oPale (severe anemia or blood loss), blue (low blood oxygen, lack of O2 being delivered to tissues (cyanotic), icteric, dark red: abnormal mucous membrane colors Assess hydration status: oTent skin over the dorsal shoulder/caudal neck oAssess eyes and mucous membranes (capillary refill time -CRT) Cardiovascular: Normal heart rate and rhythm Presence of murmurs Synchronous pulses Do the distal pulses match the auscultated heart rate? • Pulse quality oStrong o Weak Respiratory: Auscultate dorsally and ventrally (all lung fields) and over trachea oBronchovesicular sounds oDepth oEffort Evidence of dyspnea? Respiratory rate • Rate • Effort we mostly focus on cardiovascular and hydration status in anesthesia
NMDA Antagonist- Ketamine Use- Examples
Target modulation Somatic pain Wind up pain Prevent central sensitization Wide therapeutic index Repeat injection/bolus or continuous rate infusion Ketamine (injectable) Amantadine (oral)
Sodium Channel Blocker- Local Anesthetics Use-
Target transduction, transmission and modulation Gold standard to prevent transmission of pain Regional anesthesia: epidural, intratesticular, retrobulbar, femoral sciatic blocks Can use lidocaine intravenously in dogs Narrow therapeutic index
Alpha 2 agonists uses-
Target transmission, modulation and perception Effective adjunct analgesic in small animal Good analgesic in horses Also provides sedation if needed Repeat injection/bolus or continuous rate infusion Moderate therapeutic index Not used in cardiovascular unstable patients Synergistic with opioids
NSAIDs Use: Targets-
Targets transduction and modulation Somatic pain Inflammatory and acute pain Visceral analgesia from flunixin meglumine in horses Standard of care in most surgeries unless contraindicated for co-morbidities Part of the multimodal protocol Return threshold of nociceptors to normal range Narrow therapeutic index - Repeat injection every 12-24 hours
Opioids use- Targets-
Targets transduction, modulation and perception Most effective analgesic Commonly used to treat mild to severe pain Standard of care Wide therapeutic index Minimal clinically significant side effects (respiratory depression, bradycardia) Repeat injection/bolus or continuous rate infusion Distribution of opioid receptors and response to treatment is species dependent
Good CPR =
Team Work STEP 1: Recognize arrest STEP 2: Compressions STEP 3: Airway & ventilation Monitoring IV/IO catheter
How to select a route of administration
Temperament of the animal Access Timing -Sedation of animals it to achieve stress free IV catheter placement -If there is already an IV catheter in place, there is no need to give a painful IM injection Required response -Need a rapid and reliable sedation - IV is better; there is less variability without absorption Some drugs have to be administered a certain route based on their drug properties and FDA approval
Temperature regulation
Temperature-responsive cells throughout the body Changes in temperature sensed = afferent input reaches the CNS CNS -THERMOREGULATORY CENTER IN THE HYPOTHALAMUS • Appropriate physiological responses occur Example: decreased temperature -shivering, vasoconstriction, behavior
LOCAL ANESTHETICS Basic structure
Tertiary amine separated from an unsaturated benzene ring by an intermediate chain Intermediate chain = Ester or Amine linkage Short duration of action
Anesthesia Machines- 2 separate units:
The "mixing" machine -combines the carrier gas (oxygen) with the anesthetic vapor -"fresh gas" - fresh oxygen and isoflurane out of the anesthesia machine to the patient --> the carrier gas plus the anesthetic vapor The breathing circuit Rebreathing Non-rebreathing
The blood pressure of horses is maintained ____ than other species (at ____ mm Hg ) to ensure effective _______ .
The blood pressure of horses is maintained higher than other species (at 70 mm Hg ) to ensure effective muscle perfusion .
Oxygen content
The body always needs oxygen. Therefore, if oxygen content is low, it will try to compensate to maintain the delivery of oxygen
Nerve block for dehorning
The cornual branch of the lacrimal nerve (zygomaticotemporal) is blocked behind the root of the supraorbital process (1) and the cornual branch of the infratrochlear nerve is blocked at the dorsomedial margin of the orbit (2)
Significance of partial pressure
The environmental partial pressure should be about 160 mmHg O2 After warming and humidification the partial pressure O2 (PO2) in the alveolus (ready for ventilation) is closer to 100 mmHg An estimate and easier formula to remember: PaO2 = FiO2 (%) x 5 PaO2= Partial pressure of oxygen in the arterial blood FiO2= Fraction inspired O2 Example for anesthesia using 33% oxygen (minimum required for anesthesia) - PaO2 = 33% x 5 = 165 mmHg
Anesthetic Breathing Systems
The first portion of the anesthetic machine delivers a carrier gas (oxygen) containing a known concentration of anesthetic vapor (e.g. isoflurane) The mixture of oxygen and anesthetic vapor is called FRESH GAS The fresh gas is delivered to the patient via FRESH GAS OUTLET Attached to the fresh gas outlet is a breathing circuit FRESH GAS INLET
Which side of the heart has a higher pressure system?
The left side- has to push blood through the body Right side goes to the lungs so it can't have too high of a pressure system there
Ceiling effect
The maximum effect when administering a drug, so increasing the dose does not increase efficacy Buprenorphine and butorphanol
Pediatric renal system
The neonatal kidney is functionally characterized by: -cannot clear and metabolize drugs as effectively -drugs will have a longer effect Low clearance rate Decreased glomerular filtration Low renal plasma flow Decreased filtration fraction Depressed reabsorption of amino acids and phosphate, Exaggerated proximal tubule natriuresis Low concentrating ability There is marked variation in the degree of renal maturation at birth between species In puppies, nephrogenesis is not complete until the third week of life
Vaporizers- Physics-> Saturated Vapor Pressure (SVP):
The partial pressure of an anesthetic vapor at equilibrium above the anesthetic liquid at a given temperature (20°C). SVP determines maximum concentration of an anesthetic vapor in a gas mixture. Maximum % = SVP INHALANT /Barometric Pressure (normally 760 mm Hg) Usually maximum concentration is much higher than clinically relevant concentrations [Minimum Alveolar Concentration (MAC)]
What prevents one from introducing a carbon dioxide E tank to the oxygen yolk of the anesthesia machine?
The pins of the pin index system
Induction agents- Shouldn't use:
Thiopental Cross the placenta barrier Reduced puppy vigor and increased mortality Has to be heavily metabolized in liver before elimination: -high mortality rates Not recommended
Thoracic pump vs Cardiac pump
Thoracic= Large & barrel-chested dogs Cardiac= Small & keel-shaped conformation
Thermal burn facts
Threshold for human thermal burn: 44°C (111.2°F) over 6 hours Temperature gradient between patient and heating source Similar in dogs and cats Burn threshold NOT dependent upon: Perfusion Underlying disease
Dissociative anesthetic agent
Tiletamine IV - Only comes already combined with zolazepam (benzodiazepine) Ketamine IV- For induction of anesthesia Combine with muscle relaxer Combine with a benzodiazepine Combine with propofol
What is the most important part?
Time management You need a plan for each phase -Premedication -Induction -Maintenance -Recovery
Inflammatory Pain
Tissue injury or immune cell activation Example: Surgical wound
If the patient has central eyes, no jaw tone, and no palpebral reflex it is most likely that they are:
Too deep
Challenging intubations- swine
Tortuous course in the larynx Pharyngeal diverticulum in the pharyngeal walls -small mouth, large tongue, difficult -rotate tube 360, make sure its not in diverticulum -lube endotracheal tube -progressive respiratory distress (cyanosis) -hyperthermia (107.5) -Inability to oxygenate by face-mask
Fluid bolus calculation for 32 kg dog-
Total volume to infuse = 32kg * 10mL/kg = 320mL 320mL * 6 = 1920 mL/hr But the fluid pump only goes to 999mL/hr so set it at 999mL/hr and the VTBI at 320mL Set VTBI as 320 mL and rate 999mL/hr (this will take slightly longer than 10 minutes)
Local Anesthetics- Toxicity related to:
Toxicity related to: Drug potency Sensitivity of the species Dose given Rate of absorption (lidocaine can be given via IV but bupivocaine CANNOT) observed with increasing plasma concentrations of lidocaine
When there is perfusion but no ventilation- how?
Tracheal collapse Bronchial collapse Anything that causes collapse of a lung (atelectasis) -Pneumothorax -Space occupying lesion in the thorax -Pleural effusion Foreign body
Pain Pathway
Transduction Transmission Modulation Projection Perception
Use of local anesthetics blocking sodium channels modulates what parts of the pain pathway?
Transduction, transmission, modulation
Occulocardiac reflex:
Trigeminal-vagal reflex Compression of the eyeball, ocular trauma, retrobulbar block, hematoma
Sevoflurane produces shorter induction/recovery time when compared with isoflurane True or False
True
Full chest recoil improve outcome of CPR a) True b) False
True vacuum effect for negative pressure
Anesthesia and CPR steps:
Turn inhalant off first Turn any CRIs off (e.g. fentanyl CRI off) -turn anything off that can decrease efficiency of CPR Start chest compressions • Ventilate (PPV) • Administer drugs Reverse all drugs on board Blood work -get a sample
Wind Up Pain
Type of central sensitization Repeated firing of primary neurons causes release glutamate in the dorsal horn of the spinal cord Amplification, prolongation and recruitment of NMDA receptor Low level noxious stimuli result in pain response Example: Hind leg fracture that was not repaired until one week post injury
Blood products
Typically, replace what is lost Whole blood Replace whole blood Packed red blood cells Replace red blood cells Combination with plasma for 'whole blood' transfusion Plasma Oncotic support Need 22.5 mL/kg to raise albumin 0.5 g/dL
Alfaxalone -MOA -uses
Ultra-short acting sedative hypnotic anesthetic • Like propofol • Commonly used in dogs and cats Dose-dependent depression of CNS GABA-agonist Modulates GABAA receptor • Depression of the CNS through enhancement of the actions of the inhibitory neurotransmitter GABA Rapid onset of action Short duration of anesthesia Smooth induction Usually good recoveries • may be worse than w/ propofol, especially in un-premedicated animals -more vocalization Alfaxalone is rapidly redistributed and metabolized by the liver • cats and dogs produce different active metabolites Drug accumulation: does not appear to occur with repeated dosing No analgesia Administer slowly over 40 seconds given to quickly: -post induction apnea -vasodilation
Anesthesia and CPR
Under general anesthesia = More controlled environment • IV access • Monitoring equipment connected • Knowledge of all drugs patient received • Knowledge of signalment, history, co-morbidities • Crash carts and defibrillator close by • Ideally CPR code-> if not, start CPR right away and call owners CPA under GA: also consider blood loss and drug overdose
What is the use of cuffed endo tracheal tubes?
Under inflation of cuff -Possible aspiration pneumonia Over inflation of cuff -Possible Necrosis of tracheal mucosa Deflate cuff for extubation -However sometimes you want to leave cuff partially inflated to clean up airway during extubation
Mixture of LA
Unpredictable blockade (pH of final mixture) Toxicity is additive Shorter/similar onset and shorter duration of action compared with long-acting LA along -Such as bupivicaine alone or mixed
Rapid Recognition
Unresponsive No palpable pulses or heart beat Not breathing Absence of normal breaths IF IN DOUBT: Start chest compressions Faster recognition if monitoring is in place (ICU, anesthesia) -EtCO2 (CO2 expiration measurement) --> measurement of CO2 during expiration --> If arrest, start compressions to re-establish perfusion --> main value used to check perfusion -ECG (arrest rhythms) --> based on this, lets us know when and if we should give chest compressions
Endotracheal intubation
Use a laryngoscope (ideally) Insert endotracheal tube between the arytenoid cartilages Should not stop compressions Confirm correct placement -Visualization -Chest excursions with positive pressure ventilation (PPV) -Palpation ( feel only 1 harder structure = trachea) -Capnography (end tidal CO2 -EtCO2) Inflate ETT cuff Secure (tie) ETT in place
Minimizing Exposure to Waste Gases: VERY IMPORTANT
Use a scavenger system Keep equipment and vaporizers in good condition Identify and repair leaks in system Fill vaporizers at the end of the day Fill vaporizers in well-ventilated area Inflate endotracheal tube cuffs adequately Keep patient connected to the machine on O2 as long as possible after the anesthetic is turned off to scavenge all expired gases Pregnant women should avoid exposure, especially during first trimester
Multimodal analgesia
Use of multiple drugs modulating different receptors Usually act at different areas of the nociceptive pathway Produce superior analgesia Reason for providing multiple drugs during the perioperative period
How to prevent/minimize complications
Use sterile technique •Wear gloves •Know and perform adequate prep for each local block E.g. Epidural--clip hair, sterile prep, sterile needle and technique Know anatomy & pharmacology •If not sure how to perform the block: DON'T •Practice in cadavers if possible •Know toxic doses!! ALWAYS aspirate before injecting local anesthetic •If blood noted = DO NOT INJECT DRUG
Ketamine
Used IM for chemical restraint of animals that are difficult to restrain Commonly used IV for induction of anesthesia BUT Rarely used on its own -Use with benzos or propofol co-induction Ketamine = poor muscle relaxation (no muscle relaxation)
Alpha 2 agonists -decision to use Used for- Contraindications- careful-
Used for -Chemical restraint, sedation of healthy patients -Pre-medication of healthy patients -Post-op sedation ("micro dose") -Dexmedetomidine -->Very useful for chemical restraint, especially combined with butorphanol or pure-agonist opioid Contraindications -Sick animals -> do not use -Some cardiac disease Careful Geriatric animals (dose reduction) -Renal disease
Colloids
Used for volume expansion, particularly in hypoproteinemic patients, massive resuscitation, persistently hypovolemic/hypotensive patients Can be used with crystalloids (to make sure patient is well hydrated and gets that volume expansion Greater intravascular volume expansion compared to crystalloids because the oncotic pressure and ability to 'pull' fluid into the intravascular space from the interstitium -stays longer because of the proteins that don't diffuse across the membrane -unlike with crystalloids where only 25% remains after 30 mins; and less volume expansion since it diffuses into the interstitium Degree of volume expansion depends on the type of colloid used but it is equal to or greater than the volume infused Colloids remain in the intravascular space longer than crystalloids because the proteins Typically, peak effect lasts 4-6 hours; total effect up to 24 hours depending on the type of colloid used
Buprenorphine (partial agonist) Useful for: Not useful for:
Useful for: Mild to moderately painful procedures Post-op analgesic, stable patients Good post op choice for cats (IM, IV, SC, OTM) Not useful for: Sedation Intra-op (slow onset, not titratable, hard to reverse) Severe pain
Regional and local anesthesia
Using local anesthetic we can block the transmission of a signal along a nerve This is gold standard If the signal does not progress up the nerve to the spinal cord there is no modulation or perception
Multimodal approach to drug protocols
Using multiple drugs usually allows you to reduce the dose of each which will reduce the side effects as well Will provide analgesia vis different mechanisms Side effects Negative cardiovascular, respiratory, behavioral effects Example: Sedation for an anxious dog Dexmedetomidine 10 mcg/kg or acepromazine 0.05 mg/kg IM (alpha 2 agonist) (alpha 1 antagonist)
Assessment of Visceral Pain
Usually dull, generalized referred pain in muscles, tendons or joints that share the same dermatome Behavioral change Nausea Vomiting Praying position or hunched
Sedation for neonatal, pediatric, geriatric
Usually not necessary for neonatal dogs and cats Intravenous butorphanol + midazolam works well in foals Avoid alpha-2 agonists There is nothing such as a single sedative protocol for the geriatric patients ... based on coexisting issues
V/Q Mismatch
V = Ventilation Air circulating to lung Q = Perfusion Blood circulating to lung Because of gravity there is slightly higher ventilation than perfusion in the upper part of the lung ↑ V/Q ratio And lower ventilation to perfusion in the lower lung ↓V/Q ratio This is normal
Dynamic and Interactive Visual Analogue Scale
VAS plus distance observation, approach and ineraction with the animal and palpation of the site
Pain Scores in Veterinary Medicine- Accuracy and validity
Validated pain scales Each pain score should be validated for the type of pain and species Dog, cat, mouse, horse, cow, goat Acute vs chronic Somatic vs visceral Accuracy of subjective methods Accuracy improves with experience with using pain scores and working with the species, drugs, types of surgeries performed Vulnerable to variability, subjectiveness and bias Owner evaluation vs. student, veterinarian, technician Age, gender, clinical experience, school, personal experience
Pain Scales in Veterinary Species
Validation and repeatability Ease of use Definable point of intervention Species specific Specific to the type of pain Acute vs chronic Somatic vs visceral Wind up
Physical properties- pressure
Vaporizers dilute the liquid (isoflurane) with oxygen, gets vaporized and to the patient
Morbidity data: Problems and what it helps-
Variation in data is due to ASA status of patients seen at the institution, small number of cases analyzed, differences in protocols, types of procedures performed, limited multi-institution studies, among others Poor reporting in veterinary medicine Morbidity studies help us assess the problems and improve protocols to reduce the risk
Oncotic pressure
Vascular endothelium fairly freely permeable to water and electrolytes Selectively permeable to proteins like albumin -These are osmotically active and exert oncotic pressure -Important in the maintenance of vascular volume draw fluid into the intravascular space
Alpha 1 Receptors: Location and effects when activated
Vascular smooth Muscle- vasoconstriction Pupil- dilation (mydriasis) Heart- Increase force of contraction Kidneys- vasoconstriction Uterus- contraction
Which variable is known to interfere with pulse oximeter readings?
Vasoconstriction
What is the main cardiovascular effects seen after administration of dexmedetomidine?
Vasoconstriction, hypertension with compensatory bradycardia
What is the main side effects seen after administration of acepromazine?
Vasodilation and hypotension
You are anesthetizing a dog and the patient appears to at a dep plane of anesthesia meaning it is receiving too much inhalant anesthetic. What are the two most common cardiovascular and respiratory effects reported with the use of too much inhalant anesthetic, respectively?
Vasodilation and hypoventilation inhalant typically causes vasodilation for muscle relaxation
Why epinephrine and vasopressin?
Vasopressors -Increase peripheral vascular resistance --> Increase venous return to the heart (help direct blood to the heart; increases SV and : -->Increase cardiac output -Only peripheral vascular resistance shown to be beneficial during initial CPR phase
Body position
Vena cava- along the spine when put on back during surgery- may compress those vessels Usually very small change If has more weight due to an abnormality- can put pressure on that vessel, decreases the amount of blood getting to the heart
Ventilatory or respiratory?
Ventilation: movement of a volume of gas into and out of the lungs- what we are measuring (only CO2) Respiration: exchange of O2 and CO2 across a membrane either in the lungs or at the cellular level Respiratory = CO2 and O2 Ventilatory - CO2
What should you do next? (look at pic) a) Continue CPR for 2min and give low dose epinephrine b) Continue CPR while getting defibrillator ready c) Continue CPR for 1 full cycle d) Stop CPR
Ventricular Fibrillation b) continue CPR and get defibrillator ready
The ECG wave marked with an arrow represents an example of an [a]?
Ventricular depolarization
This dogs ECG is showing which type of arrhythmia?
Ventricular fibrillation
• Interpret the ECG. What is your diagnosis? a) Asystole b) Ventricular tachycardia c) Ventricular fibrillation d) Tachycardia
Ventricular fibrillation
ECG: shockable rhythms
Ventricular fibrillation, pulseless ventricular tachycardia • Continue CPR while charging the defibrillator • Give 1 shock • Resume CPR immediately for 1 cycle (2 min)
Evaluate Patient: < 10sec, after 2min CPR cycle Check : Ventricular fibrillation:
Ventricular fibrillation: • ContinueCPR while charging the defibrillator • Give1 shock • Resume CPR immediately for 1 cycle
Eye position and nystagmus
Ventromedial is ideal for surgical anesthesia Horizontal nystagmus means the horse is light -so may give low does ketamine and increase inhalant slightly
Hypertonic Saline
Very concentrated- hypertonic solution used with crystalloids for: Rapid resuscitation, draws water from intracellular space Use with crystalloids Dogs: 4-7 mL/kg; cats 2-4 mL/kg Duration of action 30 minutes
Respiratory acidosis- how is it harmful?
Very tightly regulated Enzyme and protein function rely on normal pH Contractility will decrease Metabolism of drugs will decrease
Pharmacokinetics
Vessel Reach Group (VRG) (organs with high perfusion pressure) -90 % of equilibration in 4 - 8 min: -meaning- it takes this long for inhalant to reach • Brain • Heart • Hepatosplanchnic bed • Kidney • Endocrine glands -Short procedure- inhalant will stay here where perfusion is very high Muscle Group (MG), equilibration over 2 - 4 hours: • Muscle • Skin -longer procedure, more difficult for inhalant to move out of muscle and skin Fat group, equillibration over 2 - 30 hours -really prolonged recovery; fat does not receive a lot of perfusion, diffusion from fat to blood to alveolars will take longer Short procedure, short recovery
Challenges
Veterinary patients are non-verbal Varied reaction in hospital environments, species, individuals, past experiences Different reactions if ill or injured Protective vs hiding Assessment must be tailored to the species and type of pain Must be able to tailor the treatment plan as well Must be able to tailor to the individual An aggressive cat vs. a very friendly cat will be assess differently Quantification is difficult Multidimensional physiologic and emotional process Includes intensity, duration and frequency and quality Pain behaviors may be similar to stress behaviors In order to generate a pain scale with assessment of abnormal behavior, you must first understand the normal behavior Training Accuracy improves with training and experience Study from Georgia demonstrated that students in general assigned higher pain scores than trained anesthesiologists
Hunched posture and praying position are postural indicators of what type of pain?
Visceral
Facial Pain Scale
Visual scale - determine pain by how animal's face looks -ear change (down and back) -whisker change -mice- grimace scale
Inhalant Anesthetics
Volatile liquids: -Isoflurane (most used, cheap) -Desflurane (least used, better, expensive) -Sevoflurane (used sometimes, more expensive than Iso) Gases: -Nitrous Oxide (N2O) - (analgesic, Old, but still used) -Oxygen, Nitrogen, CO2
High temperature gradient
Warm gloves Palpation gloves with shavings in it Space blankets
Ideal injectable anesthetic
Water soluble Long shelf-life Stable when exposed to heat and light Small volume needed Large safety margin Short duration of effect Non-cumulative -if need to give more, should not accumulate in the system and cause more side effects Readily metabolized into non-toxic metabolites This ideal injectable DOES NOT exist yet No ideal or innocuous anesthetic drugs. Only safe anesthetists!
Stages of GA 4
Way too deep and may die if not dealt with Eye position- central Palpebral reflex- absent Jaw tone- lost Corneal reflex- lost Nystagmus- none
Respiratory System - GERIATRIC
Weakening of the respiratory muscles Loss of elastic tissue Pulmonary fibrosis Increased airway resistance Decreased pulmonary diffusion capacity Decreased capillary blood volume Increased susceptibility to respiratory infections geriatric = at life expectancy and beyond
Assessment of Blood Loss and Transfusion Trigger
Weigh gauze assuming 1 g = 1 mL blood Assessment of fluid in suction container Blood loss (mL) = PCV of suction fluid x volume in canister (mL) / preoperative patient PCV Acute blood loss may be noticed as decrease in TS before PCV Transfusion trigger -Hb < 6 g/dL (approximately PCV 18%) without anesthesia -Anesthesia decreases PCV by approximately 3-5% -->Transfusion trigger for a patient undergoing anesthesia is closer to 22%
Important points to consider about pain-
What species Expected level of pain Type of pain Location of surgery Animals behavior before surgery Responsiveness during surgery/procedure What analgesic protocols were used
Ketamine -caution/avoid
When an increase in HR is harmful • Cat w/ hypertrophic cardiomyopathy (HCM) Severe heart disease, cardiac arrhythmias Severe renal injury -especially with cats Liver dysfunction (metabolism, prolonged recoveries)- cannot metabolize the drug Animal with intracranial disease? • Controversial
DOSES: Premedication & injectable anesthetics When combining: Aim is to:
When combining drugs, dose reduction is usually needed Drug dose depends on route of administration -Propofol IV (after premed): 2 -4 mg/kg -Propofol + Ketamine IV (after premed): 2mg/kg + 2 mg/kg Decrease dose of each drug Decrease side-effects Decrease volume (some drugs i.e. alfaxalone) Drugs may have synergistic effect: potentiate good and/or bad effects o Good: analgesic effect (dexmedetomidine + opioid) o Bad: respiratory depression (opioid + propofol) -opioid minimal respiratory depression effects; but with propofol will see more of a respiratory effect
What is usually needed when combining drugs?
When combining drugs, dose reduction is usually needed (fast effect but with less side effects) Butorphanoldose range 0.1 -0.4 mg/kg Butorphanol IM: 0.4 mg/kg Butorphanol + dexmedetomidine IM: 0.2 mg/kg + 4 mcg/kg, respectively
When is V/Q Mismatch a Problem? treatment?
When there is ventilation and no perfusion Pulmonary embolism - a blood clot that blocks blood flow Treat the cause Increase oxygen % if possible Ventilation
Reflexes
Withdrawal -hard toe pinch Lost during surgical plane of anesthesia Useful with mask inductions Corneal Lost relatively late so not a useful monitoring tool DON'T touch the cornea, you could damage it Palpebral Brushing or tapping the eyelid or canthus Maintained during surgical plane of anesthesia in horses and camelids -every 5 minutes ( do not overdue)
Alpha-2 agonists
Xylazine IV • Onset of action -2 to 5min • Duration of action -15 to 30min • Side effects -ataxia, hypertension, brady-arrhythmias Detomidine IV • Onset of action -5 min • Duration of action -40min to 1h • Side effects -ataxia (less than xylazine), hypertension, brady-arrythmias Remember (bi-phasic action): 1. Vasoconstriction (hypertension) Compensatory bradycardia later will see (with longer duration): 2. Vasodilation (hypotension) None/minimal change in HR
Why checking for leaks at 20-30 cmH2O?????
You will never use the anesthesia machine with pressures higher than 20cmH2O (20-30) - so, it is irrelevant if your system is leaking at 40 or 60cmH20 It is like checking your car break at 200 miles/hour speed... they probably wont work well but, that is irrelevant since you don't drive that fast anyway.
Temperament
Young vs old Hot blood vs warm blood Trained vs. unhandled Sick (colic) vs healthy (painful) Genetically driven to flee Induction Recovery
Zoletil or Telazol
Zolazepam not sold alone Zolazepam (benzodiazepine) + Tiletamine (dissociative agent) - Tiletamineis similar to ketamine IM premed or chemical restraint for dogs, cats, pigs, zoo/wild animals Pigs, cats: Reliable sedation Generally good but prolonged recoveries Dogs: Generally rough recoveries
General anesthesia
a state of unconsciousness, amnesia and analgesia. A reversible depression of CNS and perception
Continuous rate infusion
a technique of providing injectable drugs at a constant rate
Negative pressure from chest compressions results in:
a vacuum creates: -filling of the heart -pulls air in -created coronary artery blood flow -lowers ICP
You are performing CPR on a 2.5kg cat. Which type or chest compressions would be preferred according to the RECOVER guidelines? a) Cardiac pump b) Thoracic pump
a) Cardiac pump
Analgesia
absence of pain in response to normally painful stimulus in a conscious patient
VG 26 (vaso-governor 26)
acupuncture point that stimulates CNS
Types of Receptor binding
agonist-> full response stimulated antagonist-> inhibits response partial agonist - binds as an agonist but 'partial' refers to the efficacy or amount of response; less analgesic effect but binding affinity is much higher (longer duration)
What is wrong with the capnopraphy? (in pic)
airway obstruction Blue line is the capnograph- missing first portion of the graph obstructed airway = shark fin capnograph -get suction ready and clean up tube
normoventilation
all similar, same shape, height
If given dexmedetomidine, what will happen?
alpha 2 agonist- will vasoconstrict, increases afterload and increases BP and HR, barroreceptor reflex (stretch receptors) will compensate to maintain CO (CO will increase slightly)
Alpha 2 Agonists- What does it do? What cardiovascular effects are caused by their activation?
alpha 2 receptors are adrenergic, G protein coupled receptors In the CNS and spinal cord activation causes decreased sympathetic discharge leading to sedation and analgesia Inhibit neurotransmitter release from nociceptive neurons Causes vasoconstriction - increased HR?
Pain
an unpleasant emotional and sensory experience caused by actual or potential tissue damage A cognitive and conscious response
Kappa Opioid receptor: effects when activated-
analgesia decreased GI propulsive motility decreased GI secretions diuresis increased appetite Miosis/mydriasis sedation thermoregulation altered
Sigma Opioid receptor: effects when activated-
analgesia immunomodulation increased appetite
Mu Opioid receptor: side effects when activated-
analgesia (spinal and supraspinal) Emesis/antiemesis (drug specific) Euphoria Miosis/mydriasis (species specific) (pupil contaction/dilation) Respiratory depression Sedation
Inhalant anesthesia
anesthesia maintain by inhalant anesthetics only
Total intravenous anesthesia
anesthesia maintained by infusions of drugs (injectable) without the use of inhalant anesthetics (TVA) Anesthetic protocol with no inhalant Anesthesia is maintained with an intravenous anesthetic drug like propofol, alfaxalone or ketamine May include the use of other injectable drugs like analgesics (opioids), muscle relaxants (benzodiazepines)
Partial intravenous anesthesia
anesthesia maintained by inhalant and injectable anesthetics (PVA) Anesthetic protocol with inhalant Protocol includes the use of other injectable drugs like analgesics (opioids), muscle relaxants (benzodiazepines)
Lidocaine spray
anesthetic for arrytenoids as cats are oversensitive -then attempt -too many time trying to put in endotracheal tube can cause laryngospasms
If you administered hydromorphone in your premedication and intraoperative your patient is very reactive to surgical stimulus, you can administer
another pure mu opioid like fentanyl as a CRI which provide constant pain relief
Vasomotor center in the medulla oblongata controls Efferent nerves are via the
arterial and venous vasomotor tone sympathetic nervous system
ECG -normal What is it? How to put together leads?
assessment of arrest rhythm determine intervention (resume CPR, defibrillation, drugs) Leads: black- left arm white- right arm red- left leg SMOKE over FIRE P wave= atrial depolarization QRS complex= ventricular depolarization T wave= atrial repolarization Also pay attention to segments
Interpret the ECG post-CPR. What is your diagnosis? a) Asystole b) Ventricular fibrillation c) Ventricular tachycardia d) Pulseless electrical activity
asystole
Muscarinic commonly used drugs Result:
atropine and glycopyrrolate INHIBIT this receptors resulting in: Increased heart rate and contractility, bronchodilation, decreased watery component of respiratory secretions *
To diagnose arrest think of what three variables?
awareness pulses breathing
What is the recommended tidal volume (VT) and respiratory rate during CPR? a) VT = 5 ml/kg RR = 10 breaths/pm b) VT = 10 ml/kg RR = 10 breaths/pm c) VT = 10 ml/kg RR = 20 breaths/pm d) VT = 5 ml/kg RR = 20 breaths/pm
b) 10 and 10
Question • 1y old, 20kg, male, mix breed dog. Anesthetized for abdominal explore to remove a foreign body. Dog had mild jaw tone, no palpebral reflex, eyes is ventrally rotated Dog now has mild jaw tone, mild palpebral reflex and eye is central What do you think is happening? a) Dog is getting into a deeper plane of anesthesia b) Dog is getting into a lighter plane of anesthesia c) Dog is maintaining same plane of anesthesia
b) Dog is getting into a lighter plane of anesthesia want to assess HR, ETCO2, BP -HR and BP increased-> lighter plane -increase inhalant dose -> decreases BP and HR so... -administer analgesic drug full mu agonist (remember how long ago you gave analgesic and how long it lasts for!!) -may becoming light because starting to feel pain
Question Other than Sp02, which other information can a pulse ox give you? a) Pulse rate, blood pressure b) Pulse rate, pulse quality c) Pulse quality, blood pressure
b) Pulse rate, pulse quality can also help determine if patient is responsive to fluids or not
You are performing CPR on a dog. Which equipment would best predict adequate chest compressions and likelihood of ROSC? a) ECG b) Pulse oximeter c) Capnography d) Blood pressure
c) capnography
Interpret the ECG post-CPR. What is your diagnosis? a) Asystole b) Ventricular fibrillation c) Ventricular tachycardia d) Tachycardia
c) ventricular tachycardia
Which is the most appropriate agent to administer to a painful dog? a. benzodiazepine (midazolam) b. phenothiazine (acepromazine) c. Opioid (methadone) d. Anticholinergic (glycopyrrolate)
c. opioid (methadone) all others do not have analgesia
Endotracheal tube air leakage
can cause isofluorane to be leaking in OR or cause aspiration pneumonia
Anesthetic complications- decreased HR causes- treatment- do you need to treat?
causes- -vagal stimulation -disease (arrhythmias) -drugs (a2 agonist- causes vasoconstriction -> increased blood pressure, stimulating barroreceptor reflex -> causes bradycardia) -cardiac arrest Treatment- -depends on cause and if BP is low -reduced dose of drug causing side effect treat underlying disease if present
Sedation
central depression with relaxation and drowsiness. Patient is unaware but can be aroused
Opioid receptors- Bradycardia resulting from
centrally mediated increased parasympathetic sympathetic activity • More common from activation of mu opioid receptors • Usually not a clinically relevant problem
Focus should be given to
co-existing diseases Pre-op profile: History: •CNS depression •Polyuria/polydipsia •Exercise intolerance •Syncope/seizures • Family history Physical examination: -oral exam -chest auscultation -arterial pulsations --> •Arrhythmias •Cyanosis •Abnormal pulse quality •Cardiac murmurs Use your tools to diagnose anything you feel may not normal (ECG, x-rays, blood, etc)
Tank pressure manometer
connects to oxygen tank If at 0= either off or empty If turn on and its at 2000psi= full
The percentage of inhalant anesthetic coming out of the vaporizer is ______ when the flow rate is higher than 500 ml/min
constant
Stroke volume has three determinants: What are they influenced by?
contractility- afterload- pressure heart works against to eject blood during systole ->influenced by vasodilation/vasoconstriction venous return (preload)- blood flow returning to the heart -> venous return influenced by vasodilation, circulating blood volume, body position, positive pressure ventilation
Transduction
conversion of noxious stimuli to an action potential -at the level of the nociceptors
Vaporizers
converts liquid anesthetic agent to a gas that can be inhaled by a patient Function: - A container in which liquid anesthetic is converted into its vapor and controlled amounts of the vapor are added to the carrier gas that is ultimately delivered to the patient -door closes when cold -door opens when hot Able to control concentration of isoflurane independent of temperature
Oxygen saturation- Low hemoglobin concentration= Low PO2= Low oxygen saturation of hemoglobin=
cooperative binding Low hemoglobin concentration- low oxygen carrying capacity; don;t have enough hemoglobin; less molecules to bind oxygen Low PO2- Not enough oxygen to bind hemoglobin that is present Low O2 saturation of hemoglobin- Not enough oxygen bound to hemoglobin
Tracheostomy
creation of an artificial opening into the trachea
Decrease in HR and SV will: Vasoconstriction will:
decrease CO, decreases MAP increases afterload but causes a reflexed decrease in HR and ultimately may decrease CO In healthy patients, the body can tolerate changes and compensate -> not in patients with co-morbitities
Geriatric renal system
decreased Drug elimination decreased filtration function decreased Reabsorption of protein, water and sodium decreased Secretion of aldosterone decreased Secretion and reabsorption of anionic and cationic compounds decreased Formation of vitamin D decreased Elimination of protein-bound compounds decreased Regulation of blood pressure Acid-base imbalance decreased Erythropoietin formation need more fluids and lower doses
Cardiovascular system- hypotension
decreased baroreceptor activity (both geri and peds) decreased circulation speed decreased blood volume decreased cardiac output ○ Limited renal, hepatic and CNS ability to adapt to hypotension
Geriatric hepatic system What tests should be done prior to anesthesia?
decreased cardiac output: decreased liver mass decreased hepatic blood flow decreased microsomal enzyme activity decreased reduction of metabolic activity Liver function and coagulation test should be requested prior to the beginning of anesthesia or sedation
Narcosis
deep sleep that cannot be aroused
Dissociative anesthesia
dissociate thalamocortic and limbic systems can be given in muscle of veins
Supraglottic airway device
does not enter the trachea or esophagus tip blocks esophagus and air goes into trachea -designed for rabbits and cats who are harder to intubate
How do determine if a cat or dog is bradycardic?
dog- less than 50% of resting heart rate cat- less then 100 beats per minute
In general, drug/dose needed to sedate or anesthetize- ranked among horse, mules, and donkeys
donkeys > mules > horses Donkeys Typically less affected by premed, induction drugs May be due to differences in body water distribution & drug metabolism Dose around 1.5x the horse dose EXCEPT guaifenesin (GG) Donkeys more sensitive to central effects of GG • hypotension and apnea after a bolus -don't give too much or use something else
Potency
dose or concentration required to produce a desired effect
Agonist -
drug that binds a receptor and activates it to generate a physiologic response Example: morphine is the prototypical opioid agonist
Partial agonist
drug that binds a receptor, activate it but produces a less than maximal response Example: buprenorphine is a partial mu opioid agonist with less peak analgesic response. Note that buprenorphine also has a high binding affinity.
Antagonist -
drug that occupies a receptor and blocks the activity Binding affinity - strength of binding
cardiopulmonary resuscitation
during CPR CO2 should increase during chest compression sudden increase means patients heart now beating on own again pic= what effective CPR looks like- should be increasing
atelectasis in anesthesia
during anesthesia, the lungs are collapsing and less air is filling the alveoli and less gas exchange
Upper airway obstruction
edema, hematoma, swelling, trauma, laryngeal paralysis, laryngospasm -administer intransal phenylephrine (allows patient to breath through the nsoe) -0.3 - 3.7% horses present upper airway obstruction in recovery Could be from: 1. ET Tube 2. Technique 3. Trauma 4. Time 5. Specie 6. Overextension 7. Head position
Considerations for C Sections
emergency- -dehydration -hypovolemic -sepsis -sympathetically depleted -hypocalcemia Elective procedures- -bright, alert and healthy Staff and equipment- -multiple people -2 teams -warming devices -analgesia -suction -iodine -suture -dry and warm towels Time
Opioid receptor- Kappa endogenous and exogenous ligands
endogenous- dynorphin exogenous- buteophanol
Opioid receptor- Mu endogenous and exogenous ligands
endogenous- endorphin exogenous- morphine
Opioid receptor- Delta endogenous and exogenous ligands
endogenous- enkephalin exogenous- etorphine
Adrenal glands -Release:
epinephrine and norepinephrine sympathetic nervous sytem
Excitatory= inhibitory=
excitatory= analgesia inhibitory= sedation
Beer's Law
explains the relationship between absorbance, at a given wavelength and concentration, A = εbc Beer's law: the amount of light absorbed is porportional to the concentration of light absorbing substance
Assessment of Acute Pain- other
facial expression reaction to wound locomotor activity vocalization -anxiety -->separation -->kennel anxiety -dysphoria -pain
Speed of injection- Rapid administration of intravenous drugs results in:
greater effect and side effects Example: administration rate of propofol to induce animals for anesthesia is slow and steady, to effect: Administer 2 mg/kg IV very fast (within 3 seconds) will cause induction of anesthesia AND hypotension and respiratory depression Administer 2 mg/kg IV slowly (over 1 minute) will cause induction of anesthesia with less hypotension and respiratory depression
If you have 1000psi, how many liters do you have?
half of the capacity H- 7000 L at 2200 psi -> so half capacity (~1000 psi) = 3500 L
What removes CO2 out of a non-rebreathing system to avoid high inspiratory concentration of CO2
high fresh gas flow
Diagram
http://www.asevet.com/resources/circuits/circle.htm
What is the most common cardiovascular side-effect observed with propofol administration?
hypotension decreased periferal vascular resistance
Thoracotomy
incision into the chest cavity
To increase CO:
increase contractility and HR
Physiological Assessment of Pain- Sympathetic nervous system activation
increased circulating catecholamines
Capnography
increasing portion of graph = expiration (CO2 going up) decreasing portion of graph= inspiration (CO2 going down) Alpha angle= first top curve - expiration Beta angle- last curve -inspiration phase 1- inspiration Phase 2- beginning of expiration phase 3- end of expiration ETCO2- largest, highest concentration of CO2 after the slow raise of expired concentration A noninvasive method to quickly and efficiently provide information on a patient's ventilatory status, circulation, and metabolism; effectively measures the concentration of carbon dioxide in expired air over time.
Hypnosis
induced sleep from moderate CNS depression, readily arousable
Re-breathing CO2
inspiring CO2- something wrong with machine -bain- fresh gas flow is too low -circle- soda lime exhausted, higher dead space (endotracheal too long)
laryngoscope
instrument used for visual examination of the larynx -used when need to be intubated right now! In emergencies!! Used for dogs, cats, pigs, ferrets, sheep, goats NOT used for bovine, equine, rabbits, birds, reptiles, mosquitoes -bovine (palpate) -equine and rabbits (blind) -birds (do not have epiglottis) You should learn how to handle it, how to change blades, check if the light functional before each use, and choose blades size and shape.
Perception
integration of nociceptive information by the brain
Gamma-aminobutyric Acid (GABA) receptor
ion channel- quick Ionotropic receptor: ligand gated GABAA - anion channel (Cl- into cell) = inhibitory Endogenous ligand: GABA Physiologic response: hyperpolarization of neuron --> Inhibition of action potential Reduced CNS activity (want agonist) Location: CNS
Which injectable anesthetic agent has analgesic properties? propofol alfaxalone etomidate ketamine
ketamine NMDA receptor agonist
Isoflurane requires ____ liver metabolism
less
Regional analgesia
loss of pain sensation in a larger but specific body area usually by using local anesthetics to block transmission of pain affected by specific nerves
Local analgesia
loss of pain sensation in a specific area
Endotracheal tube selection in dogs
measuring the distance between one nostril to the next -> DOES NOT WORK palmate trachea -imagine how thick cartilage is -imagine the internal diameter -compare with available ET tubes
Esophageal intubation
minimum CO2 levels- not getting air
Morphine is a full mu opioid agonist. The dose to achieve clinically relevant analgesia using morphine is 0.5 mg/kg Buprenorphine is a partial mu opioid agonist. The dose to achieve clinically relevant analgesia using buprenorphine is 0.03 mg/kg Given that buprenorphine is a partial mu opioid agonist and will therefore achieve less peak analgesic response: which drug is more efficacious?
morphine
Glasgow pain scale
multiple questions
Challenging intubations- Brachycephalic syndrome
narrow rima glottis elongated solf palate enlarged tonsils everted laryngeal saccules hypoplastic trachea
Invasive blood pressure monitoring
need arterial catheter- dorsal pedal or medial coccygeal artery Fluid filled tubing for blood pressure monitoring connect to blood pressure transducer that connects to the monitor Ex: 120/80 120=systolic 80=diastolic
Obligated nasal breathers and other animals with different anatomy
need to be intubated and extubated at right time rabbits- only when fully awake alligators- have a gulla- keeps airway closed -must inset large pipe to keep mouth open birds- very long trachea -more resistance as trachea curves
Nociception
neural process transforming an external stimulus to an action potential The process that underlies the conscious perception of pain
Alfaxan® solution
new formulation • Clear, aqueous solution for intravenous (IV) injection -part of premedication combo • Registered for induction/maintenance of anesthesiain DOGS and CATS much more expensive • 10 mL vial (10mg/mL alfaxalone solubilized in 2-HPβCD (Hydroxypropylβcyclodextrin)
Depth of anesthesia Based on this dog's clinical signs, What is his depth of anesthesia? Why?
no palpebral reflex with central eyes may be indicator that dog is too deep
Modulation
nociceptive information augmented or inhibited at the level of the spinal cord
The pop-off valve should be _____ during maintenance of anesthesia to prevent pneumothorax!!!
open
Age is a predictor of:
outcome Age is not a disease, however it is considered an important independent risk factor of anesthesia related morbidity and mortality and therefore is often used as a predictor of perioperative outcome for anesthetized patients. -A decreased risk of anesthetic mortality is observed in cats and dogs younger than 6 months of age -A significant increase in mortality rate is observed in older patients -The odds of anesthetic-related casualties are higher in patients with coexisting diseases, especially those one that lead to poor functional organ capacity, such as pulmonary, cardiac, renal, hepatic, and endocrine diseases alone or in combination. -Physiological status of older patients is more relevant than their chronological age The geriatric patients should be sub classified into different categories on the basis of their physiological status
What is referred pain?
pain perceived at a location other than the site of the painful stimulus
Partial pressure of O2
partial pressure of oxygen in the blood stream or similar to the amount of oxygen in the blood
Tranquilization
patient is aware of surroundings but relaxed and relieved from anxiety
Ketamine -pharmacodynamics Cardiovascular- Respiratory- CNS-
pharmacodynamics- What a drug does to the body Cardiovascular • Indirect (centrally stimulating): Increases HR, BP, CO and stroke volume • Direct effect on the heart: myocardial depression Respiratory • Bronchodilation • Apneustic breathing- abnormal pattern of breathing characterized by deep gasping inspiration with a pause at full inspiration followed by brief insufficient release Central nervous system (CNS) • Increases CSF and intraocular pressures if used alone -noted more when used alone (large dose of one drug) • Increases ICP due to increased cerebral metabolism
Ketamine -pharmacokinetics
pharmacokinetics -What body does to the drug Relatively rapid onset of action (especially when given IV) Metabolized by the liver In most species • Hepatic metabolism= produces active metabolite norketamine then • Inactive metabolite excreted in urine Cat • Active norketamine is excreted unchanged in the urine
Preganglionic Ganglia: Postganglionic Neurotransmitters:
preganglionic ganglia- Collection of nerve cell bodies outside the CNS Acetylcholine (Ach) - cholinergic - all preganglionic fibers -All postganglionic parasympathetic fibers - Some sympathetic fibers Norepinephrine (NE) and Epinephrine (EPI) - adrenergic - Postganglionic sympathetic fibers Dopamine (D) - Postganglionic sympathetic fibers - Renal vasodilation
Pressure Regulators
pressure-reducing valves : -maintain a constant flow of gas from the high pressure side (cylinder) to the low pressure side (flow meter) -One separated regulator for each gas source -Safety operating pressures for machine, anesthetist, and patient -pipeline inlet x cylinder Point- tank holds 2000 psi but we only want 50 psi to be delivered to the patient -regulator allows for this to happen #1 connects to A tank #2 connects to H tank
Projection
propagation of action potential by afferent neuron to brain
Transmission
propagation of action potential by afferent neuron to spinal cord
Pressure Relief Valve
protect patient from being over pressurized -can release pressure to save patient
Non invasive blood pressure NIBP
provides Systolic blood pressure and heart rate -much better than doppler -not all of them work -unreliable -new for vet med -have to find the one that works best (cheaper= unreliable) --> only two brands= petMAP and SunTech
Overall protocol for vasodilation
reduce dose check heart rate (check before fluids)- if low, have to get HR up before giving IV fluids in order to really get the increase in CO that you want) IV fluids
Pre-anesthetic blood work- CEPSAF recommendations:
reduction in risk with preoperative blood work in high ASA patients Blood work for ASA 1 will remain a controversial issue
Normoventilation
refers to normal ventilation in which a PaCO2 of about 40 mmHg is maintained
Armored ET tubes-
reinforced tracheal tubes ensure the airway unobstructed
Assessment of Acute Pain - Posture
relaced sleeping hunched tense neck, abdomen, back non-weight bearing lame
Why 60 mmHg ?
renal blood flow constant if blood pressure between 60 and 160 mmHg GFR constant until pressure is around 60, as blood pressure drops, GFR drops and urinary production falls If blood flow falls below 60 mmHg, you are risking the patient developing acute renal disease monitoring blood pressure ensures renal perfusion
Cardiac oscillations
respiratory rate is low Heart is moving and is also moving air movement do not have to react
Diffusion Impairment
results from thickening of the alveolar membranes or a decrease in their surface area. it causes blood PO2 and alveolar Po2 to fail to equilibrate. Alveoli is one cell thick In certain conditions the cell wall thickens Pulmonary edema Pulmonary contusions Asthma Chronic airway disease This may affect V/Q mismatch Treatment: Reduce thickness if possible Increase oxygen % Mechanical ventilation
If your patient received a pure mu opioid like hydromorphone and is dysphoric then you can use a mu antagonist - like butorphanol to:
reverse the dysphoria and provide mild analgesia (if it is a non painful procedure)
An ideal drug for pregnant animals:
short acting- transfers to placenta as well as is metabolized and eliminate drugs reversible lowest dose- ensure less side effects Do not cross blood - placenta barrier
What removes the CO2 out of a rebreathing system to avoid high inspiratory concentration of CO2
soda lime
What happens with alpha-2 agonists?
the blood pressure is high and the heart rate is low (baroreceptor reflex) this is well tolerated in healthy patients -the CO will be slightly reduced but most healthy patients can tolerate Reversal is a treatment if required
Cmax
the maximum concentration of the drug
Can only use iso or sevo at a time because:
they potentiate each other and end up with a small dose
Clinical case 1 1y old healthy (ASA I) beagle, female, 10kg Physical exam and blood work unremarkable Presented for desexing(ovariohysterectomy -OVH) today How to choose your pre-anesthetic agents?
think about signalment, physical exam findings, pain?, medical conditions, procedure pain level -healthy, friendly/calm, young dog, for painful procedure Sedative- acepromazine or dexmedetomidine Analgesic- hydromorphine or methadone ace + hydro or dex + methadone
Half life- Important for-
time to remove ½ the concentration of the drug from the body This is important to determine dosing intervals, continuous rate infusions, withdrawal times
V-gel
to establish an effective airway during general anesthesia
Dexmedetomidine, an alpha-2 agonist, causes vasoconstriction- true or false
true- hypertension -and reflex bradycardia
Equine intubation is done blindly:
twist the tube and keep it centered until it gives into the trachea -push on the chest to see if air is coming out of the tube neck held in straight line
How many unidirectional valves the circle system have? (one word)
two
A study of 1500 dogs reported that if no issues were identified on physical exam and history, that alterations noted in the blood work were ________ change anesthetic technique
unlikely Same study indicated that 8% would be reclassified to a higher ASA status 1.5% additional bloodwork 0.2% would change anesthetic protocol
Balanced anesthesia
use of multiple drugs and techniques to induce amnesia, antinociception, muscle relaxation and alteration of autonomic reflexes
Devices- Mask
useful for pre-oxygenation & resp distress -Some animals will NOT accept the mask without getting more stressed -Tight fit connected to reservoir that can meet minute ventilation (MV) requirements (i.e. 30kg dog, 300mL VT, 1 sec IT = 18L peak inspiratory flow = not feasible) -Provides 35-60% FiO2 (inspired o2) (lasts for about 3 mins) Flow by = 3 mins 100mL/Kg/min -from the circle Y-piece 2.5 cm from the nares -minimal difference between flow by air and room air -much better when using mask- patient will be less stressed and happier (pre-oxygenate to help calm the patient)
Sodium Channel Blocker- Local Anesthetics
voltage gated ion channel Activation leads to propagation of the action potential along the nerve Located on neurons Inhibition leads to a complete cessation in the transmission of the nociceptive input to the spinal cord Local anesthetic binds to receptor causing a conformational change leading to reduced sodium flux
Cardiac output = MAP = What will using anesthetic inhalants do to MAP?
volume of blood pumped by the heart per minute: heart rate X stroke volume MAP = CO x SRV SRV= systemic vascular resistance - the resistance to blood flow by all vasculature Inhalants cause vasodilation which will decrease resistance which will decrease MAP
Hyperventilation
waves decreasing over time ventilating too much too often Low CO2 interferes with pH which interferes with drug metablism
Hypoventilation
waves increasing over time not breathing deep or often enough - CO2 builds up Can also see ventilating normal over first waves, then one large wave and back to normal- -close pop off valve and give breaths every 20 minutes to ensure patient is not hypoventilating -general anesthesia depresses respiratory
Pharmacokinetics
what the body does to the drug Absorption, Distribution, Metabolism and Excretion (ADME)
Pharmacodynamics: effect and side effects
what the drug does to the body Effect Desired clinical effect Side effects Negative effect associated with its administration We will focus on the cardiovascular, respiratory, behavioral
Pharmacodynamics -
what the drug does to the body Effect or response Dependent on the amount of drug and receptors available Potency and efficacy Drug Receptor interaction
If you administer a partial agonist (buprenorphine) that has a high binding affinity, when can you administer another mu agonist?
you will not be able to administer another mu agonist until the duration of effect of buprenorphine has worn off (6-8 hours)
How many unidirectional valves the Bain system have? (one word)
zero
Adrenergic receptor Agonists- Dexmedetomidine, xylazine, Detomidine
α2 agonist bind to the α2a receptor in the cerebral cortex and brainstem (in areas responsible for sympathetic outflow) (this decreases sympathetic outflow to the brain Leads to sedation and supraspinal analgesia by decreasing discharge frequency Also causes central bradycardia Baroreceptor reflex stimulated α2b receptor causing peripheral vasoconstriction causes an increase in blood pressure (will decrease HR) This is sensed by the baroreceptors in the carotid sinus and aortic arch which stimulates the parasympathetic nervous system to decrease the heart rate
Blood Product Administration
• 0.25-1 mL/kg/hr for first 15-30 minutes to assess for transfusion reactions • Then increase to 10-20 mL/kg/hr for the remaining • Administer all product over maximum of 4 hours to avoid bacterial contamination • Can increase if severe blood loss and hypovolemia
Analgesia
• Absence of pain in the presence of stimuli that would normally be painful
Pre-medication agents used as part of a pre-anesthetic protocol
• Alfaxalone IM -GABA agonist • Ketamine IM -Dissociative agent, NMDA antagonist • NSAIDs SC -COX inhibitor (pre or post-op)
Tranquilizer -higher doses do and don't do:
• Alter the emotional state and calm the patient -reduce anxiety and stress • Patient remains aware of its surroundings -Higher dose increases duration and side effects -Higher dose does not produce general anesthesia
Short Duration Anesthesia
• Castration • Flush wound or joint • Change cast • Laceration repair Use intravenous agents only (TIVA)
Start Monitoring
• Connect the ECG leads • Blood pressure: indirect with Doppler or direct with arterial catheter • Blood sample for blood gas analysis • Start the ventilator -adjust the tidal volume if necessary • HR does notchange with increased depth, only BP does -Adult horses normal HR: 28 -35 bpm
Once induced and intubated
• Connect to breathing circuit • O2 flow at 8-10 L/min • Isoflurane at 4-5% • Start the ventilator • Keep at this for ~ 10 min, then turn down: -O2 to 3-6 L/min, -isoflurane to 3%, then 2.5%, then 2%
Sedation -Benzodiazepines -Mechanism of action
• Diazepam, Midazolam, Zolazepam -D and M most commonly used Mechanism of action GABA agonist: -Bind to benzodiazepine receptor, enhancing effects of inhibitory neurotransmitters (GABA, glycine) -increases effects of GABA- increases inhibitory effects IM, IV, intranasally(IN), rectally (seizures) Diazepam is not water soluble • Viscous, difficult to inject IM = pain • Avoid IM use Midazolamis water soluble -no pain IM Both have hepatic metabolism
Analgesics
• Drugs that produce analgesia -opioids, alpha-2 agonists; without causing loss of consciousness
Capnography
• Early indicator of CPA -during CPA values are low (below 15mmHg) • Indicator of efficient compressions(A) -want to see a generation of ETCO2 above 15mmHg • Early indictor of ROSC (B)
Control of Breathing
• Efferent from CN IX and X • Output to diaphragm and intercostal muscles • Control of respiratory is complex • Much more input for conscious control of respiration than control of blood pressure
Isoflurane- general information
• First synthesized in 1965, human use in 1981. • Approved for veterinary practice in 1985. • Not a convulsive agent. • Adequate muscle relaxation. • Rapid and smooth induction. • Rapid and smooth recovery.
Opioids Classification:
• Full Mu-agonists (pure)-> binds to receptor and has full conformational changes) -morphine, hydromorphone, methadone, fentanyl, sulfentanil, etorphine • Partial Mu-agonists -> binds with receptor but only some degree of receptor activation - buprenorphine (used the most) • Mu-antagonist & Kappa-agonist -> does not activate receptor, only blocks - butorphanol * Weak Mu-agonist-> consider a mu and kappa agonist for this class
What affects pulse ox readings?
• Hair • Pigmented skin/mucosa • Movement -make sure people are not moving or bumping the pulse ox -can give inaccurate readings • Light - light absorption at different wavelengths- makes sure there is no light directly on it • Tissue thickness • Vasoconstriction (hypothermia, drugs e.g. Alpha-2 agonists) • Arrythmias • Methemoglobin (tends to read 85%) • Carbon monoxide toxicity (some newer machine can recognize this)- can't distinguish between CO2 and CO -pulse ox not helpful for these types of patients
Temperature- Prep and procedure
• Hair shaved area, alcohol-prep, cold OR table, large incisions/surgical site
Amine-linked drugs
• Hepatic metabolism -Lidocaine -Bupivacaine -Mepivacaine -Ropivacaine -Prilocaine
Alveolar Concentration and induction- Factors lowering alveolar concentration:
• High cardiac output tends to slow induction. -more blood sent through the lungs, the more diffusion will happen -Increases in blood flow through the lung serves to maintain the diffusion gradient between the alveoli and blood. (gradient between alveolar and blood will decrease and uptake of inhalants will decrease significantly) ❖ Extends time required for PA PB • High solubility in blood and other tissues. -promotes diffusion and lowers alveolar concentration -High solubility of an inhalant -> inhalant will leave the alveolars quicker and concentration of inhalant in the alveolars will decrease and induction rate will decrease. (until next inspiration)
Sedation -Butorphanol
• IV dose (0.01 -0.02mg/kg) after giving the IV dose of alpha-2 agonist • May cause head bobbing sedation protocol for standing procedures commonly used for horses most used opioid
S02 -PO2 relationship Make sure the machine is reading the pulse rate correctly why?
• If not, SpO2 unlikely to be correct - make sure your HR reading matches with machine reading -adjust clips During anesthesia with 97%+ oxygen • PaO2 can be between 300 - 500 mmHg range • Hypoventilation, V/Q mismatch, atelectasis and R to L shunt can reduce this
Regional analgesia
• Insensibility to pain in a larger, though limited, body area • Usuallydefined by the pattern of innervation of the affected nerve(s)
Alveolar Concentration and induction- Factors that increase alveolar concentration:
• Inspired concentration: -The higher the inspired concentration, the higher the alveolar concentration. • Alveolar ventilation: -The greater the ventilation rate, the greater the delivery to the alveoli. Thus, a more rapid induction is achieved. • Poor solubility in blood and peripheral tissues If patient is waking up, as you give propofol you also ventilate High solubility of an inhalant -> inhalant will leave the alveolars quicker and concnetration of inhalant in the alveolars will decrease and induction rate will decrease. Low solubility-> inhalant will stay in the alveolar longer and equilibrium will be reached quicker
Local analgesia
• Loss of pain sensation in a circumscribed body area
Longer duration anesthesia
• Major surgery • colic, orthopedic • Most eye procedures Use IV then inhalant anesthesia
Monitoring during anesthesia Fundamental aspects:
• Oxygenation • Ventilation • Circulation Adequately oxygenated blood + Efficient circulatory system
Propofol -protein binding % alfaxalone- ketamine- Hypoalbuminemia=
• Propofol 96% -more protein binding • Alfaxalone 17.6% • Ketamine 35-54% Bound drug is not able to pass into brain Hypoalbuminemia--> Less drug protein bound and less drug needed for induction
Eyes
• Protect both eyes, especially the lower most one • Check palpebral reflex • Apply lubricant to both eyes - only to lowermost eye for ophthocases
Ester-linked drugs
• Rapidly hydrolyzed by plasma cholinesterase • Not commonly used in vet med • Allergic reactions common (e.g. procaine) Benzoic Acid: -cocaine -benzocaine Para-aminobenzoic acid: -Procain -Chloroprocaine
CPR code
• Red -no CPR (no chest compression or drugs) • Yellow -CPR but no open chest • Green -open chest CPR, do everything possible! - not always successful bit if animal is critical, may be only option to save them -cardiac tamponade (pericardium full of blood, heart cannot pump) to help owners decide what they want us to do and to help protect yourself
Asystole/PEA- what to do:
• Resume CPR immediately for 1 cycle • Low dose epinephrine or vasopressin q 3-5 min • Consider atropine if high vagal tone
Evaluate Patient: < 10sec, after 2min CPR cycle Check : Asystole/PEA
• Resume CPR immediately for 1 cycle • Low dose epinephrineor vasopressin q 3-5min • Consider atropine if high vagal tone -atropine has a faster onset -instead of glycopyralate -> longer time to onset and lasts longer
Sacro-coccygeal NB - Horse and cat
• Sedation • Sterile prep, technique • LA (e.g. lidocaine) • Tail up and down Great to unblock cats with urinary obstruction (UO)
How are horses different?
• Size (can accidentally harm or kill you) • Temperament/attitude • Unique Anatomy • Small mouth opening and long oral cavity -intubation • Obligate nasal breathers -recovery • Drugs to induce anesthesia are not titrated to effect
Dental Blocks- Equipment
• Specialized/expensive equipment not required Needle Syringe Gloves Local anesthetic • Always maintain sterility
Sedative
• State characterized by central depression accompanied by drowsiness • Generally unaware of surroundings but responsive to painful stimulation • "Chemical restraint"
Epidural -dog
• Sternal or lateral recumbency (legs forward, patient straight) • Thumb and middle finger = highest point of ileum wings • Index finger = palpates lumbosacral space between L7 - S1 • Insert spinal needle in the midline - may feel a "pop" when go through the ligamentum flavum) • Remove the stylet • Hanging-drop technique (add some drops of your drug or sterile saline to the needle hub) • Advance needle slowly until the fluid is aspirated into the needle - negative pressure that confirm you are within the epidural space Draw back, if no blood or CSF • slowly inject the drug • LA, morphine (preservative free) * No resistance to injection
Sevoflurane- general information
• Synthesized in 1970, described in 1975. • Rapid & smooth induction & recovery • Dog MAC 2.4). • More expensive than isoflurane • Less potent than isoflurane - Requires higher concentration for the same plane of anesthesia Note: Some people believe that isoflurane will get out of the market and Sevo will replace Iso as costs decrease and isoflurane popularity decreases in human medicine.
Minimum Alveolar Concentration (MAC)
• The MAC value is the minimum alveolar concentration of an inhaled anesthetic in the alveolar gas at 1atm that will produce immobility in 50% of a tested population during a supramaximal noxious stimulation. • MAC is a measure of potency and is used for comparing anesthetics. • 95% of patients should hold still at 1.2 MAC. Surgical MAC (100% not moving) appr. 1.5 x MAC Within population only small variability around MAC Individual MAC in general within +/- 30% of population MAC Similar values for most agents across species
Esophageal temp. probe
• The esophagus passes close to the trachea Esophagus is located at left of midline • Pre-measure the probe from the incisors to 3-5cm caudal to the thoracic inlet • Open animal's mouth, gently pull tongue forward and introduce the esophageal probe
Alfaxalone IM Possible side effects
• Tremors • Rough recoveries • Vasodilation, hypotension NO analgesic properties
Jaw tone
• Varies with depth of anesthesia • Very subjective • Changes are what is significant -assess immediately after induction •Tip: use only one hand (thumb and index finger), Be gentle!
Advanced life support (ALS)
• Vascular access • Drug administration • Defibrillation • Open-chest CPR -expensive -can develop other complications -small % of survival
STEP 1: Evaluate/monitor your patient
• What is the SpO2%? 98-100% is what to expect • How does the plethysmograph look? • Does the pulse rate from the pulse ox matches the pulse rate and/or heart rate you manually or mechanically checked? • How does your patient look? Any changes in ventilatory pattern, mucous membrane color, ECG, BP, HR, temperature, etc.? • Any surgical complications noted? E.g. thoracotomy --pneumothorax mucous membrane pink, alone does not mean hypoxic patients with anemia - pulse ox may still read normal due to those RBC being fully saturated
Rationale for loco-regional analgesia Limited:
•Agents for pain management -Multi-modal analgesia -Reduced side-effects (e.g. dysphoria) -Target site of pain •Analgesia w/out systemic or centrally acting agents Painful procedures Prolonged analgesia LIMITED OPIOID AVAILABILITY
PREMED drugs, THINK:
•Analgesics (opioids for ex) •Tranquilizers •Sedatives
