Anaesthesia
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11. Understand the difference between trade name and generic name.
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What are the purposes and / or advantages of premedication? Be able to discuss FOUR reasons for premedication.
1. Decrease the amount of induction agent 2. Decrease the amount of maintenance agent 3. Smooth the induction and recovery periods 4. Sedate the patient 5. Analgesia -(preemptive analgesia) 6. Offset the physiological consequences of other agents and procedure
Describe three ways to assess the respiratory rate in an anesthetised patient
1. Respiratory rate can be assessed by watching the patient breathe. Watching the chest rise and fall is equivalent to one breath. 2. observing the rebreathing bag move 3. watching condensation 'fog' in the endotracheal tube during expiration.
What the results of General anaesthesia ?(CNS depression)
1. Unconsciousness 2. Muscle relaxation 3. Analgesia 4. Amnesia
3. Discuss the problems associated with "red rubber" ET tubes.
1. they are opaque (making it impossible to see if the tube has become blocked. 2. They also have "high-pressure, low-volume" cuffs (see below), 3. can not be heat sterilised. 4. prone to kinking 5. cause tissue reactions
Morbidity in small animals is much higher than for cats and dogs. why?
A high-surface area to volume ratio Ø Perioperative hypothermia High metabolic demand Ø Higher heart rate Ø Hypoglycemia Ø Hypoxemia Ø Fast metabolism of anesthetic drugs Unique Anatomy and Physiology Technically difficulty in Ø Assessing underlying diseases Ø Venous catheterization Ø Endotracheal intubation Ø Perioperative monitoring Inexperience of veterinarians Stress Ø Rabbit and Guinea pig
What information does a pulse oximeter provide us with?
A pulse oximeter assesses the degree of oxygenation of the blood in the part of the animal where it is positioned. also gives pulse rate
d. An aggressive 8-year-old dog (e.g. Rottweiler) for x-rays for fracture repair
Ace and Buprenorphine
Describe what the terms apnoea, hypoventilation and tachypnoea mean
Apnoea = Cessation of breathing tachypnoea: increased respiratory rate hypoventilation: decreased removal of carbon dioxide
6. Know the general effects of all groups of anaesthetic agents on the cardiopulmonary system.
Barbiturates e.g. thiopentone. -Causes dose dependent respiratory (decrease tv and rate) and cardiovascular depression (decrease in blood pressure, -Apnoea, mild hypotension and tachycardia are common first few minutes.
Gas exchange occurs in the alveoli and carbon dioxide is more diffusible than oxygen so:
Carbon dioxide is a measure of adequacy of ventilation (movement in and out of alveoli) Oxygen is a measure of adequacy of gas exchange (movement across alveoli and into arterial blood)
When does cerebral function stop?
Cerebral function stops following 1 min of anoxia but can be revived if under 4 minutes. Other organs are more resilient
Know how to place a Doppler correctly
Concave surface of probe is used * Covered with ultrasound or KY gel * Placement of probe, over a peripheral artery * Metacarpal (palmar surface) medial * Metatarsal (plantar or dorsal surface) * Coccygeal (tail) * Cuff width is ideally 40% circumference of limb and is placed: * Proximal to probe * With the bladder overlying artery
7. Describe the appearance of a dog or cat at an appropriate plane of anaesthesia suitable for most surgical procedures. Know how these signs might differ in horses and ruminants.
Dog -decreased respiratory rate and tidal volume -no palpebral reflex, but corneal and PLR is still present -eyeball is ventromedial in cats and dogs but still centre in horses and sheep -jaw tone is looser -heart rate is normal or slightly slowed -Strong pulse
6. Describe the appearance of a patient who is very "deep".
Dog If in the deep plane of stage 3, the eye will be constricted. The palpebral relfex will not be present. The PLR and corneal relfex are sluggish Respiratory rate and TV are reduced.
MAC is not affected by
Duration of anesthesia, sex, species(a little bit)
ENDOTRACHEAL INTUBATION
Endotracheal intubation is usually performed following the induction of general anaesthesia (i.e. once the patient is unconscious), but may occasionally be performed in conscious patients (e.g. nasal intubation in foals), or as an emergency procedure (e.g. for cardiopulmonary resuscitation in a patient who has arrested).
7. Describe the various ways of cleaning and sterilising ET tubes.
Following thorough rinsing and removal of organic material with warm water, ET tubes for veterinary use can be sterilised with heat (autoclave) or gas (ethylene oxide), or disinfected with liquid agents (e.g. chlorhexidine).
Palatal ostium: What is it? What species has it?
Guinea pigs In the guinea pig the soft palate extends down to the base of the tongue. It is difficult to pass an endotracheal tube through this small opening. The central opening between the caudal tongue and the soft palate
Signs of pain in animals • Dog • Cat • Cow • Horse
Horse -kicking -rolling -restlessness Dog- Restlessness -Change in behaviour -decreased appetite and activity -vocalisation -circling Cat and cow -change in behaviour -quieter -decrease activity -decreased appetite
Describe different methods of warming patients postoperatively. Discuss the advantages and disadvantages of these different techniques. Why is it so easy to accidentally burn patients during recovery?
Hypothermic patients require thermal support in the form of blankets, circulating warm-water heating pads, and heat lamps. Ensuring that the recovery area is well heated and ‚draft-free‛ is also important. It is essential to remember that hypothermic patients, particularly those that are sedated or moribund, are particularly prone to burns. These patients should never be placed on electric heating pads or in front of hot-air "blowers".
Why would you need to re apply eye ointment? What else should you do?
If a anticholinergic aws administered. Express the bladder to relieve distension related discomfort.
Monitoring, support and complications
In order to monitor a patient in a logical and thorough way we can divide the patient into a series of organ systems. Including the: respiratory system cardiovascular system neuromuscular system thermoregulatory system
What is IPPV?
Intermittent positive pressure ventilation or IPPV, refers to the technique of ventilating an intubated patient by periodically squeezing the rebreathing bag of the anaesthetic circuit.
Intubation Whats special for rabbits?
Intubation Ø Extremely difficult Ø Blind technique Ø Scope technique Ø Laryngeal Mask for rabbits
What is anaerobic metabolism?
Lactic acid production (not easily excreted)
After extubation, make sure the patient can? Also you need to monitor...
Make sure the patient can swallow adequately (put moisture on the tongue) Monitor respiratory parmeters such as 1. Breathing patterns and chest movements 2. Tongue colour 3. Coughing To treat dysphoria and emergence delirium give post anaesthetic sedation and analgesia
Premedication in birds
Opioids Ø The most opioids receptors in pigeons Ø Kappa receptors: Butorphanol Sedatives Ø Midazolam Ø Excellent sedation and muscle relaxant
Post-anesthetic monitoring. What do you monitor?
Post anaesthetic monitoring 1 (directly after you turn off gas) 1. Pulse oximetry 2.capnography 3.temperature 4.ECG 5. blood pressure monitoring - Periodic auscultation (heart and lung) - Keep recording all parameters Stop monitoring when they return to near baseline. Post anaesthetic monitoring 2 (after extubation) 1. TPR, MM, CRT 2. Periodic auscultation (heart and lung) -keep recording -Monitor ECG and blood pressure in patients at high risk of hypotension or dysrhythmias Can stop when they return to near baseline. Ensure you keep reassessing the patients pain level and adjust the post operative pain management appropriately. Adequate alagesia and a quiet environment encourages smooth recoveries.
Hypothermia causes prolonged and increased..
Prolonged recovery Increased morbidity and oxygen demand Important to provide adequate thermal support AND oxygen
Speed vs quality of the recovery.
Quick recovery -tends to cause the rough recovery -makes you feel relieved Quality -slow recovery tends to cause smooth recovery -requires more time to watch the patients he preferred slow.
What affect does anaesthesia have on the medulla?
Reduces the response of the medulla to carbon dioxide - reducing RR, increasing carbon dioxide and decreasing pH (hypnotics and inhalants have the greatest effect)
Small mammal fasting which species can vomit?
Rodents and rabbits DO NOT vomit -DO NOT necessarily withhold food However - Rabbits have relatively small thoracic cavities so Respiration is impaired by distended GI tract This is a Precaution for positioning Guinea pigs and chinchillas DO vomit -Do fast for several hours (around 3 ~ 4 hours) DO NOT withhold water
What was normal toby given? What was the affect?
She gave him benzodiazepam to stop the seizuring. This can be used as a sedative aswell. However in patients that have an underlying potential to become aggressive or excited and you remove the anxiety that keeps them normal../passive/submissive.
Know what to record in a post anaesthetic recovery record (using the S.O.A.P format) Describe how you would recover a cat after anaesthesia
The larynx of the cat is particularly sensitive. extubation can be a danger time when laryngospasm and airway obstruction may occur. as soon as the cat coughs, remove the tube. SOAP Subjective Objective Assessment Plan
12. Describe basic properties of commonly used induction agents e.g. thiopentone, ketamine, Zoletil, propofol, guaifenesin, alphaxalone/alphadolone, and etomidate.
Thiopentone -IV only -metabolised by liver and rapid emergence from thiopentone is due to the redistribution, relapses into unconsciousness if liver function is impaired or if the patient does not have much body fat. So in neonates/paediatric patients and patients with liver disease avoid. ** -Causes dose dependent respiratory (decrease tv and rate) and cardiovascular depression (decrease in blood pressure, -Apnoea, mild hypotension and tachycardia are common first few minutes. -arrhythmogenic Propofol -hypnotic -is in a solution which is good for bacterial growth (wound infection more common) -hypotension -decreased heart rate but UNLIKE thiopentone the cardiovascular effects are not compensated by an increase in heart rate. -anti arrhythmic agent. -rapid NON HEPATIC metabolism - Recoveries can be prolonged in CATS if CRI used Etomidae -short acting -This agent is a useful induction drug in patients with cardiac or respiratory disease because it produces minimal cardiorespiratory depression when used at low doses. -Side effects include vomitting Alphaxalone -depresses cns- so hypnotic. -only commonly used steroid in anaesthesia -no/little cardiovascular or respiratory effect -pain on injection -alfaxan is the induction agent of choice for compromised patients. (can be used in cats and dogs) Ketamine -dissociative (produce anaesthesia by interupting the flow of information from the unconscious to the conscious parts of the brain) -acidic so painful im or sq -produces respiratory depression but CARDIOVASCULAR STIMULATION (inc hr and blood pressure) -Ketamine results in the production of copious amounts of thick, "ropy" saliva which may cause airway obstruction (thus atropine is often used in cats in an attempt to offset this effect). -Ketamine will result in excitement and seizure-like activity in unpremeditated patients (except cats) and in particular, must never be administered to a horse that is not adequately sedated. Dogs that have not been properly premedicated prior to ketamine anaesthesia will often have extremely rough, "dysphoric" recoveries. -Ketamine is usually combined with a sedative-type agent to produce a combination which is then used to induce anaesthesia. Common ketamine combinations include xylazine, ketamine/diazepam, acetylpromazine/ketamine - In dogs must be administered with a benzo or a-2 agonist *zoletil* -similar to ketamine (longer duration of action) -expensiev -has the ability to cause convulsiona and seizure like activity and raise intracranial pressure (similar to ketamine) -Advantage: water soluble so more reliable absorption IM or SQ -cats with renal dysfunction will have prolonged recovery with zoletil or ketamine so avoid with these.
Be able to discuss basic facts about atropine, acetylpromazine, diazepam, midazolam, xylazine, medetomidine, the opioid analgesics (e.g. morphine) and ketamine Be familiar with the following agents: - atropine, acepromazine, diazepam, midazolam, xylazine, medetomidine, ketamine, Zoletil, morphine. Describe basic facts about the FOUR major groups of drugs commonly used for sedation and premedication in small animals
Types of premidication agents 1. Anticholinergic agents: These agents act competitively to prevent binding of acetylcholine to muscarinic receptors within the ans, resulting in a blockade of parasympathetic activity. Causes -increased heart rate (think of why this might be bad..bradycardia is generally better..starlings law) -reduction in respiratory tract and salivary secretions -bronchodilation -decrease in git motility exmaples: atropine (can pass through blood brain barrier and placenta) Often given preop to reduce laryngospasm and decrease secretions and prevent vagally mediated bradycardia. Indications for use: As a general statement, their use may be justified in cats and brachycephalic-type dogs (where every effort should be made to reduce bronchial secretions and minimise laryngospasm); in patients receiving drugs which result in reflex inhibition of heart rate (e.g. opioids); and in patients undergoing surgical or diagnostic procedures which may result in vagally mediated bradycardia (e.g. thoracotomies, and surgical traction on the eye or viscera). Contraindicated: marked tachycardia and / or tachyarrythmias, hyperthyroidism, and glaucoma. 2. Analgesics -Opioids e.g. morphine. "gold standard" *bradycardia, fast IV causes histamine release, respiratory depression, emesis *methadone is similar to morphine but can be used iv and does not cause emesis. -NSAIDS 3. Sedative type agents -Acepromazine (causes vasodilation and reflex mild tachycardia and hypothermia) -Aswell as a sedative, acts as an antiemetic *Although well tolerated in fit, healthy animals, the sympatholytic action of "ace" may be sufficient to produce precipitous, potentially fatal hypotension in shocked, severely injured or hypovolaemic patients. Contraindications: Acepromazine should be avoided in the very young, the very old and the very sick. The use of acepromazine is contraindicated in patients with marked cardiac, renal or hepatic disease; in stressed, fatigued or injured patients; in patients who are hypovolaemic or dehydrated; and in patients undergoing Caesarian-section -Benzodiazepines (diazepam (injectable form is very irritable) and midazolam and zolazepam) results in.. *sedative *anticonvulsant *muscle relaxant *appetite stimulant Causes little change in cardiovascular function The benzodiazepines are particularly useful sedatives in the very young, the very old and the very sick. However, lone administration of these drugs to fit, healthy cats and dogs often results in excitement, extreme restlessness, and bizarre behaviour patterns; and should therefore be avoided. Most of the benzodiazepines are metabolised in the liver to active metabolites. Benzodiazepines should be used with extreme care in cats with liver disease. These drugs are highly protein bound: changes in plasma protein concentrations and resultant drug-protein binding may significantly alter the response to a given dose, particularly in severely hypoproteinaemic patients. -Alpha 2 agonists (xylazine and medetomidine) *causes bradycardia in all species. *decreases tv and respiratory rate Used for -sedation for minor procedures -restraint for aggressive animals These drugs are contraindicated in patients with cardiac, hepatic, renal or respiratory disease. (should only be used in fit healthy patients) Medetomidine is an excellent anticonvulsant, muscle relaxant and gives analgesia 4. Dissociative agents -the dissociatives, are often used in combination with sedative-type agents to produce restraint in cats (especially aggressive ones!), pigs, exotic species and laboratory animals. -Ketamine *should always be used with a muscle relaxant e.g. alpha 2 agonist as it causes muscle ridgidity *provides analgesia (anticholinergics and antihistamines offset the physiological consequences of toehr agents and procedure being performed)
MAC is increased by
Young, Hypernatremia, Ephedrine
b. a fit healthy normal, young (> 4 month) cat for castration
benzodiazepines and morphine????
stage 4 aka
bulbar paralysis -starts with respiratory arrest -ends with cardiac arrest -respirations and jerky and irregular -all reflexes are gone -no intrinsic muscle tone remains -no palpable pulses -eye ball is dull and dry, central, dilated memorise chart at end of 1/2 lecture
never premed in dystocia.
unless aggressive and if so still never give NSAIDs. they ruin the kidneys of neonates
a. a fit healthy normal, dog anaesthetised for ovariohysterectomy
Ace and morphine together. OR alpha 2 agonist and buprenorphine
4. What is "pre emptive analgesia"?
Administration prior to painful event - reduced consumption post op = PRE EMPTIVE ANALGESIA
Avian anaesthesia
Admit several hours prior to anesthesia Ø Allows acclimatization Ø Keep in own environment in own cage Ø Feed regular food Ø High metabolic rate Ø DO NOT fast small birds Ø Can FAST ratites and larger birds 6-12 hours
. List the advantages and disadvantages of endotracheal intubation.
Advantages 1. A properly positioned ET tube ensures airway patency 2. Allows for the dlivery of 100% oxygen to the patient 3. Minimises risk of aspiration or regurgitant or other foreign material. 4. Facilitates the delivery of inhalation anaesthetic agents 5. Decreases respiratory effort ( by reducing mechanical deadspace) 6. Facilitates support and control of ventilation 7. Minimises contamination of the working environment with waste gases 8. Facilitates cardiopulmonary resuscitation ET tube cuff minimises: Aspiration of foreign material Prevents environmental contamination Permits positive pressure ventilation (MOST IMPORTANT) Disadvantages 1. Kinking or obstruction of ET tube 2. Leaks 3. Accidental endobronchial intubation 4. Laryngeal oedema, haemorrhage or trauma (usually due to poor technique) 5. Laryngospasm (at intubation or extubation) 6. Tracheal stenosis (only if cuff is over-inflated) 7. Coughing, breath-holding, bronchospasm, and cardiac arrhythmias (only if patient is too light at intubation) 8. Potential spread of infection
c. a fit healthy young, but very aggressive cat for a dental procedure
Agressive cats are given ketamine -medetomidine Routes of administration are IM, intracat, orally Effective sedation/restraint can be achieved in "difficult" or aggressive cats by adding a dissociative agent to a neuroleptanalgesic technique e.g. ketamine in combination with midazolam, morphine and atropine. Because the ketamine stings, intramuscular administration seems better tolerated by most cats.
3. ventilation and perfusion mismatching
Alveolar perfusion is also altered by ga and recumbancy. the uppermost lung becomes underperfused while the down lung becomes overperfused. anaesthetic agentes depress cardiovascular function resultin gin hypotension and reudced cardiac output. relfexes which serve to protect the normal alveolar ventilation to perfusion ratio (e..g hypoxic pulmonary vascoconstriction) are inhibited by many anaesthetic agents, permitting perfusion of poorly ventilatead alveoli and the addition of poorly oxygenated blood to the general circulation- a phenonmenon known as shunt. results in V/Q mismatch. The development of hypoxaemia and hypercapnia with resultant acidosis and catecholamine release.
4. Describe the stages and planes of anaesthesia, and be familiar with the changes in patient parameters which occur in each stage.
Stage 1: the stage of voluntary excitement Signs -increased hr -rapid deep respiration -pupils normal or dilated Stage 2: stage of involuntary excitement -exaggerated relfex struggling -irregular breathing and breath holding -dilated pupisl whch constrict in response to light -chewing, swallowing, vomitting -laryngeal reflexes are still present -nystagmus (especially in horses) Stage 3: state of surgical anaesthesia (divided into 4 planes) Stage 4:bulbar paralysis
What are the four stages?
Stage I ›Voluntary excitement Stage II ›Involuntary excitement Stage III - Surgical anaesthesia ›Plane 1 - Light plane ›Plane 2 - Medium plane ›Plane 3 - Deep plane ›Plane 4 - Very deep plane Stage IV ›Bulbar paralysis (essentially dead, in respiratory arrest)
When does the recovery period start and end?
Start: When the anesthetic gas is turned off End: When the patient is awake, aware, warm, and comfortable -It does not end at the time of extubation
What is the surgical mac?
Surgical MAC 1.3~1.5MAC (95 % patients)
7. Know which drugs can be given by a route other than IV and know which drugs cannot.
Thiopentone has a pH of 11 and therefore must ONLY be administered IV. Ketamine can be administered by any route propofol any route?
8. Know the relative onset and duration of action (i.e. short, moderate or long) of the various groups of injectable agents.
Thiopentone has a rapid onset of action (10-15 sec) -Ultra short acting Ketamine has an onset of action of 20-30 seconds. -Duration of action 1--15 mins
9. Know which drugs can be administered as top ups without significantly increasing duration of recovery.
Thiopentone: multiple top ups will prolong recovery. -SO DO NOT use as top up Alphaxalone lacks accumulation when given as constant rate infusions or top ups (desired property). so does not result in prolonged recovery. Propofol can be topped up wtihout increasing recovery times. Etomidae is non cumulative.
Discharge of patients.
This occurs after the patient is awakae, aware, warm and comfortable. Provide written intructions for owners outlining the dose and potential side effects of analgesics and other medications to be given to the patient at home + any other requirements.
14. Describe in simple terms how a Doppler works
Ultrasonic waves emitted * Reflected back at different frequencies due to: * Movement of red blood cells * Pulsations of vessel walls * Cuff is inflated to suprasystolic pressure * Until sound is no longer heard * Slowly released until sound is heard * Pressure where sound is heard = systolic blood pressure
Know the normal heart rates of various species and heart rates of concern under anaesthesia
Under anaesthesia Cat= 100-180 Dog = 50-160 Sheep = 50-140
What is an appropriate fluid administration rate for normal, healthy cats and dogs during anaesthesia?
Under most circumstances, fluids are normally delivered at a rate of 10 ml/kg/hr in healthy patients.
10. Know which breeds of dogs thiopentone is contraindicated in.
Use of thiopentone is contraindicated in the greyhound
Two settings control Fresh Gas Flow (FGF)
Vaporizer setting (%) Flow meter setting (L/min)
Describe how to perform IPPV in veterinary patients.
When performing IPPV a positive pressure is used to inflate the alveoli. By raising the pressure in the trachea to a value above atmospheric pressure, air is forced down the conducting airways to expand the lungs. The expanding lungs stretch the diaphragm and lift the chest wall. When the pressure in the trachea is released (returning to atmospheric pressure), the chest wall and "stretched" lung tissue will collapse back to their resting states, and the patient will exhale. Intermittent positive pressure ventilation (IPPV) is performed by gently squeezing the rebreathing bag on a regular basis (e.g. 4 - 20 times / min). The anaesthetist should try to mimic normal ventilation by providing a normal tidal volume and respiratory rate for a given patient. Tidal volume is usually estimated at about 10 ml/ kg. Remember that the rebreathing bag should have a volume of approximately 6 - 10 x tidal volume. Trying to empty the entire volume of the rebreathing bag during IPPV would obviously over-inflate the chest, and may even result in rupture of the airway ("barotrauma" - trauma due to excessive pressure). IPPV is best performed by carefully observing the patient (not the bag), and inflating the chest so that it rises by a normal amount. The manner in which the bag is squeezed is also important. Inspiration should be smooth but not overly rapid. An inspiratory time of 1 - 2 sec is reasonable in small animals, with horses requiring an inspiratory time of 2 - 3 sec.
Pre-emptive Analgesia: Providing analgesia _________ to surgery ______________ post-operative pain and __________ the dose of analgesics to control post-operative pain.
prior, decreases, decreases
13. Know how to treat the accidental perivascular administration of thiopentone.
"dilution is the solution to pollution". A solution of 0.9% saline with or without lignocaine should be infused around the area in order to dilute and neutralise the drug.
Know the normal respiratory rates of various species under anaesthesia
Cat: 12-25 Dog: 6-25 Sheep: 6-20 cow: 4-10
Define pain
'an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage' 2 Components 1. Sensory - nociceptive receptors/pain fibres - Mechanical, thermal, chemical 1. Emotional - requires consciousness, higher brain functions
What is myopathy?
'muscle disease' Damage to the muscle due to reduced blood flow resulting in ischaemia Points in contact with the ground are usually at risk Pressure -monitor blood pressure and treat accordingly * Usually use positive inotropes (ie dobutamine) * Position * Position as symmetrically as possible * Elevate upper limbs (so parallel with lower) * Padding * Use padding where possible * In the field (ground is actually quite soft)
Outline the requirements of an anaesthetic recovery area (five things)
(Before moving) A patient that has been maintained on a gaseous anaesthetic agent for any procedure will continue to exhale gas for some time after cessation of that agent. The patient should therefore ideally be kept on oxygen at high flow rates (2 - 4 L/min) for a period of time after the agent is switched off (at least 5 and ideally 10 mins). The ideal recovery area should: 1. be close to the surgery / main traffic area 2. be well ventilated but free from draughts (inhalants should be scavenged) 3. be warm and quiet (as hypothermia is common and to prevent dysphoria) 4. have access to emergency equipment 5. have access to an oxygen source (hypoventilation and hypoxemia are common)
4. Know the factors that influence the level of anaesthesia produced by administration of thiopentone.
**exception to dose to effect is thiopentone. With thiopentone where too slow administration results in exacerbation of the excitement phases of anaesthesia. As such the initial "half dose" of thiopentone is administered rapidly. -highly protein plasma bound. so in hypalbuminaemia there is more free drug -Acidosis enhances effect -Amount of fat as its redistributed to fat -Metabolism of drug needed for full recovery
Describe stage one STage of voluntary excitement
-Analgesia and consciousness with disorientation -Ends at loss of consciousness (may still be moving) Signs and reflexes › Increased heart rate (due to catecholamine release) › Rapid deep respiration or breath holding (inhalation agent may not smell nice) › +/- salivation, struggling, urination, defecation › Pupils normal or dilated
MAC is decreased by
-Elderly, Hypo/Hyperthermia, Anemia - Severe Hypoxia/Hypercarbia, Hypotension - Hypercalcemia, Hyponatremia -Pregnancy, Anesthetic drugs
Describe stage 2 Stage of involuntary excitement
-Loss of consciousness -Loss of voluntary control Signs and reflexes › Exaggerated reflex struggling › Irregular breathing and breath holding › Laryngeal reflexes still present › Chewing, swallowing, vomiting may occur › Eye reflexes prominent, nystagmus may be present › Pupils dilated (constrict in response to light)
17. Know how to place an oesophageal stethoscope correctly
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2. impairment of thoracic wall movement
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A few other numbers are worth remembering: ›"10" can be useful TV = 10 ml/kg (up to 15mL/kg) Anaesthetic fluid rates = 10 ml/kg/hr (recently 5mL/kg/hr identified as more appropriate) Minimum flow rate of oxygen of a rebreathing anaesthetic circuit = 10 ml/kg/min Blood volume of most species is 'about' 10% of body weight (cats are somewhat less than this at 5%)
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Anaesthesia can alter both ventilation and gas exchange
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Be able to classify, compare and contrast meperidine, morphine, methadone, fentanyl, buprenorphine and butorphanol for: Potency Onset and duration of action (including dosing interval) Efficacy for variable degrees of pain Routes of administration Potential side effects
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Faster→Slower induction and recovery
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Lecture 14. small mammal and avaian
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Maintenance anaesthesia lecture ~injectables and inhalants~
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Pain and analgesia
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Signs and stages of GA-New lecture
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What is the Therapeutic index?
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studyguide During normal ventilation in the standing animal, air moves preferentially into ventral alveoli because the "resting" dorsal alveoli are more distended and thus less compliant. Alveolar perfusion (blood flow) follows a similar pattern with ventral alveoli receiving a greater proportion of total lung blood flow than more dorsal alveoli. This occurs as a consequence of gravity, and due to normal physiological responses such as hypoxic pulmonary vasoconstriction (perfusion of poorly ventilated alveoli is reduced via reflex vasoconstriction of the capillary beds supplying those alveoli). In this arrangement, poorly ventilated alveoli also tend to be poorly perfused, while well ventilated regions of the lung receive a rich blood supply - alveolar ventilation and perfusion are therefore said to be well matched, resulting in normal ventilation to perfusion ratio (V/Q ratio).
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3. Know the position of at least two peripheral veins that can be used for the administration of drugs to the cat and the dog.
1. cephalic vein 2. Saphenous vein Alternatives 3. Ear vein 4. Juggular
What are the different ways agents can affect the cardiovascular system? Give examples
1. Alter heart rate -Bradycardia e.g. opioids and alpha 2 agonists -Tachycardia (less time for diastole) e.g. ketamine, atropine. May cause arrhythmia's (bradycardia is preferable as a slowed heart results in increased SV) 2. Alter myocardial contractility e.g. negative inotropes like halothane 3. Alter cardiac rhythm e.g. atropine and thiopentone 4. Drugs that alter vascular resistance. e.g. acepromazine which causes peripheral vasodilation
What other effects does anaesthesia have on the respiratory system?
1. Decrease respiratory muscle strength (reduces TV) 2. Recumbancy interferes with diaphragmatic function (reducing TV) 3. Bypass the URT(upper respiratory tract) - dry gases interfere with normal function of cilia (as the nasal usually moistens the air- this may also cause dehydration) -This is why fluids are also given. 4. Intermittent positive pressure ventilation (so instead of negative, its positive) interferes with normal cardiovascular function 5. anaesthesia and recumbancy leads to a ventilation and perfusion mismatch -hypoventilation -reduction in hypoxic pulmonary vascoconstriction 6. anaesthesia agents can affect the cardiovascular system (pump and tubes), therefore reducing -cardiac output -arterial blood pressure CO= HR x SV BP (arterial) = CO x Resistance They affect this in many ways
13. Name two pieces of equipment for assessing the blood pressure of a patient
1. Doppler flow detector (non-invasive) 2. oscillometric (non-invasive) 3. direct arterial catheterisation (invasive)
What do you do if it is a rough recovery? 3 steps rough reovery is due to pain, dysphoria or emergence delirium.
1. First sedate the patient with anything you have e.g. ace 2. Second reassess the patients -cardiovascular and respiratory parameters 3. Third re assess pain score or plan -high hr or rr -reaction at surgical sites -administer analgesics
Injectable vs Inhalational agents Choice of agent usually depends on:
1. Function 2. Expected duration of procedure 3.Availability of drugs and equipment 4. Speed and quality of recovery 5. Experience and preference 6. Patients' conditions
What is the difference for aggressive animals?
1. Heavily sedate them for reovery 2. Extubate earlier than usual 3. Remove catheter after extubation 4. Monitoring should be minimal 5. Keep the lead or put the muzzle on *You need to explain the higher risk of anaesthesia for these animals to the owner*
*Injectable anaesthetic agents used for the induction of anaesthesia fall into two broad categories.
1. Hypnotic agents: produce anaesthesia through generalised CNS depression -Most agents are under this e.g. Barbiturates 2. Dissociative agents: produce ga under excitation of areas of the brain thus preventing normal inputs from being remembered
What are the three phases of breathing?
1. Inspiration. Active process. Creates negative intrathoracic pressure. 2. Expiration. Passive process (active in horses) 3. Expiratory pause. Gap between expiration and inspiration -Becomes shorter as RR increases.
Give examples of single injectables for maintenance I wouldnt worry too much about this
1. Ketamine and midazolam (diazepam) -Can be administered IV or IM (except diazepam) -Lasts for approx 30 minutes -Ketamine provides analgesia -Prolonged and rough recovery. 2. Ketamine, medetomidine and opioids -Same as above -Longer duration and better recovery 3. Propofol and alfaxalone 4. Triple drips for horses
General anesthesia -4 characteristics
1. Muscle relaxants 2. Loss of consciousness 3. Analgesia of the entire body. 4. Amnesia
Halothane
1. Myocardial depression 2. Blunted baroreceptor *3. Bradycadia* 4. Arrhythmogenic 5.Halothane hepatitis 6.Malignant Hyperthermia *Least respiratory depression in veterinary medicine*
Factors which may influence the choice of anaesthetic agents and the development of the overall anaesthetic plan include:
1. Patient factors 2. The procedure to be performed 3. Available equipment and facilities
Why are veterinary patients anaesthetised?
1. Perform surgeries 2. Restrain (e.g. for CT scans or for physical exams)
What are the 5 phases of anaesthesia?****
1. Pre-anaesthetic period 2. Premedication 3. Induction (of general anaesthesia) 4. Maintenance (general anaesthesia) 5.Recovery
Describe simple techniques for supplying additional oxygen to patients recovering from anaesthesia (your answer should consider different species).
1. Preoxygenation refers to the technique of supplying a high concentration of oxygen to the patient immediately prior to induction. 2. Oxygen supplementation may also be given post operatively. Can be given in a number of ways -anaesthetic mask -flow by technique -nasal oxygen. the nasal catheter technique is when a small feeding tube is inserted into the ventral meatus of the nose and glued into position. -oxygen cage
Name three pieces of equipment used for monitoring the cardiovascular system
1. Stephoscope 2. Oesophageal stethoscope:It is inserted into the mouth and if the patient is intubated it generally moves easily down the oesophagus. 3.ECG 4. Pulse oximetry
3. What are the potential disadvantages of premedication?
1. Synergism with other agents in cardiopulmonary depression 2.Prolonged recovery 3. Additional cost to the anaesthetic protocol 4. cardiovascular deprssion
5. Discuss the benefits of thiopentone for induction of anaesthesia.
1. Thiopentone has a rapid onset of action (10-15 sec) -MOST COMMONLY USED IN DOGS -Solutions do NOT grow bugs -Ultra short acting -Anticonvulsant
Why fast? (fast dogs and cats for ~12 hours)
1. Vomitting can occur at induction 2. Regurgitation can occur due to -decreased LOS tone -Positioning -Surgeon factors There are two consequences of regurgitation and vomitting 1. Pulmonary aspiration may occur because during anaesthesia laryngeal function is impaired 2.Chemical irritation due to the low pH stomach contents to the oesophagus. -oesophagitis -oesophageal stricture formation However disadvantages of fasting are pH of gastric fluid is lower, resulting in regurgitation causing oesophageal stricture and aspiration causing chemical pneumonitis A small meal given within 3-4 hours of anaesthesia is likely better than 12-18 hours fasting ALSO Secondly, fasting reduces the weight of the gastrointestinal tract, and therefore the pressure exerted on the chest and diaphragm when anaesthetised animals are placed in dorsal recumbency.
How does anaesthesia increase dead space?
1. excessively long endotracheal tubes 2. connectors between the anaesthetic machine and ET tube Factors during anaesthesia that may increase dead space (and therefore reduce the volume of air available for gas exchange) include an excessively long endotracheal tube, many connectors between the patient and the anaesthetic circuit, and the fresh gas flow rate.
Describe the various reflexes that can be used to assess the depth of a patient under anaesthesia
1. pedal withdrawal : The pedal withdrawal reflex is tested by pinching the skin between the toes of a patient. In the conscious or ‚very light‛ patient the limb will be withdrawn. so only helpful at the start really... 2. pharyngeal/laryngeal - "gag" : As with pedal withdrawal, pharyngeal reflexes are usually only present in the early stages of anaesthesia. The presence of these reflexes is extremely significant when we consider this is the main reason we must give a large dose of a drug to induce anaesthesia i.e. to allow endotracheal intubation. 3. palpebral reflex The palpebral (blink) reflex is the most commonly used reflex for monitoring anaesthetised veterinary patients. The palpebral reflex is assessed by either gently touching the medial canthus of the eye, or brushing the eyelashes. Depth of anaesthesia is directly related to the strength of this reflex, when an animal is first induced this reflex is very prominent and the patient often blinks spontaneously, as depth increases the strength of the reflex diminishes until it finally disappears. -For most small animal species presence of this reflex indicates a light plane of anaesthesia 4. pupillary light reflex When a light is shined directly into the pupil of a patient the pupil should constrict, as with the corneal reflex the papillary light reflex is maintained for a long period and its absence indicates a deep plane of anaesthesia 5. corneal reflex
What is the order of loss of function as anaesthesia increases?
1.Pain and memory 2.Consciousness 3.Motor coordination 4.Response to external stimuli 5.Muscle tone 6.Protective reflexes 7.Autonomic function 8.Normal control of cardiopulmonary system 9.Control of ventilation - respiratory arrest 10.Control of cardiovascular system - cardiac arrest
What proportion of tidal volume is dead space?
1/3 to 2/3 Ventilation is the movement of air in and out of the alveoli - MV = RR x TV = equation for ventilation
Surgical MAC of sevoflurane is
2.4 ~ 2.6
What is anaesthesia controlled by?
Anaesthesia is controlled CNS toxicity General anaesthesia results from (and in) changes in CNS function The main and most profound effect of most anaesthetic is CNS DEPRESSION The response of the various organ systems to noxious stimulation forms the basis of classifying the signs and stages of anaesthesia The non-vital functions and reflex responses such as the blink reflexes are lost earlier than control of the cardiopulmonary system. Under GA the patient must be constantly monitored -heart rate -respiratory rate -blink reflex -muscle tone
What is Anaesthesia?
Anaesthesia is the state produced by drugs that leaves the patient insensible/insensitive to pain "anaesthesia is the production of insensibility" General anaesthesia: Unconscious and without memory of the event (amnesia) Local anaesthesia: conscious with memory of the event
Why do anaesthetised patients develop hypothermia?
Anaesthetic agents increase heat loss and decrease heat production resulting in the potential for profound hypothermia. Anaesthetic-induced central nervous system depression, decreased metabolic rate, and loss of muscle tone and muscular activity, all serve to minimise the patient's ability to produce heat. Heat loss is enhanced by drug-induced vasodilation; the use of cold, alcohol-based prep-solutions; the delivery of cold, dry anaesthetic gases; the infusion of cold intravenous fluids; and positioning of patients on cold, non-insulated surfaces (e.g. stainless steel operating table). Further heat loss occurs due to the evaporative loss of fluid from open body cavities or exposed muscle during surgery. * Temperatures decrease under anaesthesia * Lack of vasoconstrictive response in the skin * Heat loss through airways * Lack of ability to shiver * Use of cold prep solutions * Use of cold IV fluids * Open body cavities
1. Understand and describe the concept of anaesthetic depth.
Anaesthetic depth is divided into four major stages based on the presence or absence of various signs and reflexes in the patient, and the degree of respiratory and cardiovascular depression. Important to ensure the patient is in a suitable depth of anaesthesia.
Why is it important to administer intravenous fluids to anaesthetised patients?
Anaesthetised patients are prone to fluid loss and potential hypovolaemia (reduced blood volume) for several reasons, including the evaporative loss of fluid from body cavities (open chest or open abdomen) and exposed muscle (e.g. femoral fracture repair). Large volumes of fluid can also be lost from the respiratory tract, especially in patients maintained with inhalational techniques. Anaesthetic gases are cold and dry. The upper airway (nose and nasopharynx) is normally responsible for warming and humidifying inspired gases. When the upper airway is by-passed by an endotracheal tube, the anaesthetic gases are delivered directly to the lower respiratory tract where they tend to cause cooling and drying of the respiratory epithelium. So we give fluids to -help maintain blood pressure for adequate tissue perfusion
premedication
Anticholinergics - 40 % of rabbits produce atropinesterase - Glycopyrrolate Opioids Ø Analgesia Ø Butorphanol, Buprenorphine, Morphine Sedatives Ø Midazolam, Ketamine, Dexmedetomidine and Alfaxalone
Know the correct time to extubate a patient what needs to be done before extubation
As a general rule extubation should not occur until the patient has full control of pharyngeal and laryngeal reflexes (until they are swallowing spontaneously). Dogs: swallowing in dogs Cats: as soon as it can sense the tube in cats (e.g. coughing). so earlier than in dogs. Also before extubation -Make sure the oropharyngeal area is clean (no blood, fluid etc) AND -keep oxygen on at high rate. (2-4L/min) When your ready to extubate -untie the ET tube and put tube ties and cuff to one side -Cuff deflator. Deflate the cuff immediately before removing the ET tube. -Tongue must be pulled out Ensure you keep the catheter banaged for the recovery.
Be able to design a premedication protocol for each of the FOUR examples below. Note the actual breeds or specific physiological status may be altered in any questions asked in exams Benzodiazepines may replace acepromazine when:
Benzodiazepines may replace acepromazine when: Older or younger patient Patient has CV disease Patient is epileptic or having myelography Morphine may be left out if: Vomiting is contraindicated IV administration is required
What types of rewarming methods can you use to increase the body temperature of a patient with anaesthetic induced hypothermia? What are the advantages and disadvantages of using electric heating pads for preventing intraoperative hypothermia and for providing thermal support post operatively?
Can be passive or active rewarming Passive warming consists of methods to aid in reducing further heat loss to the environment such as placing paper and or blankets on the floor of the cage. Active rewarming consits of an active eating source e.g. 1. Heat lymps and heat pads 2. Bair hugger (most efficient device to warm up the patient). this is a hot air blower that conneccts to a blenket. 3. hot water bottles advantages/diadvantages Diadvantages: -have been assocaited with severe burns in animals recovering
What is aerobic metabolism?
Carbon dioxide (easily excreted if ventilating)
2. Identify the two (three including subtype) main types of ET tube used in veterinary anaesthesia. What is the purpose of the "Murphy eye"?
Classifications 1. Magill -A Magill tube is a straight tube the same diameter at each end but a bevel at the "lung end". 2. Cole -A Cole tube is a tube with two distinct sections of separate diameters. (smaller @ patient) -The smaller "patient end" of the Cole tube is designed to sit in the proximal trachea while the shoulder presses gently against the arytenoid cartilages to form a seal at the larynx. -Uncuffed (used in birds as cant use cuff with birds) Subtype A "Murphy" tube is a Magill tube with the presence of a "Murphy eye" or side-hole opposite the tube bevel. The Murphy eye is a safety feature which allows air flow through the tube, even if the bevelled end becomes occluded. Magill and Murphy tubes may be cuffed or un-cuffed.
5. Describe how to select an appropriately sized ET tube for a particular patient.
Correct tube length can be estimated by holding the ET tube next to the patient. Ideally, the tube should reach from the incisors to the point of the shoulder. Tubes which extend excessively beyond the level of the patient's incisors contribute to dead space ventilation (which may be considerable in a very small patient). In addition, the use of an excessively long tube increases the risk of accidentally intubating a main stem bronchus (i.e. endobronchial intubation, which may result in hypoxia and hypercapnia). Poiseuille's law states that the resistance to flow through a tube is inversely proportional to the radius of the tube raised to the fourth power (i.e. proportional to 1 / r4) this means that halving the radius results in a 16 fold increase in resistance. An ET tube with a diameter similar to that of the patient's trachea will offer the least resistance to breathing. Therefore, the best tube for a given patient is the largest diameter tube which can be inserted through the larynx without force. Tube size can also be estimated by gently palpating the patient's trachea prior to induction and in dogs, measuring the distance between the nostrils.
What is hypoxemia?
Decrease in arterial oxygen tension - <60mmHg Hypoxia is rare during the maintainence of anaesthesia. (100% oxygen is usually provided) Hypoxia is more commonly seen at -premedication -induction -recovery
Explain how extubation is different for a dental procedure or oral surgery. Describe differences for brachycephalic dogs
Dental/oral -Position the nose slightly lower than the back of the head. -Leave the ET tube cuff slightly inflated during extubation These things lower the risk of aspiration For brachycephalic dogs leave the ET tube in as long as possible due to their unique anatomy. (should be chewing vigorously) these breeds are always in a constnat state of respiratory obsturction.
What is the goal of inhalational anesthesia?
Development of therapeutic tension of anesthetic agent in the brain
5. Describe the appearance of a patient who is very "light".
Dog. If in the light plane of stage 3, the eye will be ventromedial. The palpebral, PLR and corneal relfex will be present. -muscle/jaw tone is strong -pharyngeal reflexes prominent (difficult to intubate) -heart rate normal to rapid, pulse strong
16. Know the location of a peripheral artery to place a catheter for invasive blood pressure monitoring in the dog and the horse
Dog: Dorsal pedal artery Anterior tibial artery Femoral artery Auricular artery Horse: -Transverse facial artery -Facial artery
Understand the importance of pre-anaesthetic fasting and be familiar with fasting recommendations for common domestic species.
Dogs and cats: 12 hrs Horses: 12-24 hrs Cattle: 24-36 hrs Small ruminants: 24 hrs Birds: no longer than 1 hr Pocket pets: no longer than 1-2 hrs Guinea pigs:12 hrs
15. Give the advantages and disadvantages of three methods of determining blood pressure
Doppler Advantages: 1. Non invasive 2. Requires little technical skill to put into place 3. Can be used and is reliable in a wide range of patient sizes Disadvantages: 1. Only gives intermittent *systolic* blood pressure. so can only guess mean blood pressure. 2. also no continuous monitoring Oscillometric blood pressure monitors Advantages: -non-invasive -It provides readings of systolic, diastolic and mean blood pressure and it is the only method that automatically determines the mean blood pressure. disadvantage -This method has been shown to give unreliable estimate of blood pressure in cats and is unreliable in conditions where hypotension(low blood pressure) exists -expensive equipment Catheter advantage -Most accurate way of determining blood pressure -provides continous monitoring disadvantage -technicially difficult to perform -the equipment required is expensive -rish of infection of artery -risk of severe haemorrhage or large hematoma formation if the catheter is inadvertently pulled out or the artery is not held off properly after removal
6. Discuss the factors involved in pre-anaesthetic assessment of a given patient. ***fix
Drugs and Dose depends on 1. Age 2. Physical condition 3. Temperament 4. Type of procedure 5. Planned technique 6. Presence and degree of disease process 7. Other potential causes of compromise
Nitrous Oxide characteristics:
Excellent analgesia Possible teratogenic effects Tends to diffuse into air containing cavities more rapidly than air -Pneumothorax, air embolism, acute intestinal, obstruction, intracranial air
Pathway of inhalations
FGF > FI > FA > Fa > Fbrain
Injectable vs Inhalational agents Function, expected duration, equipment, speed of recovery of injectables:
Function of injectables: Expected duration of procedure of injectables:Suitable in shorter procedures e.g. cat castration, radiograph, minor examination Avaliability of drugs and equipment for injectables: -Simple technique and equipment -IV access is required -No environmental pollution Speed and quality of recovery for injectibles: -Possible prolonged recovery -Better quality of the recovery Patients conditions that injectables are for: -Tracheal surgery and pneumothorax surgery -Suspected intracranial disease (as lowers intracranial pressure) -Cardiovascular system is more stable with constant rate infusion
Function, expected duration, equipment, speed of recovery of inhalations:
Function: Expected duration of procedure: does not matter Availability of drugs and equipment: Anesthetic machine and Oxygen are required, IV acess is not needed, environmental pollution Speed and quality of recovery: -Possibly quicker recovery and is independent of the patients metabolism. Patients suitable: -Can be used for most patients -Tends to cause severe vasodilation and therefore hypotension (need to have cardiovascular drugs ready)
3. List the effects of general anaesthesia on central nervous system function as anaesthesia progressively deepens.
Functions are lost in this order 1. Pain and memory 2. Consciousness 3. Motor coordination 4. Response to external stimuli 5. Muscle tone 6. Protective reflexes (e.g. the gag reflex) 7. Autonomic function (i.e. the normal control of the sympathetic and parasympathetic nervous system) 8. Normal control of the cardiovascular and respiratory systems 9. Control of ventilation ending in respiratory arrest 10. Control of the cardiovascular function resulting in cardiac arrest
avian monitoring
Heart rate Ø Auscultate over the keel Ø Most small birds < 500 g Ø Should be almost uncountable Ø Birds > 1-2 kg Ø > 150 BPM Respiratory rate Ø Should be > 10-20 / min Eye signs Ø Variable ECG Capnography - EtCO2 is not unreliable - Visualization of respiratory exist - Temp dependent • Pulse oximetery - SpO2 - Pulse rate • Doppler - Pulse rate Ø Fluid Ø IV access is useful Ø Intravenous fluids Ø Medial tarsal vein Ø Brachial vein Ø Addition of 2% glucose Ø Subcutaneous fluids Ø Temperature Ø Hypothermia
Describe the sites for palpating a peripheral pulse in the following species: cat dog horse
Horse: transverse facial artery facial artery This is the most common and crude way of assessing blood pressure. Palpating a peripheral pulse * Provides pulse rate * Difference between systolic and diastolic Mean arterial blood pressure (MAP) * The heart spends more time is diastole than systole * MAP is not half way between systolic and diastolic * MAP = DAP + 1/3 (SAP - DAP) * MAP must be > 65 - 70 mmHg to maintain peripheral perfusion
Describe simple support techniques for horses during the recovery phase of anaesthesia. What problems might you anticipate during this time?
Horses are obligate nasal breathers i.e. they can only breathe through their nose and are not capable of "mouth-breathing". Anaesthetised horses may develop severe upper airway obstructions in recovery due to nasal passage swelling (oedema and congestion of the nasal mucosa). Horses with a good swallow reflex may still obstruct once the ET tube has been removed. For this reason, it is often wise to recover horses with an orotracheal or nasotracheal tube in place. Horses are also prone to musculoskeletal and nerve injuries during the recovery phase of anaesthesia. Ideally, horses should recover from anaesthesia in a warm, quiet, darkened and well-padded recovery box. The horse should be placed in lateral recumbency with the down forelimb extended as far forward as possible.
Describe how to properly position and pad an anaesthetised horse placed in lateral recumbency, and in dorsal recumbency.
Horses are particularly prone to anaesthetic-induced nerve and muscle injury. If possible, it is always preferable to place anaesthetised horses on a large, deep pad. Horses positioned in lateral recumbency should have the down forelimb extended as far forward as possible, with the up limbs supported parallel to the ground. The halter should be removed to prevent injury to the facial nerve, and the down eye should be protected by using a small inner tyre or foam wedge to raise the head and prevent the eye from touching the ground. If a large pad is not available, inner tyres can be used to relieve pressure on the shoulder and hip of the down-side. Horses placed in dorsal recumbency should be positioned squarely. The limbs should be allowed to flex naturally. Some horses have a tendency to over-abduct their hind limbs: this problem can be alleviated by placing a soft rope around the hocks to prevent the limbs from spreading excessively.
Be able to recognise a normal and an abnormal ECG trace.
How does it work? n electrical field is generated when a cardiac cell is excited (i.e. when the cell is activated by an action potential). Electrical fields generated by the cardiac cells, extend through the tissues of the body and may be measured with electrodes placed on the skin. These electrical fields are displayed as the ECG trace. the P, QRS and T waves, which are caused by atrial depolarisation, ventricular depolarisation, and ventricular repolarisation respectively.
Describe three ways that a patient may become hypoxic or hypercapnic when connected to an anaesthetic machine
Hypoxemia is low blood oxygen content, while hypoxia is low tissue oxygenation; these terms are often used interchangeably. 1. Incorrect placement of endotracheal tube 2. Endotracheal tube kinking 3. Lack of oxygen in the breathing circuit Hypoxia doesn't only occur during apnoea (cessation of breathing) it may also occur if respiration is depressed (by drugs or head trauma), or if there is disease of the lung or heart. Disease of the lung may prevent absorption of oxygen across the alveoli. Likewise hypoxia may occur if there is disease of the cardiovascular system affecting delivery of oxygen to tissues. Hypercapnic means : accumulation of co2. causes acidosis. 1. Apnoea 2. A non rebreathing circuit witha respiratory rate thats too low 3. A rebreathing circuit wtih its soda lime exhausted.
Preanaesthetic assessment and preparation.
Important tasks during this phase 1. preanaesthetic assessment (exam e.g. tpr, crt, bloodwork, weight) and preparation of the patient (e.g. fasting of patient, fluids, medications, correction of acid base abnormalities) 2. development of an anaesthetic plan (premedication, induction and maintenance) -Most anaesthetic plans involve what agents you shouldn't use not what agents you should use 3. preparation of anaesthetic drugs and equipment 4. premedication of the patient
Also what exactly is induction? 1. Know what the term "dose to effect" means and its practical application (i.e. how much to give and how fast).
Induction agents are used to produce unconsciousness (usually given IV) Dose to effect Based on published dose rates of agent (either through reference sources such as the Veterinary Drug Handbook (by Plumb) or label doses) a dose rate is selected for the individual patient. The dose (number of mg of active drug) and volume of agent is then calculated and the volume required drawn up based on the concentration of the formulation you have available. Half of the calculated volume of drug is then injected IV (through a catheter or "off the needle"). A period of time sufficient for the onset of drug action is then spent waiting prior to further administration. This waiting time is different for each individual induction agent but with modern anaesthetic agents the expected onset time is within one minute, and often much less than this. If a plane of anaesthesia suitable for intubation (or surgical manipulation) has not been reached then a further half of the remaining volume is administered. After another appropriate period of waiting occurs and if anaesthetic depth is still insufficient the remaining volume is administered.
Avian intubation
Larynx: No epiglottis so easy to intubate. Trachea: may be -complete rings -incomplete rings = booming calls -double trachea in penguins -loop and coils -long trachea means lots of dead space Birds should be intubated with un-cuffed ET tubes to prevent tracheal damage from over-distension of the cuff. Because both inspiration and expiration are active processes, anaesthetic-induced ventilatory depression can result in marked hypoxia and hypercapnia
Inhalants and Maintenance in birds
Mask induction Ø Ensure nostrils are covered Ø Whole head can be put into mask Ø Mask can be made from syringe cases Injectable induction Ø Rare Ø Used for big birds Ø MAC: Minimum Anesthetic Concentration Ø Isoflurane: 1.3 ~ 1.4%
Inhalational agents -Mechanisms and sites of action
Mechanism of action: NOT SPECIFIC have multiple macroscopic site of action e.g. -lipid solubility -GABA -NMDA -Glycine receptor Sites of action 1. The reticular activating system 2. The cerebral cortex 3. The hippocampus 4.Excitatory transmission in the spinal cord
The recovery period importance
Most anesthetic-associated deaths occur during recovery 47 % of canine anesthesia mortalities 61 % of feline anesthesia moralities Most postoperative deaths occurred within 3 hours
usculoskeletal and peripheral nervous system injuries are a relatively common complication of anaesthesia and surgery, because anaesthetised patients have no ability to protect vulnerable areas from injury or reposition themselves if placed in abnormal positions.
Nerve injuries are most common in small animals, while large animals tend to suffer both musculoskeletal and neural injuries. Damage to the peripheral nervous system is best prevented by careful positioning of patients, and padding of vulnerable areas. Take care to avoid over-extension of limbs, particularly in elderly animal's who may already have some degree of joint disease (arthritis). Also avoid allowing limbs to dangle.
Isoflurane characteristics most popular
No contraindication Pungent inhalant -May not be suitable for mask induction
Sevoflurane
No odor May be suitable for mask induction Ø Compound A (nephrotoxic?) -High temperature, Low flow, Dry absorbent EXPENSIVE
Why are we treating pain?
Not treating pain in animals is a welfare compromise and therefore against the VCNZ Code of Practice
8. Discuss the importance of pre-anaesthetic preparation and support for an individual patient.
One of the aims of a good anaesthetist is to have the patient anaesthetised for the shortest period of time possible. Any procedure which can be performed before the patient has been anaesthetised (e.g. preoperative radiographs, removing horses' shoes, and washing or clipping the surgical site) should therefore be done at this time if at all possible rather than waiting until the patient is "asleep". Some patients may require extensive stabilisation and supportive therapy (specific medications, fluid therapy, blood transfusions, and correction of acid-base and electrolyte disturbances etc.) prior to anaesthesia and surgery. In some situations, a pre-existing disease or condition may pose a much greater threat to the animal than the reason it presents for anaesthesia e.g. suturing a laceration in a dog with marked cardiac disease. There are very few emergencies which require the patient to be anaesthetised and taken to surgery immediately. The stresses of anaesthesia and surgery impose significant physiological insults, which may prove fatal, in a patient who is already severely compromised. Surgery should therefore be delayed until the patient's vital organ functions have been stabilised, as best as possible, under the given circumstances. Always continue current medications (particularly steroids, endocrine or cardiac drugs) as abrupt cessation of medication is often associated with intra or postoperative problems. Preoperative stabilisation and support ensures the patient is in the best condition possible to tolerate the physiological insults of anaesthesia and surgery, and increases the chances of a successful recovery. Every effort should be directed towards achieving this goal. number of other tasks should also be performed during the preanaesthetic period. Once the anaesthetic plan has been chosen (drugs, dose rates and route of administration) it is necessary to prepare the drugs, draw the drugs into syringes and organise any ancillary anaesthetic equipment (i.e. endotracheal tubes, laryngoscope, bite-block, IV catheters, fluids etc.), so that everything is ready for use. In addition, it is important to perform a thorough check of the anaesthetic machine. Check to see there is sufficient oxygen, that the correct vaporiser is mounted and that the vaporiser is filled.
Know what different mucous membrane colour can indicate
Oxygenation of tissues may be crudely estimated by looking at the colour of the mucous membranes (hairless areas inside the mouth, inner eyelids and the vulva). Pink = normal Blue = Hypoxia Grey = Hypoxia White = poor blood flow (perfusion) to tissue or anaemia Red: Can be normal or due to excessive carbon dioxide in blood Dark red/purple: Septicaemia (certain bacteria get into blood stream)
Name one piece of equipment used for monitoring the respiratory system
Physical Monitoring * Observe the patients chest * Observe the rebreathing bag Equipment based 1. Capnography Provides information about * Respiration rate and character * the amount of carbon dioxide the patient is expiring and inspiring * Pulse oximetry Apnoea Alert An apnoea alert is a simple device that fits between the endotracheal tube and the patient breathing circuit. The apnoea alert usually uses a thermistor detecting that there is a difference between the temperature of the inspired and expired gases, an alarm sounds if there has been a constant gas temperature for a set period of time. It simply indicates whether the patient is breathing, listerning to the beeping allows you to determine respiratory rate but provides you with no further information about adequacy of ventilation.
Stage 3 "state of surgical anaesthesia"
Plane 1 -light surgical anaesthesia -Able to do minor surgeries/radiographs -regular respirations -eye reflexes present, slow nystagmus -muscle/jaw tone is strong -pharyngeal reflexes prominent (difficult to intubate) -heart rate normal to rapid, pulse strong plane 2- moderate surgical plane -able to do most procedures here -decreased respiratory rate and tidal volume -no palpebral reflex, but corneal is still present -eyeball is ventromedial in cats and dogs but still centre in horses and sheep -jaw tone is looser -heart rate is normal or slightly slowed plane 3- deep surgical plane -deeper than necessary -decreased respiratory rate and tidal volume -corneal and pupillary light reflex sluggish -eyeball centrally positioned -pupil constricted or starting to dilate -pulse moderate to weak -cardiopulmonary system does not respond to surgical stimulation plane 4- very deep surgical plane -never needed -starts with paralysis of intercostal and abdominal muscles -ends with respiratory arrest -all eye reflexes abolished -eyeball centrally positoined and dilated -jaw tone loose -pulse weak and blood pressure low -mucous membranes pale or blue
Define "premedication
Premedicants or "premeds" are often given to sedate or calm patients so they will be less stressed and easier to handle during the induction phase of anaesthesia. Commonly sedative agents that are administered SQ or IM (so they can be calm when we put the catheter in) A single agent or combination can be used A neuroleptanalgesia is a sedative plus an opioid. -Should be considered in EVERY PATIENT (c section may be an exception)
Anaesthesia is divided into 4 major stages What are these stages based on?
Presence or absence of various reflexes Degree of respiratory depression Degree of cardiovascular depression
9. Understand the concept of developing an anaesthetic protocol and be familiar with factors important to this process.
The anaesthetic technique should be planned after consideration of the patient's preoperative evaluation and likely anaesthetic risk. Ideally, the plan should be based on those agents which meet the patient's requirements and, in the very young, the very old and the very sick, those which will cause the least interference with the patient's compromised body system(s). In some patients (e.g. patients classified as Fair or Fair-to-Poor), it may be satisfactory to simply modify the protocols used for normal, healthy animals. However, in critically ill patients the "ideal" protocol is often non-existent, and a decision must be made as to which agents will cause the least amount of harm in an individual patient. Ruling out drug that you shouldn't use is the first step in this process followed by evaluation of the remaining agents. The development of an anaesthetic plan requires an understanding of the pathophysiology of the condition requiring anaesthesia and surgery; the pathophysiology of any concurrent disease; the basic pharmacology of anaesthetic agents; and the possible influence or interaction of any concurrently administered drugs with the anaesthetic agents.
Understand the concept of neuroleptanalgesia and be able to give examples of this.
The combination of an opioid and a sedative-type drug results in marked synergism, producing analgesic effects, and a degree of sedative (or restraint) greater than that achieved by either agent alone. Acepromazine/atropine/morphine -Atropine used commonly in cats Opioids tend to sedate dogs well but not cats Common neuroleptanalgesic techniques include the combination of acepromazine with an opioid (morphine, pethidine, buprenorphine, methadone or butorphanol); the combination of a benzodiazepine with an opioid; or commercially available products such as Innovar-Vet® (fentanyl and droperidol).
Know the change in eye position and pupil size seen in the various stages of anaesthesia in small animals
The common pattern following the induction of anaesthesia and subsequent deepening of anaesthesia with inhalational maintenance agents is central positioned eye with a dilated pupil , the eye rapidly rolls into a ventromedial position with the white sclera of the eye easily seen, and with the palpebral (blink) reflex diminishing until it disappears the eye then rolls centrally again and the pupil is constricted the eye stays centrally positioned but the pupil begins to dilate the pupil dilates fully In most small animals (particularly cats and dogs) when the eye has rolled down intubation can be achieved and transition to gaseous anaesthesia, via an anaesthetic machine, begun. When the palpebral reflex disappears it is usually a reliable sign that a surgical plane of anaesthesia has been reached. As the patients depth increases further, the eye rolls centrally with a constricted pupil. This eye position is consistent with a depth that is considered too great for dogs and cats. However in sheep this is the desirable eye position. So all species follow the pattern of central ventral central.
4. Discuss the differences between high-volume low-pressure cuffs, and low-volume high-pressure cuffs. Which are best? Why?
The cuff is a small inflatable "balloon" located near the patient end of the tube. The cuff system consists of the cuff itself, the inflating tube (some of which is often incorporated into the wall of the tube), a pilot balloon and a one-way inflation valve. The cuff is inflated by injecting air through the one-way valve with a syringe - once the syringe is removed the valve seals, preventing the escape of air. Cuff deflation is performed by reattaching a syringe to the inflation valve and aspirating the air in the cuff. The pilot balloon inflates as the cuff is inflated, but serves only as an indicator of cuff inflation, not a measure of the adequacy of inflation. Inflation of the cuff applies pressure to the tracheal mucosa which, under certain circumstances, may be sufficient to impair perfusion of the tracheal wall. These damaged areas heal with scarring and possible stricture of the tracheal lumen. The perfusion pressure of the tracheal mucosa ranges from 25 to 35 mm Hg. High-pressure, low-volume cuffs (like those found on red-rubber tubes), produce a seal by distending and distorting the tracheal wall, often resulting in mucosal pressures > 35 mm Hg. Cuffs with a large residual volume (i.e. low-pressure, high-volume cuffs) tend to "drape' freely over the tracheal wall and seal at mucosal pressures of 20 - 25 mm Hg, although these still have channels present which can allow the passage of fluids through. Some recommend that you use KY jelly on the cuffs in order to "fill" cover the surface of the cuff and prevent fluid from tracking down through the channels. Over inflation of the high-volume, low-pressure cuffs may still result in tracheal damage. The cuff of the ET tube is inflated to enable the patient to be ventilated as well as to minimise the chance of aspiration of foreign material and prevent environmental contamination with inhalational anaesthetic agents. high-volume, low pressure cuffs are preferred in most veterinary patients.
6. Briefly describe the correct technique for intubating common domestic species.
The larynx is best visualised with the dog positioned in sternal recumbency, with the jaws opened widely. In many dogs, the epiglottis may initially be displaced dorsal to the soft palate, obscuring the larynx. Gentle upward pressure on the soft palate with the ET tube or laryngoscope will cause the epiglottis to fall back to its normal position. It is important to visually confirm intubation This is achieved by lifting the ET and looking for the V shaped vocal folds If the tube is in the oesophagus you will see the fleshy arytenoid cartilages ventral to the tube when the tube is lifted
Minimum Alveolar Concentration (MAC)
The minimum alveolar concentration that prevents purposeful movement in 50% of patients in response to a supramaximal stimulation So this indicates the potency of the extract.
e. 4 week old female dog for a fracture repiar
benzo and morphine and anticholinergic
Autoregulation curve A higher inhalational concentration increases
cerebral blood flow??
14. List common problems that may occur during induction and discuss the role of the veterinarian in managing these problems.
excitement apnoea vomiting or regurgitation cardiovascular problems (tachycardia, bradycardia, hypotension and arrhythmias) extravascular injections. -Prevention is achieved by always injecting irritating substances via an IV catheter and/or using dilute concentrations of the agent. The treatment of accidental perivascular injection of thiopentone includes injecting large volumes of "normal saline" around the site to dilute the drug,
Clinical pharmacodynamics **all** inhalation agent decreases blood pressure
halothane is the only one that can decrease heart rate.** important.** -causes vasodilation which decreases blood pressure. but it makes our baroreceptors insensitive so heart rate doesnt increase *so may have more severe cardiovascular effect others can increase
Describe at least five parameters that can be used to assess and monitor the cardiovascular system
heart rate heart rhythm pulse rate pulse rhythm pulse strength (arterial blood pressure) - covered fully in monitoring equipment Electrical activity - ECG capillary refill time mucous membrane colour
2. List the patient parameters used to assess anaesthetic depth. 7 things
heart rate and rhythm e.g. fast or slow, regular or irregular quality of the heart sounds e.g. strong or faint capillary refill time (CRT) and mucous membrane colour (i.e. a measure of tissue perfusion) e.g. fast, slow or normal CRT; MM colour may be pink, pale pink, cyanotic, congested, grey, jaundiced etc. blood pressure (pulse pressure) e.g. strong, moderate or weak pulse respiratory rate and pattern e.g. fast or slow, regular or irregular, jerky breathing, breath holding, apnoea etc. eye position, pupil diameter and eye reflexes e.g. central or rotated eye, dilated or constricted pupil, palpebral reflex, whether the eye is dry or moist, the presence or absence of nystagmus (oscillations of the eye from side-to-side) muscle tone e.g. jaw tone, and the presence or absence of spontaneous movement
1. respiratory centre depression
in the recumbent horse the normal pattern or "distribution" of ventilation is altered in the following ways. The administration of central nervous system (CNS) depressant drugs (i.e. anaesthetic agents) results in medullary respiratory centre depression and hypoventilation. Most anaesthetic agents alter the body's ability to respond to hypercapnia by shifting the carbon dioxide response curve to the right and "flattening" the response curve i.e. a significantly higher level of carbon dioxide is now required to stimulate ventilation. Because of the sigmoid shape of the oxyhaemoglobin dissociation curve versus the linear shape of the carbon dioxide dissociation curve, anaesthetised patients may well become dangerously hypoxic before their blood carbon dioxide levels elevate sufficiently to stimulate ventilation.
What is hypercapnia?
increase in carbon dioxide >50mmHg While hypoxia is rare, hypercapnia occurs immediately once ventilation ceases.
PREANAESTHETIC PERIOD (3RD LECTURE)
l
Lecture 1
lectures not covered are 15, 7, 8, 10.
The higher MAC is, the***** potency is.
lower
What can be done to minimise hypothermia in surgical patients?
minimising the duration of the anaesthetic avoiding excessive hair / fur removal being careful not to wet the patient excessively during the surgical prep covering the patient with a towel or blanket when possible placing the patient on a circulating warm-water pad warming IV fluids warming and humidifying inspired gases if possible e nsuring the operating room and prep area are warm and draft free warming flush or irrigating solutions
Describe the path of airflow during ventilation What is anatomic dead space? What is physiological dead space?
nose, nasopharynx, larynx, trachea, bronchi and bronchioles = conducting airways = "anatomic dead space" to the alveoli = "diffusing airways" = gas exchange poorly perfused alveoli = "physiological dead space"
2. Know what factors influence the dose of drug required to induce anaesthesia. "Why use injectable agents IV"
species size - the smaller the patient the higher the dose physiological status - total protein level influence the amount of active drug available and pH status alters the ionisation of some agents individual variability - population dynamics dictate a normal distribution and some individual may be outliers degree of sedation - heavily sedated patients may require much less agent than a non-sedated patient Why use 1. To induce anaesthesia 2. To maintain for short procedures or where intubation cannot be achieved -IV allows rapid control and short duration of action
