Lesson 2: Analgesia, Anesthetic Agents, & Special Techniques

List anesthetic agents and adjuncts commonly used as preanesthetic medications, and describe their indications, mode of action, effects, adverse effects, and use.

Anticholinergics (aka: parasympatholytics): used to prevent/treat bradycardia, decrease salivary secretions arising from parasympathetic stimulation. 2 common examples = Atropine & glycopyrrolate. - MOA: competitively block binding of the neurotransmitter acetylcholine at the muscarinic receptors - Effects: limited CNS effects; prevent bradycardia but can induce cardiac arrhythmias (avoid in animals with preexisting rapid heart rates or heart disease); reduces & thickens respiratory & salivary secretions (cats = thick mucous secretions = not usually used; NOT recommend in ruminants = causes saliva to be thick/ropy = risk of respiratory obstruction); bronchodilation = increases dead space = risk of hypoventilation & hypoxemia - Adverse effects: mydriasis (PLR may be depressed = unreliable); reduces GI tract & salivary secretions (can lead to dry mouth); reduces lacrimal secretions (corneal drying = eye lube used to prevent); inhibition of peristalsis (colic in horses & bloat in ruminants) - Use: prevent adverse effects associated with reversal of nondepolarizing neuromuscular blocking agents; atropine & glycopyrrolate not frequently used as much anymore; atropine good for emergency tx for bradycardia associated with CPA but glycopyrrolate is less likely to induce arrhythmias, suppress salivation mor effectively, & minimally crosses placental barrier in pregnant animals Tranquilizers & sedatives —> Phenothiazines (-azine): *Acepromazine = "Ace"* - MOA: depresses reticular activating center of the brain & blocks alpha-adrenergic, dopamine, & histamine receptors; metabolized by liver; peak effects occur w/in 30-60 mins; duration is 4-8 hrs - Effects: CNS - calms/sedates/decreases P's interest in surroundings; no pain control but decreases anxiety in P's in pain; anti-arrhythmic effect; anti-emetic effect; antihistamine effect (decreases allergic rxns - do not used in sedated animals undergoing allergy testing) - Adverse effects: can induce seizures in P's with epilepsy or seizures from other causes; may induce excitement or aggression rather than sedation... Cardiovascular: can cause tachycardia in response to hypotension or bradycardia; peripheral vasodilation (causes hypotension, a reflex increase in HR; & increased heat loss = leads to hypothermia); severe hypotension (dose dependent)... Respiratory System: does NOT cause significant respiratory depression but worsens depressive effects of other sedative & anesthetic agents... penile prolapse in horses (avoided in breeding stallions); decreases PCV - Use: sedative effects can be overridden if P is stimulated to sufficient degree; manufacturer's rec'd dose is higher than req'd for preanesthesia; have increased potency or duration in geriatric animals, neonates, animals with liver or cardiac dysfunction, and generally debilitated patients; responses to this drug are also species and breed dependent; hypotension resulting from overdose is worsened by epinephrine and should instead be treated with phenylephrine or norepinephrine —> Benzodiazepines (*-pams*; mild tranquilizers; controlled, reversible drugs; most often used in combination with other agents for their muscle relaxant, and anticonvulsant properties; produce unreliable sedative effects, and in dogs, cats, and horses may instead produce dysphoria, excitement, and ataxia, especially when administered to young, healthy animals; - MOA: depress CNS; exact MOA is unknown, but increase activity of endogenous GABA, an inhibitory neurotransmitter in the brain; - Effects: Antianxiety and calming only in old or ill patients; anticonvulsant activity; few cardiopulmonary effects; skeletal muscle relaxation - Adverse effects: Disorientation and excitement in young, healthy dogs; dysphoria and aggression in cats; muscle fasciculations in horses; ataxia or recumbency in large animals; pain on IM injection of diazepam - Use: Diazepam and midazolam are both commonly used in combination with other agents to induce anesthesia; in dogs, small mammals, and birds, midazolam is usually used in combination with ketamine and/or opioids for sedation and intubation. It can also be administered before induction of anesthesia with propofol or etomidate to increase muscle relaxation and reduce adverse effects —> Alpha2-adrenoceptor agonists (alpha2-agonists) (a group of noncontrolled, reversible agents used alone and in combination with other anesthetics and adjuncts in both large and small animal patients for sedation, analgesia, and muscle relaxation. They are commonly given before minor procedures such as radiography, wound treatment, or bandaging and subsequently reversed with an alpha2-adrenoceptor antagonist) - MOA: act on alpha2-adrenergic receptors (also called alpha2-adrenoceptors) of the sympathetic nervous system (SNS) both within the CNS and peripherally, causing a decrease in the release of the neurotransmitter norepinephrine - Effects: Dose-dependent sedation that can be profound; analgesia; muscle relaxation - Adverse effects: agitation or aggression when touched; reaction to loud noises; muscle tremors in horses • Cattle often lie down • Initial hypertension, bradycardia, and pale mucous membranes followed by hypotension, decreased cardiac output, and a further decrease in the heart rate • Severe decrease in heart rate, blood pressure, cardiac output, and tissue perfusion especially when high doses are given • Respiratory depression that can be severe • Vomiting in dogs and cats • Adverse GI effects including bloat and colic • Hyperglycemia • Hypothermia • Increased urination • Premature parturition in cattle • Horses may sweat - Use: Careful monitoring of vital signs is always essential for patients receiving these drugs, all of which should be used with caution; To reduce the incidence of bradycardia, some veterinarians give atropine or glycopyrrolate as premedication. However, this is not always effective and may in fact increase the workload of the heart and myocardial oxygen consumption —> Alpha2-Antagonists (Yohimbine, Tolazoline, & atipamezole - all used to reverse effects of alpha2-agonists) Opioids - MOA: Although opioid receptors are found on neurons throughout the body, the analgesic and sedative effects are chiefly the result of their action on receptors located in the brain and spinal cord. Three major types of opioid receptor have been identified: mu (μ), kappa (κ), and delta (δ), each of which has two or more subtypes. This variety of receptors produces a wide spectrum of effects because each opioid agent differs in its action at each of these sites and therefore in its overall effects on the body - Effects: CNS depression or excitement depending on the dose, route, agent used, species, patient's temperament, and pain status • CNS depression in dogs (except for those not in pain) • CNS stimulation (excitement, dysphoria, and increased motor activity) in cats and large animals • Excellent somatic and visceral analgesia • Dose-dependent bradycardia and respiratory depression that can be pronounced • Panting in dogs • Hypothermia in dogs and hyperthermia in cats • Salivation and vomiting in small animals • Initial vomiting, diarrhea and flatulence, then ileus and constipation • Colic and sweating in horses • Increased responsiveness to noise • Miosis in dogs and mydriasis in cats and large animals • Decreased urine production and urine retention - Adverse effects: - Use: are a common component of preanesthetic protocols. For high-risk patients, some anesthetists prefer to use an opioid such as morphine or hydromorphone as the sole preanesthetic agent. More commonly, however, opioids are mixed with a tranquilizer (such as acepromazine, diazepam, or dexmedetomidine) and/or an anticholinergic (atropine or glycopyrrolate) and given during the preanesthetic period —> Opioid antagonists (reversible drugs for opioids) - MOA: binds competitively to the mu, kappa, and sigma receptors - Effects: reverses both desirable & undesirable effects of opioids; action is often dramatic - causes P to appear nearly unaffected shortly after administration - Adverse Effects: rare at clinical doses, although sudden loss of analgesic effects resulting from routine use may precipitate excitement, anxiety, and SNS stimulation, resulting in tachycardia and cardiac arrhythmias - Use: not necessary for routine anesthesia, however, the technique is extremely useful in emergencies, after an overdose, or to reverse opioid effects after neuroleptanalgesia for nonpainful procedures.

The advantages of alpha2-adrenoceptor agonists (alpha2-agonists) in veterinary anesthesia are that they

Aren't scheduled drugs Provide short-term analgesia Have reversal agents available Have fast onset Can be used in conjunction with drugs such as opioids for a more balanced anesthetic technique

Why do inhalant anesthetics differ in their anesthetic effects?

B/c of their differences in physical & chemical properties Properties of importance = vapor pressure, partition coefficient, minimum alveolar concentration (MAC), & rubber solubility These properties affect the speed of induction and recovery, the type of vaporizer that should be used, and the vaporizer setting that is required for anesthetic induction and maintenance.

Describe the differences between the two classes of neuromuscular blocking agents, including mode of action and reversibility

Depolarizing - MOA: cause a single surge of activity at the neuromuscular junction, which is followed by a period in which the muscle is refractory to further stimulation; - Reversibility: reversal agents have no effect on depolarizing agents Non-depolarizing - MOA: act by blocking the receptors at the endplates; do not cause an initial surge of activity at the neuromuscular junction, and spontaneous muscle movements are not seen - Reversibility: reversed with an anticholinesterase agent

Hypercarbia

Increased carbon dioxide level in the bloodstream

Neuromuscular blockers

Infrequently used in general practice; used to relax or paralyze skeletal muscles during ophthalmic, orthopedic, or other surgeries

Infiltration

Injection

Most commonly used halogenated agents

Isoflurane & sevoflurane

Most commonly used inhalant anesthetic is ______________, followed by ______________.

Isoflurane; sevoflurane ***do NOT provide analgesia

Benefits of nitrous oxide

It is MAC reducing, allowing for isoflurane and sevoflurane vaporizer settings to be turned down. It also has analgesic properties.

Describe Guaifenesin

It is a muscle relaxant used in conjunction with other agents, especially in large-animal anesthesia. It helps facilitate endotracheal intubation and helps provide a more smooth induction and recovery.

Describe Alfaxalone

It is an ultrashort-acting injectable anesthetic with a wide safety margin. It is is administered in the same manner as propofol. It can also be used for sedation via IM administration or as a constant rate infusion for total or partial intravenous anesthesia. It is expensive and doesn't have a preservative. The shelf life is six hours after first puncture of the vial. Like propofol, coinduction with a benzodiazepine can aid in administering lesser amounts of alfaxalone.

Describe Propofol

It is an ultrashort-acting nonbarbiturate anesthetic agent with an onset of action of 30-60 seconds and a duration of 10 minutes after a single bolus. It will show dose- and rate-dependent transient hypotension and apnea. Induction should be accomplished over a few minutes to minimize these side effects. Coinduction with a benzodiazepine can lessen the overall amount of propofol needed for anesthetic induction. Standard propofol doesn't contain a preservative and therefore must be discarded six hours after the bottle is first punctured.

Describe Propofol 28

It is very similar in the mechanism of action and time to effectiveness as standard propofol. The main difference between standard propofol and propofol 28 is that propofol 28 has a benzyl alcohol preservative. This gives it a 28-day shelf life after the first draw. Due to the preservative, it's contraindicated for use in cats.

Neuromuscular blocking agents (NMBA), also known as muscle-paralyzing agents - Advantages & Disadvantages

Paralyzing the patient helps provide muscle relaxation, stabilize the surgical site (in the case of ophthalmic surgery by causing the eye to stay in a central position), and sometimes facilitate intubation. However, ventilatory capabilities must be in place, as the intercostal muscles and diaphragm will be paralyzed. Anesthetic depth can be difficult to assess when using a NMBA because of the absence of normal reflexes and jaw tone. Heart rate and blood pressure are often the best indicators of depth under this situation

The disadvantages of opioids in veterinary anesthesia include

Scheduled drugs require additional paperwork to be filled out May stimulate vomiting May cause hypotension, respiratory depression, bradycardia (low heart rate), and decreased gastrointestinal motility May cause histamine release and/or excitement with IV administration (histamine release occurs with morphine and meperidine when IV is administered too quickly) May cause panting

Most common side effects of opioids

Sedation, respiratory depression, & bradycardia

Local anesthetics block the __________ nerves & the __________ neurons

Sensory Motor

Methadone

Similar characteristics to oxymorphone & hydromorphone with the exception that it has the lowest likelihood of causing vomiting in cats & dogs An antagonist at NMDA receptor - makes it a favorable choice for treating pain when CNS hypersensitivity is present or likely to develop

Describe the technique for performing an epidural block, and give examples of clinical situations in which this block could be used.

Technique: Gather equipment, sedate (or anesthetize) P in sternal or lateral recumbency; shave & prepare the area; palpate the lumbosacral space & place the spinal needle in the area of the greatest depression, perpendicular to the skin surface and exactly on the midline; remove the stylet and examine the needle hub for blood or cerebrospinal fluid (for 2 minutes); if no blood or CSF are observed, aspirate needle to ensure neither is prevent; inject the calculated dose of lidocaine or bupivacaine over 1 minute (should be resistant free) Clinical situations: tail amputation, anal sac removal, perianal and perineal surgery, urethrostomies, obstetric manipulations, cesarean sections, and some hind limb operations

Respiratory minute volume

The amount of air moved into and out of the respiratory system (lungs) each minute - found by multiplying avg VT by RR

Define local anesthesia, list their advantages, & discuss their purpose

The use of a chemical agent on sensory neurons to produce a disruption of nerve impulse transmission, leading to a temporary loss of sensation. Advantages: low cardiovascular toxicity, low cost, excellent pain control in the immediate postoperative period, and minimal patient recovery time. Local anesthetics can be used in conjunction with general anesthesia to enhance pain control during and after surgery. The dose of the general anesthetic required may be significantly reduced because of the analgesia provided by the local anesthetic.

Describe the uptake, distribution, and elimination of the commonly used inhalation anesthetic agents

The vaporizer is turned on & the anesthetic air travels via the P's air passages to the lungs, where it diffuses across the alveolar cell membranes & enters the blood stream. The blood carries the inhalation agents to the body's tissues. Tissues with high blood flow (brain, heart, kidney) are more quickly saturated with anesthetic than tissues with lower blood flow (skeletal muscle & fat). Because of their relatively high lipid solubility, most inhalation agents readily leave the circulation and enter the brain, inducing anesthesia. Isoflurane, sevoflurane, and desflurane undergo minimal liver metabolism because they are eliminated from the body chiefly through the lungs.

Describe barbiturates

They are considered safe, low-cost, rapid-induction agents. They may be ultrashort-acting, short-acting, intermediate- acting, or long-acting agents based on their chemical structure. Barbiturates aren't currently available for use as a common and accepted injectable anesthetic in the United States.

Explain the mechanism of action of nonsteroidal antiinflammatory drugs.

They inhibit prostaglandin synthesis (PGs) = a group of extremely potent chemicals that are normally present in all body tissues & are involved in the mediation of pain & inflammation following tissue injury Most NSAIDs prevent pain & inflammation by inactivating enzyme (COX) - which catalyze one of the steps in the production of prostaglandins Most NSAIDs inhibit both COX-1 and COX-2, although the ratio of COX-1 to COX-2 inhibitory effects of individual NSAIDs varies considerably.

Describe dissociative anesthetics

They produce a cataleptoid state in patients, in which the patient doesn't respond to external stimuli and has muscle rigidity, during which the limbs remain in the position in which they're placed. Dissociative anesthetics include ketamine and Telazol. Telazol comes in powder form and is reconstituted prior to use. The drug itself is a mixture of a benzodiazepine called zolazepam and a dissociative, tiletamine. Dissociatives shouldn't be used alone as a single anesthetic injection; therefore, they're often mixed with benzodiazepines. Etomidate is a short-acting hypnotic imidazole that acts in a manner similar to propofol. It has minimal effects on the cardiovascular and respiratory systems. Etomidate is considered safe for many high-risk patients. Etomidate should be used in conjunction with a benzodiazepine due to potential pain on injection and myoclonus

The advantages of opioids in veterinary anesthesia are

Unsurpassed analgesia Flexibility of administration (IV, IM, SC, PO, transdermal, CRI, and epidural) Availability of reversal agents

List the uses for and adverse effects of nonsteroidal antiinflammatory drugs.

Uses: commonly used to provide analgesia postoperatively and in patients with less severe or inflammatory pain Adverse effects: liver and renal toxicity, increased bleeding times, and gastrointestinal ulceration

Mechanical ventilation

Using a machine to move air into and out of the lungs (lungs are being ventilated)

Tranquilizers and sedatives - use/disadvantage/examples

aid in relaxing patients and potentiate the effects of analgesia, but they may also show dose-dependent vasodilation leading to an increased chance of hypotension. Some of these agents can't be used alone; they must be administered as part of a balanced anesthetic plan. Such drugs include phenothiazines (acepromazine) and benzodiazepines (diazepam and midazolam)

Define multimodal therapy and list two examples of multimodal therapy.

also known as combination or balanced analgesia The use of more than 1 type of analgesic to relieve pain as pain perception is affected at several points & different mechanisms are targeted Ex: Acetominophen & codeine Morphine + injectable NSAID (carprofen)

Local anesthetics with epinephrine should not be administered _________________ and should be avoided when blocks of extremities are performed, as circulation to these areas may become compromised. Local anesthetic injections may be _____________ in the awake patient. Some anesthetists add _______________ ______________ (one tenth the volume of local anesthetic) to decrease pain on injection.

intravenously painful sodium bicarbonate

Neuroleptanalgesia + example

is a state of profound sedation and analgesia that's produced by the concurrent administration of an opioid and a tranquilizer with or without general anesthesia administration Acepromazine + an opioid

NSAIDs are metabolized by the _____________ & ____________, so they may be contraindicated in patients with ____________ or ____________ dysfunction.

liver and kidneys renal or hepatic

Alpha2-agonists - use/disadvantage/reversal agents

may be used as preanesthetic agents to provide sedation, analgesia, and muscle relaxation. These agents have profound effects on the cardiovascular system, and they may not be safe for patients outside physical status classifications P1 and P2. Alpha2-agonists have significant drug-sparing properties that must be taken into consideration when dosed with other anesthetic drugs. Failure to recognize this may result in an overdose. Alpha2-agonists are easily reversed by using any one of the following common alpha2-antagonists: Yohimbine Tolazoline Atipamezole

The partition coefficient is a

measure of the solubility of an inhalant anesthetic in blood as compared with alveolar gas. It helps indicate the speed with which induction and recovery of the patient will take place

Anesthetic depth may be difficult to assess in animals that have been given ______________________ because of the inhibition or absence of normal reflex responses and the absence of jaw tone. Heart rate and blood pressure may give some indication of anesthetic depth. If salivation, tongue curling, or lacrimation is seen, the patient is likely not deeply anesthetized enough for surgery.

neuromuscular blocking agents

Side effects of NSAID's include

possible liver damage, gastrointestinal mucosa damage, renal toxicity, and impaired platelet aggregation

Anticholinergics - use/disadvantage/examples

prevent bradycardia and decrease GI tract secretions, but they cause bronchodilation and can potentially cause arrhythmias. Common anticholinergics include Glycopyrrolate and atropine

NSAIDs should not be used in conjunction with _____________.

steroids

Characteristics and Effects of Buprenorphine

• Partial mu agonist—Schedule III • Effective for mild to moderate visceral and somatic pain • Duration of action of most preparations is felt to be 6 to 12 hours after IM injection and 18 to 24 hours after epidural injection • The duration of action of the veterinary-label injectable product Simbadol™ has been shown to be 24 to 48 hours. • Given by IV, IM, SC, and epidural injection • Can be used to reverse sedation and respiratory depression of pure agonists while maintaining some analgesia • Effects include: • Little sedative effect on its own • Respiratory depression that is difficult to reverse, especially at high doses

Predisposing factors for hypercarbia, hypoxemia, and atelectasis include the following:

• Prolonged anesthesia (more than 90 minutes) • Obesity • Administration of neuromuscular blocking agents (see following section) • Preexisting lung disease such as pneumonia • Recent head trauma • Surgical procedures involving the chest or diaphragm. These animals may have preexisting cardiovascular or pulmonary disease and are at significant risk for cardiovascular collapse or respiratory arrest if conventional anesthesia with unassisted ventilation is attempted • Species differences. Horses in particular are prone to the problems listed previously, regardless of physical status. Adult ruminants also tend to hypoventilate and become hypercarbic

Characteristics and Effects of Morphine

• Pure opioid agonist-Schedule II • Effective for visceral and somatic pain • Duration of action ½ to 3 hours • Given by slow IV, IM, SC, intraarticuar, epidural, and spinal injection and CRI • Rapid IV injection may cause histamine release with resulting hypotension, pruritus, and flushing • Effects include: • Excitement or dysphoria in cats and horses • Restlessness in dogs especially in the absence of pain • Hypothermia (dogs) or hyperthermia (cats) • Miosis (dogs) or mydriasis (cats) • Bradycardia • Respiratory depression • Panting in dogs • GI stimulation including vomiting, salivation, and defecation • Colic in horses due to ileus • Urinary retention • Increased intraocular and intracranial pressure

Characteristics and Effects of Oxymorphone

• Pure opioid agonist—Schedule II • Effective for visceral and somatic pain • As compared with morphine: 1) more potent; 2) fewer adverse effects; 3) longer duration of analgesia (4 hours); 4) less vomiting • Given by slow IV, IM, SC, and epidural, routes, and CRI • Effects include: • Excitement especially after rapid IV injection in cats • Hyperresponsiveness to sound • Respiratory depression • Panting in dogs • Bradycardia

Characteristics and Effects of Fentanyl

• Pure opioid agonist—Schedule II • Effective for visceral and somatic pain • Duration of action 20 to 30 minutes • Given by IV, IM, SC, epidural, and transdermal routes, and CRI • Effects include: • Profound sedation • Bradycardia • Respiratory depression • Panting in dogs • Hyperresponsiveness to sound

Characteristics and Effects of Hydromorphone

• Pure opioid agonist—Schedule II • Effective for visceral and somatic pain • Given by slow IV, IM, SC, epidural, and CRI • Effects are very similar to those of oxymorphone

Cauda equina

"horse's tail", a fan of nerve fibers below the spinal cord

Explain the risks involved and the adverse effects that may be seen with the use of local anesthetic agents

1. Motor neurons may be affected by the local anesthetic, and the patient may lose voluntary motor control of the body part innervated by the affected neurons. The loss of motor function to the limbs typically results in recumbency. This may be inconvenient (e.g., for a standing procedure in a cow) or undesirable and dangerous (e.g., a horse that falls and thrashes repeatedly as it tries unsuccessfully to stand). 2. If local anesthetic is injected into a nerve, temporary or permanent loss of function may result. Direct injection into a nerve should be avoided, except for animals undergoing an amputation. 3. Tissue irritation may occur after injection of some local anesthetics. Some veterinarians prefer mepivacaine to other local anesthetics because it appears to cause less tissue irritation. 4. Paresthesia, an abnormal sensation of tingling, pain, or irritation, may be apparent during recovery from local anesthesia. (Human patients also experience this tingling sensation, for example during recovery from "numbing" of the oral cavity with Novocain.) Animals should be monitored during recovery because they may chew or otherwise traumatize affected areas and may require chemical or physical restraint or the use of E-collars (for cats and dogs). 5. Human and animal patients may exhibit allergic reactions to local anesthetics, usually in the form of a skin rash or hives. Anaphylaxis is also occasionally seen. Local anesthetics should not be used in patients when an allergic reaction to these drugs has been previously observed. 6. Systemic toxicity may occur, particularly if a local anesthetic is inadvertently given intravenously without the use of a tourniquet. Systemic toxicity may be seen even if the drug is placed in the subcutaneous tissues if a large amount of local anesthetic is injected. The most common signs of systemic toxicity originate in the central nervous system. The first sign of systemic toxicity is usually sedation, followed by nausea, restlessness, muscle twitching, hyperexcitability, seizures, respiratory depression, and, eventually, coma. Treatment of central nervous system signs may include IV or intrarectal diazepam (0.2 to 0.4 mg/kg) and administration of oxygen. Cardiovascular effects may also be observed, because of the direct effect of local anesthetics on the heart. Intravenous injection of lidocaine may inhibit the conduction of electrical impulses within the heart muscle and decrease the force of cardiac contractions. This is undesirable when local anesthesia is performed but makes this drug useful in the treatment of some types of ventricular tachyarrhythmia. Bupivacaine is more cardiotoxic than lidocaine. The dose of lidocaine given subcutaneously to dogs, cows, and horses should not exceed 10 mg/kg and in cats should not exceed 4 mg/kg to avoid systemic toxicity. The smallest possible dose should be used. If the drug is given intravenously, the dose of lidocaine should not exceed 4 mg/kg in dogs, 2 mg/kg in large animals, and 0.5 mg/kg in cats. The dose of bupivacaine given subcutaneously should not exceed 2 mg/kg in dogs and 1 mg/kg in cats. For the average (4 kg) cat, the maximum dose of 2% (20 mg/mL) lidocaine is 0.8 mL (16 mg) if given subcutaneously and 0.1 mL (2 mg) if given intravenously. For 0.5% (5 mg/mL) bupivacaine, the maximum subcutaneous dose for a 4 kg cat is 4 mg (0.8 mL). Bupivacaine should never be given by IV injection. Dilution of the calculated dose of lidocaine or bupivacaine with sterile saline is helpful in small patients because it increases the volume and decreases the concentration of the solution to be injected. 7. Epidural or spinal injection may, rarely, traumatize the spinal cord or cauda equina, particularly if the animal struggles during placement of the needle. Inflammation and fibrosis have been reported after epidural infiltration of local anesthetics containing preservatives. In addition, myelitis (spinal cord inflammation) and meningitis (inflammation of the pia mater, arachnoid, or dura mater) may occur if asepsis is not maintained. 8. If local anesthetics are permitted to infiltrate into the cranial portion of the spinal cord, serious toxicity and even death may occur. If the local anesthetic reaches the midthoracic vertebrae, innervation of the intercostal muscles may be blocked, interfering with normal respiration. If local anesthetic diffuses as far forward as the cervical spinal cord, the phrenic nerve may be affected. This nerve innervates the diaphragm, and loss of function may result in respiratory paralysis. When epidural anesthesia is performed, care should be taken to keep the patient's head elevated to avoid gravitational flow of the anesthetic cranially to the level of the thoracic and cervical spinal cord. The anesthetist should be prepared to intubate and artificially ventilate any patient undergoing epidural anesthesia, because this may be necessary if intercostal and phrenic nerve function is impaired. 9. Diffusion of local anesthetic into the cervical and thoracic spinal cord may also affect sympathetic nerves supplying the heart and blood vessels, resulting in a sympathetic blockade with symptoms of bradycardia, decreased cardiac output, and hypotension. If blood pressure measurement is unavailable, careful monitoring of the capillary refill time, heart rate, and pulse strength will alert the anesthetist to a fall in blood pressure. If this occurs before the entire dose has been administered, injection should be halted. Hypotension should be treated

Tidal volume

Amount of air that moves in and out of the lungs during a normal breath (VT) P's breathing deeply = large VT P's with shallow breathing/panting = small VT

What is an adjunct?

An adjunct is a drug that's not a true anesthetic, but one that's used along with anesthetics to increase the desired effects of sedation, muscle relaxation, and analgesia

List the advantages and disadvantages associated with the use of local anesthetic agents

Advantages: - Can be used in conjunction with general anesthetic to enhance pain control during & after some surgical procedures - Multiple methods of delivery - Relatively few effects on cardiovascular or respiratory systems - Not transferred across placenta (used in C-sections) Disadvantages: - Does not produce sedation - Injections may be painful in the awake patient - Requires precise placement of drug immediately adjacent to target nerve

Options for pain relief in patients discharged from the hospital include

Fentanyl patches, NSAIDs, oral opioids, transmucosal (TM) buprenorphine (cats only), gabapentin, amantadine, and tramadol

Inhalation anesthetics include ....

Halogenated organic compounds & nitrous oxide

Describe the effect of protein binding, lipid solubility, and redistribution on the pharmacokinetics and pharmacodynamics of injectable anesthetics.

*Propofol as an example* Protein binding: only unbound molecules of Propofol are able to enter the brain to induce anesthesia b/c the molecules bound to proteins are unable to cross cell membranes, so in P's that are hypoproteinemic, there is less plasma protein to bind Propofol molecules & more Propofol in the active, unbound form. Potency w/in the body is therefore increased. Lipid solubility (aka: partition coefficient): tendency of a drug to dissolve in fats, oils, lipids & is related to ability to penetrate fatty layer of cell membranes. Propofol is highly lipid soluble & therefore passes into brain cells quickly, causing faster onset of action than other drugs with low lipid solubility. Low solubility is related to duration of action. Propofol and other drugs with high lipid solubility are rapidly removed from the brain by a process known as tissue redistribution. Tissue Redistribution: occurs b/c of the way in which Propofol is distributed to various tissues based on blood flow - absorption most rapid in tissues with high blood flow (CNS, heart, liver, kidney, endocrine tissues). Large amounts of the drug rapidly reach the brain because of the excellent blood supply this organ receives. Propofol is highly lipid-soluble, and its entry into brain tissue is enhanced by the high lipid content of the brain. The rapid absorption of propofol into the brain causes the animal to lose consciousness within 30 to 60 seconds of injection. Once the propofol concentration in the blood falls below that in the brain tissue, the drug begins to leave the brain and reenter the circulation, where it is redistributed to muscle, fat, and other body tissues. Propofol leaves the brain because it, like all drugs, diffuses from areas of high concentration to areas of low concentration. The animal shows signs of recovery (often within 5 to 10 minutes) as the concentration in the brain decreases, although the drug is still present in other tissues. Over the next 1 to 2 hours, propofol is gradually released from the muscle and fat and is eliminated from the body by liver metabolism and excretion of the metabolites in urine. Because metabolism is rapid, propofol is relatively safe and effective in animals with liver or kidney disease.

Differentiate agonists, partial agonists, agonist-antagonists, and antagonists based on their action and effect. List anesthetics and adjuncts that can be reversed.

- Agonists: bind to & stimulate tissue receptors - Antagonists bind to but do not stimulate receptors; given after an agonist of same class to "wake" P from anesthesia or sedation; aka: reversal agents - Partial agonists bind to and partially stimulate receptors. - Agonist-antagonists bind to more than one receptor type and simultaneously stimulate at least one and block at least one ***Both partial agonists and agonist-antagonists are sometimes used to partially block the effects of pure agonists

List the inhalation anesthetic agents in common use, and describe their indications, mode of action, effects, adverse effects, and use

1) Halogenated Organic Compounds - liquids at room temp that are stored inside a vaporizer of an anesthetic machine that evaporate in O2 that flows through the vaporizer; regulating mixture is delivered to P thru breathing circuit *Isoflurane, sevoflurane, and desflurane undergo minimal liver metabolism because they are eliminated from the body chiefly through the lungs* —> Indications: —> MOA: suggested that these anesthetics inhibit nerve cell function in the brain and spinal cord —> Effects: Dose-related CNS depression • Hypothermia • Paddling, excitement, and muscle fasciculations during recovery • Variable effect on the heart rate • Vasodilation, and decreased cardiac output, blood pressure, and tissue perfusion • Dose-dependent respiratory depression • Hypoventilation, retention of carbon dioxide, and respiratory arrest • Adequate to good muscle relaxation • Depression of respiration in neonates • Production of carbon monoxide when exposed to desiccated CO2 absorbent —> Adverse effects: —> Use: A. Isoflurane —> Indications: used for induction and maintenance of general anesthesia; most commonly used inhalant —> Adverse effects: has the fewest adverse cardiovascular effects and is therefore considered to be the inhalation agent of choice for patients with cardiac disease —> Use: requires precision vaporizer; has an extremely rapid induction & recovery B. Sevoflurane —> Indications: 2nd most commonly used for induction/maintenance; —> Use: requires precision vaporizer; allows for even more rapid induction & recovery than isoflurane; non irritating & has more pleasant odor than isoflurane = best suited to mask & chamber inductions C. Desflurane —> Indications: closely related to isoflurane; can be used for induction and maintenance of anesthesia, although its expense and some adverse effects currently preclude common use in veterinary patient —> MOA: —> Effects: —> Adverse effects: very pungent and may induce coughing and breath-holding —> Use: induction & recovery are ~2x as fast as those of isoflurane ("one-breath anesthesia") D. Halothane - similar characteristics of isoflurane; has been replaced over last 30 years by iso & sevoflurane; unlikely to encounter E. Methyoxyflurane - no longer available in NA; vapor pressure is significantly lower than iso & sevoflurane so it can be delivered w/ nonprecision vaporizer; slow induction/recovery = not useful for mask or chamber inductions F. Enflurane - used in human medicine - causes profound respiratory depression, and spontaneous ventilation is poor. In the dog, enflurane also induces significant muscle hyperactivity, and seizure-like muscle spasms may result 2) Nitrous oxide - Unlike other inhalation anesthetics, nitrous oxide is a gas at room temperature, is stored in blue compressed gas cylinders, and does not require a vaporizer. Like oxygen, it is administered with a flowmeter, and it is mixed in concentrations of 40% to 67% with oxygen before being delivered to the patient - When used with other agents, nitrous oxide (N2O) speeds induction and recovery and provides additional analgesia. Nitrous oxide also reduces the MAC (and therefore the vaporizer setting) of other anesthetics by 20% to 30%. This reduces the risk of adverse effects on the cardiovascular, pulmonary, and other systems. - Now seldom used in general practice

What are NBA's most useful for?

1) P's that require mechanical ventilation - prevents spontaneous inspiratory effects & allows more rapid & complete control of ventilation (useful for thoracic or diaphragmatic sx 2) Orthopedic sx: provide excellent muscle relaxation - may be helpful for procedure 3) Ophthalmic surgery: prevent movement of the eyeball and cause it to remain in a central rather than ventral position, which facilitates intraocular surgery. 4) Cesarean sections: not transferred across the placenta to the fetus and provide abdominal muscle relaxation, allowing easier access to the uterus. 5) Useful in facilitating difficult intubation (e.g., intubating animals with laryngospasm) because they allow rapid control of the airway without coughing or gagging. 6) Occasionally, used in "balanced anesthesia" techniques.

Regional anesthetic techniques include:

1) Paravertebral anesthesia's: can be used in many species but is often used as an alternative to a line block for a standing laparotomy in cattle 2) Epidural anesthesia is used in both large and small animals for bone and soft tissue surgeries of the pelvis, hind limbs, abdomen, thorax, and the forelimbs in some cases. Local anesthetics can be used with or without opioids to provide pain relief for surgical procedures 3) Intravenous regional anesthesia; aka: bier block - Used to provide local anesthesia to the lower extremity for up to one hour for surgical procedures such as laceration repairs, toe amputations, mass removals, and so on; lidocaine is injected into the distal segment of superficial vein after a tourniquet has been applied proximally to the vein *bupivacaine not used for this block b/c it's more cardio toxic when given via IV*

List injectable anesthetic drugs in common use, and describe their indications, mode of action, effects, adverse effects, and use.

1) Propofol —> Indications: used in small P's for brief procedures or for anesthetic induction b4 intubation & maintenance w/ inhalant agents —> MOA: minimally water-soluble and is available either as a macroemulsion (milky) or a microemulsion (clear) *milky should never be given via IM*; appears to augment action of the inhibitory neurotransmitter GABA in a similar manner to other hypnotics; has a rapid onset and short duration of action because it is highly fat-soluble —> Effects: • CNS depression ranging from sedation to general anesthesia • Transient excitement, muscle tremors, and seizure-like activity during induction • Bradycardia, decreased cardiac output, and hypotension that can be significant and prolonged in some patients • Respiratory depression including apnea especially after rapid injection or high doses • Prolonged apnea, decreased oxygen saturation, and cyanosis • Muscle relaxation • Antiemetic effect • Decreased intracranial and intraocular pressure • Pain on IV injection —> Adverse effects: —> Use: give slowly via IV over 1-2 mins; dose of drug & duration of anesthesia depend on type of premed used; do not give too slowly = paradoxic excitement; boluses can be given every 3-5 mins in dogs/cats up to 20 mins or by CRI *Propofol macroemulsion has poor storage characteristics - ingredients support bacterial growth - once opened, should be handled aseptically & disparaged w/in 6 hours - Propofol 28 contains benzyl alcohol (preservative) - use strict aseptic technique & drug can be stored for 28 days after opening **only for dogs** 2) Etomidate - a noncontrolled, sedative-hypnotic imidazole drug —> Indications: occasionally used for induction of anesthesia in dogs, cats, and exotics; due to minimal effects on cardio/respiratory systems, it's very useful in high-risk P's, but not routinely used due to high cost —> MOA: appears to affect GABA receptors in a similar manner to propofol and barbiturates. The duration of effect 78is short because, like propofol, the drug is redistributed away from the brain and rapidly metabolized —> Effects: • Hypnosis with minimal analgesia • Anticonvulsant effect • Minimal effect on cardiopulmonary function • Good muscle relaxation • Myoclonus during induction and recovery • Pain after IV injection • Hemolysis in cats after rapid injection • Decreased cortisol levels • Nausea, vomiting, and excitement during induction and recovery —> Adverse effects: —> Use: given via IV only; adverse effects minimized by premedicating w/ opioid or diazepam 3) Alfaxalone - an ultrashort-acting injectable anesthetic with a wide margin of safety —> Indications: administered IV'ly for induction of anesthesia and can be used to maintain anesthesia for at least 1 hour by administration of repeat boluses or CRI. It can also be given by IM to cats to produce deep sedation or light anesthesia —> MOA: appears to bind to GABA receptors; rapidly metabolized —> Effects: CNS depression ranging from sedation to general anesthesia • Minimal cardiovascular depression • Tachycardia • Hypotension especially when used with inhalant anesthetics • Respiratory depression including apnea especially after rapid injection or high doses • Muscle relaxation • Excitement may occur during recovery —> Adverse effects: —> Use: given slowly; since there is a risk of respiratory depression, P should be intubated & O2 administered after induction *No preservative - use strict aseptic technique & discard unused portions w/in 6 hours after opening a vial* 4) Barbiturates —> Indications: pentobarbital sodium is used as a euthanasia agent, as a general anesthetic for small laboratory animals, and for treatment of intractable seizures; phenobarbital is used primarily to control seizures, to treat intractable seizures in dogs, cats, and horses; and occasionally as a sedative in dogs and cats Guaifenesin - noncontrolled muscle relaxant that is sometimes given to large animals to increase muscle relaxation, facilitate intubation, and ease induction and recovery; not an anesthetic or analgesic by itself and so is usually given in combination with other agents —> MOA: believed to block nerve impulses in the CNS —> Effects: Skeletal muscle relaxation • Minimal cardiopulmonary effects • Few adverse effects at therapeutic doses • Thrombophlebitis after IV injection • Tissue reaction after perivascular injection —> Adverse effects: —> Use: usually given as a part of an anesthetic induction protocol in combination with ketamine; also used to maintain anesthesia for short periods (less than 1 hour) in horses; should not be used without premedication or as the sole agent, because excitement is likely to be seen during induction and large doses will be required for recumbency, which increases the risk of side effects

Reasons for giving Preaneshtetic Agents

1) Provide tranquilization & sedation 2) Ease induction & recovery 3) Decrease adverse side effects & amount of general anesthetic required 4) Provide muscle relaxation 5) Minimize bradycardia & salivation 6) Provide analgesia

Common local blocks include:

1) Topical: splash block (use of sprays or soaked gauze sponges into an open wound or surgical site); placement of local anesthetic cream onto skin for catheter placement; bupivacaine instilled through a chest tube placed during thoracic sx; ophthalmic administration; patches 2) Infiltration anesthesia: Injection of a local anesthetic under the skin and in proximity of a nerve to facilitate administrating analgesia or anesthesia to that particular area; aka: line block or ring block; can be given intradermally, subcutaneously, or between muscle planes; used for minor wound closures, dew claw removal, declaws, small mass removals, tail amputations, and so on 3) Dental nerve blocks: Infraorbital block is used to provide anesthesia to the rostral portion of the maxilla; Inferior alveolar block is used to provide anesthesia to the caudal portion of the mandible; Mental block is used to provide anesthesia to the rostral portion of the mandible 4) Intraarticular block—injection of local anesthetics directly into the joint cavity

Epinephrine is added to lidocaine for the following two reasons:

1. Epinephrine causes constriction of blood vessels in the area of the injection. This decreases the rate of drug absorption and thereby prolongs the effect of the lidocaine by approximately 50%. 2. By causing vasoconstriction, epinephrine reduces the concentration of local anesthetic that enters the circulation at any given time, thereby reducing toxicity of the drug. This is most effective for short-acting drugs such as lidocaine and less helpful for long-acting drugs such as bupivacaine.

Epidural anesthesia is most commonly used in three classes of patient:

1. Ruminants, in which procedures such as replacement of a vaginal prolapse can be undertaken with epidural anesthesia alone or in combination with a sedative. Epidural procedures are also useful to prevent straining during obstetric procedures, including cesarean sections. 2. Debilitated small animal patients in which general anesthesia is problematic but that may tolerate sedation and a lidocaine or bupivacaine epidural block. One example is patients requiring cesarean section. 3. Patients requiring profound pain control after surgical procedures involving the hind limbs, pelvis, or caudal abdomen. For example, morphine or lidocaine epidural blocks are useful for animals undergoing surgical repair of a fractured femur.

Define adjunct

A drug that is not a true anesthetic but that is used during anesthesia to produce other desired effects such as sedation, muscle relaxation, analgesia, reversal, neuromuscular blockade, or parasympathetic blockade. They are used as a part of balanced anesthesia.

Examples of injectable anesthetics

Barbiturates, propofol, dissociative anesthetics, etomidate, alfaxalone, & guaifenesin

Describe the uses for and procedure for application of fentanyl transdermal patch.

Convenient option for long-term opioid administration The patch is applied to the clipped skin of a P ad left in place for several days *large P's may require several patches* To achieve preemptive analgesia, apply the patch at least 6 hours before the start of anesthesia in cats and at least 12 hours before the start of surgery in dogs Procedure: 1. Various locations can be used for patch application, including the lateral thorax, dorsal neck (commonly used in small animals), or upper part of the limb (commonly used in horses). Any location that is hard for the animal to reach with its mouth or limb will work. Once applied, the patch should not contact sources of external heat. 2. The skin is clipped, taking care not to nick the skin (which may result in the fentanyl being absorbed too rapidly). If soiled, the skin can be cleansed with water (only) and dried thoroughly. 3. The patch is removed from its protective backing, and should be handled by its edges only; or gloves should be worn to avoid contact with the patch membrane. 4. The adhesive side of the patch is applied to the shaved skin and held in place for 1 to 2 minutes. If the patch does not adhere to the skin, a Tegaderm™ (3M) transparent dressing or other light dressing can be placed over the fentanyl patch. Skin staples can also be used to secure the patch if it is placed while the animal is anesthetized, taking care not to puncture the drug chamber. Tissue adhesive should not be used to attach the patch to the patient because it alters the absorption of the fentanyl. If necessary, the patch may be covered with bandage material to prevent removal by the patient (particularly dogs*). 5. The patch remains in place for several days, during which time the fentanyl is gradually absorbed. Blood levels remain at therapeutic levels for approximately 5 days in cats and 3 days in dogs, although there is considerable variation in duration and effectiveness among patients. 6. At the end of this time the patch should be peeled off and disposed as medical waste. If the patient has been discharged in the interim, it is advisable that the patient return to the clinic for patch removal and assessment. 7. If a longer duration of analgesia is required, a new patch can be applied at a separate, clipped site.

Motor neuron

Conveys impulses from the brain to muscle fibers & is responsible for initiating & controlling voluntary movements

Define dissociative anesthesia; describe the actions and effects of dissociative anesthetics, and explain ways in which these drugs differ from other injectable anesthetics.

Dissociative agents (given via IV or IM) —> Dissociative anesthesia: a distinctive trancelike state (so called because it dissociates various regions of the brain), in which the animal appears awake but is immobile and unaware of its surroundings —> Indications: do not produce unconsciousness when given alone, but are frequently used in combo with tranquilizers & opioids to produce sedation & general anesthesia —> MOA: cause disruption of nerve transmission in some parts of the brain and selective stimulation in others. Inhibit NMDA receptors in the CNS that are responsible for "windup." Result = P appears awake but is immobile and unaware of its surroundings —> Effects: Cataleptoid state • Intact reflexes • Eyes open, pupils central and dilated • Normal or increased muscle tone • Analgesia (primarily somatic) • Sensitivity to sound, light, or other sensory stimuli, seizure-like activity, or bizarre behavior, especially during recovery • Nystagmus • Increased heart rate, cardiac output, and mean arterial pressure (MAP) secondary to SNS stimulation • Decreased inotropy • Apneustic respiration at higher doses • Increased salivary and respiratory tract secretions Pain after IM injection —> Adverse effects: —> Use: when given in combo with a tranquilizer, they are used for brief procedures (castration) or means of induction before intubation & inhalation anesthesia; useful for chemical restraint of intractable cats, allowing exams & minor tx's w/o endangering hospital personnel *One limitation = lack of reversal agent*

Apply principles of safe administration of anesthetic agents and adjuncts.

Do not mix 2 drugs together unless there is significant evidence to prove that it is okay

Injectable anesthetics are

Drugs characterized by their ability to produce unconsciousness when given alone; do not provide all effects of general anesthesia (analgesia & muscle relaxation); must be used with other agents to produce complete spectrum of effects of general anesthesia

Assisted ventilation vs controlled ventilation

During assisted ventilation, the anesthetist ensures an increased amount of gas delivery, but the patient initiates each breath. With controlled ventilation, the anesthetist delivers all of the air that's required by the patient & P does not make spontaneous respiratory efforts. This is called intermittent positive pressure ventilation (IPPV) and can be provided via manual (hand bagging) or mechanical (ventilator) methods.

Risks of controlled ventilation include the following:

Excessive airway pressure Decrease in cardiac output Hyperventilation and hypocarbia Too deep of a plane of anesthesia if not carefully monitored Failure on the part of the anesthetist to pay close attention to overall patient monitoring

Describe nursing care that relieves discomfort in hospitalized patients.

Keeping the animal and its cage or stall clean and dry, affording ample opportunity for defecation and urination (including bladder expression or catheterization if necessary), providing comfortable bedding and quiet surroundings, and gently reassuring the patient can all significantly affect the way the patient responds. Also, treatments and monitoring should be scheduled so that the patient is not disturbed unnecessarily. Other interventions that optimize the environment include positioning the patient so that it does not lie on a surgery site or traumatized area. Some patients benefit from being turned every 2 to 3 hours. Unconscious animals may require the application of ophthalmic ointment to prevent corneal drying. Anxious patients may benefit from having a blanket, towel, an article of the owner's clothing, or toy from home with them. When appropriate, allowing the owner to visit can increase the patient's sense of security, and owners are often much more successful in coaxing a patient to eat that otherwise would not. Cats and dogs should be separated, noise should be minimized, and ideally patient cages should be positioned so that animals cannot be able to see one-another. Cats should not be housed in bottom row cages because many cats feel more vulnerable when they are near the floor.

2 major local anesthetics used in vet med

Lidocaine & bupivacaine

Sympathetic blockade

Loss of function of the sympathetic nervous system's neurons via local anesthetic Main effect in peripheral tissues = vasodilation, resulting in flushing & increased skin temperature of the affected area. If severe, vasodilation may cause blood pressure to fall, leading to hypotension

Describe the techniques of manual, mechanical, periodic, and intermittent mandatory ventilation and their application to anesthesia**********

Manual ventilation: performed on periodic basis; pop-off valve is closed & reservoir bag is compressed until the lungs are inflated; when pressure on the reservoir bag is released, exhalation can occur; helps expand collapsed alveoli and reverse atelectasis - Can be done periodically (*already described) or by intermittent mandatory ventilation —> IMV: used for animals with preexisting heart or lung disease, diaphragmatic hernias, low VT (have shallow breaths) and/or respiratory rate (RR) less than 6 breaths/min; performed using Rebreathing or non-rebreathing system********* Mechanical ventilation: p's breathing is controlled by ventilation; when a ventilator is connected to the breathing circuit, it functionally replaces the reservoir bag and becomes a part of the breathing circuit; particularly indicated for patients with compromised respiration. It is not normally necessary for healthy anesthetized patients, where periodic manual bagging (once every 5 minutes) is usually sufficient. Mechanical ventilation is particularly helpful for animals undergoing a thoracotomy or other lengthy operation, when manually providing intermittent mandatory ventilation would be difficult for the anesthetist

The disadvantages of alpha2-agonists in veterinary anesthesia are that they

May produce profound hypertension, heart block, and other arrhythmias May cause respiratory depression Generally cause bradycardia Require prolonged recovery Are associated with gastric dilatation-volvulus (GDV) in susceptible breeds Provide short duration of analgesia Reduce cardiac output May cause vomiting in some species

_________ is the drug most commonly used for epidural analgesia

Morphine

Outline the methods for performing a nerve block and a line block, and list clinical situations in veterinary practice in which these blocks are used

Nerve block - Method: Clip the skin & prepare for sx; palpate the nerves location; inject small amount of local anesthetic immediately adjacent to the nerve *avoid injecting directly into the nerve b/c temporary or permanent loss of nerve fxn can occur *IV injection of local anesthetic should be avoided - may cause unwanted CNS & cardiovascular effects* - Clinical Situations: dental blocks in dogs & cats, inter coastal nerve blocks in P's undergoing chest sx; infiltration of nerves during amputation of a limb; nerve blocks to provide analgesia for declawing cats; paravertebral blocks for abdominal sx or C-sections in cattle; corneal blocks for dehorning cattle; dx nerve blocks in awake horses as part of lameness exam Line block (consists of a continuous line o flcoal anestehtic placed in the SQ or subcuticular tissues immediately proximal to target area; if it completely encircles an anatomic part = ring block - Method: Area is clipped & skin is prepared; insert needle along proposed line of infiltration, then gradually withdraw the needle while simultaneously injecting small amount of local anesthetic - Clinical Situations: used extensively in food animal and equine surgery, particularly in cattle. Examples include teat surgery and wound repair.

Sensory neuron

Neurons that convey sensations (pain, heat, cold, & pressure)

NSAID's + purpose + usage

Nonsteroidal anti-inflammatory drugs (NSAIDs) help treat many different types of pain, such as dental, orthopedic, and soft tissue pain. NSAIDs can be used alone or in conjunction with other drugs such as opioids, tramadol, gabapentin, and so on. NSAIDs are used for chronic pain and postoperatively after painful procedures have been performed

___________ are considered the most effective agents for pain control

Opioids

Manual ventilation

P's lungs are ventilated using the anesthetic machine breathing circuit to force delivery of oxygen and anesthetic gases by squeezing of the reservoir bag of the anesthetic machine. May be used to provide periodic breaths (aka: "sighs") or intermittent mandatory ventilation (done using rebreathing OR non-rebreathing system)

Ex's of opioids include

Pure opiate agonists (most commonly used = *) Morphine* Fentanyl* Oxymorphone* Hydromorphone* Meperidine Methadone* Remifentanil Partial opiate agonist/antagonist—Buprenorphine Mixed agonist—Butorphanol

Classify anesthetic agents and adjuncts based on route of administration, time of administration, principal effect, or chemistry.

Route of administration - Inhalant agents: administered from anesthetic machine into lower respiratory tree via ET tube or mask - Injectable agents: injected IV, IM, SC, IP, intralesionally, or into number of other locations - Oral: given by mouth - Topical: applied to body surface such as skin or mucous membranes Time of administration: - Given before general anesthesia = preanesthetic medications - Used to induce general anesthesia = induction agents - Used to maintain general anesthesia = maintenance agents Principle effect: - Local anesthetics - General anesthetics - Sedatives - Tranquilizers - Analgesics - Muscle relaxants - Neuromuscular blockers - Anticholinergic agents - Reversal agents Chemistry: - For anesthetic agents & adjuncts, the primary target tissue is most often the CNS, & the most common effect is depression and/or stimulation of one or more parts of the CNS —> Most are classified as agonists (bind to & stimulate tissue receptors) —> Antagonists bind to but do not stimulate receptors; given after an agonist of same class to "wake" P from anesthesia or sedation; aka: reversal agents —> Partial agonists bind to and partially stimulate receptors. —> Agonist-antagonists bind to more than one receptor type and simultaneously stimulate at least one and block at least one ***Both partial agonists and agonist-antagonists are sometimes used to partially block the effects of pure agonists

Scheduled drugs - examples

Schedule I - no current accepted medical use Schedule II - high potential abuse — Full mu opioids — Barbiturates (pentobarbital) Schedule III - less potential for abuse compared to schedules I and II — Buprenorphine — Dissociatives Schedule IV - less potential for abuse compared to schedule III — Butorphanol — Benzodiazepines — Alfaxalone

Define vapor pressure, partition coefficient, minimum alveolar concentration (MAC), and rubber solubility; explain the ways in which these properties affect the action and use of inhalant anesthetic agents.

Vapor pressure is a measure of the tendency of a liquid anesthetic to evaporate and is significant to the anesthetist because it determines whether a precision or nonprecision vaporizer is used to deliver the agent - it determines how readily the anesthetic liquid evaporates in the anesthetic machine vaporizer - Agents with a high vapor pressure, such as isoflurane, sevoflurane, desflurane, and halothane, are described as volatile because they evaporate readily & must be delivered from a precision vaporizer, which precisely controls the amount of anesthetic delivered and therefore allows them to be used safely The blood-gas partition coefficient is a measure of the solubility of an inhalant anesthetic in blood as compared with alveolar gas. It is significant because it indicates the speed of induction and recovery one should expect for a given inhalant anesthetic. The lower the blood-gas partition coefficient, the faster the expected induction and recovery The MAC of an anesthetic agent is the lowest concentration at which 50% of patients show no response to a painful stimulus. It is significant because it is a measure of the potency of the agent and is used to determine the average vaporizer setting that must be used to produce surgical anesthesia

Intermittent Mandatory Ventilation (IMV)

When the patient requires bagging throughout the anesthetic period

Examples of alpha2-agonists include

Xylazine (large animal) Romifidine (large animal) Detomidine (large animal) Dexmedetomidine (small animal)

The most commonly used preanesthetic medications are

anticholinergics, tranquilizers, sedatives, and opioids

MOA of local anesthetics

block Na+ channels w/in the nerve membrane normally do not affect the brain and they have no sedative effect *The primary targets of local anesthetic drugs are the neurons that convey sensations (i.e., pain, heat, cold, and pressure) from the skin, muscles, and other peripheral tissues to the brain. These neurons (called sensory neurons) are affected by even small amounts of local anesthetic, provided the drug is deposited in proximity to the neuron. Local anesthetics result in antagonism, also referred to as blockade, of sodium channels. When the sodium channels of a neuron are blocked, the neuron cannot generate electrical impulses. A local anesthetic drug therefore acts as a membrane stabilizer, stopping the process of nerve depolarization. The result is a loss of nerve conduction. Reversal of this effect occurs as the drug is absorbed into the local circulation. Local anesthetics are then redistributed to the liver, where they are metabolized.&

Atelectasis

collapsed lung; incomplete expansion of alveoli can be reversed with manual ventilation

Hypoxemia

decreased level of oxygen in the blood

Vapor pressure

determines whether a precision or nonprecision vaporizer will be used with an inhalant agent. Currently, precision vaporizers are used in the majority of veterinary practices

The minimum alveolar concentration (MAC) of an agent is

the lowest concentration at which 50 percent of patients show no response to painful stimuli. MAC is different for different species. Therefore, it's important to know the MAC of the animal you're working with. The MAC for an agent is a very rough guideline; the veterinary anesthetist must monitor each patient's response to inhalant agents. Many factors affect the MAC of a patient, including core body temperature, disease status, age, and current drug protocol. These factors must be taken into account when adjusting the vaporizer settings.

Characteristics and Effects of Butorphanol

• Opioid agonist-antagonist—Schedule IV • Effective for mild to moderate visceral pain • Duration of action short (as little as 1 hour after IM or SC injection in dogs) • Given by IV, IM, SC injection and by CRI • Injectable formulation is available in multiple concentrations • Can be used to reverse sedation and respiratory depression of pure agonists while maintaining some analgesia • Effects include: • Less sedation, dysphoria, cardiac depression, and respiratory depression than opioid agonists

Characteristics and Effects of NSAIDs

• These agents vary widely in terms of indications, adverse effects, and use. • All NSAIDs are effective for somatic pain. Newer NSAIDs effective for both visceral and somatic pain. • Given by oral and/or parenteral routes (IV, IM, SC) depending on the specific agent. • Most NSAIDs have antiinflammatory and analgesic effects. • Generally safe to use in well-hydrated young to middle-aged animals with normal renal and hemostatic function. • Use with care or avoid entirely in dehydrated patients and in animals with coagulopathies or liver or kidney dysfunction. • Avoid in patients with gastrointestinal disorders and in patients that are receiving corticosteroids. • Animals with low blood pressure, congestive heart failure, or hemostatic disorders such as thrombocytopenia are generally at high-risk for NSAID therapy. • Effects include: • GI toxicity due to increased gastric acid production and decreased mucous production. Signs may include vomiting, bleeding, inappetence, and melena, or may be absent. • Decreased platelet aggregation with prolonged bleeding time. • Renal toxicity due to decrease in blood flow. • The risk of adverse effects is increased if the patient is dehydrated or hypotensive. • For some patients (e.g., geriatric patients and patients with renal disease) NSAIDs should be used only in conjunction with IV fluids and blood pressure monitoring. • Don't use these agents intraoperatively unless the patient is hydrated, is receiving intravenous fluids, and arterial blood pressure is monitored. • Patients with trauma should not receive NSAIDs unless they are in stable condition with no indication of hemorrhage, they are receiving IV fluids, and general anesthesia is not anticipated within the next 48 hours.