Animal Medicine 1 ch. 3 *AI

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Questions and Answers

What is the primary purpose of using anxiolytics in veterinary practice?

To minimize stress, anxiety, and fear in animals (correct)

To promote appetite in reluctant eaters

To induce anesthesia in surgical patients

To increase the physical activity of animals

Which of the following describes the appropriate storage requirements for Schedule II drugs?

Can be stored openly on a countertop

Must be stored with other medications

Should be kept in a refrigerator

Must be stored in a securely locked cabinet (correct)

What is the primary function of alpha2-antagonists in veterinary medicine?

To increase pain sensitivity in patients

To replace tranquilizers in treatment protocols

To enhance sedation effects of alpha2-agonists

To reverse the effects of alpha2-agonists (correct)

Which preanesthetic medication is known for its anticholinergic properties?

Atropine Signup and view all the answers

What is a significant adverse effect associated with opioids in veterinary patients?

Severe respiratory depression Signup and view all the answers

Which controlled substances require the use of DEA Form 222 for ordering?

Schedule II drugs Signup and view all the answers

What is the effect of benzodiazepines when used in young, healthy animals?

May induce disorientation and excitement Signup and view all the answers

Which opioid is classified as a partial agonist?

Buprenorphine Signup and view all the answers

What adverse effect is associated specifically with phenothiazines?

Penile prolapse in large animals Signup and view all the answers

Which type of medication induces neuroleptanalgesia when administered with opioids?

Alpha2-agonists Signup and view all the answers

Which of the following is not classified as an anesthetic agent?

Reversal agents Signup and view all the answers

Agonists primarily function by doing what?

Stimulating target tissues to produce desired effects Signup and view all the answers

Which of the following routes of administration is least likely to provide rapid onset of anesthetic effects?

Subcutaneous Signup and view all the answers

What is a common characteristic of agonist-antagonist agents?

They can provide partial stimulation and block full agonists Signup and view all the answers

Which statement about analgesics used during anesthesia is true?

True analgesics do not render the patient unconscious. Signup and view all the answers

Which of the following statements best describes the pharmacokinetics of injectable anesthetics?

Redistribution can significantly impact effects on target tissues. Signup and view all the answers

What is a critical consideration when mixing anesthetic drugs in a syringe?

Drugs must be compatible to avoid precipitation. Signup and view all the answers

Which drug scheduling is NOT correct according to government regulations for controlled substances?

Schedule V drugs have a lower potential for abuse than Schedule I. Signup and view all the answers

Which of the following best represents an adjunct in anesthesia?

A substance that enhances sedation without causing loss of sensation Signup and view all the answers

What is a characteristic of injectable anesthetic drugs?

They produce unconsciousness. Signup and view all the answers

Which effect is primarily associated with propofol?

Decreased intracranial pressure Signup and view all the answers

What differentiates dissociative anesthetics from other injectable anesthetics?

They cause the animal to appear awake. Signup and view all the answers

What is the role of the blood-gas partition coefficient in inhalation anesthetics?

It measures the solubility of the anesthetic in blood versus alveolar gas. Signup and view all the answers

Which of the following is an adverse effect commonly associated with inhalation anesthetics?

Hypotension Signup and view all the answers

What is a primary concern when using dissociative anesthetics in animals with liver disease?

Altered metabolism of the drug Signup and view all the answers

Which injectable anesthetic is noted for its ultra-short-acting properties?

Propofol Signup and view all the answers

What is the minimum alveolar concentration (MAC) used to measure?

The required dosage for effective anesthesia Signup and view all the answers

Which injectable anesthetic is utilized primarily in cats for light anesthesia or deep sedation?

Alfaxalone Signup and view all the answers

How do halogenated inhalation anesthetics primarily achieve their effects?

By diffusing into the bloodstream from the alveoli Signup and view all the answers

Which statement accurately describes the relationship between MAC and anesthetic potency?

Lower MAC values denote greater anesthetic potency. Signup and view all the answers

What is a key characteristic of isoflurane regarding its effects on cardiovascular health?

It has the fewest adverse cardiovascular effects. Signup and view all the answers

What is the predominant elimination route for isoflurane following anesthesia?

Exhalation through the lungs Signup and view all the answers

Which agent primarily requires a precision vaporizer due to its high vapor pressure?

Sevoflurane Signup and view all the answers

How does nitrous oxide affect the Minimum Alveolar Concentration (MAC) of other inhalant agents?

It decreases MAC by 20% to 30%. Signup and view all the answers

Which adverse effect is associated with the use of doxapram?

Hyperventilation Signup and view all the answers

What is the blood-gas partition coefficient of desflurane relative to other inhalants?

It has the lowest blood-gas partition coefficient. Signup and view all the answers

Why is doxapram considered an analeptic agent?

It stimulates respiration and speeds recovery. Signup and view all the answers

In which condition must doxapram be administered to ensure safety?

With adequate oxygen levels in the brain. Signup and view all the answers

Which anesthetic agent is noted for having a MAC value range that is the least potent among the inhalant agents discussed?

Desflurane Signup and view all the answers

Study Notes

Anesthetic Agents and Adjuncts

An anesthetic agent is any drug that induces loss of sensation with or without unconsciousness
An adjunct is any drug that is not a true anesthetic, but is used during anesthesia to create other desired effects, such as anxiolysis, sedation, muscle relaxation, analgesia, reversal, neuromuscular blockade, or parasympathetic blockade

Classifications of Anesthetic Agents and Adjuncts

Classified based on route of administration, time of administration, principal effect, and chemistry

Clinically Important Properties of Anesthetic Agents

Pharmacokinetics: how the drug moves within the body
Pharmacodynamics: the effect the drug has on the body
Target tissues and stimulation: the CNS is typically the target for depression or stimulation

Agonists, Partial Agonists, Mixed Agonist-Antagonists, and Antagonists

Agonists: bind to and stimulate target tissue, most anesthetic agents and adjuncts are agonists
Partial Agonists and Mixed Agonist-Antagonists: opioids
Antagonists: bind to target tissue but do not stimulate, used as reversal agents

Analgesia

Most general anesthetics are not analgesics
Must provide analgesia before and after the procedure
True analgesics do not provide general anesthesia

Route of Administration

Inhalant
Injectable: intravenous, intramuscular, subcutaneous
Oral
Topical

Drug Combinations

Do not mix drugs in a single syringe unless compatible
Do not administer a drug combination if a precipitate develops
Most anesthetic agents and adjuncts are water soluble, diazepam is not

Controlled Substances Regulations

Governmentally regulated drugs
Five drug schedules: I, II, III, IV, V
Dispensed: DEA in the US, CSA in Canada
Enforced: RCMP in Canada

Controlled Substances Recordkeeping

Enforced by DEA
Inventory every two years in a veterinary practice
Use of a controlled substance log

Ordering Controlled Substances

Schedule II drugs: DEA Form 222
Schedule III and IV drugs: no special order form

Storing Controlled Substances

Schedule II through V drugs: securely locked, substantially constructed cabinet, not in public areas
Opioid agonist and antagonist drugs: safe or steel cabinet
Report any unexpected, significant loss or suspected theft to DEA and local police

Prescribing Controlled Substances

Take precautions to prevent abuse: keep Rx pads in a secure location, prevent illegal alteration of prescriptions

Preanesthetic Medications

Anxiolytics: gabapentin, trazodone
Anticholinergics: atropine, glycopyrrolate
Tranquilizers and sedatives: phenothiazines (acepromazine), benzodiazepines (diazepam, zolazepam, midazolam), alpha2-adrenoceptor agonists (alpha2-agonists)
Opioids (agonists, partial agonists, agonist-antagonists, antagonists)
Antiemetics: prevent nausea and vomiting

Preanesthetic Medications - Indications

Calm or sedate excited animals
Minimize adverse drug effects
Reduce the dose of concurrent drugs
Smoother anesthetic induction and recovery
Analgesia
Muscle relaxation

Anxiolytics

Gabapentin: analgesic properties, anxiolysis, anticonvulsant
Trazodone: reduces stress, fear, and anxiety

Preanesthetic Anticholinergics

Parasympatholytic drugs: block acetylcholine
Prevent and treat bradycardia
Decrease in salivary secretions
Atropine and glycopyrrolate: intravenous, intramuscular, subcutaneous, or intratracheal
Atropine: faster onset, shorter peak, shorter duration
Glycopyrrolate: slower onset, longer peak, longer duration

Anticholinergic Effects

Central nervous system: limited effect
Cardiovascular: prevent bradycardia
Decrease in respiratory and salivary secretions
Bronchodilation
Eyes: mydriasis and corneal drying
Decrease in gastrointestinal and lacrimal secretions

Anticholinergic Adverse Effects

Cardiac arrhythmia: contraindicated in patients with elevated heart rates or cardiac diseases
Temporary bradycardia: atropine
Thickened respiratory and salivary secretions: may lead to airway blockage
Intestinal peristalsis inhibition: may lead to colic or bloat

Tranquilizers and Sedatives

Tranquilizer: reduces anxiety
Sedative: reduces mental activity, causes sleepiness
Phenothiazines: acepromazine
Benzodiazepines: diazepam, zolazepam, midazolam
Alpha2-adrenoceptor agonists

Tranquilizers and Sedatives: General Risks

Patient should not be left unattended
Sedatives can cause respiratory distress
Animals can exhibit unusual behavior when sedated

Phenothiazines: Acepromazine Maleate

Only drug in class typically used as an anesthetic adjunct
Usually administered IV or IM

Effects and Adverse Effects of Phenothiazines

Calming/sedation
Tachycardia or bradycardia
Antiarrhythmic effects
Peripheral vasodilation
Hypotension
Antiemetic
Hypothermia
Penile prolapse in large animals
Decreased PCV

Use of Acepromazine

Dose and needle placement
Increased potency: geriatrics, neonates, debilitated animals
Breed considerations: Australian shepherds, Collies (low dose), giant breeds, Boxers, Greyhounds (increased sensitivity), terriers and cats (resistance)
Overdose treatment

Benzodiazepines

Minor tranquilizers, controlled substances
Rapid onset of action
Short duration of action
May produce opposite effect in young, healthy animals

Effects and Adverse Effects of Benzodiazepines

Calming and antianxiety in old or ill patients
Anticonvulsant
Disorientation and excitement in young dogs
Dysphoria/aggression in cats
Muscle fasciculations in horses
Ataxia or recumbency in large animals
Few cardiopulmonary effects
Skeletal muscle relaxation
Pain on IM injection of diazepam

Alpha2-Adrenoceptor Agonists

Noncontrolled agents
Sedation, analgesia, and muscle relaxation
Large and small animals: intravenous or intramuscular
Administered before minor procedures
Reversed with alpha2-antagonist

Effects and Adverse Effects of Alpha2-Adrenoceptor Agonists

Dose-dependent sedation
Analgesia
Agitation or aggression
Muscle tremors in horses
Cattle may lie down
Initial hypertension, bradycardia, pale mucous membranes, then hypotension, decreased output, decreased heart rate
Severely decreased heart rate, blood pressure, cardiac output, tissue perfusion
Respiratory depression
Muscle relaxation
Vomiting
Adverse GI effects
Hyperglycemia
Hypothermia
Increased urination
Premature parturition in cattle
Sweating in horses

Use of Alpha2-Adrenoceptor Agonists

Use with caution
Monitor patients closely
Avoid use in geriatric, diabetic, pregnant, pediatric, or ill patients
Administer anticholinergics 10 to 20 minutes before

Alpha2-Antagonists

Reverse the effects of alpha2-agonists
Wide margin of safety
Effects of overdose: neurological, cardiovascular, gastrointestinal

Opioids

Produce analgesia and sedation
Anesthetic induction when combined with other drugs
Classified as agonists, partial agonists, agonist-antagonists, or antagonists
Most are controlled substances
Administered through multiple routes
Wide margin of safety

Commonly Used Opioids

Agonists: morphine, hydromorphone, methadone, oxymorphone, fentanyl, meperidine
Partial agonist: buprenorphine
Agonist-antagonists: butorphanol, nalbuphine
Antagonists: naloxone

Opioids: Pharmacodynamics

Mimic endogenous opioid peptides: β-endorphins, dynorphins, enkephalins
Analgesia and sedative effects: receptors in the brain and spinal cord: mu (μ), kappa (κ), and delta (δ) receptors
Agonists: bind to and stimulate mu and kappa receptors (best for moderate to severe pain)
Partial agonists: bind to and partially stimulate receptors
Agonist-antagonists: bind to mu and kappa receptors but stimulate only kappa receptors
Antagonists: bind to but do not stimulate mu and kappa receptors

Effects and Adverse Effects of Opioids

CNS depression or excitation
Excellent somatic and visceral analgesia
Dose-dependent bradycardia and respiratory depression
Panting
Hypothermia or hyperthermia
Salivation/vomiting
Initial vomiting, diarrhea, flatulence followed by constipation
Colic and sweating
Increased responsiveness to noise
Miosis or mydriasis
Decreased urine production and urine retention

Use of Opioids

Preanesthetic: agonists, partial agonists, or agonist-antagonists alone or in combination with tranquilizers or anticholinergics
Analgesia: prevent and treat postoperative pain, neuroleptanalgesia

Neuroleptanalgesia

Profound state of sedation and analgesia
Wide margin of safety when properly administered
Sedation for minor procedures
Induction of general anesthesia

Opioid Antagonists

Undesirable effects of opioids can be reversed
Wake up patient following sedation
Naloxone hydrochloride: IM or slow IV administration
Naltrexone: used in wild animals, longer lasting

Effects of Opioid Antagonists

Reversal of effects of opioid agonists, partial agonists, and agonists-antagonists
Reversal can be complete in a few minutes
Adverse effects are rare: sudden analgesia loss

Use of Opioid Antagonists

Emergencies
Overdose
Reverse neuroleptanalgesia
Reviving neonates delivered by C-section

Injectable Anesthetics

Can cause unconsciousness
Do not provide analgesia or muscle relaxation
Must be used with other drugs to produce complete effects of general anesthesia
Administered intravenously
Examples include: propofol, etomidate, alfaxalone, and barbiturates

Propofol

Ultra-short-acting, nonbarbiturate anesthetic
Schedule IV drug
Used for anesthetic induction and short-term maintenance in small animals, small ruminants, exotic animals, and neonates of all species.
Used intravenously in boluses and CRI for treating status epilepticus in dogs and cats

Effects and Adverse Effects of Propofol

Dose-dependent CNS depression, resulting in sedation to general anesthesia
Transient excitement and muscle tremors during induction
Bradycardia, decreased cardiac output, hypotension
Respiratory depression, including apnea
Prolonged apnea, decreased oxygen saturation, and cyanosis
Muscle relaxation
Antiemetic effect
Decreased intracranial and intraocular pressure
Pain on IV injection

Propofol Handling and Storage

Shake thoroughly before use
Poor storage characteristics due to bacterial growth in the ingredients
Use aseptic technique
Discard unused drug after 6 hours of opening
3-year shelf life if unopened

Alfaxalone

Short duration of action
Wide margin of safety
Used intravenously for anesthetic induction and maintenance
Used intramuscularly for deep sedation and light anesthesia in cats
Schedule IV controlled substance
Steroid molecule, works similar to other hypnotics

Effects and Adverse Effects of Alfaxalone

Dose-dependent CNS depression
Minimal cardiovascular depression
Tachycardia
Hypotension
Respiratory depression, including apnea
Muscle relaxation
Excitement during recovery

Etomidate

Administered only intravenously
Start with ¼ to ½ calculated dose
Adverse effects include vomiting and muscle contractions, which can be minimized with premedication
Can be administered in repeated boluses for short-term anesthesia.

Barbiturates

Large class of controlled drugs
Use declined with development of new drugs
Specific uses:
- Short-acting pentobarbital sodium: induce and maintain general anesthesia in lab animals, treat status epilepticus in small animals, and euthanasia agent.
- Long-acting phenobarbital: seizure control, occasionally sedative in dogs and cats

Dissociative Anesthetics

Only ketamine is used in veterinary medicine
Used alone for minor procedures or to facilitate restraint in cats
Used with other drugs such as tranquilizers and opioids to induce general anesthesia
Subanesthetic dose is used as CRI for analgesia

Dissociative Anesthetics Mode of Action

Disrupts nerve transmission in some brain sections
Selective stimulation in parts of the brain
Decreases windup through NMDA inhibition
Trance-like state, where the animal appears awake but immobile and unaware of surroundings
All dissociatives are metabolized in the liver or excreted unchanged in the urine, so avoid use in animals with liver or kidney disease.

Effects and Adverse Effects of Dissociative Anesthetics

Cataleptoid state
Intact reflexes
Eyes open, pupils central and dilated
Normal or increased muscle tone
Analgesia (somatic)
Sensitivity to stimuli
Nystagmus
Increased heart rate, cardiac output, mean arterial pressure
Decreased inotropy
Apneustic respiration at higher doses
Increased salivary and respiratory tract secretions
Pain after IM injection

Use of Dissociative Anesthetics

Administered intramuscularly or intravenously
Wide margin of safety
Useful in cats and horses
Used in combination with tranquilizers for short procedures, anesthetic induction for intubation, chemical restraint in cats, immobilization of large and exotic animals, and pain control.
No effective reversal agent.

Dissociative Anesthetic: Use of Guaifenesin

Used with ketamine in anesthetic induction protocols, often with premedication of an alpha2-agonist or acepromazine
Triple drip: GG, ketamine, xylazine is a common combination used in horses for maintaining anesthesia for less than an hour
Administered intravenously rapidly until the animal is ataxic and after premedication.
Smooth recovery.

Dissociative Anesthetic: Use of Guaifenesin

Part of an anesthetic induction protocol in combination with ketamine
Must premedicate, as guaifenesin may cause excitement or an increased risk of side effects without premedication
Not used as a sole agent, as sedation and analgesia are inadequate for surgery.

Inhalation Anesthetics

Examples include isoflurane, sevoflurane (halogenated compounds), nitrous oxide, and desflurane
Enflurane is not used in veterinary medicine
Halothane and methoxyflurane are no longer available

Inhalation Anesthetics: Halogenated Organic Compounds

Isoflurane and sevoflurane are the most commonly used agents in this class
Liquid at room temperature
Stored in a vaporizer on an anesthetic machine
Vaporized in oxygen that flows through the vaporizer

Halogenated Organic Compounds: Mode of Action and Pharmacology

Liquid anesthetic is vaporized and mixed with oxygen gas
The mixture is delivered to the patient via a mask or endotracheal tube
Mixture travels to the lungs (alveoli) and diffuses into the bloodstream
Diffusion rate is dependent on the concentration gradient (alveoli/capillary) and lipid solubility
Concentration gradient is greatest during initial induction
Distribution to tissues is dependent on blood supply and lipid solubility, which determines entry into tissues through cell walls
Depth of anesthesia is dependent on the partial pressure of anesthetic in the brain, which depends on the partial pressure of the anesthetic in blood and alveoli
Maintenance of anesthesia is dependent on sufficient quantities of anesthetic delivered to the lungs

Effects and Adverse Effects of Halogenated Inhalation Anesthetics

Dose-related CNS depression
Hypothermia
Paddling, excitement, and muscle fasciculations during recovery
Variable effect on heart rate
Vasodilation and hypotension
Decreased cardiac output and tissue perfusion
Dose-related 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

Inhalant Anesthetics: Physical and Chemical Properties

Key properties to consider include vapor pressure, partition coefficient, minimum alveolar concentration (MAC), and rubber solubility.

Vapor Pressure

Tendency of an inhalation anesthetic to vaporize to its gaseous state
Determines how readily an inhalation anesthetic will evaporate in the anesthetic machine vaporizer
Dependent on the temperature and on the anesthetic agent
Volatile agents have a high vapor pressure (e.g., isoflurane, sevoflurane, desflurane, and halothane) and are delivered from a precision vaporizer to control the delivery concentration
All precision vaporizers are made to deliver only one specific halogenated agent
Nonvolatile agents have a low vapor pressure (e.g., nitrous oxide) and are delivered from a nonprecision vaporizer.

Blood-Gas Partition Coefficient

Measure of the solubility of an inhalation anesthetic in blood as compared to alveolar gas (air)
Indicates the speed of induction and recovery for an inhalation anesthetic agent
Low blood-gas partition coefficient: agent is more soluble in alveolar gas than in blood at equilibrium, resulting in faster induction and recovery
High blood-gas partition coefficient: agent is more soluble in blood than in alveolar gas at equilibrium, resulting in a slower induction and recovery
Determines the clinical use of the anesthetic agent, including induction (e.g., can a mask be used?), maintenance (e.g., how fast will the anesthetic depth change in response to changes in the vaporizer setting?), and recovery (e.g., how long will the patient sleep after anesthesia?).

Minimum Alveolar Concentration (MAC)

Measure of the potency of a drug
Used to determine the average setting on the vaporizer that will produce surgical anesthesia
The lower the MAC, the more potent the anesthetic agent and the lower the vaporizer setting
MAC may be altered by age, metabolic activity, body temperature, disease, pregnancy, obesity, and other agents present
Every patient must be monitored as an individual.

Halogenated Organic Compounds: Isoflurane

Approved for use in dogs and horses, commonly used in other species
Most commonly used inhalant agent in North America

Halogenated Organic Compounds: Physical and Chemical Properties of Isoflurane

High vapor pressure: need a precision vaporizer
Low blood: gas partition coefficient: rapid induction and recovery
Good for induction with mask or chamber
MAC = 1.30% to 1.63%: helps determine initial vaporizer setting
Low rubber solubility
Stable at room temperature; no preservatives needed
Maintains cardiac output, heart rate, and rhythm, with the fewest adverse cardiovascular effects
Depresses the respiratory system
Maintains cerebral blood flow
Almost completely eliminated through the lungs
Induces adequate to good muscle relaxation
Provides little or no analgesia after anesthesia
Can produce carbon monoxide when exposed to a desiccated carbon dioxide absorbent

Halogenated Organic Compounds: Sevoflurane

High vapor pressure: precision vaporizer required
Blood-gas partition coefficient: rapid induction and recovery
Good for induction with a mask or chamber
High controllability of depth of anesthesia
MAC = 2.34% to 2.58%

Halogenated Organic Compounds: Desflurane

Closely related to isoflurane
Expensive
Lowest blood-gas partition coefficient: very rapid induction and recovery
Used with a special precision vaporizer
MAC = 7.2% and 9.8%, making it the least-potent inhalant agent
Eliminated by the lungs

Halogenated Inhalation Agents: Nitrous Oxide

Used sparingly in veterinary medicine
Gas is at room temperature; no vaporizer required
Used with a flowmeter and mixed with O2
Reduces MAC by 20% to 30%

Miscellaneous Anesthetic Adjuncts: Doxapram

Analeptic agent
Non-controlled substance
Stimulates respiration and speeds recovery
Used in neonate puppies and kittens after C-section
Intravenous administration or sublingual drops (neonates)
Mode of action: stimulates the central nervous system, including respiratory centers in the brain

Effects and Adverse Effects of Doxapram

Wide margin of safety
Can cause hyperventilation, hypertension, arrhythmia
Lowers seizure threshold
Must be used in the presence of adequate oxygen levels in the brain
Can cause central nervous system damage

Use of Doxapram

Repeat injections may be necessary
Reverses respiratory depression from inhalant agents and barbiturates

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