Animal Medicine Chapter 3

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Questions and Answers

Which schedule of drugs requires a DEA Form 222 for ordering?

Schedule II (correct)

Schedule III

Schedule I

Schedule IV

Which type of agent primarily binds to and stimulates the target tissue?

Antagonists

Partial agonists

Adjuncts

Agonists (correct)

What is the primary purpose of using anticholinergics in preanesthetic medications?

Prevent bradycardia (correct)

Induce general anesthesia

Increase salivary secretions

Enhance respiratory rate

What is a common property that does not typically characterize most general anesthetics?

Analgesic effects Signup and view all the answers

Which drug class does acepromazine belong to?

Phenothiazines Signup and view all the answers

Which route of administration is NOT commonly associated with injectable anesthetics?

Inhalant Signup and view all the answers

What significant adverse effect can occur with the use of opioids?

Bradycardia Signup and view all the answers

Which term describes a drug that does not produce general anesthesia but can provide additional desired effects during anesthesia?

Adjunct Signup and view all the answers

How often should inventory of controlled substances be conducted in a veterinary practice?

Every 2 years Signup and view all the answers

What effect does the use of alpha2-adrenoceptor agonists typically have during sedation?

Bradycardia followed by hypotension Signup and view all the answers

What is the effect of protein binding on the pharmacokinetics of anesthetic agents?

Decreases drug distribution Signup and view all the answers

Which of the following medications is classified as a partial agonist?

Buprenorphine Signup and view all the answers

Which type of drug combination should always be avoided during the administration of anesthetics?

Drugs producing a precipitate when mixed Signup and view all the answers

What can be a consequence of improperly monitoring a patient that received tranquilizers?

Fall risk due to sedation Signup and view all the answers

Which classification of drug is used primarily as a reversal agent and does not stimulate target tissues?

Antagonists Signup and view all the answers

What is the effect of lipid solubility on injectable anesthetics?

Decreases onset time Signup and view all the answers

Which adverse effect is most commonly associated with benzodiazepines in young dogs?

Disorientation or excitement Signup and view all the answers

What is a key characteristic of agonist-antagonists in relation to their action?

They can simultaneously activate and block receptors Signup and view all the answers

What is the recommended action if there is an unexpected, significant loss of controlled substances?

Report to the DEA and local police within 24 hours Signup and view all the answers

What is a requirement for the classification of controlled substances in the U.S.?

The substance must be regulated by the CSA Signup and view all the answers

What is the primary action of dissociative anesthetics in veterinary medicine?

Induce a cataleptoid state with intact reflexes Signup and view all the answers

Which injectable anesthetic is known for causing transient excitement and muscle tremors during induction?

Propofol Signup and view all the answers

What is a significant adverse effect associated with the use of alfaxalone?

Excitement during recovery Signup and view all the answers

Which inhalation anesthetic is known for its relatively low vapor pressure?

Nitrous oxide Signup and view all the answers

What does a high blood-gas partition coefficient indicate about an inhalation anesthetic agent?

Increased absorption into blood and tissues Signup and view all the answers

Which injectable anesthetic is particularly noted for being used in treating status epilepticus?

Propofol Signup and view all the answers

Dissociative anesthetics, like ketamine, cause what type of state in animals during their use?

Trancelike state with awareness Signup and view all the answers

What should be done to minimize the adverse effects when using Guaifenesin as part of an anesthetic protocol?

Premedicate with alpha2-agonist or acepromazine Signup and view all the answers

Which of the following is true regarding the handling and storage of Propofol?

Should be shaken before use Signup and view all the answers

Which inhalation anesthetic is classified as non-halogenated and commonly used?

Nitrous oxide Signup and view all the answers

Which statement about Minimum Alveolar Concentration (MAC) is true?

MAC indicates the average setting required for surgical anesthesia. Signup and view all the answers

What is a notable characteristic of Isoflurane?

It provides good muscle relaxation with little analgesia. Signup and view all the answers

What is the effect of Sevoflurane compared to Desflurane?

Sevoflurane has a lower MAC than Desflurane. Signup and view all the answers

Which anesthetic agent is associated with significant cardiovascular stability?

Isoflurane Signup and view all the answers

What is a primary usage of Doxapram in veterinary medicine?

Stimulating respiration in neonates post-surgery. Signup and view all the answers

Which of the following correctly describes the elimination of Desflurane?

Almost completely eliminated through the lungs. Signup and view all the answers

What effect does Nitrous Oxide have on Minimum Alveolar Concentration (MAC)?

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

What is a potential adverse effect of using Doxapram?

Hyperventilation and hypertension. Signup and view all the answers

Which halogenated compound generally requires a precision vaporizer?

Isoflurane Signup and view all the answers

What is a common feature of Sevoflurane's pharmacological properties?

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

Study Notes

Anesthetic Agents and Adjuncts

An anesthetic agent is a drug used to induce a loss of sensation with or without unconsciousness.
An adjunct is a drug that is not a true anesthetic but used during anesthesia for additional effects. These effects include anxiolysis, sedation, muscle relaxation, analgesia, reversal, neuromuscular blockade, or parasympathetic blockade.

Classification of Anesthetic Agents and Adjuncts

Classified by route of administration, time of administration, principal effect, or chemistry.

Clinically Important Properties of Anesthetic Agents

Pharmacokinetics, pharmacodynamics, drug distribution, target tissues and stimulation (central nervous system-depression or stimulation).

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

Agonists bind to and stimulate target tissue.
Partial agonists and mixed agonist-antagonists are usually opioids.
Antagonists block target tissue by binding, but don't stimulate.

Analgesia

Most general anesthetics are not analgesics.
Analgesics should be given before and after procedures, as pain perception is not prevented during anesthesia.

Route of Administration

Inhalant, injectable (IV, IM, SC), oral, topical.

Drug Combinations

Do not mix drugs in a single syringe unless compatible.
Do not administer a drug combination if a precipitate forms.
Most anesthetic agents and adjuncts are water-soluble, except Diazepam.

Controlled Substances Regulations

Regulated by the government.
Five drug schedules: I, II, III, IV, V.
Dispensed by the CSA in the U.S. or CDSA in Canada, enforced by the DEA in the U.S. or RCMP in Canada.

Controlled Substances Recordkeeping

Enforced by the DEA in the U.S.
Inventory every 2 years in veterinary practice.
Controlled substance log is required.

Ordering Controlled Substances

Schedule II drugs – require a DEA Form 222 to track.
Schedule III and IV – no special order forms needed.

Storing Controlled Substances

Schedule II through V drugs must be stored in a securely locked, substantially constructed cabinet, not on countertops or other public areas.
Opioid agonist and antagonist drugs must be stored in a safe or steel cabinet.
Report any significant loss or suspected theft to the DEA and local police within 1 business day.

Prescribing Controlled Substances

Take precautions to prevent abuse.
Keep Rx pads in a secure location
Prevent illegal alteration of prescriptions.

Preanesthetic Medications

Anxiolytics, anticholinergics, tranquilizers and sedatives, opioids, and antiemetics.

Preanesthetic Medications - Uses

Calm or sedate an excited animal.
Minimize adverse drug effects.
Reduce the dose of concurrent drugs.
Promote smoother anesthetic induction and recovery.
Provide analgesia and muscle relaxation.

Anxiolytics

Gabapentin (mostly cats) - analgesic properties, anxiolysis, anticonvulsant.
Trazodone (mostly dogs) - reduces stress, fear, and anxiety

Preanesthetic Anticholinergics

Parasympatholytic drugs - block acetylcholine and prevent/treat bradycardia, decrease salivary secretions.
Atropine and glycopyrrolate (dogs and cats) - administered via IV, IM, SC, or intratracheally
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.
Eye - mydriasis and corneal drying
Decrease in gastrointestinal and lacrimal secretions.

Anticholinergic Adverse Effects

Cardiac arrhythmia - contraindicated in animals with high heart rates or cardiac diseases.
Temporary bradycardia - atropine
Thickened respiratory and salivary secretions - can lead to airway blockage-ex: cats and ruminants.
Intestinal peristalsis inhibition - can lead to colic (horses) or bloat (ruminants).

Tranquilizers and Sedatives

Tranquilizer - reduce anxiety but not awareness or wakefulness.
Sedative - reduce mental activity and cause sleepiness.
Three classes used in veterinary medicine - phenothiazines, benzodiazepines, and alpha2-adrenoceptor agonists.

Tranquilizers and Sedatives - General Risks

Patient should not be left unattended, fall risk.
Sedatives can cause respiratory distress.
Animals can exhibit unusual behavior including aggression when sedated.

Phenothiazines: Acepromazine Maleate

Also known as acepromazine or “ace”.
Typically used as an anesthetic adjunct.
IV or IM route.

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 - Considerations based on age, breed, and health of the patient.
Increased potency and duration in geriatric, neonates, debilitated animals.
Breed considerations - Australian shepherds, Collies use low doses; giant breeds, Boxers, Greyhounds increased sensitivity; terriers and cats have resistance.
Overdose treatment.

Benzodiazepines

Minor tranquilizers, controlled substances.
Diazepam, Zolazepam, Midazolam.
Rapid onset of action and short duration.
May produce the 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

Written as alpha2-agonists or 2-agonists.
Noncontrolled agents.
Provide sedation, analgesia, and muscle relaxation.
Large and small animals - intramuscular or intravenous route.
Administered before minor procedures.
Readily reversed with alpha2-antagonist.

Effects and Adverse Effects of Alpha2-Agonists

Dose-dependent sedation.
Analgesia.
Agitation or aggression.
Reaction to loud noises
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 (can be severe).
Muscle relaxation.
Vomiting (in cats & dogs).
Adverse GI effects (bloat, colic).
Hyperglycemia
Hypothermia.
Increased urination.
Premature parturition (cattle).
Sweating (horses).

Use of Alpha2-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 all effects of alpha2-agonists (beneficial effects - for example, analgesia and sedation; detrimental effects - for example, bradycardia).
Wide margin of safety.
Overdose effects include neurological (excitement and muscle tremors), cardiovascular (hypotension and tachycardia), and gastrointestinal (salivation and diarrhea).

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 via IV, IM, SC, oral, rectal, transdermal, subarachnoid, and epidural routes.
Wide margin of safety.

Commonly Used Opioids

Agonists - Morphine, hydromorphone, methadone, oxymorphone, fentanyl, and meperidine.
Partial agonist - Buprenorphine.
Agonist-antagonists - Butorphanol and nalbuphine.
Antagonists - Naloxone.

Opioids: Pharmacodynamics

Mimic endogenous opioid peptides (β-Endorphins, dynorphins, enkephalins).
Analgesia and sedative effects result from action on receptors in the brain and spinal cord.
Four types of opioid receptors: Mu (μ), kappa (κ), delta (δ) plus many subtypes.
Each opioid has a different action at each receptor.

Effects and Adverse Effects of Opioids

CNS depression or excitement (depends on dose, route, type, species, temperament, and pain level).
Excellent somatic and visceral analgesia.
Dose-dependent bradycardia and respiratory depression.
Panting (dogs).
Hypothermia (dogs) or hyperthermia (cats).
Salivation/vomiting (small animals)
Initial vomiting, diarrhea, and flatulence followed by constipation.
Colic and sweating (horses).
Increased responsiveness to noise.
Miosis (dogs), mydriasis (cats, large animals).
Decreased urine production and urine retention.

Use of Opioids

Preanesthetic - agonists, partial agonists, or agonist-antagonists used alone or in combination with tranquilizers and anticholinergics.
Analgesia - prevent and treat postoperative pain, used with tranquilizer to produce neuroleptanalgesia.

Neuroleptanalgesia

Profound state of sedation and analgesia induced by simultaneous administration of an opioid and a tranquilizer.
Wide margin of safety when properly administered.
Used for sedation for minor procedures.
Induction of general anesthesia (dogs) - not in young healthy dogs or cats.

Opioid Antagonists

Reverse undesirable effects of opioids including central nervous system and respiratory depression.
Wake up patient following sedation.
Naloxone Hydrochloride - IM, slow IV, used with dogs, horses, cats, exotic mammals.
Naltrexone - used for wild animals, longer-lasting.

Effects of Opioid Antagonists

Reversal of effects of opioid agonists, partial agonists, and agonist-antagonists.
Reversal is complete in a few minutes.
Adverse effects are rare - sudden loss of analgesia can cause excitement, anxiety, and sympathetic nervous system stimulation.

Use of Opioid Antagonists

Emergencies.
Overdose.
Reverse neuroleptanalgesia.
Reviving neonates delivered by C-section (if dam received opioids) - one drop placed under the tongue.

Injectable Anesthetics

Injectable anesthetics can produce unconsciousness, but not analgesia or muscle relaxation.
These drugs must be used with other agents to produce complete effects.
They are administered intravenously "to effect".
Common injectable anesthetics include propofol, etomidate, alfaxalone, and barbiturates.

Propofol

Propofol is a short-acting, non-barbiturate anesthetic.
It is used for anesthetic induction and short-term maintenance in small animals, small ruminants, exotic animals, and neonates.
It can be administered in both an intravenous bolus and continuous rate infusion (CRI) to treat status epilepticus in dogs and cats.

Effects and Adverse Effects of Propofol

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

Propofol Handling and Storage

Shake thoroughly before use.
It has poor storage characteristics due to its ingredients supporting bacterial growth.
Use aseptic technique.
Discard unused drug within 6 hours of opening.
It has a 3-year shelf life if unopened.

Alfaxalone

Alfaxalone is a short-acting anesthetic with a wide margin of safety.
It's used intravenously for induction and maintenance anesthesia.
It can be administered intramuscularly in cats for deep sedation/light anesthesia.
Alfaxalone is a Schedule IV controlled substance.
It's a steroid molecule that produces a similar effect 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

Etomidate is administered only intravenously.
It is important to start with ¼ to ½ the calculated dose.
Adverse effects include vomiting and muscle contractions.
Muscle contractions can be minimized by premedication.
Etomidate can be administered in repeated boluses for short-term anesthesia.

Barbiturates

Barbiturates are a large class of controlled drugs.
Their use as general anesthetics declined due to newer drug development.
Specific uses include:
- Pentobarbital Sodium (short-acting):
  - Induces and maintains general anesthesia in lab animals.
  - Treats status epilepticus in small animals.
  - Euthanasia agent.
- Phenobarbital (long-acting):
  - Seizure control.
  - Occasionally used as a sedative in dogs and cats.

Dissociative Anesthetics

Only ketamine is used in veterinary medicine.
It can be used alone for minor procedures or to facilitate restraint in cats, and in combination with other drugs for anesthetic induction.
It can also be administered in a subanesthetic dose as a CRI for analgesia.

Dissociative Anesthetics: Mechanism of Action

Disrupts nerve transmission in some brain sections.
Selective stimulation in specific parts of the brain.
Decreases "windup" through NMDA inhibition.
Produces a trancelike state where the animal appears awake but is immobile and unaware of their surroundings.
All dissociatives are metabolized in the liver or excreted unchanged in the urine, therefore, avoiding them in animals with liver or kidney disease is necessary.

Effects and Adverse Effects of Dissociative Anesthetics

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

Use of Dissociative Anesthetics

Administered intramuscularly or intravenously.
They have a wide margin of safety.
They are useful in cats and horses.
They can be used in combination with tranquilizers for:
- Short procedures.
- Anesthetic induction for intubation.
- Chemical restraint (especially cats).
- Immobilization (large and exotic animals).
- Pain control.
There is no effective reversal agent for dissociatives.

Dissociative Anesthetic: Use of Guaifenesin

Guaifenesin is used with ketamine in anesthetic induction protocols, often premedicating with an alpha2-agonist or acepromazine.
The "triple drip" combines guaifenesin, ketamine, and xylazine, and is used in horses for anesthesia maintenance for less than an hour.
Guaifenesin is administered intravenously rapidly to induce an ataxic state after premedication.
It allows for smooth recovery.

Dissociative Anesthetic: Considerations for Guaifenesin

It's a part of an anesthetic induction protocol in combination with ketamine.
Premedication is crucial to prevent excitement and increased risk of side effects.
Guaifenesin is not used as a sole agent because its sedation and analgesia are inadequate for surgery.

Inhalation Anesthetics

Common inhalation agents include:
- Isoflurane
- Sevoflurane (halogenated compounds)
- Nitrous oxide
- Desflurane
Enflurane, halothane, and methoxyflurane are no longer used in veterinary medicine.

Halogenated Organic Compounds

Isoflurane and sevoflurane are the most common agents of this class.
They are liquids at room temperature and stored in a vaporizer on an anesthetic machine.
They are 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 through a face mask or endotracheal tube.
It travels to the lungs (alveoli) and diffuses into the bloodstream.
The diffusion rate depends on the concentration gradient (alveoli/capillary) and lipid solubility.
Concentration gradient is greatest during initial induction.
Distribution to tissues depends on the blood supply.
Lipid solubility determines the rate of entry into tissues.
Depth of anesthesia is dependent on the partial pressure of the anesthetic in the brain, which depends on its partial pressure in the blood and alveoli.
Maintenance of anesthesia relies on sufficient anesthetic delivery to the lungs.

Effects and Adverse Effects of Halogenated Inhalation Anesthetics

Dose-related CNS depression.
Hypothermia.
Paddling, excitement, and muscle fasciculations during recovery.
Variable effects 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).
- Rubber solubility.

Vapor Pressure

The tendency of an inhalation anesthetic to vaporize to its gaseous state.
It determines how readily an anesthetic will evaporate within the machine's vaporizer.
It depends on temperature and the specific anesthetic agent.
Volatile agents (e.g., isoflurane, sevoflurane, desflurane, and halothane) have high vapor pressure and are delivered through a precision vaporizer.
Non-volatile agents (e.g., nitrous oxide) have low vapor pressure and are delivered through a non-precision vaporizer.

Blood-Gas Partition Coefficient

Measures the solubility of an inhalation anesthetic in blood versus alveolar gas (air).
It indicates the speed of induction and recovery.
A low blood-gas partition coefficient signifies faster induction and recovery because the agent is more soluble in alveolar gas than in blood.
A high blood-gas partition coefficient signifies slower induction and recovery because the agent is more soluble in blood, leading to a longer time for the agent to be absorbed into tissues.

Minimum Alveolar Concentration (MAC)

Measures the potency of an anesthetic agent.
It helps determine the average vaporizer setting that will produce surgical anesthesia.
A lower MAC signifies a more potent anesthetic agent, requiring a lower vaporizer setting.
MAC can be altered by age, metabolic activity, body temperature, disease, pregnancy, obesity, and other agents present.
Individual monitoring is essential for each patient.

Halogenated Organic Compounds: Isoflurane

Approved for use in dogs and horses, but commonly used in other species.
It is the most commonly used inhalant agent in North America.

Halogenated Organic Compounds: Physical and Chemical Properties of Isoflurane

High vapor pressure: requires a precision vaporizer.
Low blood-gas partition coefficient: rapid induction and recovery.
Good for induction with a mask or chamber.
MAC of 1.30% to 1.63%, helpful for initial vaporizer setting.
Low rubber solubility.
Stable at room temperature; no preservatives needed.
Maintains cardiac output, heart rate, and rhythm with few 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 to no analgesia after anesthesia.
Can produce carbon monoxide when exposed to desiccated carbon dioxide absorbent.

Halogenated Organic Compounds: Sevoflurane

High vapor pressure: requires a precision vaporizer.
Low blood-gas partition coefficient: rapid induction and recovery.
Good for induction with a mask or chamber.
High controllability of anesthetic depth.
MAC of 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 of 7.2% to 9.8%: least potent inhalant agent.
Eliminated through the lungs.

Halogenated Inhalation Agents: Nitrous Oxide

Occasionally used in veterinary medicine.
It's a gas at room temperature and does not require a vaporizer.
It's mixed with oxygen and delivered with a flowmeter.
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.
Administered intravenously or sublingually (neonates).
Mode of action: stimulates the central nervous system, including respiratory centers in the brain.

Effects and Adverse Effects of Doxapram

Has a wide margin of safety.
Can cause hyperventilation, hypertension, and arrhythmia.
Lowers seizure threshold.
Must be used with adequate oxygen levels in the brain.
Can cause central nervous system damage.

Use of Doxapram

Repeat injections may be necessary.
It reverses respiratory depression from inhalant agents and barbiturates.

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