Veterinary Anesthetic Agents

• Veterinary anesthetic agents induce loss of sensation and consciousness in animals undergoing medical or surgical procedures.
• These agents help veterinarians perform procedures with minimal pain and stress to animals.
• These agents differ in their mechanisms of action, routes of administration, and effects on organ systems.

Injectable Anesthetics

• Include barbiturates, dissociatives, and alpha-2 agonists.

Barbiturates

• Enhance the effects of GABA (gamma-aminobutyric acid), an inhibitory neurotransmitter in the brain, leading to decreased neuronal activity and CNS depression.
• Pentobarbital and thiopental are examples of barbiturates.
• They are used for sedation, anesthesia, and euthanasia.

Dissociatives

• Primarily ketamine and tiletamine.
• Act by antagonizing the NMDA (N-methyl-D-aspartate) receptor, a glutamate receptor involved in neuronal excitation.
• Produce dissociative anesthesia, characterized by catalepsy, analgesia, and amnesia.
• Can increase heart rate and blood pressure.
• May cause unusual behavior during recovery.

Alpha-2 Agonists

• Xylazine, dexmedetomidine, and romifidine are examples of alpha-2 agonists.
• Bind to alpha-2 adrenergic receptors in the central nervous system.
• Reduce norepinephrine release, leading to sedation, analgesia, and muscle relaxation.
• Decrease heart rate and blood pressure.
• Often combined with other anesthetics to reduce required doses and improve anesthesia.

Propofol

• A sedative-hypnotic agent that enhances GABA activity.
• Induces and maintains anesthesia and has a rapid onset and recovery.
• Can cause respiratory depression and hypotension.

Etomidate

• A sedative-hypnotic agent that affects GABA receptors.
• It has minimal cardiovascular effects compared to other induction agents.
• Useful for patients with compromised cardiovascular function.

Inhalant Anesthetics

• Include isoflurane, sevoflurane, and desflurane.
• Delivered via a vaporizer and inhaled by the patient.
• The mechanism of action is not fully understood, but they affect multiple ion channels and receptors in the central nervous system.
• Enhance inhibitory neuronal activity and reduce excitatory activity.

Isoflurane

• Provides good muscle relaxation but depresses respiratory function.
• Can cause vasodilation and decreased blood pressure.

Sevoflurane

• Offers faster induction and recovery compared to isoflurane.
• Has a less pungent odor, making it more suitable for mask induction.
• It has similar cardiovascular and respiratory effects as isoflurane.

Desflurane

• Has the lowest solubility in blood, resulting in the fastest induction and recovery times.
• Can cause airway irritation and requires a special heated vaporizer.

Local Anesthetics

• Lidocaine, bupivacaine, and mepivacaine are examples of local anesthetics.
• Act by blocking sodium channels in nerve cells, preventing the generation and propagation of action potentials.
• This results in localized loss of sensation.

Lidocaine

• A short-acting local anesthetic used for infiltration, nerve blocks, and epidural anesthesia.
• Also has antiarrhythmic properties.

Bupivacaine

• A long-acting local anesthetic providing prolonged analgesia, used for nerve blocks and epidural anesthesia.
• More cardiotoxic than lidocaine.

Mepivacaine

• An intermediate-acting local anesthetic used in horses for nerve blocks.

Adjunct Anesthetics

• Used in combination with general anesthetics to improve analgesia, muscle relaxation, or sedation.

Opioids

• Morphine, hydromorphone, fentanyl, and buprenorphine are examples of opioids.
• Act by binding to opioid receptors in the brain and spinal cord.
• Provide potent analgesia and sedation.
• Can cause respiratory depression and bradycardia.

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)

• Carprofen, meloxicam, and ketoprofen are examples of NSAIDs.
• Inhibit cyclooxygenase (COX) enzymes, reducing the production of prostaglandins.
• Provide analgesia and reduce inflammation.
• Can cause gastrointestinal ulceration and kidney damage.

Tranquilizers and Sedatives

• Acepromazine and benzodiazepines (diazepam, midazolam) are examples of tranquilizers and sedatives.

Acepromazine

• A phenothiazine tranquilizer that blocks dopamine receptors in the brain.
• Provides sedation and reduces anxiety.
• Can cause vasodilation and hypotension.

Benzodiazepines

• Enhance GABA activity, providing sedation, muscle relaxation, and anticonvulsant effects.
• Can cause paradoxical excitation in some animals.

Mechanism of Action: GABA Enhancement

• Many anesthetic agents enhance the effects of GABA, the primary inhibitory neurotransmitter in the brain.
• By enhancing GABA's effects, these agents reduce neuronal excitability and induce anesthesia.
• Barbiturates, propofol, etomidate, and benzodiazepines are examples of drugs that enhance GABA activity.

Mechanism of Action: NMDA Antagonism

• Dissociative anesthetics like ketamine and tiletamine antagonize NMDA receptors.
• NMDA receptors are glutamate receptors involved in neuronal excitation.
• By blocking NMDA receptors, these agents disrupt neuronal communication and produce dissociative anesthesia.

Mechanism of Action: Alpha-2 Adrenergic Agonism

• Alpha-2 agonists like dexmedetomidine and xylazine bind to alpha-2 adrenergic receptors.
• Activation of alpha-2 receptors reduces the release of norepinephrine, leading to sedation, analgesia, and decreased sympathetic tone.
• These receptors are found in the central nervous system and peripheral tissues.

Considerations for Agent Selection

• Patient factors: Age, health status, concurrent diseases, and temperament.
• Procedure-related factors: Duration, invasiveness, and required level of analgesia.
• Drug-related factors: Mechanism of action, route of administration, potential side effects, and interactions with other drugs.
• Availability of monitoring equipment and trained personnel.
• Species-specific considerations: Different species may respond differently to anesthetic agents due to variations in physiology and metabolism.

Monitoring Anesthesia

• Includes monitoring vital signs: Heart rate, respiratory rate, blood pressure, and body temperature.
• Oxygen saturation: Measured using pulse oximetry.
• Capnography: Measures the concentration of carbon dioxide in the patient's exhaled breath.
• Electrocardiography (ECG): Monitors the electrical activity of the heart.
• Reflexes: Assessing palpebral, corneal, and pedal reflexes to gauge anesthetic depth.
• Overall patient appearance: Mucous membrane color, capillary refill time, and muscle tone.

Veterinary anesthetic agents induce loss of sensation and consciousness in animals undergoing medical procedures. Barbiturates enhance GABA effects, while dissociatives antagonize NMDA receptors. These agents differ in their mechanisms of action and effects on organ systems.