Lect 13

• DRUGS Acting on the Central Nervous System (CNS) Lecture 19: Injectable and Dissociative Anesthetics Anait S Levenson, M.D., Ph.D
• Thiopental is the ultra-short acting barbiturate used for induction and recovery.
• Barbiturates can cause adverse effects such as cardiac arrhythmia, bigeminy, and related to dose and rate of administration.
• Excitements can occur as adverse effects during induction and recovery.
• Pentobarbital is the short-acting barbiturate used for induction and recovery.
• Etomidate is another non-barbiturate used for anesthesia.
• Alphaxalone is a non-barbiturate used for anesthesia.
• Barbiturates have pharmacological effects that include mild sedation to unconsciousness, possible excitement at low doses, cardiac depression, increased cardiac sensitivity to epinephrine, cardiac arrhythmias, decreased respiratory rate and tidal volume, brief apnea, and shallow breaths.
• Propofol is the most commonly used anesthetic in Veterinary Medicine and is safe but expensive.
• Methohexital is a barbiturate with higher lipid solubility that can be useful on an unfasted animal and is used for rapid induction and intubation.
• Pentobarbital is largely replaced by propofol for general anesthesia in rodents.
• Anesthesia is induced by a drug or drug combination that depresses peripherally nervous tissue activity (local and regional) or centrally (general anesthesia).
• Anesthesia can be classified into barbiturates, non-barbiturates, cyclohexylamines (dissociative agents), and inhalant anesthetics.
• Anesthesia can be administered through inhalation, injectable (IM, IV), less common through oral, topical, rectal, and intraperitoneal (i.p.) routes.
• Anesthesia is a reversible process resulting in the total loss of sensation in a body part or the whole body.
• The principal effect of anesthesia can be local or general, sedative and tranquilizers or analgesics, neuromuscular blockers, anticholinergic agents, and reversal agents.
• Injectable agents of anesthesia are mainly used in anesthesia and treatment of seizers.
• General anesthesia (GA) uses intravenous and inhaled agents to allow adequate surgical access to the operative site.
• Injectable agents of anesthesia can produce unconsciousness when given alone, are used with other agents, and mainly don’t provide analgesia or muscle relaxation.
• Injectable agents of anesthesia are administered intravenously, “to effect” (titration method), and depress the CNS at all levels in a dose-dependent manner.
• General anesthesia (GA) is a state where the animal is experiencing unconsciousness, hyporeflexia, analgesia, and skeletal muscle relaxation.
• Propofol is only good for 6 hours.
• Propofol is available in an egg lecithin/glycerin/soybean oil aqueous emulsion, which has poor storage characteristics due to the support of bacterial growth by egg lecithin, glycerol, and soybean oil.
• Propofol causes complete and quick recovery in dogs (20 minutes) and cats (30 minutes), faster than barbiturates.
• Propofol is safe to use in animals with head trauma or increased intracranial pressure.
• Etomidate is a sedative hypnotic non-barbiturate drug of ultra-short duration with high margin of safety.
• Alphaxalone is a GABA A receptor agonist and is used for short procedures, induction of anesthesia, and transition to an inhalant.
• Alphaxalone has adverse effects such as respiratory depression when given with other sedative and anesthetic drugs, and apnea.
• Propofol may not be suitable for prolonged infusion in cats.
• Etomidate shows GABA-like effects and binds to GABA receptor and allosterically enhances the affinity of GABA to its receptor.
• The onset of action of Propofol is 30-60 seconds and the duration of action is 5-10 minutes.
• Propofol is more expensive than ketamine-diazepam or thiopental.
• Propofol is highly lipid soluble, highly protein bound, has rapid onset, re-distribution, and is rapidly metabolized, making it suitable for short procedures or prior inhalant anesthesia.
• Etomidate has other effects such as inhibiting adrenal steroidogenesis, reducing the normal increase in plasma cortisol levels during anesthesia and surgery.
• Alphaxalone is a synthetic neuroactive steroid with rapid, short-acting general anesthetic effects.
• Etomidate decreases cerebral blood flow, metabolic rate, and oxygen consumption, with minimal depression.
• Propofol activates GABA A receptors, similar to barbiturates, and is used in dogs and cats for status epilepticus.
• Alphaxalone is licensed for use in dogs and cats and is used as a constituent of anesthetic drug mixtures.
• Barbiturates can cause apnea, coughing, chest wall spasm, laryngospasm, and bronchospasm.
• Anesthetics include barbiturates, non-barbiturates, dissociative agents, and others.