Unit 2- Injectable Anesthetics Flashcards
General Anesthesia Effects
Unconsciousness, hyporeflexia, analgesia, skeletal muscle relaxation
Anesthesia Principal Effect
Local vs general, sedative and tranquilizer vs analgesic, neuromuscular blockers, anticholinergics, reversal agents
Anesthesia Chemistry
Barbiturate, non-barbiturate injectables, dissociative cyclohexylamines, inhalants
Injectable Anesthetic MOA
Unknown, likely not one single receptor
Injectable Anesthetic Uses
Produce unconsciousness alone, used with other agents, do not produce analgesia or muscle relaxation, titration method
Titration Method
IV administration of drug until effect is seen
Barbiturates
Sedative-hypnotic medications used for treatment of seizures, preoperative anxiety, and induction of anesthesia, high lipid solubility
Ultra Short Barbiturates
Induce general anesthesia in dogs, cats, and horses: Thiopental and Methohexital
Short Barbiturates
Induce general anesthesia and treat epilepsy in lab animals: Pentobarbital
Long Acting Barbiturates
Used as anticonvulsant and sedative: Phenobarbital
Oxybarbiturates
Methohexital, phenobarbital, and pentobarbital
Thiobarbiturates
Thiopental and thiamylal are more lipid soluble
Barbiturate MOA
Bind GABA gated Cl- channels and mimic inhibitory effects, cause CNS depression and loss of consciousness
Barbiturate Uses
Rapid anesthetic induction, can be used alone for short procedures
Thiopental Uses
To allow intubation and sustain wit inhalation anesthetic
Methohexital Uses
To allow intubation and sustained with repeated doses or infusion
Pharmacodynamics of Barbiturates
Non ionized, non protein bound, lipid soluble, blood distributes drug
Lipid Solubility of Drugs
Affects ability to penetrate membranes, high solubility results in shorter action and rapid tissue redistribution
Redistribution of Drugs
Distributed fastest to high perfusion tissue, effect occurs with drug in brain, drug leaves tissue when blood level drops, blood carries the drug to other tissues and it is eliminated
Barbiturate Redistribution
Drug given IV, travels to brain, causes unconsciousness, when drug levels in brain are higher than blood, the drug moved back into blood, patient recovers, the drug is released from muscle and fat and metabolized
Barbiturate Pharmacological Effects
Mild sedation to unconsciousness, excitement, cardiac depression, increased sensitivity to epinephrine, decreased respiratory rate, increased GI motility to decreased
Thiopental Pharmacological Effects
Cardiac arrhythmia, brief apnea
Pentobarbital Pharmacologic Effects
Shallow breaths
Barbiturate Adverse Effects
Cardiac arrhythmia, heart skipping a beat, apnea, neonate respiratory depression, exaggerated potency in sighthounds, must be IV
Barbiturate excitement during induction
Perivascular, slow rate of administration, stage II excitement if insufficient concentration in brain to induce stage III, administer more drug
Barbiturate excitement during recovery
Pentobarbital causes paddling and vocalization, administer diazepam or pre anesthetics
Barbiturate Drug Interactions
Enhance muscle relaxants, increase hepatic enzyme activity, enhanced effects when administered with chloramphenicol
Thiopental
Ultra short acting, used in small animal and horses, crystalline powder is reconstituted
Methohexital
Ultra short acting, higher lipid solubility than thiopental, safe in sighthound, used on unfasted animal, powder that is reconstituted
Pentobarbital
Short acting, replaced by propofol, IP to rodents, treatment during status epilepticus, narrow margin of safety, used for euthanasia
Propofol
Ultra short acting, good for outpatient, small animal, small ruminant, exotics, and neonates
Propofol MOA
Activates GABAa receptors
Propofol Use
Status epilepticus, short procedures or prior to inhalant anesthetic, short onset of action and duration, quick recovery, safe in head trauma, cats may not tolerate prolonged, safe in hepatic or kidney disease
Propofol Handling
Poor storage characteristics, aqueous emulsion supports bacterial growth, more expensive
Propofol Pharmacologic Effects
Depression, poor analgesia, euphoria, cardiac depression, transient hypotension, respiratory depression, apnea, twitching, appetite stimulant
Propofol Adverse Effects
Excitement and muscle tremor during induction, movement resembling seizure, transient hypotension, apnea, pain with injection, can cause issues in cats
Etomidate
Sedative hypnotic, used in animals with preexisting cardiac dysfunction, head trauma, or critical illness
Etomidate MOA
Binds GABA receptor and enhances affinity of GABA
Etomidate Adverse Effects
Pain and hemolysis, may inhibit cardiac contractility
Etomidate Pharmacologic Effects
Decreased cerebral blood flow, metabolic rate, and oxygen consumption, minimal cardiac and respiratory depression, reduces plasma cortisol levels
Alphaxalone
Synthetic neuroactive steroid
Alphaxalone MOA
GABAa receptor agonist
Alphaxalone Use
Short procedures, induction of anesthesia, use in dog and cat
