Lecture 4 8/28/24 Flashcards
What is the goal of anesthetic induction?
transition from a state of consciousness to unconsciousness while minimizing undesirable effects
What are the benefits of injectable induction?
-smooth transition
-no waste gas
What is the disadvantage of injectable induction?
cannot be immediately controlled or eliminated once administered
What are the two main ways that injectable induction agents work?
-GABA binds to receptor, allowing Cl- to enter and hyperpolarize cell to inactivate it
-glutamate is inhibited so that sodium cannot enter the cell, preventing an action potential
What are the primary uses of benzodiazepines?
-sedation
-amnesia
-muscle relaxation
Which drugs fall into the benzodiazepines category?
-midazolam
-diazepam
-zolazepam
What are the characteristics of midazolam?
-water soluble
-can be given IM, SQ, IV
-mixes well with other drugs
-does not adhere to syringe
-does not cause precipitants
What are the characteristics of diazepam?
-lipid soluble
-given IV only
-mixes only with ketamine
What are the CNS effects caused by benzodiazepines?
-decreased cerebral metabolic rate
-decreased cerebral blood flow
-decreased intracranial pressure
-anti-convulsant
-mild, patient-dependent sedation
What are the cardiovascular and respiratory effects caused by benzodiazepines?
minimal CV and resp. effects
What are the GI effects caused by benzos?
-appetite stimulant in cats
-causes hepatic failure after PO admin. in cats
In which patients are benzos a good pre-medication selection?
-debilitated small animals and small ruminants (ASA 3-5)
-neonates
-geriatrics
Why are benzos only used along with a dissociative drug for induction in healthy adult patients?
they lead to excitement when used alone
What is the mechanism of action for propofol?
potentiates GABA
What is the main use of propofol?
-rapid, smooth induction
-unconsciousness
-immobility
-muscle relaxation
What are the characteristics of propofol?
-formulated in lipid emulsion
-not shelf stable
-used for CRIs; do not want the side effects of the preservative in the shelf stable version
What are the characteristics of propofol 28?
-stable for 28 days
-benzyl alcohol preservative
What are the physiologic characteristics of propofol?
-short duration of action
-must be given IV
-narrow therapeutic index/possible to overdose
-mainly hepatic metabolism
-extra-hepatic metabolism possible, allowing for safe use in patients with liver failure
What are the CNS effects associated with propofol?
-decreased cerebral metabolic rate
-decreased cerebral blood flow
-anti-convulsant
-decreased intracranial and intraocular pressures
What are the resp. effects associated with propofol?
-resp. depression
-apnea
What measures should be taken to ensure proper resp. support when using propofol?
-pre-oxygenate
-avoid use if intubation and ventilation is not feasible
What are the cardiovascular effects associated with propofol?
vasodilation and hypotension with no compensatory increase in heart rate
What are the other potential effects of propofol?
-occasional pain on injection
-rapidly metabolized by fetus
-heinz body anemia and hemolysis in cats
-vomiting in cats
What are the clinical uses of propofol?
-induction of anesthesia
-partial intravenous anesthesia
-total intravenous anesthesia
What is the mechanism of action for alfaxalone?
GABA agonist
What is the main use of alfaxalone?
-unconsciousness
-immobility
-muscle relaxation
What are the physiologic characteristics of alfaxalone?
-IV or IM administration
-rapid induction
-short duration around 10 minutes
-hepatic metabolism
What are the CNS effects associated with alfaxalone?
-decreased cerebral metabolic rate
-decreased cerebral blood flow
-decreased intracranial and intraocular pressures
-myoclonus
What are the cardiovascular effects associated with alfaxalone?
dose-dependent vasodilation and decreased contractility in sick patients
What are the respiratory effects associated with alfaxalone?
dose-dependent apnea and cyanosis
What are the clinical uses of alfaxalone?
-IM sedation
-induction of anesthesia
-PIVA
-TIVA
What is the mechanism of action for etomidate?
potentiates GABA
What are the main uses of etomidate?
-unconsciousness
-immobility
Why must etomidate be combined with a benzo?
because etomidate does not induce adequate muscle relaxation
Why is it important that etomidate is formulated in propylene glycol?
-causes pain on injection
-can cause hemolysis with large doses or if used for infusion
What are the physiologic characteristics of etomidate?
-IV admin. only
-rapid and rough induction
-short duration
What are the resp. effects associated with etomidate?
resp. depression and possible apnea
Why is etomidate useful?
it has nearly no cardiovascular effects and is therefore safe for patients with CV disease
What are the CNS effects associated with etomidate?
-decreased cerebral metabolic oxygen rate
-decreased cerebral blood flow
-decreased intracranial pressure
-myoclonus possible
Why is it important that etomidate causes immunosuppression and decreased cortisol production?
-should not be used for CRIs or repeat injections
-should be avoided in Addison’s patients
What are the characteristics of etomidate clinical use?
-for use in patients with clinically significant cardiac disease
-not for routine patients
-not for CRIs
-combined with a benzo to provide muscle relaxation and smoother induction
Which drugs fall into the dissociative category?
-PCP derivatives
-ketamine
-tiletamine formulated with zolazepam (telazol)
Why are dissociatives combined with benzos?
dissociatives do not achieve muscle relaxation on their own
What is the main use of dissociatives?
-dissociation of thalamus and limbic system to produce a cataleptoid state
-unconsciousness
-analgesia
What is the mechanism of action for dissociatives?
NMDA antagonist
What are the characteristics of dissociative use for analgesia?
-work through NMDA antagonism and opioid receptor interactions
-adjunct agent as a CRI
-causes hyperalgesia good for chronic pain and neuropathic pain
How can dissociatives be administered?
-IV
-IM
-SQ
-OTM
What are the CV effects associated with dissociatives?
-increased sympathetic output
-tachycardia
-hypertension
-increased cardiac output
Which cardiac disease patients should not receive dissociatives?
those with hypertrophic cardiomyopathy
What are the resp. effects associated with dissociatives?
-apneustic breathing/inhaling and holding breath
-bronchodilation
-laryngeal reflexes maintained
What are the CNS effects associated with dissociatives?
-increased cerebral metabolic rate
-increased cerebral blood flow
-increased intracranial pressure
What are the clinical uses of ketamine?
-IM for heavy sedation/immobilization
-induction of anesthesia
-PIVA
-TIVA
What are the characteristics of telazol clinical use?
-duration of action around 30 minutes
-expensive but used in small volumes
-used in fractious animals/zoo animals
What is the use of guafenesin?
disrupts nerve impulse transmission in the CNS to cause muscle relaxation
What are the adverse effects of guafenesin?
-hypotension
-resp. depression
-necrosis if administered peri-vascularly
-thrombophlebitis
What are the clinical uses of guafenesin?
-equine induction
-TIVA and PIVA
