Clinical Pharmacology of Anesthetics Flashcards
what are the injectable anesthetics used in vet med (5)
- propofol
- steroid anesthetics: alfaxalone
- barbiturates: thiopentone, pentobarbitone
- imidazole derivatives: etomidate
- dissociative agents: ketamine, tiletamine (+ zolazepam = zoletil)
what is the onset of propofol
rapid
what is the duration of propofol
short duration IV anesthetic
what is the structure of propofol
hindered phenol
what is the mechanism of propofol
potentiates GABA
what is the formulation of propofol
oil in water emulsion
soyabean oil, egg lecithin & glycerol
what is the route of administration of propofol
IV
what are the pharmacokinetics of propofol
highly protein bound
rapid metabolism in liver + lungs, kidneys, blood?
what is the recovery from propofol initially from
due to redistribution
do cats or dogs have a more rapid metabolism of propofol
slower in cats because less able to conjugate with glucuronide –> avoid IV infusions
what are the effects of propofol on the CNS (3)
- rapid loss of consciousness (~5 min)
- reduced intracranial pressure (ICP)
- anticonvulsant action
what are the effects of propofol on the CVS (2)
- vasodilation & transient fall in BP
- mild myocardial depression at high doses
what are the effects of propofol on respiratory system
- post-induction apnea
- occasional cyanosis at induction
what other effects can propofol have
- pain on injection?
- occasional muscle twitching/hypertonus
- heinz body anemia in cats (oxidative damage to RBCs)
what is propofol licensed for
IV admin in dogs and cats
what are the uses of propofol
what is propofol use cautioned in (3)
- shocked/hypovolemic patients
- cats with hepatic dysfunction
- cats requiring repeat anesthetics
what are the 2 formulations of propofol
- preservative free: in use shelf life 6 hours
- with preservative: propofol plus with benzyl alcohol
what is the propofol with preservatives contraindicated for
prolonged infusion (>30 mins)
dont give >24mg/kg per anesthetic
what is the structure of alfaxalone
steroid anesthetic
what is the mechanism of alfaxalone
potentiates GABA
what is the formulation of alfaxalone
solubilized in cyclodextrin
some have preservatives
what is alfaxalone
rapid onset, short duration injectable anesthetic with high therapeutic index
what are the admin routes for alfaxalone
IV (IM & SC)
how is the protein binding of alfaxalone vs propofol
lower protein binding
what is the recovery from alfaxalone initially due to
redistribution
how is alfaxalone metabolized
liver
is alfaxalone suitable for TIVA in dogs and cats
yes
what are the effects of alfaxalone on CNS
rapid loss of consciousness
what are the effects of alfaxalone on the CVS
mild hypotension at clinical doses, primarily due to vasodilation
what are the effects of alfaxalone on respiratory system
post-induction apnea (less frequent compared to propofol)
how is the recovery from alfaxalone
can be poor quality, esp if limited/poor premedication
what is the clinical use of alfaxalone
- admin IV to induce anesthesia
- admin IV (intermittent bolus or continuous infusion) to maintain anethesia in dogs & cats
- IM/SC for sedation (not authorized, large volume of injection)
what is ketamine
dissociative anesthetic and analgesic
what is the mechanism of ketamine
NMDA receptor antagonist
what is the formulation of ketamine
acidic pH
what are the pharmacokinetics of ketamine
rapid hepatic metabolism
what are the routes of admin of ketamine
IV, IM, SC
which species is TIVA ketamine suitable for
horses
what effects do dissociative anesthesia ketamine cause (5)
- sensory loss with analgesia
- increased muscle tone
- eyes open +/- slow nystagmus
- active relfexes including laryngeal/pharyngeal reflexes
- less profound CVS & resp depression
what are the effects of ketamine on the CNS (4)
- loss of consciousness with analgesia
- increased ICP
- convulsions in dogs/horses (esp if used as sole agent)
- hallucinations/emergence delirium
what are the effects ketamine has on the musculoskeletal system
increased muscle tone
what are the effects ketamine has on the CVS
- in vitro direct -ve inotropic effect
- in vivo increased sympathetic tone –> increased HR, contractility, CO & BP
what are the effects of ketamine on the respiratory system (2)
- transient apnea possible with IV admin (ventilation usually well maintained when given by SC or IM)
- laryngeal and pharyngeal relfexes maintained?
what are the clinical uses of ketamine (3)
- to induce anesthesia in dogs, cats, horses + combine with benzodiazepams & injected IV
- to induce anesthesia & maintain anesthesia (~30 mins) in dogs and cats + a2 agonist and butorphanol & injected IM (“triple combo”)
- to provide analgesia in dogs and cats (lower dose IM or IV)
what are the cautions of ketamine (3)
- elavated intracranial pressure
- history of seizures
- pre-existing tachycardia
when might you use TIVA
- where inhalational agents not available
- where airway cannot be shared (bronchoscopy, some airway surgeries)
what are examples of TIVA in dogs
propofol or alfaxalone are suitable
poor reflex suppression so can combine with analgesics
what are TIVA examples in cats
only alfaxalone suitable
what are examples of TIVA in horses
triple drip
alpha2 agonist plus GGE plus ketamine
field anesthesia
how do you select the right agent
little to chose between propofol, alfaxalone
when would ketamine be used
- IM anesthesia required –> aggressive patient, no IV access, no facilities for delivering inhaled agents
- hemodynamic instability is present
what would reduce CVS depression in cases with hemodynamic instability
co-induction
how is anesthesia maintained
- TIVA or IM triple combo
- inhalational agents
what are the advantages of inhalational anesthetic agents
delivery/elimination depends on ventilation –> rapid adjustment of anesthetic depth
what are the disdvantages of inhalational anesthetic agents (2)
- equipment required: ET tube, carrier gas, vaporizer, breathing system
- environmental pollution
what are inhalational agents
- isoflurane
- sevoflurane
what is the minimum alveolar concentration
steady state minimum alveolar concentration of anesthetic required to prevent gross purposeful movement in response to noxious stimulation in 50% of test subjects
compares the potency of different inhaled anesthetics
which is more potent isoflurane or sevoflurane
sevoflurane more potent (higher MAC)
what is the oil:gas partition coefficient
measure lipid solubility
high oil:gas PC confers high potency
what is the blood:gas partition coefficient
measures solubility in the blood
low blood solubility confers to rapid onset, recovery & rate of change of anesthetic depth
which has a higher blood:gas coefficient between isoflurane and sevoflurane
isoflurane
how are inhalational agents metabolized and eliminated
exhalation
liver metabolism
can produce toxic metabolites
compare the differences of isoflurane and sevoflurane (MAC, oil:gas, blood:gas coefficient, metabolism)
what are the effects of isoflurane and sevoflurane on the CVS (2)
- hypotension: CO maintained (except deep plane) and peripheral vascular resistance falls
- no sensitization to catecholamines
what are the effects of isoflurane and sevoflurane on the resp system
- depression: reduced rate
sevo causes less depression
what are the effects of desoflurane on CVS and resp rate
CVS: rapid increases in inspired concentration can increase heart rate and arterial BP (catecholamines)
resp: high inspired concentration can cause airway irritation
which agents have the highest onset
isoflurane > sevoflurane > desflurane
which agents can be used for mask induction
sevoflurane is the only one that has a pleasant odour
which agent has the least airway irritation
desflurane > isoflurane > sevoflurane
compare the authorization, potency, rate of change of depth, mask induction, metabolism and cost of isoflurane, sevoflurane, desflurane
what is nitrous oxide
weak anesthetic and weak analgesic
