IV General Anesthetics Flashcards
T/F general anesthetics produce unconsciousness and inhibit pain signal propagation
F; they produce unconsciousness but do not inhibit pain signal propagation
why do we administer an analgesic with a general anesthetic
to stop pain signal generation from stimulating the RAS to the point that the patient wakes up
how and why do we reduce the dose of induction anesthetic
using premedication (opioids, benzodiazepines); to reduce the incidence of agent-specific adverse effects
what are the 4 stages/planes of anesthesia that a patient passes through during induction
1) stage of analgesia
2) stage of excitement
3) stage of surgical anesthesia
4) stage of medullary depression (AVOID)
why is it better to induce with an injectible vs inhalant
inducing with an inhalant is pretty slow, so healthy patients will experience a prolonged stage of excitement and struggle; in contrast inducing with an injectable is quick so the excitement phase is essentially bypassed
T/F we do not induce healthy animals with inhalants
T
what routes can we give propofol
IV only
what is the duration of propofol
2-8 min, often only 30s for full anesthetic effect
what is propofol used for
induction or very short sx procedures
T/F propofol is associated with a bad recovery
F; very smooth
what is propofol MoA
slows the dissociation of GABA from its receptor -> Cl flow into channel -> inhibition of APs
how is propofol metabolized
redistributes from CNS to fat and muscle; hepatic metabolism as well as extrahepatic (lung, kidney) metabolism
what are some pros of propofol
1) smooth induction (and can top up for > 5 min without accumulation as well as titrate to effect without excitation
2) rapid smooth recovery (20 min)
3) can be administered as a CRI
what are the CVS effects of propofol (2)
depresses myocardial contractility and causes peripheral vasodilation -> get dose-dependent drop in BP
with propofol, the degree of hypotension is worse with ________
rapid injection
propofol should be used with caution in:
hypotensive patients, those with myocardial disease, geriatrics
what are the respiratory effects of propofol
inhibits in a dose-dependent manner; may see transient cyanosis; apnea for 30-60s if you give a bolus
what is a blood consideration with propofol and what species is especially prone
damages Hb -> Heinz bodies; cats prone
what is the contamination risk with propofol
many hospitals use multi-dose propofol vials, which can become contaminated and lead to wound infection
how long should you use multi-dose propofol vials for and what is the catch?
28 days; need to sterilize with alcohol for up to 60 seconds
some single and multi-dose vials of propofol contain __________, which is toxic to cats
benzyl alcohol (however, they do not appear to cause toxicity in the concentrations and quantities involved in induction - cannot use for a CRI)
what are some other adverse effects of propofol
1) pain
2) anorexia
3) diarrhea
4) myoclonus in dogs
5) toxicity in cats (daily doses for more than 2-3 days causes accumulation)
6) excitement if used alone in horses
ketamine produces a dream-like state of pseudo-consciousness known as
dissociative anesthesia
what does dissociative anesthesia associated with sole ketamine use look like
- intense muscle rigidity
- eyes open
- hear normally
- swallow reflex intact
- hallucinogenic
how do we use ketamine while avoiding dissociative anesthesia
by administering pre- or co-medications
what is ketamine’s MoA
blocks NMDA receptors; also blocks opioid and GABA receptors, which causes CNS overstimulation and CVS effects
ketamine produces ______________ if unpremedicated and ______________ if premedicated
hyperthermia; hypothermia
T/F patients induced with ketamine may move in response to pain
T
what are the CV effects of ketamine
increases RR and HR (due to CNS stimulation)
what are some other effects of ketamine
- can precipitate seizures
- can cause excitement in dogs if used alone
- very rough recovery if used alone
how do we give ketamine in small animals for:
- heavy sedation or GA in cats
- induction
- heavy sedation or GA in cats: ketamine IM + an opioid, alpha-2 or benzodiazepine
- induction: ketamine IV + diazepam
how is ketamine used for induction in large animals
ketamine + xylazine
alfaxalone is a __________ __________
neuroactive steroid
what is alfaxalone’s MoA
facilitates GABA
what do we use alfaxalone for
induction
what is special about administration and effect of alfaxalone
greater effect when administered slowly
how does the induction and recovery of alfaxalone differ from propofol
both have smooth induction and fast recovery, but alfaxalone can induce a rough recovery if used alone
what are the CVS effects of alfaxalone
BP may fall only slightly with little or no change in HR or contractility
what does rapid injection of alfaxalone do to the CVS
faster drop in BP, may see reflex increase in HR
if administered as a bolus, what are the respiratory effects of alfaxalone vs propofol
longer apnea with alfaxalone (100s in dogs, 60s in cats)
this is longer than with propofol
T/F as with propofol, alfaxalone contains nutrients that support bacterial growth, so re-use of single vials is not recommended
T
what is the MoA of barbiturates
inhibit the dissociation of GABA from its receptor
why do barbiturates have a low therapeutic index
1) slow hepatic metabolism by p450 enzymes
2) more intense depression
what are the 2 clinical uses of barbiturates today
1) euthanasia
2) to stop a seizure when diazepam fails
what barbiturate is used for euthanasia
pentobarbital sodium
what are the 2 reasons why you should ALWAYS place a catheter before giving pentobarbital
1) excitement if less than half the calculated dose given (do not want to lose vein)
2) convulsions if accidentally injected into carotid
what are the 6 steps for euthanasia with pentobarbital
1) sedate animal
2) place IV catheter
3) flush catheter
4) induce with propofol
5) give 1.5x dose of pentobarbital
6) confirm death
what is the post-mortem indication of barbiturate overdose
spleen enlarged 4-5 fold
what is the euthanasia drug used by humane societies, since no license is required
T-61
