Injectable Anesthetics

Question 1

therapeutic index

which drugs have high/low TIs?

Answer 1

ketamine-high

alfaxalone >20

etomidate 16

thiopental 5

propofol 3

Question 2

redistribution

Answer 2

• drug goes to brain first after IV administration and is then redistributed to inactive tissues
• return of consciousness is usually dependent on redistribution rate and not elimination rate in most injectable anesthetics

Question 3

continuous infusion of drug

Answer 3

• repeated bolus or CRI
  
  • 1st bolus-redistribution
• can lead to accumulation of drug
• rate of decay depends on elimination rate
• context sensitive half-life

Question 4

context sensitive half-life

Answer 4

amount of time it takes to wake up once CRI is discontinued

or

amount of time for plasma drug concentration to decrease by 50% after CRI discontinued

Question 5

MOA of barbiturates

Answer 5

• interaction with GABA receptor
  
  • opens chloride channel and increases [C] inside cell -> hyperpolarization

Question 6

thiopental

Answer 6

• ultra short-lasting barbiturate with rapid onset
• decreases cerebral blood flow, intracranial pressure, and cerebral metabolic O₂ requirements
• awakening due to redistribution
• long half-life aand context sensitive half-life
  
  • not recommended for repeated bolus
• metabolized by liver through P450 (slowly)
  
  • careful with patients w/ low hepatic function

Question 7

propofol

Answer 7

• short acting non-barbiturate
• MOA: interacts w/ GABA receptor
• recovery due to redistribution
• smooth induction and recovery
• short context sensitive half-life
  
  • good for infusion rate
• fast clearance, possible extra hapatic metabolism
• good for portosystemic shunt patients
• can lead to severe respiratory and cardiac depression

Question 8

complications of propofol and its vehicle

Answer 8

• vehicle: soy bean oil and egg lecithin
  
  • bacterial growth (throw away after 24 hrs)
  • fat embolism
  • high plasma triglyceride

Question 9

complications due to long term use of propofol

Answer 9

• phenolic compound: oxidative injury in cats
• heinz body, methemoglobinemia, diarrhea, anorexia and malaise

Question 10

etomidate

Answer 10

• GABA agonist (CNS depression)
• poorly water soluble
• CV stability is good, even in hypovolemic states
• minimal respiratory depression
• decreased ICP and cerebral O₂ consumption
• metabolized by liver

Question 11

adverse effects of etomidate

Answer 11

• inhibits conversion of cholesterol to glucocorticoids and mineralocorticoids (decreased cortisol…)
  
  • short term = probably ok
  • long term suppression = increased mortality
  • Addisonian crisis

Question 12

ketamine

Answer 12

• dissociative anesthetic
  
  • limbic and thalamocortical systems are dissociated which alters awareness
• non-competitive NDMA antagonist
  
  • prevents binding of excitatory glutamate
  • also acts at opioid and muscarinic receptors
• highly lipid soluble
  
  • good IM absorption, or buccal

Question 13

physiologic effects of ketamine

Answer 13

• direct myocardial depressant effect
• increases sympathetic tone in animals with intact sympathetic drive
  
  • increases CO, BP and HR
• increases muscle tone
  
  • used in conjuction with drugs that promote muscle relaxation (diazepam)
• provides some analgesia

Question 14

alfaxalone

Answer 14

• neurosteroid selective for GABAA
• water soluble
• IV and IM
• does not causes histamine release
• high TI

Question 15

physiologic effects of alfaxalone

Answer 15

• CV: decrease in BP and increase in HR
  
  • good for heart
• good muscle relaxation
• no analgesia