Injectable Anesthetics

Question 1

Thiopental

Answer 1

• MOA: GABA-A agonist (at benzodiazepine site)
• No analgesia
• Uses: muscle relaxation
• AE:
  
  • CV: vasodilation and hypotension, compensatory HR incr
  • Resp: dose dep resp depression, suppression of central ventilatory centers
  • Neuro: decr cerebral metab rate and ICP
    
    • Induces hepatic microsomes enzymes
    • fetal depression > propofol -
  • Sight hounds = particularly sensitive to this/barbiturates

Question 2

Propofol

Answer 2

• MOA: GABA-A agonist; maybe NMDA antagonist (glycine receptors)
• Debated analgesic effect due to interaction w/ other receptors
• Uses: Muscle relaxation - myoclonic movements (twitching)
• AE:
  
  • ​CV: vasodilation and neg inotropic effects, decr BP, no comp incr or effect on conduction
  • Resp: dose dep resp depression; post-induction cyanosis + apnea possible
  • Neuro: decr cerebral met rate and ICP
  • Propofol Infusion Syndrome: Severe metabolic acidosis after prolonged infusions (>24hr)
• SAFE in liver dz patients

Question 3

Alfaxalone

Answer 3

• MOA: GABA-A agonist
• Uses: premed, anesthetic (esp. cats/exotics)
• No analgesia!!
• AE:
  
  • CV: dose dep depression and hypotension (safe at low doses) -more likely to be used w/ heart issues
  • Resp: dose dep depression; apnea possible
  • Neuro: decr cereb metab rate and ICP
  • Suitable for puppies/kittens <12wks
    
    • May see twitching/paddling in recovery (decr scores for horses)

Question 4

What is the Triad of Anesthesia?

Answer 4

1. Muscle relaxation
2. Analgesia
3. Unconsciousness

Cannot be accomplished with a single agent!

Question 5

Etomidate

Answer 5

• MOA: GABA-A agonist
• No analgesic effect!
• Uses: muscle relaxation for cardiac dz patients
• AE: inductions not very smooth: myoclonus, swallowing/gagging - usually co-administered w/ benzodiazepine (midazolam)
  
  • Used for CV EFFECTS!!- min HR changes, SV, vasc tone
  • Resp: min resp depr unless rapid bolus
  • Neuro: decr cerebral metab rate and ICP
  • Endocrine effects - causes decr adrenocortical activity < 24hr after bolus (supp exogenous steroids)

Question 6

Ketamine

Answer 6

• MOA: NMDA antagonist (Ketamine)
  
  • Exert anesthetic action by “dissociating” higher thalamo-cortical brain centers from the lower, limbic/brainstem structure
• Analegic effect: due to NMDA antagonism- occurs at SUB-ANESTHETIC DOSES!; poor visceral analgesic, good for neuropathic pain
• AE:
  
  • ​CV: sympathomimetic effect of ketamine> incr HR, contractility, vasoconstriction; BP incr - contraindicated w/ HCM!
  • Resp: not much vent depr unless rapid bolus
  • Neuro: incr cereb metab rate and ICP when given ALONE
    
    • may attenuate w/ GABA agonist
    • fetal depr during C sections
    • Emergence delirium and rough recoveries - may require sedation

**Metabolized hepatically -active metabolite = Norketamine produced - excreted UNCHANGED in cats (AVOID in blocked patients)

Question 7

Telazol (Tiletamine)

Answer 7

• NOT sold by itself, but formulated w/ benzodiazepine -zolazepam
• MOA: NMDA antagonist + GABA-A agonist (at benzodiazepine site)
  • Exert anesthetic action by “dissociating” higher thalamo-cortical brain centers from the lower, limbic/brainstem structure
• Uses: in aggressive/feral animals: reliable restraint, anesthetic; used in patients w/ hepatic/renal dz
• Analegic effect! due to NMDA antagonism- occurs at SUB-ANESTHETIC DOSES!; poor visceral analgesic, good for neuropathic pain
• AE:
  
  • ​CV: sympathomimetic effect of ketamine> incr HR, contractility, vasoconstriction; BP incr - contraindicated w/ HCM!
  • Resp: not much vent depr unless rapid bolus
  • Neuro: incr cereb metab rate and ICP when given ALONE, may attenuate w/ GABA agonist
    
    • fetal depr during C sections
    • Emergence delirium and rough recoveries - may require sedation
      • In cats: benzo outlasts dissociative, may see sedation
      • In dogs: dissociative outlasts benzo - see dissociative emergence effects (dysphoria) -
      • In pigs: usually smooth recovery
      • Horses: additional sedation needed for recovery

Question 8

Recovery of consciousness is due to what?

Answer 8

redistribution of the anesthetic in the tissues