General Anesthetics (save pharmaco)

Question 1

What is:

1. halothane
2. enflurane
3. sevoflurane
4. nitrous oxide
5. propofol

Answer 1

Halothane - inhalation anesthetic, volatile liquid
Enflurane - inhalation anesthetic, volatile liquid
Sevoflurane - inhalation anesthetic, volatile liquid
Nitrous oxide - inhalation anesthetic, gaseous
Propofol - intravenous anesthetic

Question 2

Proposed MOA of GA

Answer 2

• exciting inhibitory neurotransmitters by allosterically modifying the GABA receptor, increasing its sensitivity to GABA molecules
• NMDA receptor antagonism

Question 3

MAC (sort from highest to lowest)

Answer 3

1. nitrous oxide
2. sevoflurane
3. enflurane
4. halothane

Question 4

Blood solubility (sort from highest to lowest)

Answer 4

1. halothane
2. enflurane
3. sevoflurane
4. nitrous oxide

Question 5

Metabolism of halothane, enflurane

Answer 5

Halothane - hepatotoxic

Enflurane - nephrotoxic

Question 6

Halothane characteristics

Answer 6

• medium rate of onset of action
• volatile, non-flammable, non-reacting
• bradycardia and hypotension due to decreased cardiac output and BP
• halothane-induced hepatitis
• little or no analgesia until unconsciousness supervenes.

Question 7

Sevoflurane

Answer 7

• more rapid rate of onset of action

- metabolised in the liver to reduce inorganic fluoride, which is also nephrotoxic

Question 8

Nitrous oxide

Answer 8

• high MAC, less potency
• non-flammable
• nitrous oxide alone gives analgesia and amnesia but not complete unconsciousness or surgical anesthesia
• used alone as analgesic agent

Question 9

Propofol

Answer 9

• the most common IV anesthetic in Singapore
• induction rate is similar to thiopentone, and recovery is rapid
• rapid onset
• extensively used in day surgery
• significant cardiovascular effect (negative inotropic) - hypotension

Question 10

Ketamine

Answer 10

• racemic (potency: S- > R+)
• dissociative anesthesia
• rapid induction
• large Vd, rapid clearance -> suitable for continuous infusion without lengthening the duration of action.
• risk of psychologic adverse reactions may be reduced with the premedication of diazepam or midazolam

Question 11

remifentanil

Answer 11

• NSAID
• only NSAID with ultra-short onset of action (other NSAIDS have intermediate onset of action)
• most NSAIDS are metabolised in liver, remifentail is hydrolysed by tissue and plasma.