pharm: general anaesthesia

Question 1

Describe the stepwise operation procedure.

Answer 1

Pre-assessment → Induction (usually involves anaesthetic adjuvants for fast onset) → Maintenance → Reversal → Post-Op Care

Question 2

Characteristics of an ideal GA?

Answer 2

Suppress all sensations:
Analgesia, Muscle relaxation
Unconsciousness, Amnesia (unawareness)

Brief and pleasant
Depth of anaesthesia can be raised or lowered with ease
Minimal adverse effects
Large margin of safety

** Need a combination of GAs to achieve all the desired effects!!

Question 3

What are the possible modes of administration of GA?

Answer 3

IV, Inhalation

Question 4

List the types of GA administered by inhalation.

Answer 4

Gases: Nitrous Oxide
Volatile liquids: Halothane, Enflurane, Desflurane, Isoflurane, Sevoflurane

Question 5

What is MAC & what is it indicative of?

Answer 5

Minimum Alveolar Concentration.
Min conc of drug in alveolar air that will produce immobility in 50% of pts exposed to a painful stimulus .
Low MAC = high anaesthetic potency

Question 6

How are inhalation GAs eliminated?

Answer 6

Almost entirely through expired air.

Question 7

Describe the proposed mechanism of action of inhalation GAs.

Answer 7

1. GAs enhance neurotransmission at inhibitory synapses
   - via allosterically increasing GABA receptor sensitivity to action by GABA itself (positive allosteric modulator)
2. GAs depress neurotransmission at excitatory synapses
   - via blocking glutamate neurotransmitter acting on NMDA receptor, preventing NMDA receptor activation (negative allosteric modulator)

Question 8

State the principle adverse effects of GA.

Answer 8

Depression of respiratory & cardiac performance.

Question 9

How is Nitrous Oxide different from other inhalation GAs?

Answer 9

1. Very high MAC, hence very low anaesthetic potency → cannot be used alone to produce GA
2. High analgesic potency → frequently combined with other gases to supplement their analgesic effects

Question 10

How is induction of anaesthesia usually accomplished?

Answer 10

Using a short-acting barbiturate (sedative-hypnotic medication)
eg thiopentone (anticonvulsant)

Question 11

What is dissociative anaesthesia and which GA causes it?

Answer 11

An altered stage of consciousness where the pt is conscious but feels detached from the environment.
Caused by IV Ketamine.

Question 12

What are the advantages of using inhalation GA and IV GA together?

Answer 12

1. Lower dosage of inhalation GA required, which is good cos it takes a longer time to recover from an inhalation GA rather than an IV GA.
2. Production of effects that cannot be achieved with inhalation alone.

Question 13

Relationship of solubility of GA and onset of GA?

Answer 13

The higher the blood solubility, the slower the onset of the GA.

Question 14

List examples of IV GAs.

Answer 14

Thiopentone (Sodium thiopental)
Propofol
Ketamine

Question 15

List examples of anaesthetic adjuvants.

Answer 15

Midazolam (IV) — Benzodiazepine
Dexmedetominide (IV) — alpha 2 adrenergic agonist
COXIBs, paracetamol — NSAIDs
Fentanyl, morphine — Opioids
Succinylcholine — Neuromuscular blocker