Ketamine produces dissociative anaesthesia by its primary action on which receptor system, and which co-administered drug most effectively prevents emergence reactions?

• A GABA-A receptor agonism; droperidol
• B Mu-opioid receptor partial agonism; naloxone
• C NMDA receptor non-competitive antagonism; benzodiazepines ✓
• D Alpha-2 adrenergic receptor agonism; atropine

Explanation

Ketamine's primary anaesthetic mechanism is non-competitive antagonism at the NMDA (N-methyl-D-aspartate) glutamate receptor, binding in the open-channel conformation at the phencyclidine site. It also has opioid, monoaminergic, and muscarinic activity. Emergence reactions (dysphoria, hallucinations, nightmares) occur in up to 30% of adults and are significantly reduced by pre-medication with benzodiazepines (midazolam being most practical). Low-dose ketamine (0.1–0.5 mg/kg IV) is used as an opioid-sparing analgesic adjunct.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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