Ketamine produces dissociative anaesthesia by acting as a non-competitive antagonist at which receptor, and what unique haemodynamic profile does this produce?

• A GABA-A receptor; cardiac depression with hypotension
• B Nicotinic acetylcholine receptor; bradycardia and hypertension
• C NMDA receptor; sympathomimetic tachycardia and hypertension ✓
• D Mu-opioid receptor; respiratory depression with mild tachycardia

Explanation

Ketamine blocks the NMDA (N-methyl-D-aspartate) receptor in an open-channel, non-competitive fashion. It stimulates central sympathetic outflow, causing increased heart rate, systemic blood pressure, cardiac output, and myocardial oxygen demand — making it useful in haemodynamically compromised patients. The intrinsic myocardial depressant effect is usually masked by sympathetic stimulation; in catecholamine-depleted patients (e.g., septic shock), myocardial depression may be unmasked. This makes it the agent of choice for induction in hypovolaemia and bronchospasm.

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

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