Ketamine produces dissociative anaesthesia primarily by acting at which receptor, and which feature of its pharmacology explains the unique preservation of laryngeal reflexes?

• A GABA-A agonism; reflexes preserved due to cortical sparing
• B Opioid receptor agonism; reflexes preserved because respiratory drive is unaffected
• C Alpha-2 adrenoceptor agonism; reflexes preserved because sympathetic tone is augmented
• D NMDA receptor antagonism (non-competitive); reflexes preserved because of maintained pharyngeal muscle tone unlike propofol ✓

Explanation

Ketamine is a non-competitive antagonist at the NMDA (N-methyl-D-aspartate) receptor, blocking the ion channel when it is open. Unlike propofol or benzodiazepines, ketamine does not suppress pharyngeal and laryngeal reflexes to the same degree because it dissociates thalamocortical from limbic systems without fully abolishing brainstem protective mechanisms. However, the reflexes are not fully intact — aspiration can still occur — so airway management precautions still apply during ketamine sedation.

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

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