Which intravenous anaesthetic agent produces 'dissociative anaesthesia' characterised by profound analgesia, amnesia, and cataleptic state without loss of airway reflexes, and what is its primary mechanism?

• A Propofol — enhances GABA-A receptor chloride conductance causing cortical depression
• B Midazolam — positive allosteric modulation of GABA-A receptors causing anxiolysis and amnesia
• C Dexmedetomidine — alpha-2 agonism in the locus coeruleus mimicking natural sleep with preserved airway
• D Ketamine — non-competitive antagonism of NMDA receptors blocking glutamate excitatory transmission ✓

Explanation

Ketamine produces a unique 'dissociative' state — eyes open, nystagmus, cataleptic posture, profound analgesia and amnesia — by non-competitive blockade of NMDA (N-methyl-D-aspartate) receptors, interrupting thalamocortical and limbic activation while preserving brainstem function. This explains preserved pharyngeal/laryngeal reflexes and respiratory drive (though aspiration risk is still present). Additional mechanisms include mu/kappa opioid receptor agonism (analgesic), sigma receptor binding (emergence phenomena), and monoamine reuptake inhibition (bronchodilation, sympathomimetic cardiovascular effects).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.