Anaes Vivas · Intravenous induction agents
Data viva — the NMDA open-channel block versus the GABA-A allosteric site
A data viva contrasting the two mechanistic families of intravenous induction agent — ketamine as the non-competitive NMDA open-channel (use-dependent) blocker, versus the GABA-A positive allosteric modulators (propofol, thiopental). The clinical consequences: dissociative state versus smooth sleep, analgesia versus no analgesia, bronchodilation versus neutral or bronchoconstrictor, sympathomimetic pressor versus hypotension, and the antidepressant mechanism of esketamine via synaptic plasticity.
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A side-by-side schematic shows two ligand-gated ion channels. On the left, the NMDA receptor: glutamate and glycine are bound, the channel is open, and a ketamine molecule is plugging the open pore from inside the channel — a use-dependent open-channel block that stops the calcium and sodium influx. On the right, the GABA-A receptor: propofol or thiopental is bound at an allosteric site on the outside of the channel, increasing the frequency or the duration of chloride channel opening, with chloride influx into the neuron. Interpret the two mechanisms and their clinical consequences.
References3ShowHide
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