Anaes Vivas · Intravenous induction agents
Data viva — thiopental and the GABA-A receptor
A Primary/Final data viva — interpret the GABA-A receptor diagram contrasting barbiturate (duration) and benzodiazepine (frequency) binding. Explain the chloride-channel hyperpolarisation mechanism, the direct channel opening at high barbiturate concentrations, the redistribution-driven rapid onset and recovery, the steeply rising context-sensitive half-time that rules out maintenance infusion, the CMRO2 reduction and neuroprotection (burst suppression), the obstetric RSI rationale, and the absolute porphyria contraindication.
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A diagram of the GABA-A ligand-gated chloride channel shows two distinct modulatory binding sites side by side. At the barbiturate site the diagram indicates an increase in the DURATION of channel opening — each chloride burst is held open for longer. At the benzodiazepine site the diagram indicates an increase in the FREQUENCY of opening — there are more numerous, shorter bursts. Both increase the total chloride influx and hyperpolarise the neuron. Identify the receptor and the two binding sites, explain the kinetic difference, and relate it to the pharmacology and clinical use of thiopental.
References4ShowHide
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- [42244827]Bersten AD, Soni N (eds) Oh's Intensive Care Manual. 8th edition, Elsevier, 2018.