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Volatile CO2 Response 50% at 1 MAC — FRCA Primary MCQ

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ModeratePharmacology - Inhalational AgentsVolatile CO2 Response 50% at 1 MACFRCA Primary

Volatile agents cause dose-dependent respiratory depression. At 1 MAC the ventilatory response to CO2 is:

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Correct answer: C — Reduced by approximately 50% with a rightward shift of the response curve

At 1 MAC the slope of the CO2 ventilatory response curve is reduced by approximately 50% and shifted rightward (higher PaCO2 threshold for ventilatory response). At 1.5-2 MAC the response is nearly abolished. This is why spontaneously breathing patients under volatile anaesthesia develop a dose-dependent rise in PaCO2.

Reference: Peck Hill Williams 2014 Pharmacology for Anaesthesia and Intensive Care