Respiratory quotient calculation — FRCA Primary MCQ

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ModeratePhysiologyRespiratory quotient calculationFRCA Primary

A patient has respiratory quotient measured during indirect calorimetry in critical care. Oxygen consumption is 250 mL min-1 and carbon dioxide production is 200 mL min-1. What is the respiratory quotient?

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Correct answer: D — 0.6

Respiratory quotient is carbon dioxide production divided by oxygen consumption, so 200/250 = 0.8. The common error is to invert the ratio and obtain 1.25. An RQ around 0.8 is typical for a mixed substrate diet. The value can help interpret metabolic state and adequacy of nutritional support.

Reference: RCoA Primary FRCA Syllabus 2026; Ganong's Review of Medical Physiology; West's Respiratory Physiology