skip to main content

Carbon dioxide rise during apnoea — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

EasyPhysiologyCarbon dioxide rise during apnoeaFRCA Primary

A preoxygenated patient becomes apnoeic after induction. Oxygen saturation remains high initially, but PaCO2 rises steadily. Which process best explains the rising PaCO2?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Oxygen uptake from alveoli into blood

During apnoea, tissue metabolism continues to generate carbon dioxide while alveolar ventilation is absent, so PaCO2 rises. Oxygen uptake explains falling alveolar oxygen, not the CO2 rise. Preoxygenation delays desaturation but does not remove CO2 production. The pearl is that apnoeic oxygenation can maintain oxygenation but does not provide ventilation.

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