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Oxygen-induced hypercapnia — RCPSC IM MCQ

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ModerateRespirologyOxygen-induced hypercapniaRCPSC IM

A 62-year-old man with severe COPD is admitted with worsening dyspnoea and somnolence after receiving high-flow oxygen in the ambulance. ABG on FiO2 0.60 shows pH 7.24, PaCO2 78 mm Hg, PaO2 132 mm Hg, bicarbonate 31 mmol/L. Chest radiograph shows hyperinflation without pneumothorax. What is the most likely cause?

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Correct answer: C — Oxygen-induced worsening of hypercapnia

Excess oxygen in severe COPD can worsen hypercapnia through V/Q mismatch, Haldane effect, and reduced hypoxic drive contribution. Controlled oxygen and ventilatory support are needed.

Reference: Canadian Thoracic Society COPD guidance