Chronic Hypercapnic Respiratory Failure — RACP Adult Medicine MCQ

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ModerateRespiratoryChronic Hypercapnic Respiratory FailureRACP Adult Medicine

A 55-year-old man with severe COPD (FEV1 28% predicted) develops progressive hypoxaemia. ABG shows PaO₂ 48 mmHg, PaCO₂ 58 mmHg, pH 7.37, HCO₃ 33 mmol/L on room air. He is breathless at rest. What does the compensated respiratory acidosis indicate?

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Correct answer: C — Chronic stable hypercapnic respiratory failure

The pH is within normal range despite elevated PaCO₂, indicating chronic compensation with elevated HCO₃ (metabolic compensation). This represents chronic stable hypercapnic respiratory failure rather than an acute exacerbation (which would show acidosis). This patient meets criteria for LTOT (PaO₂ ≤55 mmHg) and should also be assessed for domiciliary NIV for chronic hypercapnia, particularly if there are recurrent hospitalisations with acute-on-chronic respiratory failure (HOT-HMV trial).

Reference: Lung Foundation Australia/TSANZ – 2025 – COPD-X Plan; TSANZ – 2024 – Domiciliary NIV Guidelines