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Chronic respiratory acidosis — SCE Respiratory MCQ

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ModerateRespiratory physiologyChronic respiratory acidosisSCE Respiratory

A 71-year-old man with severe COPD attends clinic after a stable period. ABG on air shows pH 7.37, PaCO2 7.4 kPa, PaO2 7.8 kPa and HCO3− 34 mmol/L. He is alert and has no increase in sputum or wheeze. SpO2 is 91% on air. What is the most likely diagnosis?

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Correct answer: D — Chronic compensated respiratory acidosis

Raised PaCO2 with near-normal pH and elevated bicarbonate indicates chronic compensated respiratory acidosis. Acute hypercapnia would produce a lower pH before renal compensation develops. This pattern is common in advanced COPD and affects oxygen and NIV decisions during exacerbations.

Reference: BTS/ICS acute hypercapnic respiratory failure guideline; ARTP standards