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Obesity hypoventilation syndrome — RCPSC IM MCQ

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HardRespirologyObesity hypoventilation syndromeRCPSC IM

A 49-year-old with BMI 48 kg/m² has morning headaches, awake oxygen saturation 88%, PaCO2 58 mmHg, bicarbonate 34 mmol/L and near-normal spirometry. What diagnosis best explains the chronic gas-exchange abnormality?

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Correct answer: E — Obesity hypoventilation syndrome after excluding other causes of alveolar hypoventilation

The best answer is “Obesity hypoventilation syndrome after excluding other causes of alveolar hypoventilation”. Obesity plus awake daytime hypercapnia and chronic bicarbonate compensation, without obstructive or neuromuscular explanation, defines obesity hypoventilation syndrome. Pulmonary vascular disorders usually cause hypocapnia, asthma is not supported by spirometry, and diabetes insipidus does not cause ventilatory failure.

Reference: Canadian Thoracic Society, sleep-disordered breathing resources: https://cts-sct.ca/guideline-library/