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Intrapulmonary shunt — SCE Respiratory MCQ

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HardRespiratory physiologyIntrapulmonary shuntSCE Respiratory

A 40-year-old woman has severe hypoxaemia after an episode of pancreatitis. On 15 L/min oxygen, PaO2 rises from 7.0 to 8.1 kPa and chest radiograph shows bilateral alveolar infiltrates. Echocardiography shows no intracardiac shunt and there is no pulmonary embolism. She is tachypnoeic with reduced lung compliance. What is the most likely underlying cause?

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Correct answer: E — Intrapulmonary shunt from alveolar flooding

Minimal improvement in PaO2 with high inspired oxygen suggests shunt, here due to alveolar flooding in acute lung injury. Diffusion limitation and V/Q mismatch usually improve more with supplemental oxygen. Understanding oxygen response helps distinguish mechanisms of hypoxaemia at the bedside.

Reference: ERS/ATS respiratory physiology standards; Faculty of Intensive Care Medicine ARDS guidance