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Pulmonary embolism dead space — FRCA Primary MCQ

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ModeratePhysiologyPulmonary embolism dead spaceFRCA Primary

A ventilated patient with pulmonary embolism develops a large PaCO2 to ETCO2 gradient. What is the most likely explanation?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: EVentilation of poorly perfused alveoli increases dead space

Pulmonary embolism produces alveolar dead space. Pain and temperature ascend in the spinothalamic tract is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Chronic hypertension shifts cerebral autoregulation right is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. High oxygen consumption and low FRC shorten safe apnoea time is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Hypocapnia causes cerebral vasoconstriction is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. In Primary FRCA physiology, the correct answer is usually the variable that best explains the observed change in the anaesthetised patient.

Reference: West's Respiratory Physiology; Ganong Review of Medical Physiology; Primary FRCA textbooks