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HPV Shunt Reduction — FRCA Primary MCQ

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HardPhysiology - RespiratoryHPV Shunt ReductionFRCA Primary

During one-lung ventilation, hypoxic pulmonary vasoconstriction reduces perfusion of the non-ventilated lung by approximately what proportion of its pre-collapse blood flow?

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Correct answer: C — 50%, substantially reducing shunt through the hypoxic lung

The best answer is “50%, substantially reducing shunt through the hypoxic lung”. Hypoxic pulmonary vasoconstriction decreases blood flow to a hypoxic, non-ventilated lung by approximately 50%, reducing rather than abolishing shunt. Its effectiveness is modified by cardiac output, pulmonary vascular tone, volatile anaesthetic concentration, acid–base state and surgical factors. It is incorrect to describe the percentage as diversion of total cardiac output.

Reference: Royal College of Anaesthetists, Primary FRCA Syllabus 2021: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf