skip to main content

Heliox and turbulent airway flow — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

HardPhysics and Clinical MeasurementHeliox and turbulent airway flowFRCA Primary

A patient with a tracheal tube is ventilated with helium-oxygen for severe airflow obstruction. Which physical property of helium is most helpful?

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

Reveal the answer and explanation

Correct answer: E — High viscosity reducing laminar resistance

Helium has low density, which reduces turbulent flow resistance and may improve ventilation through narrowed airways. Laminar flow resistance depends more on viscosity, and helium's advantage is mainly in turbulent or transitional flow. Low density reduces, not increases, Reynolds number. The pearl is that heliox is most useful when turbulent flow contributes substantially to resistance.

Reference: RCoA Primary FRCA Syllabus 2026; Davis and Kenny Basic Physics and Measurement in Anaesthesia