skip to main content

Heliox Density Effect — FRCA Primary MCQ

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

ModeratePhysics & Clinical MeasurementHeliox Density EffectFRCA Primary

Heliox reduces work of breathing in upper airway obstruction because helium:

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

Reveal the answer and explanation

Correct answer: A — Has lower density than nitrogen reducing turbulent flow resistance

Helium (density 0.18 g/L) is much less dense than nitrogen (1.25 g/L). In turbulent flow resistance is density-dependent so substituting helium reduces turbulent resistance. In laminar flow resistance depends on viscosity and helium is slightly more viscous than nitrogen so there is no benefit in small airways.

Reference: Al-Shaikh Stacey 2019 Essentials of Anaesthetic Equipment