Heliox: Airway resistance

Heliox (70% helium, 30% oxygen) therefore affects gas flow in two ways – first, the Reynold’s number is lower (because density is lower), and thus flow is more likely to be laminar, and second, if flow IS turbulent, resistance to flow will be lower, becuase Heliox is less dense (~ 0.5 g/L versus 1.2 5g/L).

Note that in laminar flow, Heliox offers no advantages, as it has approximately the same viscosity as air. Also note that Heliox is ~ 70% helium, thus the potential benefit of improved gas flow must be balanced by the knowledge that a lower FiO2 may be delivered

Heliox: Summary

• ~ 70% helium, ~ 30% oxygen
• Significantly less dense than air (0.5 vs 1.2 5g/L), but viscosity is about the same
• Improves gas flow by lowering Reynold’s number (converting to laminar flow) or decreasing resistance when flow is turbulent (lower density)