Heliox
| Heliox | |
|---|---|
| Intervention | |
| ICD-9-CM | 93.98 |
Heliox is a breathing gas composed of a mixture of helium (He) and oxygen (O2).
Heliox is a medical treatment for patients with difficulty breathing. The mixture generates less resistance than atmospheric air when passing through the airways of the lungs, and thus requires less effort by a patient to breathe in and out of the lungs.
Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of the low density of the gas. Heliox is also used in saturation diving and sometimes during the deep phase of technical dives.
In medicine heliox may refer to a mixture of 21% O2 (the same as air) and 79% He, although other combinations are available (70/30 and 60/40).
Heliox generates less airway resistance than air and thereby requires less mechanical energy to ventilate the lungs. "Work of Breathing" (WOB) is reduced. It does this by two mechanisms:
Heliox has a similar viscosity to air but a significantly lower density (0.5 g/l versus 1.25 g/l at STP). Flow of gas through the airway comprises laminar flow, transitional flow and turbulent flow. The tendency for each type of flow is described by the Reynolds number. Heliox's low density produces a lower Reynolds number and hence higher probability of laminar flow for any given airway. Laminar flow tends to generate less resistance than turbulent flow.
In the small airways where flow is laminar, resistance is proportional to gas viscosity and is not related to density and so heliox has little effect. The Hagen–Poiseuille equation describes laminar resistance. In the large airways where flow is turbulent, resistance is proportional to density, so heliox has a significant effect.
Heliox has been used medically since the early 1930s. It was the mainstay of treatment in acute asthma before the advent of bronchodilators. Currently, heliox is mainly used in conditions of large airway narrowing (upper airway obstruction from tumors or foreign bodies and vocal cord dysfunction). There is also some use of heliox in conditions of the medium airways (croup, asthma and chronic obstructive pulmonary disease).
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