Heliox

Overview
Heliox is a breathing gas that is composed of a mixture of helium (He) and oxygen (O2).

Heliox has been used in a medical context since the 1930s, and although the medical community adopted its use initially to alleviate the symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, most of which are dependent on the low density of the gas. Heliox is also used in saturation diving and sometimes during the deep phase of technical dives.

Medical uses
In medicine, "heliox" generally describes a mixture that is 21% O2 (the same as air) and 79% He, although other mixtures are available.

Airway resistance is dictated by the diameter of the airways and by the density of the inspired gas. Therefore when nitrogen (of air) is replaced by helium, airway resistance is reduced due to the lower density of the inspired gas. This means that when one breathes Heliox, airway resistance is less, and therefore the mechanical energy required to ventilate the lungs, or the Work of Breathing (WOB) is decreased. Heliox is used mainly in the alleviation of many medical conditions that involve a decrease in airway diameter (and consequently increased airway resistance), such as upper airway obstruction, asthma, chronic obstructive pulmonary disease (COPD), bronchiolitis and croup. Patients with these conditions may suffer a range of symptoms including dyspnea (breathlessness), hypoxemia (below-normal oxygen content in the arterial blood) and eventually a weakening of the respiratory muscles due to exhaustion, which can lead to respiratory failure and require intubation and mechanical ventilation - Heliox may reduce all these effects, making it easier for the patient to breathe, and as it will reduce work of breathing, Heliox can help to prevent this respiratory failure. Heliox has also found utility in the weaning of patients off mechanical ventilation, and in the nebulization of inhalable drugs.

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