Chemical information

E939; Helio; Hélium.
He = 4.002602.
CAS — 7440-59-7.
ATC — V03AN03.
ATC Vet — QV03AN03.


In Eur. and US.

Ph. Eur. 6.2

(Helium). A colourless, inert gas. Store as a compressed gas or liquid at cryogenic temperatures, in appropriate containers.

USP 31

(Helium). A colourless, odourless, tasteless gas which is not combustible and does not support combustion. Very slightly soluble in water. Store in cylinders.


As helium is less dense than nitrogen, breathing a mixture of 80% helium and 20% oxygen requires less effort than breathing air. Thus mixtures containing various concentrations of oxygen (‘Heliox’) have been used in patients with respiratory disorders. Due to the low solubility of helium, mixtures of helium and oxygen are used by divers or others working under high pressure to prevent the development of decompression sickness (caisson disease); they are preferred to compressed air as they do not cause nitrogen narcosis. Helium has been used in pulmonary function testing. Breathing helium increases vocal pitch and causes voice distortion. Cerebral artery gas embolism has been reported after inhalation of helium from a pressurised container.
1. Rodrigo GJ, et al. Use of helium-oxygen mixtures in the treatment of acute asthma: a systematic review. Chest 2003; 123: 891–6
2. Colebourn CL, et al. Use of helium-oxygen mixture in adult patients presenting with exacerbations of asthma and chronic obstructive pulmonary disease: a systematic review. Anaesthesia 2007; 62: 34–42
3. Harris PD, Barnes R. The uses of helium and xenon in current clinical practice. Anaesthesia 2008; 63: 284–93.
Published October 16, 2018.