Helium
Helium is an inert gas which is used to reduce the specific gravity of inhaled gas mixtures. It is typically provided as a 0.79/0.21 Helium-Oxygen (Heliox) mixture (though other dilutions exist).
| Helium | Heliox (0.79/0.21) | Oxygen | |
|---|---|---|---|
| Specific Gravity (as compared to air) | 0.18 | 0.34 | 1.09 |
Reduced specific gravity results in a proportional reduction in Reynolds Number, improving laminar flow within the airways.
| Property | Action |
|---|---|
| Class | Inert Gas |
| Uses | Obstructive lung disease, deep water diving |
| Presentation | Clear, colourless solution |
| Route of Administration | Inhaled |
| Dosing | Typically as Heliox: 79% He/21% O2 |
| Absorption | Diffusion across the alveolar capillary membrane in proportion to membrane area and partial pressure gradient, and inversely proportional to membrane thickness |
| Distribution | Distributes proportionally to solubility and tissue partial pressures |
| Metabolism | Not metabolised |
| Elimination | Respiratory exhalation along a pressure gradient |
| Resp | Significantly decreases the specific gravity of inhaled gas mixtures |
| Toxic Effects | High Pressure Neurologic Syndrome at >16 atm |
References
- RAH Advanced Diving Medicine Course Notes: Chapter 6 Oxygen and Carbon Dioxide Toxicity