Helium is a low-density inert gas whose physical properties are very different from those of
nitrogen and
oxygen. Such properties could be clinically useful in the adult
critical care setting, especially in patients with upper to more distal
airway obstruction requiring moderate to intermediate levels of FiO2. However, despite decades of utilization and reporting, it is still difficult to give any firm clinical recommendation in this setting. Numerous case reports are available in the context of upper
airway obstruction of different origins, but there is a lack of controlled studies for this indication. One study reported a
helium-induced beneficial effect on surrogates of work of breathing after extubation in non-
COPD patients, possibly in relation to laryngeal consequences of tracheal intubation. Physiological benefits of
helium-
oxygen breathing have been demonstrated in the context of acute severe
asthma, but there is a lack of large controlled studies demonstrating an effect on pertinent clinical endpoints, except for a study reported only as an abstract, which mentioned a reduction in the intubation rate in
helium-treated patients. Finally, there are a number of physiological studies in the context of COLD-
COPD patients demonstrating a beneficial effect, mainly by a reduction in the resistive inspiratory work of breathing but also by a reduction in hyperinflation. Reduction of
hypercapnia was mainly observed in spontaneously breathing and noninvasively ventilated
helium-treated patients but not in intubated patients during controlled ventilation, suggesting that the decrease in PaCO2 was mainly in relation to a diminution in CO2 production, related to the diminution in work of breathing and not an improved alveolar ventilation. Moreover, there is little evidence that
helium-
oxygen could improve parameters of heterogeneity in such patients. Two RCTs were unable to demonstrate a reduction in the intubation rate in such setting, but they were likely underpowered. An adequately powered international multicentric study is ongoing and will help to determinate the exact place of the
helium-
oxygen mixture in the future. The place of the mixture during the weaning period will deserve further evaluation.