To my knowledge, the successful clinical use of heliox was first published in anecdotal reports in the 1930s for the treatment of patients with severe asthma and upper airway obstruction.2–4 Between the 1930s and the 1990s, there are few published accounts of heliox use for status asthmaticus.1 Since 1990, numerous investigators have examined the utility of heliox for acute airflow obstruction, leading to the current meta-analysis showing no outcome benefits of this intervention. Nonetheless, the review points out that heliox can improve some physiologic variables (ie, peak flow and pulsus paradoxus) of patients with status asthmaticus.,5–6 Thus, there are both theoretical and empiric data to suggest that heliox might be useful. In fact, in our study,5 heliox was associated with a 30% reduction in pulsus paradoxus, which is thought to reflect the work of breathing in patients with acute asthma. Why does that not translate to an observable difference in outcomes? The reason may be that most patients with acute asthma (ie, more than two thirds) get better without it.,7–8 In my opinion, the correct experiment has not been performed yet. If we hypothesize that heliox reduces the rate of intubation of all patients with acute asthma from 1 to 0.2%, then one needs 654 patients (to demonstrate this fivefold reduction in intubation) at a power of 80%. Even if 5% of all patients are intubated (which is more than the number in most published series), 116 patients are required to demonstrate a fivefold difference at an 80% power. No study has been powered sufficiently to answer the question. It is not the right question anyway. Why use heliox on the two thirds of asthmatic patients who get better after three back-to-back aerosol treatments? What we really need to know is whether heliox can be used to reduce the need for intubation in those patients with the worst exacerbations. Thus, it is premature to conclude that heliox cannot be used to reduce the rate of intubation of patients with severe asthma.