Supportive care remains the mainstay of therapy in bronchiolitis. Earlier studies suggest that helium-oxygen therapy may be beneficial, but evidence is limited. We aimed to compare efficacy of 2 treatment gases, Heliox and Airox (21% oxygen + 79% helium or nitrogen, respectively), on length of hospital treatment for bronchiolitis.


This was a multicenter randomized blinded controlled trial of 319 bronchiolitic infant subjects randomly assigned to either gas; 281 subjects completed the study (140 Heliox, 141 Airox), whose data was analyzed. Treatment was delivered via facemask (nasal cannula, if the facemask intolerant) ± continuous positive airway pressure (CPAP). Severe bronchiolitics received CPAP from the start. Primary end point was length of treatment (LoT) required to alleviate hypoxia and respiratory distress. Secondary end-points were proportion of subjects needing CPAP; CPAP (LoT); and change in respiratory distress score.


Analysis by intention to treat (all subjects); median LoT (inter-quartile range, days): Heliox 1.90 (1.08–3.17), Airox 1.87 (1.11–3.34), P = .41. Facemask tolerant subgroup: Heliox 1.46 (0.85–1.95), Airox 2.01 (0.93–2.86), P = .03. Nasal cannula subgroup: Heliox 2.51 (1.21–4.32), Airox 2.81 (1.45–4.78), P = .53. Subgroup started on CPAP: Heliox 1.55 (1.38–2.01), Airox 2.26 (1.84–2.73), P = .02. Proportion of subjects needing CPAP: Heliox 17%, Airox 19%, O.R. 0.87 (0.47–1.60), P = .76. Heliox reduced respiratory distress score after 8 hours (mixed models estimate, −0.1298; P < .001). The effect was greater for facemask compared with nasal cannula (mixed models estimate, 0.093; P = .04).


Heliox therapy does not reduce LoT unless given via a tight-fitting facemask or CPAP. Nasal cannula heliox therapy is ineffective.

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