High-flow (HF) oxygen therapy is being used increasingly in infants with bronchiolitis, despite lack of convincing evidence of its superiority over low flow (LF). We aimed to compare the effect of HF to LF in moderate to severe bronchiolitis.

Multicentre randomised controlled trial during four winter seasons (2016–2020) including 107 children under 2 years of age admitted with moderate to severe bronchiolitis, oxygen saturation of <92% and severely impaired vital signs. Crossovers were not allowed. HF was administered at flow rates of 2 L/kg for the first 10 kg, plus 0.5 L/kg for every kg >10 kg, LF with a maximum flow rate of 3 L/min. Primary outcome was improvement of vital signs and dyspnoea severity within 24 hours assessed by a composite score. Secondary outcomes were comfort, duration of oxygen therapy, supplemental feedings, hospitalisation duration and intensive care admission for invasive ventilation.

Significant improvement within 24 hours occurred in 73% of 55 patients randomised to HF and in 78% of 52 patients with LF (difference 6%, 95% CI −13% to 23%). Intention-to-treat analysis revealed no significant differences in any secondary outcome: duration of oxygen therapy, supplemental feedings, hospitalisation and need for invasive ventilation or intensive care admission, except for comfort (face, legs, activity, cry, consolability), which was one point (out of a scale of 0–10) higher in the LF group. No adverse effects occurred.

We found no measurable clinically relevant benefit in the use of HF compared with LF in hypoxic children with moderate to severe bronchiolitis.

NCT02913040.