Over the last decade, high-flow nasal oxygen therapy (HFN) has emerged as a new method to provide respiratory support in children with moderate to severe bronchiolitis.

However, any randomized clinical trial (RCT) have demonstrated that earlier support with HFN is superior to standard care including low -flow nasal oxygen therapy to reduce the risk of acute respiratory failure requiring non invasive (or tracheal) ventilation and subsequently the need of PICU transfer.

Open label, non-blinded multi-centre, randomised controlled trial comparing standard care including oxygen delivery via HFN versus standard nasal oxygen therapy in infants admitted to hospital with moderate-to-severe bronchiolitis.

Inclusion Criteria:

• first episode of hospitalised bronchiolitis (as defined by American Academy of Pediatrics clinical criterions )
• aged 7 days- 6 months
• transcutaneous SpO2 in room air < 95%
• modified Wood's Clinical Asthma Score (m-WCAS) ≥ 2 et ≤ 5
• agreement of at least one of the parents or legal tutor for his child to participate in biomedical research
• affiliation to social security (beneficiary or entitled), except beneficiary of State medical help

Exclusion Criteria:

• Urgent need for mechanical ventilation support either by nCPAP ou endotracheal route
• Severe form defined by modified Wood's Clinical Asthma Score (mWCAS) exceeding 5 or 6, requiring non invasive ventilation (n CPAP)
• Uncorrected cyanotic heart disease, innate immune deficiency, cranio-facial malformation, congenital stridor, tracheotomy
• Inclusion in other observational study.