BACKGROUND: Viral bronchiolitis is the leading cause of hospitalization in children during the first 12 months of life. There is evidence to support the use of noninvasive ventilation in bronchiolitis. A recent respiratory management of bronchiolitis is the use of high-flow nasal cannula (HFNC) therapy. The primary objective of this study was to evaluate the use of HFNC as the first-line treatment for children with severe bronchiolitis and the secondary objective was to identify factors for HFNC therapy failure. METHODS: Observational prospective study in a pediatric intensive care unit (PICU), during two consecutive seasons (2013-2014 without recommendation and 2014-2015 with a study design suggesting HFNC as first-line treatment). The percentages of children treated with HFNC, nasal continuous or biphasic positive airway pressure (nCPAP/BiPAP) and invasive ventilation were compared. Associations between parameters recorded and HFCN therapy failure were established. RESULTS: The percentage of patients treated with HFNC at admission was higher during the second season (90%, n=55/61) than the first season (34%, n=14/41) (p<0.0001). In bivariate analysis, heart rate, pH, and pCO22 CONCLUSIONS: In our PICU, HFNC therapy for children with bronchiolitis can potentially decrease the use of nCPAP. In this study, the factor of failure was higher pCO22