To determine the prevalence of main inspiratory asynchrony events during non-invasive intermittent positive-pressure ventilation (NIV) for severe bronchiolitis. Ventilator response time and asynchrony were compared in neurally adjusted ventilator assist (NAVA) and in pressure assist/control (PAC) modes. Methods This prospective physiological study was performed in a university hospital's paediatric intensive care unit and included 11 children (aged 35.2?±?23 days) with respiratory syncytial virus bronchiolitis with failure of nCPAP. Patients received NIV for 2?hr in PAC mode followed by 2?hr in NAVA mode. Electrical activity of the diaphragm and pressure curves were recorded for 10?min. Trigger delay, main asynchronies (auto-triggering, double triggering, or non-triggered breaths) were analyzed, and the asynchrony index was calculated for each period. Results The asynchrony index was lower during NAVA than during PAC (3?±?3% vs. 38?±?21%, P?