Study interventions
POSITIVE
In the preventive strategy (HFNC-OIn the control group (COT ± late NIV), COT was initially administered from nasal cannula or high concentration oxygen mask, according to the oxygen supply needed to achieve a SpOIn both strategies, NIV was delivered with an ICU ventilator through the best tolerated interface (nasal mask, face mask or helmet if available). Pressure support was titrated to achieve an expired tidal volume of 7 to 10 ml/kg of predicted body weight with a respiratory rate < 25/min. Positive end expiratory pressure (PEEP) was initially set at 5 cmHDuring the first 48 h, patient’s tolerance and blood gas analysis (PaOThe summary figure of the protocol is resumed in Additional file 