Patients were randomized to be treated for four days Venturi mask at a FiO2 of 0.4 (control) or with oxygen at a FiO2 of 0.4 plus a CPAP of 10 cm H2O (CPAP). At the end of the 4-days period, patients passed a screening test breathing ambient air. Patients returned to the assigned treatment if SaO2 less than 95% a.a or respiratory rate more than 25 bpm.CPAP was generated using a flow generator with an adjustable inspiratory oxygen fraction set to deliver a flow of up to 140 liters per minute (Whisperflow, Caradyne, Ireland) and a spring-loaded expiratory pressure valve (Vital Signs Inc, Totoma NJ) and applied using a latex-free polyvinyl chloride transparent helmet (CaStar, Starmed, Italy) (15); all centers measured the inspiratory oxygen fraction using an oxygen analyzer (Oxicheck, Caradyne, Ireland) through the Venturi mask or the helmet.