Patients were randomly assigned to receive high-flow nasal oxygen therapy delivered continuously through a nasal cannula ( flow , 50 L/min ; fraction of inspired oxygen [ FiO2 ] , 50 % ) ( n = 414 ) or BiPAP delivered with a full-face mask for at least 4 hours per day ( pressure support level , 8 cm H2O ; positive end-expiratory pressure , 4 cm H2O ; FiO2 , 50 % ) ( n = 416 ) .