Patients had characteristically a history of protracted symptoms and displayed severe compromise of oxygenation compatible with ARDS throughout the study period, which only improved in survivors. At all time points, PaO 2 /FIO 2 differed significantly between survivors and non-survivors, requiring higher FIO 2 and PEEP in this last subgroup. Yet the levels of applied PEEP were only in the intermediate range, similar to mean values of 8.7 cmH 2 O of PEEP in an international study on mechanical ventilation [26] , which may explain the relatively high FIO 2 used in our study. Driving pressures were similar in both subgroups most of the time, suggesting an intention to limit alveolar excursion as part of a protective strategy.