tive end-expiratory pressure. Thus, we are not sure about the validity of these results without an ultrasound Doppler cardiac evaluation, as it cannot be excluded that some patients present de novo acute heart failure due to septic cardiac dysfunction . Second, as stated by the authors, during mechanical ventilation with PEEP Ppao may not reflect left cardiac filling pressure . Indeed, even if correct position of the catheter tip in West's zone III is confirmed after insertion using method previously described  or chest radiography, the matching of lung perfusion to ventilation may change from the initial location in patients with ALI and ARDS. Thus we may expect that misleading interpretation of Ppao during positive pressure ventilation could have influenced the results of this multicentric study. Finally, even if we agree with the authors that mandating Ppao of 18 mmHg or less may negatively impact clinical trials in which ARDS is in inclusion/exclusion criteria or an end-point, we believe that a more extensive definition in future may also be less precise than the mandatory actual combination.