<prompt> A criterion for the diagnosis of acute respiratory distress syndrome is?PaO2FiO2 400 mm HgPaO2FiO2 200 mm HgPaO2Fi02 300 mm HgPCWP 18 mm Hg  <response>: ARDS is a clinical syndrome of severe dyspnea of rapid onset, hypoxaemia, and diffuse pulmonary infiltrates leading to respiratory failure. The most definitive characteristic of ARDS is the arterial PaO2 in mmHg FiO2inspiratory O2 fraction 200 mmHg, while a PaO2FiO2 between 200 and 300 identifies patients with acute lung injury who are likely to benefit from aggressive therapy. 