A criterion for diagnosis of acute respiratory distress syndrome is?

ARDS is a clinical syndrome of severe dyspnoea of rapid onset,hypoxaemia,and diffuse pulmonary infiltrates leading to respiratory failure.The most definitive characteristic of ARDS is the aerial Po2 (in mmHg)/FIo2(inspiratory O2 fraction) <200 mmHg,while a Pao2/FIo2 between 200 and 300 identifies patients with acute lung injury who are likely to benefit from aggressive therapy. Reference:Harrison's Medicine-20th edition,page no:2032