What is A criterion for the diagnosis of acute respiratory distress syndrome is? and explain in detail?
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) / 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.