Diagnostic criteria o PaO2/fiO2 <300 (ARDS if 200 o Bilateral alveolar or interstitial infiltrates o PCWP<18 mmHg, or no clinical evidence of Increase left atrium pressure PaO2/fiO2<300 (ARDS if < 200)  Bilateral alveolar or interstitial infiltrates  PCWP < 18 mmHg, or no clinical evidence of increase left atrium pressure