- ARDS according to Berlin definition:Hypoxemia defined with PaO2 FiO2 ratio less or equal to 300 mmHg with Positive End Expiratory Pressure higher or equal to 5 cmH20, Less than seven days between a known clinical insult or new or worsening of respiratory symptoms, Bilateral opacities on chest Imaging not fully explained by effusions, lobar or lung collapse, or nodules, Respiratory failure not fully explained by cardiac failure or fluid overload