**2. Severe ARDS according to Berlin definition**

According to the recent Berlin definition, severe acute respiratory distress syndrome is defined by bilateral pulmonary infiltrates of recent onset (less than 1 week) in a patient that have a PaO<sup>2</sup> / FIO<sup>2</sup> equal or less than 100 with a positive end-expiratory pressure equal or more 5 cm H<sup>2</sup> O with no evidence of cardiac failure or hypervolemia. The patient also needs to present a risk factor for ARDS development as respiratory infection, gastric content aspiration, lungs contusion, blood products transfusion, sepsis, high-risk trauma, high-risk surgery, shock, and pancreatitis [1–4].
