Pressure volume curves were calculated with ventilator's built in application (Draeger Evita XL, Draeger Medical AG, Lubeck Germany) starting from a PEEP level of 5 cm H 2 O, with a pressure limit of 40. Ventilation parameters were set on the basis of this calculation, with a PEEP of 2 cmH 2 O above the lower inflection point of the pressure-volume curve, and a peek pressure below the upper inflection point. In all cases, pressure plateau was limited to 30 cmH 2 O and the tidal volume was kept below 6 ml/Kg [6] . Recruitment manoeuvres (40 sec at 40 cmH 2 O) were performed twice a day, if needed, to improve pulmonary gas exchange. Cannulation was conducted percutaneously with Seldinger technique in all cases, and cannulas position was confirmed by transesophageal echocardiography.