The recruitment strategy in Acute respiratory distress syndrome (ARDS) patients mechanically ventilated combines recruitment maneuvers and positive end expiratory pressure (PEEP). Recruitment maneuvers promote alveolar recruitment leading to increased end-expiratory lung volume in order to prevent repetitive opening and closing of unstable lung units and reduce the strain induced by ventilation. In addition, recruitment is effective in improving oxygenation. Variety of recruitment maneuver have been described, the most commonly used is the application of sustained continuous positive airway pressure at 40 cmH2O for 40 seconds. Staircase recruitment maneuver (SRM) is an alternative with good hemodynamic tolerance. Staircase recruitment maneuver (SRM) involves a progressive increase in positive end expiratory pressure (PEEP) (up to 40 cmH2O), in pressure control ventilation, in order to increase end-expiratory lung volume (EELV); then a decreasing PEEP trial is performed. The positive end expiratory pressure (PEEP) to prevent alveolar collapse depends on ratio between lung elastance and chest wall elastance. If chest wall elastance is high, the PEEP to obtain a positive end-expiratory transpulmonary pressure is high. The only way for the time being to know the transpulmonary pressure and the ratio between lung and chest wall elastance is the use of esophageal catheter. A non-invasive method for measuring the lung elastance by measuring volume recruited during a change of pressure (∆PEEP/∆EELV) could be used to avoid the use of esophageal catheter.

Inclusion Criteria:

Early onset (less than 24 hours)moderate or severe Acute respiratory distress syndrome (ARDS) according to Berlin Definition

Mechanical ventilation for less than 72 hours

Exclusion Criteria:

Bronchopleural fistula, Emphysema, Pneumothorax, Antecedent of pneumothorax, Increase intracranial pressure, Pulmonary arterial hypertension with right heart failure, Hemodynamic instability with mean arterial pressure < 65 mmHg, Pregnancy.