Impact of the Transpulmonary Pressure on Right Ventricle Function in Acute Respiratory Distress Syndrome

Pulmonary distension induced by mechanical ventilation physiologically alters right ventricle pre and after-load, hence might lead to right ventricle failure. The hypothesis is that in Acute Respiratory Distress Syndrome, the occurence of a right ventricle failure under lung protective ventilation might : i) be correlated to the transpulmonary pressure level, ii) lead to global heart failure, iii) and extremely result in poor outcome and death. The primary objective is to test the impact of transpulmonary pressure on right ventricular function in Acute Respiratory Distress Syndrome in adults and children. Secondary objectives are : i) to compare thresholds of transpulmonary pressure associated with right ventricle failure between children and adults. ii) to assess if there is an association between transpulmonary pressure and morbidity and mortality. \- For pediatric patients, a specific monitoring with electrical impedance tomography (EIT) will allow: * To assess if the transpulmonary pressure is associated with the level of regional pulmonary overdistention (or collapse) on electrical impedance tomography.(EIT) * To assess if there is an association between the occurrence of right ventricular failure, and distribution of ventilation on EIT.