Acute Respiratory Distress Syndrome (ARDS) is an acute inflammatory lung injury associated with a high pulmonary vascular permeability, leading to acute respiratory failure. Positive pressure mechanical ventilation,improves survival but might lead to ventilator-induced lung injury (VILI) and right ventricular failure. This hemodynamic effect is more important when compliance is decreased, especially in ARDS.~The use of long protective ventilation (with low tidal volumes and low plateau pressures) has improved prognosis of ARDS in adult patients. However, tidal volume and plateau pressures do not always reflect the lung deformation and the stress induced by the ventilation; these variables depend on the characteristics of the patient's respiratory system. Therefore, management focuses on ventilation strategies according to these characteristics.~Among tools used to evaluate respiratory physiological parameters, the esophageal pressure measurement is easily feasible at the bedside, and well estimates pleural pressure and pulmonary distension. During invasive ventilation, transpulmonary pressure (PL) can be obtained with the difference between the airway pressure and the esophageal pressure. Calculation of transpulmonary pressure in ARDS allows optimal ventilator management of adult and children treated for ARDS.~Although individualized ventilation techniques have shown some benefits in ARDS, studies have failed to show that survival could be improved by such strategies. This lack of efficacy could be partly explained by the hemodynamic impact of ventilation-induced pulmonary distension. It therefore seems essential to combine a robust assessment of right ventricular function with measurements of transpulmonary pressure in order to know the real hemodynamic impact of positive pressure ventilation in ARDS in adults and children.~The primary objective is to test the impact of transpulmonary pressure on right ventricular functionin ARDS adults and children.~Secondary objectives are :~i) to compare thresholds of transpulmonary pressure associated to 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.
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.