Early Spontaneous Breathing in Acute Respiratory Distress Syndrome

Inclusion Criteria: * Within 1 week of a known clinical insult or new or worsening respiratory symptoms * Intubation and mechanical ventilation * Bilateral opacities - not fully explained by effusions, lobar/lung collapse, or nodules lung * Report PaO2 / FiO2 ≤ 200 mmHg with a PEP of at least 5 cmH2O * Respiratory failure not fully explained by cardiac failure or fluid overload * Criteria 1, 2 and 3 presents jointly for less than 48 hours * Consent to participate obtained either from the patient himself or from a relative. Exclusion Criteria: * Age \< 18 years * Pregnancy * Predictable duration of the mechanical ventilation on endotracheal tube lower than 48 hours * Patient being in period of exclusion further to the participation in another biomedical study * intracranial hypertension (suspected or confirmed) * known or suspected COPD * Chronic respiratory failure treated by long-term oxygen and / or long-term respiratory support * Morbid obesity defined as weight greater than 1 kg / cm * Sickle Cell Disease * Marrow recent transplant, post-chemotherapy aplasia * Widened burns (\> 30% body surface area) * Severe hepatic cirrhosis (Child-Pugh C) * Pneumothorax (drained or not) * Treatment with extracorporeal support (ECMO) * Decision of active therapeutic limitation * Unavailability of the model of respirator that must be used in the study * Failure to obtain a consent by persons authorized to do so. * Patient under law protection. * Person non-beneficiary of a social security system