Effects of End-expiratory Positive Pressure Optimization in Intubated Patients With Healthy Lung or Acute Respiratory Distress Syndrome

Inclusion Criteria: * Patient over 18 years of age * ICU patients with healthy lungs or lungs with Acute Respiratory Distress Syndrome (according to Berlin criteria) under mechanically invasive controlled ventilation (intubation or tracheotomy) in the early phase of admission (\< 12h) * Patient deeply sedated (BIS between 30 and 50) and possibly under neuromuscular blocking agents (TOF \< 2/4 at the orbicular) in case of inspiratory efforts * Patient hemodynamically stable with an optimized volemia using a monitoring system (see protocol). * Consent to participate * Patient benefiting from a Social Security Insurance Exclusion Criteria: * Refusal to participate to the proposed study * Obese patient with BMI ≥ 35 kg.cm-2 * Significant hemodynamic instability defined as \> 20% increase in catecholamine doses during the last hour, despite optimization of blood volume according to a pre-established protocol * Contraindication to the use of the electro-impedance tomography technique * Thoracic lesions * Chest bandages * Pace-maker/Implantable defibrillator * Contraindication to the performance of an alveolar recruitment maneuver * Major Emphysema