SEvoflurane for Sedation in ARds

Inclusion Criteria: * Age ≥18 years * Presence for ≤24 hours of all of the following conditions, within one week of a clinical insult or new or worsening respiratory symptoms: * PaO2/FiO2 \<150 mmHg with positive end-expiratory pressure (PEEP) ≥8 cmH2O (or, if arterial blood gas not available, SpO2/FiO2 that is equivalent to a PaO2/FiO2 \<150 mmHg with PEEP ≥8 cmH2O and a confirmatory SpO2/FiO2 between 1-6 hours after the initial SpO2/FiO2 determination) * Bilateral opacities not fully explained by effusions, lobar/lung collapse, or nodules * Respiratory failure not fully explained by cardiac failure or fluid overload; need objective assessment (e.g., echocardiography) to exclude hydrostatic edema if no risk factor present Exclusion Criteria: * Absence of affiliation to the French Sociale security * Patient under a tutelage measure or placed under judicial protection * Continuous sedation with inhaled sevoflurane at enrollment * Known pregnancy * Currently receiving ECMO therapy * Chronic respiratory failure defined as PaCO2 \>60 mmHg in the outpatient setting * Home mechanical ventilation (non-invasive ventilation or via tracheotomy) except for CPAP/BIPAP used solely for sleep-disordered breathing * Body mass index \>40 kg/m2 * Chronic liver disease defined as a Child-Pugh score of 12-15 * Expected duration of mechanical ventilation \<48 hours * Moribund patient, i.e. not expected to survive 24 hours despite intensive care * Burns \>70% total body surface * Previous hypersensitivity or anaphylactic reaction to sevoflurane or cisatracurium * Medical history of malignant hyperthermia * Long QT syndrome at risk of arrhythmic events * Medical history of liver disease attributed to previous exposure to a halogenated agent (including sevoflurane) * Known hypersensitivity to propofol or any of its components * Known allergy to eggs, egg products, soybeans, and soy products * Suspected or proven intracranial hypertension * Tidal volume of 6 mL/kg predicted body weight (PBW) below 200 mL (as recommended by the manufacturer for the use of the AnaConDa-S (Sedana Medical, Danderyd, Sweden) * Enrollment in another interventional ARDS trial with direct impact on sedation and mechanical ventilation * Endotracheal ventilation for greater than 120 hours (5 days) * Persistent bronchopleural fistula despite chest tube drainage * PaO2/FiO2 (if available) \>200 mmHg after meeting inclusion criteria and before randomization