To compare in ARDS patients 2 ventilatory Strategies : One based on Lung Morphology (Focal versus non-Focal ARDS) versus ARDS networks Guidelines (PEEP based on FiO2). In Focal ARDS prone position will be promote early, with low PEEP and moderate Vt. In non-Focal ARDS, Recruitment maneuvers, high PEEP and low V twill be used.

The investigators made the hypothesis that ventilation according to Lung morphology my decrease mortality at D90.

Early ARDS, less than 12 hours will be included. After Lung imaging, they will be randomized to a control group (PEEP/FiO2 according to ARDSnetwork tables) or an intervention arm. In this arm, mechanical ventilation will be set according to lung morphology. In patients with focal ARDS, prone position will be start quickly for at least 16 hours. After, A low PEEP and 8ml/kg of PBWwill be used. In non-focal ARDS, a recruitment maneuver followed by a high PEEP and a small tidal volume strategy will be used. In both arms, patients will be sedated and paralyzed during maximum 48 hours. As soon as PaO2/FiO2 > 200 mmHG, myorelaxant and sedation will be withdrawal. Pressure support ventilation will be used as soon as possible and weaning from ventilation will be checked everyday

Inclusion Criteria:

• Man or female older than 18 years
• ARDS since less than 12 hours
• PaO2 / FiO2 < 200 avec une PEEP ≥ 5 (Berlin Moderate or severe)

Exclusion Criteria:

• brain injury with high ICP
• BMT Liver Cirrhosis Child C Pregnancy Burns Morbid obese patients (BMI > 40) Moribund