ARDS is frequent in ICU and may lead to many complications and to death. Prone position is widely used in ADRS patients and demonstrated to decrease mortality. Regarding the chest wall compliance data are missing but the theorical response is that this compliance is decreased in a prone position mainly due to anterior chest and abdomen compression in this position which are more compliant that dorsal part of the body. As well prone position could be associated with complications as pressure ulcers. Because prone position is associated with complications, air bag were developped to decrease pressure on the chest and abdomen and to decrease pressure ulcers. Then, trying to improve chest compliance in prone position and reducing the risk of pressures ulcers could be a challenge with this system in comparison with standard care.

Inclusion Criteria:

• patients with ARDS under mechanical ventilation with P/F ratio<150
• Age >18 y/o
• Admitted in the medical ICU of Amiens under mechanical ventilation sedated,
• With signed informed consent (patient or relative if patient is not conscious)

Exclusion Criteria:

• patients not eligible for a prone position
• Patients with tracheostomy