low number of patients enrolled

The objective is determine the strain measured at the bedside could be a dynamic prognostic marker of during Acute respiratory Distress Syndrome (ARDS).

Nowadays ARDS severity, and therapeutic efficiency are evaluated using PaO2/FiO2 ratio. Inflammation is a cornerstone of ARDS and the ratio is not a sufficiently accurate tool to predict the evolution of ARDS. A reproducible marker would be helpful to adapt the therapeutics and maybe limit their deleterious effects.

The investigators made the hypothesis that patients moderate to severe ARDS (comparable PaO2/FiO2 ratio) with a higher strain may have higher inflammation.

Moderate/severe ARDS will be ventilate with protective ventilation (low tidal volume and PEEP set to limit plateau pressure under 30cmH2O). Markers of inflammation will be measured in the broncho Alveolar Lavage the first day and in the blood the following days. Strain will be measured at the bedside using the nitrogen washout-washin. Markers of inflammation and strain will be analysed with ventilatory and oxygenation.

Inclusion Criteria:

• Moderate to severe ARDS (Berlin Definition)
• Acute beginning <1 week
• PaO2/FiO2 ratio ≤ 200 after 24h mechanical ventilation with PEEP≥5cmH2O
• Bilateral opacities on chest X-ray
• Respiratory failure not fully explain by cardiac failure or fluid overload
• Informed consent signed by the next of kin and secondarily by the patient when awake
• Patient with social insurance

No Inclusion criteria

• Age < 18
• Pregnancy a pregnancy test will be done to women of childbearing age
• Chronic obstructive pulmonary disease
• Severe hypoxemia PaO2/FiO2 <50% with high PEEP
• Immunosuppressive treatment
• Immunodeficiency onco-hematology, HIV