* exclusion criteria related to ards history * ards onset more than 48 hours before inclusion * previous inclusion in present study * exclusion criteria related to ards severity or complications * arterial ph \< 7.21 despite respiratory rate set to 35/min at the time of inclusion * patient under any extracorporeal co2 removal technique or ecmo * pneumothorax or bronchopleural fistula * exclusion criteria related to comorbidities * suspected intracranial hypertension * severe chronic obstructive pulmonary disease defined by a gold score ≥ 3 * chronic respiratory failure under home oxygen or non-invasive ventilation * chronic respiratory failure requiring long term oxygen or non-invasive ventilation * obesity with body weight over height ratio greater than 1 kg/cm * sickle cell disease * bone marrow transplant \< 6 months * burn injury with extension greater than 30% of body surface area * cirrhosis with child-pugh score c * advance directives to withhold or withdraw life sustaining treatment * exclusion criteria related to legislation * patient under an exclusion period relative to participation to another clinical trial, or inclusion into a clinical trial interfering with the ventilatory strategies * pregnancy, lactating women * patient under a legal protective measure. * lack of affiliation to social security as required by french regulation * lack of written informed consent by patient or next of kin (unless if recourse to the emergency procedure in the absence of a loved one)

* exclusion criteria related to ards history * ards onset more than 48 hours before inclusion * previous inclusion in present study * exclusion criteria related to ards severity or complications * arterial ph \< 7.21 despite respiratory rate set to 35/min at the time of inclusion * patient under any extracorporeal co2 removal technique or ecmo * pneumothorax or bronchopleural fistula * exclusion criteria related to comorbidities * suspected intracranial hypertension * severe chronic obstructive pulmonary disease defined by a gold score ≥ 3 * chronic respiratory failure under home oxygen or non-invasive ventilation * chronic respiratory failure requiring long term oxygen or non-invasive ventilation * obesity with body weight over height ratio greater than 1 kg/cm * sickle cell disease * bone marrow transplant \< 6 months * burn injury with extension greater than 30% of body surface area * cirrhosis with child-pugh score c * advance directives to withhold or withdraw life sustaining treatment * exclusion criteria related to legislation * patient under an exclusion period relative to participation to another clinical trial, or inclusion into a clinical trial interfering with the ventilatory strategies * pregnancy, lactating women * patient under a legal protective measure. * lack of affiliation to social security as required by french regulation * lack of written informed consent by patient or next of kin (unless if recourse to the emergency procedure in the absence of a loved one)

- exclusion criteria related to ards history - ards onset more than 48 hours before inclusion - previous inclusion in present study - exclusion criteria related to ards severity or complications - arterial ph < 7.21 despite respiratory rate set to 35/min at the time of inclusion - patient under any extracorporeal co2 removal technique or ecmo - pneumothorax or bronchopleural fistula - exclusion criteria related to comorbidities - suspected intracranial hypertension - severe chronic obstructive pulmonary disease defined by a gold score ≥ 3 - chronic respiratory failure under home oxygen or non-invasive ventilation - chronic respiratory failure requiring long term oxygen or non-invasive ventilation - obesity with body weight over height ratio greater than 1 kg/cm - sickle cell disease - bone marrow transplant < 6 months - burn injury with extension greater than 30% of body surface area - cirrhosis with child-pugh score c - advance directives to withhold or withdraw life sustaining treatment - exclusion criteria related to legislation - patient under an exclusion period relative to participation to another clinical trial, or inclusion into a clinical trial interfering with the ventilatory strategies - pregnancy, lactating women - patient under a legal protective measure. - lack of affiliation to social security as required by french regulation - lack of written informed consent by patient or next of kin (unless if recourse to the emergency procedure in the absence of a loved one)

- exclusion criteria related to ards history - ards onset more than 48 hours before inclusion - previous inclusion in present study - exclusion criteria related to ards severity or complications - arterial ph < 7.21 despite respiratory rate set to 35/min at the time of inclusion - patient under any extracorporeal co2 removal technique or ecmo - pneumothorax or bronchopleural fistula - exclusion criteria related to comorbidities - suspected intracranial hypertension - severe chronic obstructive pulmonary disease defined by a gold score ≥ 3 - chronic respiratory failure under home oxygen or non-invasive ventilation - chronic respiratory failure requiring long term oxygen or non-invasive ventilation - obesity with body weight over height ratio greater than 1 kg/cm - sickle cell disease - bone marrow transplant < 6 months - burn injury with extension greater than 30% of body surface area - cirrhosis with child-pugh score c - advance directives to withhold or withdraw life sustaining treatment - exclusion criteria related to legislation - patient under an exclusion period relative to participation to another clinical trial, or inclusion into a clinical trial interfering with the ventilatory strategies - pregnancy, lactating women - patient under a legal protective measure. - lack of affiliation to social security as required by french regulation - lack of written informed consent by patient or next of kin (unless if recourse to the emergency procedure in the absence of a loved one)