Inclusion Criteria:  person who has given oral consent or has been included in an emergency Older than 18 years On mechanical ventilation for less than 24 hours Diagnosis of ARDS for less than 24 hours. ARDS according to the Berlin classification: i.e. arterial oxygen pressure to inspired oxygen fraction ratio less than or equal to 300, with a PEEP greater than or equal to 5, presence of bilateral radiological infiltrates not fully explained by heart failure or volume overload Focal ARDS determined on pulmonary ultrasound  Exclusion Criteria:  person who is not a beneficiary of national health insurance person who is subject to a legal measure of protection (curatorship, guardianship) pregnant or breastfeeding women minor Patient having benefited from an invasive mechanical ventilation of more than one week in the previous month; ARDS in the previous month; Chronic respiratory failure under NIV or long term oxygen; Severe acute asthma; Lobectomy; Pneumothorax; Pneumomediastinum; Pulmonary fibrosis; Morbid obesity with a BMI above 40 ; Cancer with metastasis; Bone marrow transplantation; Chemotherapy-induced neutropenia; Cirrhosis with a Child-Pugh score of C; Suspected or confirmed intracranial hypertension; Concurrent participation in another ARDS study; Extensive burns on the torso.