Many patients admitted to the intensive care unit (ICU) for a severe lung disease called acute respiratory distress syndrome (ARDS) require mechanical ventilation and positive end-expiratory pressure (PEEP) to improve their oxygenation. Ventilator settings-and particularly the level of PEEP-are critical in the management of these patients. In fact, inappropriate ventilator settings can lead to a worsening of the patients' lung disease or compromise their hemodynamic status.

PEEP is a pressure maintained by the ventilator during the patient's exhalation to keep the alveoli open throughout the respiratory cycle. When PEEP is increased, if many alveoli open, this is called alveolar recruitment, which is the expected beneficial effect. However, in some patients, increasing PEEP can cause already-open alveoli to become overdistended without opening new alveoli; this is known as pulmonary overdistension. This phenomenon of overdistension will worsen the patient's pulmonary condition and may also lead to hemodynamic deterioration. To date, numerous techniques have been proposed for determining the optimal PEP level (alveolar recruitment without pulmonary overdistension) in these patients, but none can be recommended as the gold standard. The objective of our study is therefore to compare the various existing methods for determining the optimal PEEP level, in order to determine whether these methods are interchangeable and which would be the best method to use to optimize the care of these patients.

To this end, the investigators plan to conduct a prospective, observational, multicenter study in the Intensive Care Units of the Nice University Hospital and the European Hospital of Marseille. Patients on mechanical ventilation for ARDS will be included in the study, and medical and laboratory data from the electronic medical records obtained during the various PEEP measurements to determine the optimal PEEP will be analyzed.