Acute respiratory distress syndrome (ARDS) in children is associated with significant morbidity and mortality. Current studies seek to individualize the management of children by defining several phenotypes, based until now mainly on clinical presentation. A better understanding of the respiratory mechanics of each patient could allow the individualization of other phenotypes and adapt their management with individualized ventilation. The method for detecting airway opening pressure (AOP) in children has not yet been validated and the reference methods in adults are difficult to apply in children due to their physiological particularities.

The main objective of the study is to evaluate the feasibility of two methods for measuring airway opening pressure in invasively ventilated pediatric patients.

Acute respiratory distress syndrome (ARDS) in children is associated with significant morbidity and mortality. Current studies seek to individualize the management of children by defining several phenotypes, based until now mainly on clinical presentation. A better understanding of the respiratory mechanics of each patient could allow the individualization of other phenotypes and adapt their management with individualized ventilation. The method for detecting airway opening pressure (AOP) in children has not yet been validated and the reference methods in adults are difficult to apply in children due to their physiological particularities.

The main objective of the study is to evaluate the feasibility of two methods for measuring airway opening pressure in invasively ventilated pediatric patients: "pediatric slow flow method" based on a recent bench study and "fixed flow method" based on an adult study. The two methods will be separated by a wash out.

The method will be considered feasible if at least one on three measures can be interpretated.

Air flow will be recorded using a pneumotachograph connected to a T piece.

Inclusion Criteria:

• Minor patients weighing more than 5 kg, hospitalized in the pediatric intensive care unit at Necker-Enfants Malades Hospital and receiving invasive ventilation. To assess patients with acute respiratory distress syndrome, the PALICC-2 criteria are used.
• Holders of parental authority must be informed and consent to their child's participation in the study.
• The patient must be passively ventilated to ensure reliable measurements. This means that the patient must not be spontaneously ventilating and must be completely passively ventilated by the ventilator (no respiratory effort during long-term inflation).

Exclusion Criteria:

• Respiratory mechanics preventing interpretation of maneuvers (flow too low and/or resistance too high)
• Patient < 5 kg
• Refusal by those with parental authority
• Patient not affiliated with social security
• Patient receiving AME (Medical Aid for Life)
• Contraindication or impossibility of performing static respiratory mechanics measurements: pneumothorax or pleural leak, head trauma or threatening HTIC, unstable patient with SpO2 < 88%, patient receiving nitric oxide (NO) (circuit leaks) or other circuit leaks or patient leaks > 20% displayed on the ventilator