Context: Mechanical ventilation is an essential treatment for patients admitted to intensive care. It is estimated that approximately 50% of adult patients admitted to intensive care require invasive mechanical ventilation. However, inappropriate ventilator settings expose patients to the risk of ventilator-induced lung injury (VILI). In particular, the cyclical opening and closing of the alveolar units can damage lung tissue and trigger an inflammatory response. Measuring and monitoring airway pressure (Paw), particularly plateau pressure (Pplat) and driving pressure (DP), is essential in order to adjust ventilator settings and is the subject of international recommendations. However, these static pressures may not accurately reflect alveolar pressure. Partial or complete closure of the airways can influence the measurement of Pplat and DP. Airway closure corresponds to an interruption in communication between the proximal airways and the alveoli when airway pressure is below the airway opening pressure (AOP) threshold (airway opening pressure or AOP). In the event of such closure, insufflation only begins when the airway pressure reaches this critical threshold. Consequently, in the event of airway closure, the airway pressure may differ from the alveolar pressure and thus distort the assessment of respiratory mechanics. Furthermore, when positive end-expiratory pressure (PEEP) is set below the critical AOP threshold, cyclic opening and closure of the alveolar units may occur, potentially contributing to VILI.Detection of airway closure and measurement of the corresponding AOP can be performed at the patient's bedside by simply examining the ventilator curves during slow-flow insufflation or by measuring conductive pressure. Despite the potential implications of airway closure for the assessment of respiratory mechanics in mechanically ventilated patients, its prevalence is not defined. It has been reported that this phenomenon may affect 20 to 50% of patients with acute respiratory distress syndrome (ARDS). It has also been suggested that this phenomenon may affect obese patients, asthmatic patients, or patients receiving insufficient PEEP. Objectives: The main objective of this multicentre observational study is to assess the prevalence of airway closure in a large population of adults in intensive care receiving invasive mechanical ventilation. Type of study: Multicentre observational cohort study Number of centres: 39 intensive care units Study procedure: Phase 1: Identification and registration of participating centres Phase 2: Implementation of the study and data collection All patients undergoing invasive mechanical ventilation in controlled mode will undergo AOP measurement (analysis of the Paw curve during slow-flow insufflation according to standard clinical practice) between 8am and 10am on the day of inclusion, by a doctor other than the one in charge of the patient. No changes will be made to the initial ventilator settings. The data will be collected anonymously on an eCRF. A standardised protocol for measuring AOP will be provided. The measurement will be repeated at H+12 alongside the collection of the usual ventilatory mechanics and oxygenation data (compliance, driving pressure, Pplat, mechanical power, PaO2/FiO2). Phase 3: management and analysis of pseudonymised data
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The primary outcome is the proportion of critically ill receiving mechanically ventilated patients with complete airway closure (AOP higher than PEEP).
Timeframe: Data collection will be done twice (12-hour intervals) on the day of enrollment in the study. For newly admitted patients to participating ICUs, data collection will be done at day 1 and day 2.