Abbreviated Title: Airway Opening Pressure in Mechanically VENTilated Patients

Assessment of Airway Opening Pressure in Critically Ill Adults Receiving Mechanical Ventilation: a Multicenter Prospective Observational Cohort Study

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

Eligible patients will be included prospectively over a period of two weeks (14 consecutive days); the two-week period will be left to the discretion of each intensive care unit participating in the research (within a total 'window' of two months). Any patient admitted to intensive care requiring invasive mechanical ventilation in controlled mode for the condition for which they were admitted will undergo AOP measurement (analysis of the Paw curve during slow-flow insufflation according to standard 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 collated pseudonymously on an eCRF. A standardised protocol for measuring AOP will be provided. The measurement will be repeated at H12 alongside the collection of the usual ventilatory mechanics and oxygenation data (compliance, driving pressure, Pplat, mechanical power, PaO2/FiO2).

For newly admitted patients (ventilation duration < 24 hours), in participating centres that accept it, data will be collected upon discharge from intensive care or on day 28, whichever comes first, in order to gather the following prognostic information: total duration of mechanical ventilation up to day 28, time to weaning from ventilation, number of days alive without invasive ventilation support on day 28, mortality on day 28.

Inclusion Criteria:

• Age ≥ 18 years old
• Patients admitted to a participating ICU
• Patients receiving invasively ventilation for any cause We will only include patients under controlled mechanical ventilation because airway closure is difficult to assess in spontaneously breathing patients.

Non-inclusion Criteria:

• A patient admitted to hospital or transferred to the intensive care unit without a documented time of intubation
• Have a tracheotomy/tracheostomy at the time of inclusion
• Are receiving an assist ventilation mode
• Patient or relative's refusal to participate for data collection
• Pregnant or breast-feeding women
• Legal protection (i.e., patient under a tutelage, or curatorship, or placed under judicial incarceration)