Acute respiratory distress syndrome (ARDS) is a severe lung condition that often requires invasive mechanical ventilation in the intensive care unit. In these patients, setting the ventilator appropriately is essential to improve oxygenation while limiting ventilator-induced lung injury. One important ventilator setting is positive end-expiratory pressure (PEEP), which helps keep the lungs open. However, the optimal PEEP level may vary from one patient to another.
The recruitment-to-inflation ratio (R/I ratio) is a bedside measurement used to estimate the potential for lung recruitment during a decrease in PEEP. It compares the compliance of the lung volume recruited by PEEP with the compliance of the already aerated lung. A higher R/I ratio suggests that increasing PEEP is more likely to reopen collapsed lung units, whereas a lower R/I ratio suggests limited recruitability and a higher likelihood that additional pressure would mainly distend lung areas that are already open. In clinical practice, the R/I ratio is increasingly used to guide PEEP adjustment, with the aim of improving recruitment and oxygenation while avoiding unnecessary increases in airway pressure. However, although the R/I ratio is used in routine care, there are currently no data demonstrating that this measurement is reproducible when repeated in the same patient under similar conditions.
The hypothesis of this study is that the R/I ratio is reproducible when measured twice in the same patient under stable conditions, including no significant changes in ventilator settings, hemodynamic status, or ongoing treatments.
This prospective, multicenter, non-interventional study will include adult ICU patients with ARDS who are receiving invasive mechanical ventilation, deep sedation, and assist-control ventilation. For each patient, airway opening pressure will be assessed, and the R/I ratio will be measured twice on the same day by a trained clinician, between 20 and 120 minutes apart, without changes in ventilator settings or treatments likely to influence the measurement.
The main objective is to evaluate the within-patient reproducibility of the R/I ratio. Secondary objectives include describing changes in airway opening pressure and R/I ratio over time, assessing the reproducibility of expired tidal volume during the maneuvers, and evaluating the clinical tolerance of these ventilatory measurements.
The study will include 80 patients across 4 French intensive care units. No additional intervention outside routine care will be performed. Clinical, ventilatory, and biological data already collected as part of usual care will be recorded.
Adult patient (age ≥ 18 years)
Patient hospitalized in the Intensive Care Unit (ICU) for acute respiratory distress syndrome (according to the Berlin definition), requiring invasive mechanical ventilation with deep sedation and controlled mechanical ventilation mode
Patient or next of kin informed about the study and not objecting to participation
Undrained pneumothorax or any contraindication to a transient increase in airway pressure
Known or suspected intracranial hypertension
Patient under legal protection (e.g., guardianship)
Not affiliated with a social security system
Adult patients admitted to intensive care units in participating centers for acute respiratory distress syndrome and requiring invasive mechanical ventilation will be screened for inclusion. The study population will be drawn from routine clinical practice in four French academic intensive care units where airway opening pressure and recruitment-to-inflation ratio measurements are performed as part of standard care in selected patients with moderate to severe disease.
Cohort
Prospective
Not listed
Intraclass Correlation Coefficient of the Recruitment-to-Inflation Ratio (R/I)
Intra-patient reproducibility of the recruitment-to-inflation ratio (R/I) assessed using an intraclass correlation coefficient (ICC, two-way mixed-effects model, absolute agreement) between two measurements (T1 and T2) performed under stable clinical conditions.
Absolute and relative difference in recruitment-to-inflation ratio (R/I) between two measurements (T1 and T2)
Absolute (ΔR/I) and relative (%) difference in the recruitment-to-inflation ratio (R/I) between two measurements (T1 and T2) performed under stable clinical conditions.
Intra-patient reproducibility and variability of expired tidal volume (Vte)
Intra-patient reproducibility of expired tidal volume (Vte) assessed using an intraclass correlation coefficient (ICC, two-way mixed-effects model, absolute agreement), as well as absolute and relative (%) differences between two measurements (T1 and T2).
Longitudinal evolution of recruitment-to-inflation ratio (R/I)
Temporal evolution of the recruitment-to-inflation ratio (R/I) and airway opening pressure (AOP) assessed using repeated measurements during the ICU stay
Longitudinal evolution of airway opening pressure (AOP)
Temporal evolution of airway opening pressure (AOP) assessed using repeated measurements when available during the ICU stay
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