The RECRUIT study is a multinational, multicenter physiological observational study conducted by the PLUG working group. It is a single-day study (1.5-2 hours) associated with specific lung (de)recruitment maneuvers to verify the feasibility of measuring the potential for lung recruitment in mechanically ventilated patients with ARDS by electrical impedance tomography (EIT).

Despite higher positive end-expiratory pressure (PEEP) being associated with multiple physiologic benefits, randomized clinical trials comparing higher vs. lower PEEP levels failed to show improved survival of ARDS patients. Higher PEEP should fully exploit its benefits only when implemented in patients with higher potential for alveolar recruitment (i.e., the decrease of non-aerated lung tissue at higher airway pressure) or in patients with airway closure. Retrospective analysis of randomised clinical trials with PEEP suggests that when high PEEP is used in responders (oxygenation), survival may be better. Conversely, in the absence of significant recruitment, higher PEEP should be avoided and lower PEEP might be recommended.

Titration of PEEP provided by the mechanical ventilator in patients with severe lung injury should thus be based on bedside information on lung recruitability. However, no valid method exists to define the best PEEP to optimize recruitment and minimize lung overdistention. Recruitability varies and is often not assessed. Electrical impedance tomography (EIT) is a non-invasive bedside imaging technique for measuring the potential for lung recruitment in ARDS patients. By performing lung (de)recruitment maneuvers and in-depth analyses, we will define lung recruitability indices and develop methods for real-time and personalized PEEP selection. This study will prove the feasibility of minimizing risks associated with inadequate mechanical ventilation by EIT.

Inclusion Criteria:

• Intubated moderate and severe ARDS according to the Berlin definition (PaO2/FiO2 ratio <= 200 mmHg)
• Under continuous sedation with or without paralysis

Exclusion Criteria:

• Age <18 years
• Bronchopleural fistula
• Pure COPD exacerbation
• Contraindication to EIT monitoring (e.g. burns, pacemaker, thoracic wounds limiting electrode belt placement)
• Hemodynamic instability (Systolic BP < 75 mmHg or MAP < 60 mmHg despite vasopressors and/or heart rate < 55 bpm)
• Attending physician deems the transient application of high airway pressures to be unsafe

Intubated mechanically ventilated patients will be considered for enrolment in the first week of ARDS diagnosis.