Acute respiratory syndrome distress (ARDS) is a clinical common syndrome with high mortality. Mechanical ventilation (MV) is the cornerstone of management of ARDS but can lead to ventilator-induced lung injury. Positive end-expiratory pressure (PEEP), as one of main component of MV, has been widely used in the clinical practice. However, the PEEP selection is still a difficult problem for moderate to severe ARDS patients. EIT, an imaging tool evaluating the regional ventilation distribution at the bedside, can achieve the individual PEEP selection for all mechanically ventilated patients. This article compared the effect of PEEP titrated guided by EIT with fraction of inspired oxygen (FiO2)-PEEP table on the clinical outcomes.

This is a prospective, multicenter, single-blind, parallel-group, adaptive randomized controlled trial (RCT) with intention-to-treat analysis which aims to determine the effects of PEEP setting guided by EIT on the clinical outcomes for moderate or severe ARDS patients ventilated with lung protective ventilation strategy. Adult patients with moderate to severe ARDS less than 72 hours after diagnosis will be included in this study. Patients in the intervention group will receive PEEP titrated by EIT with a stepwise decrease PEEP trial, whereas patients in the control group will select PEEP based on the FiO2-PEEP table. Other ventilator parameters will be set according to the ARDSnet strategy. The primary outcome is 28-day mortality. The secondary outcomes include ventilator-free days and shock-free days at day 28, length of ICU and hospital stay, the rate of successful weaning, proportion requiring rescue therapies, compilations, respiratory variables, and Sequential Organ Failure Assessment (SOFA). This study will also perform the interim analysis and subgroup analysis.

Inclusion Criteria:

1. Age≥18 years
2. Moderate-to-severe ARDS, defined by the ARDS Definition Task Force in the Berlin definition (partial pressure of arterial oxygen [PaO2]:FiO2 ratio ≤200 mmHg with a PEEP ≥5 cmH2O)
3. Diagnosis of ARDS less than 72 hours

Exclusion Criteria:

1. Expected to be mechanically ventilated for less than 48 hours
2. Severe chronic respiratory diseases requiring long-term home oxygen therapy or noninvasive MV
3. Undrained pneumothorax or subcutaneous emphysema
4. Undergoing extracorporeal membrane oxygenation (ECMO) before enrollment
5. Contraindication to the use of EIT (pacemaker, automatic implantable cardioverter defibrillator, and implantable pumps)
6. Severe neuromuscular disease
7. Hemodynamic instability
8. Contraindications to hypercapnia, such as intracranial hypertension or acute coronary syndrome
9. Severe other organs dysfunction with a low expected survival (7 days) or palliative care
10. Solid organ or hematologic tumors with the expected survival time less than 30 days
11. Participating in other clinical trials within 30 days
12. Pregnancy
13. Refusal to sign the informed consent