Early EIT-Guided PEEP Titration on Pulmonary Physiology in Patients With Moderate-to-Severe ARDS Undergoing Prone Positioning (EIT-PEEP-PRONE)

Background: Electrical impedance tomography (EIT)-guided PEEP titration has been shown to improve regional ventilation distribution, increase respiratory system compliance, and reduce mechanical power in patients with acute respiratory distress syndrome (ARDS), but its effect on mortality remains unproven. In patients with moderate-to-severe ARDS, prone positioning for 4 hours allows pulmonary ventilation and perfusion to reach a new steady state, with optimization of ventilation-perfusion (V/Q) matching and other pulmonary physiological parameters. However, whether dynamic PEEP titration guided by EIT at this time point can further optimize V/Q matching and other pulmonary physiological parameters compared with conventional methods has not been reported. Objective: To investigate whether EIT-guided PEEP titration performed at 4 hours after prone positioning initiation can further optimize V/Q matching and other pulmonary physiological parameters in patients with moderate-to-severe ARDS undergoing prone positioning. Methods: This is a prospective, single-center, randomized, open-label, parallel-controlled physiological study. A total of 40 patients with moderate-to-severe ARDS (Berlin definition, PaO₂/FiO₂ \< 150 mmHg) will be enrolled and randomized in a 1:1 ratio to either the EIT-guided group or the control group. PEEP intervention will be performed at 4 hours after prone positioning initiation (T1) in both groups: the EIT group receives EIT-guided PEEP titration, while the control group receives PEEP set according to the ARDSNet/PEEP-FiO₂ table. The primary outcome is V/Q matching percentage assessed by EIT at 18 hours of prone positioning (T2) and 6 hours after supine repositioning (T3). Secondary outcomes include respiratory mechanics, EIT-derived parameters (regional ventilation distribution, global inhomogeneity index, center of ventilation), oxygenation indices, echocardiographic measures of cardiac function, and clinical outcomes (28-day mortality, venti