Acute respiratory distress syndrome (ARDS) remains a serious and often fatal complication in patients following severe trauma or major surgery. Mechanical ventilation is essential for supportive care in this population, but may aggravate lung injury when suboptimal ventilatory settings are applied. Positive end-expiratory pressure (PEEP) is crucial for maintaining alveolar recruitment; however, optimal PEEP selection in trauma- or postoperative-associated ARDS remains uncertain. Electrical impedance tomography (EIT) enables bedside, real-time assessment of regional ventilation and may support optimal PEEP titration by balancing alveolar overdistension and collapse. This study compares EIT-guided PEEP optimization with the conventional low FiO₂-PEEP strategy in terms of oxygenation and respiratory mechanics in patients with moderate to severe ARDS following trauma or surgery.

This single-center, prospective, randomized controlled trial was designed to evaluate whether EIT-guided PEEP titration improves clinical outcomes in patients with trauma- or postoperative-associated ARDS. Adult intubated patients with moderate to severe ARDS were enrolled.

Patients in the intervention group received PEEP settings guided by electrical impedance tomography, whereas those in the control group were managed according to the lower PEEP/FiO₂ table of the ARDS Network. Other ventilatory parameters and oxygenation targets were set in accordance with ARDS Network recommendations. Supportive care and post-trial PEEP management followed standard ARDS treatment protocols.

The primary outcomes included oxygenation and respiratory mechanics. The secondary outcomes comprised 28-day survival, ventilator-free days at day 28, length of ICU and length of hospital stay, rate of successful ventilator weaning, use of adjunctive therapies (prone positioning, neuromuscular blockade, ECMO), newly developed barotrauma (pneumothorax, pneumomediastinum, and subcutaneous emphysema) excluding cases attributable to invasive procedures) and changes in the SOFA score.

In the intervention group, PEEP was titrated under the guidance of electrical impedance tomography (EIT) according to a protocol:

• Preparation: patients underwent airway suctioning and were deeply sedated (RASS ≤ -3) to abolish spontaneous breathing. PEEP titration was performed using an EIT system (Enlight 2100, Timpel SA, Brazil), with a silicone belt containing 32 surface electrodes positioned at the fourth to fifth intercostal space in accordance with the manufacturer's instructions.
• Pressure-controlled ventilation was applied with an inspiration pressure set at 15 cmH₂O and a set PEEP of 24 cmH₂O, with a maximum airway pressure limit of 40 cmH₂O. Ventilator settings were maintained for 30 seconds with an FiO₂ of 1.0. A decremental PEEP trial was then performed by reducing PEEP in 2 cmH₂O every 30 seconds until a PEEP of 6 cmH₂O was reached or the SpO₂ decreased to ≤ 80%.
• The EIT-guided optimal PEEP was defined as the PEEP level corresponding to the intersection point of the collapse and overdistension curves.

Criteria for discontinuing: PEEP titration was terminated if any of the following occurred: a sustained decrease in mean arterial pressure of > 20 mmHg from baseline, SpO₂ < 88%, or the onset of new cardiac arrhythmias. If the event of discontinuation of the procedure, all ventilator settings were reverted to those applied prior to initiation of the PEEP titration.

In the control group, PEEP was set directly and adjusted according to the lower PEEP/FiO₂ table of the ARDS Network.

Inclusion Criteria:

• Mechanically ventilated surgical intensive care patients with trauma- or postoperative-associated moderate to severe ARDS, as defined by the 2023 Global Definition of ARDS.

Exclusion Criteria:

• Age <18 or >90 years.
• Severe acute brain injury or acute stroke with Glasgow Coma Scale <8.
• Thoracic trauma with pneumothorax or pneumomediastinum.
• End-stage diseases under palliative care (e.g., metastatic cancer, cirrhosis, end-stage renal disease).
• Severe multiorgan failure with expected survival <7 days.
• Conditions requiring prolonged mechanical ventilation (e.g., Guillain-Barré syndrome, cervical spinal cord injury).
• Contraindications to hypercapnia (e.g., elevated intracranial pressure, acute coronary syndrome).
• Prior use of advanced respiratory therapies (e.g., ECMO, inhaled nitric oxide, prone positioning, high-frequency ventilation).
• Pregnancy, breastfeeding, or skin lesions at electrode placement sites.
• Implanted electrical devices interfering with EIT (e.g., pacemaker, ICD).
• Known allergy to electrode materials.
• Refusal to participate or concurrent enrollment in another study