Active_comparator: Intervention Group

Device: electrical impedance tomography system (Enlight 2100, Timpel SA, Brazil).~\- 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.

Placebo_comparator: Control Group

PEEP was set and adjusted according to the lower PEEP/FiO₂ table of the ARDS Network