The overall concept of this group is to individualize PEEP. After enrollment, all patients underwent placement of an gastric tube for esophageal pressure monitoring.Tidal volume is adjusted to achieve a target tidal volume of 6 mL/kg predicted body weight (PBW) while controlling end-inspiratory transpulmonary pressure ≤ 20 cmH₂O. PEEP is adjusted to maintain end-expiratory transpulmonary pressure between 0 and 2 cmH₂O. FiO₂ is titrated to keep the patient's SpO₂ at 90%-95%. Respiratory rate is adjusted to maintain pH between 7.30 and 7.45 and PaCO₂ ≤ 60 mmHg.

If end-inspiratory transpulmonary pressure exceeds 20 cmH₂O, tidal volume may be reduced to 4 mL/kg PBW as necessary. For patients with severe dyspnea or respiratory acidosis, tidal volume may be increased up to 8 mL/kg PBW provided that end-inspiratory transpulmonary pressure remains ≤ 20 cmH₂O.

In this group, PEEP was titrated using the low PEEP:FiO₂ table method. Volume-assist control (V-A/C) ventilation was adopted, with tidal volume maintained at approximately 6 mL/kg predicted body weight (PBW) and plateau pressure controlled at ≤ 30 cmH₂O. PEEP was adjusted to maintain the oxygenation target of SpO₂ 90%-95% while using the lowest possible PEEP:FiO₂ combination in the table. Respiratory rate was adjusted to maintain pH between 7.30 and 7.45 and PaCO₂ ≤ 60 mmHg.

Esophageal pressure monitoring was simultaneously performed in this group to calculate and record end-inspiratory and end-expiratory transpulmonary pressures; however, ventilator parameters were not adjusted based on these measurements, and crossover to the transpulmonary pressure (Ptp) group was not permitted.

If plateau pressure exceeded 30 cmH₂O, tidal volume could be reduced to 4 mL/kg PBW as necessary. For patients with severe dyspnea or respiratory acidosis, tidal volume could be increased up to 8 mL/kg PBW

Tidal volume is adjusted to achieve a target tidal volume of 6 mL/kg predicted body weight (PBW) while controlling end-inspiratory transpulmonary pressure ≤ 20 cmH₂O. PEEP is adjusted to maintain end-expiratory transpulmonary pressure between 0 and 2 cmH₂O.

In control group, PEEP was titrated using the low PEEP:FiO₂ table method.

Right ventricular involvement is defined as the presence of one of the following findings on transthoracic echocardiography:

ACP: Right ventricular enlargement (RVED/LVED > 0.6) with paradoxical septal motion; RVF: Right ventricular enlargement (RVED/LVED > 0.6) accompanied by systemic venous congestion (CVP ≥ 8 mmHg), or if CVP is unavailable, inferior vena cava plethora; RVD: RV FAC < 35%, or TAPSE ≤ 16 mm.