In group P-eit, EIT electrode patches will be placed before the operation. "The Recruitment Maneuver - PEEP Titration - Recruitment Maneuver (RM-T-R) Strategy" will be implemented 5 minutes after endotracheal intubation. EIT-based optimal PEEP is defined as the crossing point of the overdistension and collapse curves during a decremental PEEP trial. Other parameters include the individualized PEEP value determined by EIT and inspiratory oxygen fraction (FiO2) of 0.5. PEEP value will be maintained throughout the surgery.All patients in the group P-eit will receive i.v. fluid loading before and a norepinephrine bolus by protocol during the RM in order to maintain a mean arterial pressure >70mm Hg and minimize the short-lasting haemodynamic depression usually observed during the RM.

In group P-8, mechanical ventilation will be administered in volume-controlled mode with a tidal volume of 8 ml/kg (based on ideal body weight). Additional settings include a PEEP of 8 cmH₂O, FiO₂ of 0.5, an inspiratory-to-expiratory ratio of 1:2, and a respiratory rate of 12 breaths/min. A recruitment maneuver (RM) will be performed 5 minutes after intubation and again after surgery, using the same protocol as in group P. The respiratory rate will be adjusted as needed to maintain end-tidal CO₂ between 35 and 45 mmHg throughout the procedure.

"The Recruitment Maneuver - PEEP Titration - Recruitment Maneuver (RM-T-R) Strategy" will be implemented 5 minutes after endotracheal intubation. The patient will receive an RM (peak pressure 50cm H2O, PEEP 25cmH2O, respiratory rate 6 bpm, for 10 cycles) followed by a decremental PEEP titration, during which PEEP is set to 25cm H2O and decreased stepwise by 2cm H2O every 3min until reaching 5 cmH₂O. Meanwhile, the ventilator parameters (tidal volume, respiratory rate, and inspiratory-to-expiratory ratio) will be adjusted back to their pre-recruitment settings. EIT-based optimal PEEP is defined as the crossing point of the overdistension and collapse curves during a decremental PEEP trial.

Participants who developed at least one complication are considered as meeting the primary outcome. The PPCs are defined as follows :

1. . Pneumonia (using to the US Centres for Disease Control Criteria ;
2. . Respiratory failure
3. . Bronchospasm (newly detected expiratory wheezing treated with bronchodilators);
4. . Pleural effusion
5. . Pneumothorax
6. . Atelectasis
7. . Pulmonary aspiration
8. . Cardiogenic pulmonary oedema (clinical signs of congestion, including dyspnoea, oedema, rales, and jugular venous distention, with chest X-ray demonstrating an increase in vascular markings and diffuse alveolar interstitial infiltrates).

The point-of-care lung ultrasound (LUS) score at 30 min after endotracheal extubation, 8:00 AM on postoperative day 1 (POD 1) and postoperative day 2 (POD2).