Experimental: group P-eit

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.

Active_comparator: group P-8

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.