Study intervention
PNEUMOPERITONEUM
The patients received ventilation using the same type of Anesthesia Machine (Datex-Ohmeda-Avance CS2, GE Company, Madison, USA) after induction of anesthesia and intubation. Anesthesia machine parameters were similar under the two modes (VT; 8 ml /kg, inspiratory/expiratory ratio (I/E); 1:2, positive end-expiratory pressure (PEEP); 0, inspiratory fresh gas flow rate; 2.0 L/min with an inspired oxygen fraction (Fio2) of 0.4 in an oxygen-air. and respiratory rate (RR); initially set at 12 breath/min). Subsequently, RR was adjusted to maintain an end-tidal CO2 pressure (ETCO2) of 35–40 mmHg. The peak inspiratory pressure (PIP) and pneumoperitoneum pressure were set at 40cmH