Cdyn (A), VD/VT (B), and QS/QT (C) in the four groups (without the excluded patients). T0: baseline (after anesthesia induction but before PNP and position change); T1: 5 min after PNP and position change; T2: 30 min and T3: 60 min after PEEP; T4: end of surgery but before extubation (supine position without PNP). Group I: control group (no PEEP); Group II: received PEEP at 4 cmH2O; Group III: received PEEP at 8 cmH2O; Group IV: received PEEP at 12 cmH2O. *, P<0.05; **, P<0.01; ***, P<0.001. PEEP, positive end-expiratory pressure; PNP, pneumoperitoneum.