Individualized Positive End-Expiratory Pressure (PEEP) on Oxygenation, Hemodynamics, and Early Postoperative Atelectasis in Laparoscopic Bariatric Surgery

Fixed positive end-expiratory pressure of 5 cmH2O will be maintained throughout the duration of surgery

Patients will receive the individualized positive end-expiratory pressure. Titration process will be started after establishment of pneumoperitoneum: setting the initial PEEP to 5 cmH2O, then increasing positive end-expiratory pressure (PEEP)according to the gradient of 2 cmH2O every 3 min, calculating static compliance (Cstat) according to the formula: \[Cstat = VT/Pplat - PEEP\] (Pplat = plateau pressure), then gradually increasing positive end-expiratory pressure , until the calculated Cstat shows a downward trend, set its previous PEEP (corresponding to PEEP for high Cstat) as the optimal PEEPIND for this patient. The highest PEEP is limited to 20 cmH2O