This study will be conducted to evaluate the effect of driving pressure guided ventilation compared with conventional protective lung ventilation during laparoscopic bariatric surgeries in morbid obese patients.

• the primary outcome: Intraoperative oxygenation measured by the arterial partial pressure of oxygen (PaO2).
• the secondary outcome: incidence of early postoperative pulmonary complications e.g., postoperative hypoxia, the need for supplementary oxygen, atelectasis, barotrauma, and respiratory failure.

Protective mechanical ventilation during anesthesia aims at minimizing lung injury and has been associated to a decrease in postoperative pulmonary complications (PPCs). Conventional protective ventilation strategy is consisted of the use of a low tidal volume (VT) and fixed moderate positive end expiratory pressure (peep). However, low-VT may result in the reduction of the functional volume of the lung manifested as lung collapse. Another potential consequence of lung collapse is the impairment in ventilatory efficiency.

Bariatric surgery is proven to achieve significant and sustained weight loss in the morbidly obese. Major weight loss can lead to partial/complete resolution of a range of conditions including, diabetes mellitus, ischemic heart disease, and hypertension.

Obese patients undergoing general anesthesia and mechanical ventilation during abdominal and bariatric surgeries commonly have a higher incidence of postoperative pulmonary complications (PPCs), due to factors such as decreasing oxygen reserve, declining functional residual capacity, and reducing lung compliance. And also pneumoperitoneum aggravates pulmonary atelectasis caused by mechanical ventilation, especially in obese patients.

Driving pressure (DP) which is the difference between the airway pressure at the end of inspiration (plateau pressure, (Ppl) and PEEP was first introduced by Amato et al in 2015 in their meta-analy¬sis study for ARDS patients. The authors suggested that driving pressure is the stronger predictor of mortality as compared with low VT and Ppl.

Several retrospec¬tive and prospective studies confirmed the importance of driving pressure in ARDS pa¬tients and during general anesthesia without differentiation between obese and nonobese patients .only one retrospective study showed that driving pressure was not associated with mortality in obese-ARDS patients. we hypothesize that these results may be different in obese patients having healthy lungs.

Inclusion Criteria:

• sixty patients have a BMI 40-50 kg/m2, ASA physical status III, aged between 18 and 60 years, scheduled to undergo laparoscopic bariatric surgeries.

Exclusion Criteria:

• patient refusal to participate in the study.
• Patients had a recent history of severe respiratory disease and previous major pulmonary surgeries.
• patients who are contraindicated with application of PEEP (high intracranial pressure, bronchopleural fistula, hypovolemic shock, right ventricular failure).