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).