After random assignment of group, Control group: no additional procedure apply, Low ARM group : after surgical trocha out after bariatric surgery, applying 30cmH2O recruitment maneuver 5 times every 5 seconds, High ARM group: after surgical trocha out after bariatric surgery, applying 60cmH2O recruitment maneuver 5 times every 5 seconds
Control group: no additional procedure Low ARM group : recruitment maneuver of 30cmH2O High ARM group: recruitment maneuver of 60cmH2O