With the development of economy and changing of life style, obesity is becoming a common phenomenon. More and more obese patients are undergoing bariatric surgery every year.~Obesity results in a series of physiological changes particularly the respiratory system. The decrease of lung compliance and the limited total lung capacity, vital capacity, functional residual capacity are all contributed to intraoperative hypoxemia and postoperative lung complications. Presently study mainly discuss lung protective ventilation strategies from four aspects: tidal volume,ventilation modes,positive end-expiratory pressures and lung recruitment maneuvers.~This prospective study will compare two ventilation modes in obese patients undergoing bariatric surgery:pressure-controlled ventilation(PCV) and pressure-controlled ventilation volume-guaranteed（PCV-VG).~The total of 100 patients will be divided into two groups randomly. The patients will be ventilated with PCV or PCV-VG modes plus positive end expiratory pressure (PEEP) of 5cmH2O throughout the whole operation.~The respiratory and hemodynamic parameters in six time points will be recorded, and the postoperative chest computerized tomography (CT) will be checked to identify the postoperative lung complications.
This study compares the two mechanical ventilation strategies in obese patients undergoing bariatric surgery: pressure-controlled ventilation(PCV) and pressure-controlled ventilation volume-guaranteed（PCV-VG). This is a randomized controlled trial with a sample size of 100 patients whose body mass index(BMI) is over 30kg/m².