The risk of complication associated with airway in obese patient is important. The result of pre-oxygenation gives the clinician a prolonged non-hypoxic apnea time. The relation between FRC and non-hypoxic apnea time has been correlated. However, the best condition to accomplish the pre-oxygenation in morbidly obese patient has yet to be described in the medical literature. A study previously done in our hospital (EPO2-PV) compared the effect of different positions and ventilation modes on the FRC in the laboratory. A significant difference has been established on the FRC between the inverse Trendelenburg position with positive pressure ventilation and the head up ("beach-chair") position without positive pressure. The current study, EPO2-A is designed to compared the two positions and ventilation modes during the induction of general anesthesia on morbidly obese and correlate the difference in FRC to difference in apnea time.