Steep trendelenburg posture or pneumoperitoneum for surgery causes ventilation problems during surgery, so finding a way to overcome is a challenging task for anesthesiologists. In this study, for patients undergoing robot assisted laparoscopic prostatectomy under general anesthesia, anesthesia is going to perform by applying conventional positive end-expiratory pressure (PEEP 5cmH2O) or individually determined positive end-expiratory pressure values for each patient using electrical impedance tomography. We plan to compare intraoperative ventilation through arterial blood gas analysis to find out the way to improve intraoperative ventilation.