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.

Inclusion Criteria:

1. 20 - 70 years of age who are scheduled for robotic assisted laparoscopic prostatectomy at the Department of Urology, Gangnam Severance Hospital,
2. ASA-PS (American Society of Anesthesiology Body Rating) I-IlI,
3. Patients with a BMI of 35 kg/m2 or less

Exclusion Criteria:

1. Patients with lung disease
2. BMI >35kg/m2
3. Patients for whom positive end-tidal pressure cannot be applied (large bullae, severe cardiac disease)
4. patient refusal