Optimal intraoperative positive end expiratory pressure (PEEP) improves the outcome. Optimal PEEP is not only very different among individuals, but each individual's optimal PEEP is affected by positioning, muscle paralysis, and several other factors. Several techniques have been used to determine the optimal PEEP. For example, electrical impedance tomography(EIT)can be performed at the bedside.However, the application of this technique requires special training, increases the workload of the care team, and the cost-efficiencyof this procedure remains to be determined.We hypothesized that optimal PEEP could be obtained by titration of intraoperative PEEP levels and FiO2with SpO2 guidance. Our secondary hypothesis was that maintenance of intraoperative optimal PEEP derived via this method improves intraoperative oxygenation and reduces the incidence of postoperative hypoxemia.We tested our hypothesis in patients undergoing robotic-assisted laparoscopic prostatectomy.

Lung-protective ventilation strategies are recommended for patients under mechanical ventilation with intermediate-risk and high-risk in order to minimize lung injury and respiratory complications of critically ill patients associated with mechanical ventilation , such as atelectasis and pneumonia. Low tidal volume (TV) had been proven protective . However, there is no consensus on what the optimal positive end expiatory pressure (PEEP) is for patients with healthy lungs undergoing general anesthesia, particularly for those who are undergoing abdominal surgery. A recent study showed that electrical impedance tomography (EIT) could be used to identify optimal PEEP, where both lungs collapse, hyper-insufflation is minimized, and the variation of optimal PEEP in patients with healthy lungs undergoing abdominal surgery is profound.Therefore, a fixed PEEP applied to all patients surely over-PEEP some and under-PEEP others. This study also demonstrates that maintaining the optimal PEEP intra-operatively not only improves intra-operative oxygenation but also reduces the incidence and severity of atelectasis post-operatively . Even though this study focuses on the improvement of physiology rather than the outcome, the benefit of intra-operative optimal PEEP is sustained for at least for one-hour post extubation. Therefore, optimized intra-operative PEEP could potentially have a positive impact onoutcomes. However, the cost-effectiveness of EIT used intraoperatively as routine practice still needs to be determined. Development of new methods which can be used intraoperatively and arecost-effective and user-friendly is an unmet demand.

Recently, Ferrando et al conducted a study in which the authors used minimal FiO2 to maintain clinically acceptable arterial blood O2 saturation by titrating PEEP. Even though this study was not randomized and sample size was insufficient to demonstrate improved outcomes, it clearly demonstrated its feasibility and safety. We hypothesize that titration of intraoperative PEEP using minimal FiO2 while maintaining clinically acceptable O2 saturation allows clinicians to identify the optimal PEEP. We will test this hypothesis on patients undegoing RALP. We chose this population because these patients have increased number of postoperative complications . Additionally, physicians are prone to using suboptimal ventilation strategies such as inappropriate tidal volumes and intraoperative PEEP in this population; therefore these patients are more likely to achieve maximal benefit with optimized intra-operative PEEP.

Inclusion Criteria:

• adult patients aged 18 years or older
• scheduled for elective robotic-assisted laparoscopic prostatectomy(RALP)
• ASA physical status of I-III

Exclusion Criteria:

• acute or chronic respiratory disorders
• pulmonary hypertension
• neuromuscular disease
• preoperative SpO2<95% on room air