The goal of this clinical trial is to determine whether different ventilatory strategies improve oxygenation and hemodynamic stability in patients undergoing robot-assisted radical prostatectomy under general anesthesia. The study will also evaluate the safety and physiological effects of applying positive end-expiratory pressure (PEEP) and alveolar recruitment maneuver (ARM) during surgery.

The main questions this study aims to answer are:

Does the application of PEEP or PEEP combined with ARM improve intraoperative oxygenation compared with conventional mechanical ventilation?

How do PEEP and ARM affect intraoperative hemodynamic parameters such as cardiac output and stroke volume during pneumoperitoneum and steep Trendelenburg positioning?

Are there any adverse events associated with the use of these ventilatory strategies during surgery?

Researchers will compare three ventilation strategies-conventional ventilation without PEEP, ventilation with PEEP alone, and ventilation with PEEP combined with ARM-to evaluate their effects on perioperative oxygenation and cardiovascular function.

Participants will:

Undergo robot-assisted radical prostatectomy under general anesthesia

Be randomly assigned to receive one of three ventilatory strategies during surgery

Receive standardized anesthetic management and intraoperative monitoring

Have arterial blood gas analysis and hemodynamic measurements performed at predefined time points during surgery and recovery

In the ARM group, alveolar recruitment maneuvers were performed three times at predefined time points after pneumoperitoneum and Trendelenburg positioning: 40 minutes (T2), 70 minutes (T3), and 110 minutes (T4) after pneumoperitoneum. ARM was conducted using a stepwise increase in PEEP with a maximum peak inspiratory pressure of 40 cmH₂O: PEEP was increased from 4 to 8 cmH₂O for 3 breaths, from 8 to 12 cmH₂O for 3 breaths, and from 12 to 16 cmH₂O for 10 breaths.

Sample size calculation was based on data obtained from a pilot study, using the PaO₂/FiO₂ ratio as the primary outcome for comparison among the three groups. Assuming an effect size of 0.25, a statistical power of 0.80, and a two-sided significance level of 0.05, a total sample size of 48 patients was required. To account for a potential dropout rate of 20%, a total of 60 patients were enrolled in the study.

Repeated measurements of PaO₂/FiO₂ ratio and other longitudinal variables will be analyzed using repeated-measures analysis of variance or generalized estimating equations, as appropriate. A p-value <0.05 will be considered statistically significant. Statistical analyses will be performed using SPSS version 30 (IBM Corp., Armonk, NY, USA).

Inclusion Criteria:

• Adult patients with American Society of Anesthesiologists (ASA) physical status I-III scheduled for elective robot-assisted radical prostatectomy under general anesthesia

Exclusion Criteria:

• uncontrolled asthma, chronic obstructive pulmonary disease (defined as a forced expiratory volume in 1 second to forced vital capacity ratio <60% or forced expiratory volume in 1 second <60% of the predicted value)
• hypoxemia (oxygen saturation <90% on room air)
• left ventricular ejection fraction <50%
• hypotension (systolic blood pressure <90 mmHg)
• body mass index ≥30 kg/m²
• conversion to open surgery, or intraoperative events that precluded protocolized ventilation.