Individualized vs Standard PEEP and Oxygen Reserve Index in Laparoscopic Hernia Surgery

Overview

During laparoscopic surgery under general anesthesia, lung function can be affected by increased abdominal pressure and patient positioning. Positive end-expiratory pressure (PEEP) is a ventilator setting that helps keep the lungs open during surgery. In standard practice, a fixed PEEP level is applied to all patients. An individualized PEEP approach tailors this setting to each patient based on lung recruitment maneuvers. This study investigates whether individualized PEEP improves oxygenation compared to standard PEEP in patients undergoing laparoscopic inguinal hernia surgery. Oxygenation will be continuously monitored using the Oxygen Reserve Index (ORI), a non-invasive sensor. Lung aeration will also be assessed before and after surgery using bedside lung ultrasound.

General anesthesia combined with pneumoperitoneum and Trendelenburg positioning significantly alters respiratory mechanics. These changes can reduce functional residual capacity (FRC), promote atelectasis, and impair gas exchange - particularly in laparoscopic surgery. Individualized PEEP, determined through a recruitment maneuver followed by PEEP titration, has been shown to reduce driving pressure and improve dynamic lung compliance compared to fixed PEEP strategies. The Oxygen Reserve Index (ORI) is a novel non-invasive monitoring parameter that continuously tracks partial oxygen pressure changes in the 100-200 mmHg range, providing early warning of desaturation before SpO2 drops. In this prospective observational study, 60 adult patients (ASA I-III, aged 18-75) scheduled for elective laparoscopic unilateral inguinal hernia repair under general anesthesia will be enrolled. Patients will receive either standard PEEP (5 cmH₂O) or individualized PEEP based on the attending anesthesiologist's routine clinical preference. Hemodynamic and respiratory parameters including ORI, SpO2, airway pressures, tidal volume, dynamic compliance, and BIS will be recorded at six time points: before anesthesia (T0), 5 minutes post-intubation (T1), 10 minutes post-Trendelenburg (T2), 20 minutes post-Trendelenburg (T3), after desufflation (T4), and at postoperative 20 minutes (T5). Lung ultrasound scoring (0-3 per zone, 12-zone protocol) will be performed preoperatively and postoperatively to assess atelectasis. Arterial blood gas analysis will provide additional oxygenation data. The primary outcome is the effect of individualized versus standard PEEP on perioperative oxygenation as measured by ORI. The secondary outcome is the comparison of atelectasis prevention efficacy between the two PEEP strategies assessed by lung ultrasound score.