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.
Aged 18-75 years
ASA physical status I-III
Scheduled for elective laparoscopic unilateral inguinal hernia repair under general anesthesia
Body mass index (BMI) < 35 kg/m²
Age below 18 or above 75 years
ASA physical status IV-V
Emergency surgical procedure
Severe chronic or restrictive pulmonary disease
Adult patients scheduled for elective laparoscopic unilateral inguinal hernia repair under general anesthesia at Fatih Sultan Mehmet Training and Research Hospital, Istanbul, Turkey.
Cohort
Prospective
Standard PEEP Ventilation
Procedure/SurgeryMechanical ventilation with a fixed positive end-expiratory pressure (PEEP) of 5 cmH₂O applied throughout the surgical procedure. Volume-controlled ventilation mode with tidal volume 6-8 ml/kg ideal body weight, inspiratory-to-expiratory ratio 1:2, and fraction of inspired oxygen (FiO₂) 0.40. Respiratory rate adjusted to maintain end-tidal CO₂ (EtCO₂) between 35-40 mmHg. No recruitment maneuver is performed.
Individualized PEEP Ventilation
Procedure/SurgeryIndividualized PEEP determined by a stepwise recruitment maneuver followed by PEEP titration, applied at 10 minutes after Trendelenburg positioning. The optimal PEEP level is identified based on best dynamic lung compliance and maintained for the remainder of surgery. All other ventilation parameters are identical: volume-controlled mode, tidal volume 6-8 ml/kg, I/E ratio 1:2, FiO₂ 0.40, EtCO₂ 35-40 mmHg.
Perioperative Oxygenation Assessed by Oxygen Reserve Index (ORI)
Continuous non-invasive monitoring of the Oxygen Reserve Index (ORI) to assess perioperative oxygenation. ORI values range from 0 to 1 and reflect partial oxygen pressure changes in the 100-200 mmHg range. ORI is recorded at six time points: before anesthesia induction (T0), 5 minutes after intubation (T1), 10 minutes after Trendelenburg positioning (T2), 20 minutes after Trendelenburg positioning (T3), after desufflation (T4), and at postoperative 20 minutes (T5). ORI values will be compared between the standard PEEP and individualized PEEP groups.
Perioperative Atelectasis Assessed by Lung Ultrasound Score
Lung aeration assessed using a 12-zone lung ultrasound protocol in supine position. Each zone is scored 0-3: 0 = normal aeration (A-lines, fewer than 3 B-lines), 1 = mild interstitial syndrome (3 or more well-defined B-lines), 2 = moderate interstitial syndrome (confluent B-lines), 3 = severe interstitial syndrome or lung consolidation. Total score ranges from 0 to 36. Scores will be compared between standard PEEP and individualized PEEP groups.
Dynamic Lung Compliance (Cdyn)
Dynamic lung compliance (Cdyn), expressed in mL/cmH₂O, recorded from the anesthesia ventilator at six predefined perioperative time points. All six observations represent repeated measurements of the same outcome using the same unit of measure
Arterial Partial Pressure of Oxygen (PaO₂)
Arterial partial pressure of oxygen (PaO₂), measured in mmHg in blood samples obtained through the radial arterial cannula at the predefined time points.
Postoperative Pulmonary Complications
Incidence of postoperative pulmonary complications including desaturation, dyspnea, pneumonia, or respiratory-related hospital readmission assessed at postoperative day 7 via telephone follow-up.
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