This single-center randomized interventional study evaluated the biological effects of two perioperative oxygen strategies in adults undergoing elective laparoscopic lower abdominal surgery under standardized general anesthesia. Participants were assigned to receive either normoxia (FiO2 0.35) or hyperoxia (FiO2 0.80) after intubation and throughout the intraoperative period. The study assessed perioperative changes in circulating biomarkers related to pulmonary epithelial stress, endothelial glycocalyx injury, oxidative stress, and inflammation, together with blood gas and hemodynamic parameters. The study was completed before registration and is being registered retrospectively.

Perioperative oxygen administration is widely used during general anesthesia, but the biological effects of liberal oxygen exposure remain uncertain. This randomized parallel-group study compared a normoxic strategy (FiO2 0.35) with a hyperoxic strategy (FiO2 0.80) in adult patients undergoing elective laparoscopic lower abdominal surgery. The assigned inspired oxygen fraction was initiated immediately after tracheal intubation and maintained intraoperatively under volume-controlled ventilation with otherwise standardized anesthetic management.

The primary objective was to compare perioperative changes in circulating biomarkers reflecting endothelial glycocalyx injury and inflammatory activation. Biomarkers assessed included syndecan-1, sialic acid, surfactant protein-A, ischemia-modified albumin, tumor necrosis factor-alpha, and total protein. Secondary assessments included arterial and venous blood gas variables, lactate, mean arterial pressure, and heart rate.

This study was completed before registry submission and is being entered retrospectively for transparency.

Inclusion Criteria:

• Adults aged 18 to 70 years
• Scheduled for elective laparoscopic lower abdominal surgery
• Expected surgery duration of at least 90 minutes
• ASA physical status I to III
• Body mass index 18.5 to 35 kg/m2
• Planned management under standardized general anesthesia with volume-controlled ventilation

Exclusion Criteria:

• Known chronic pulmonary disease, including chronic obstructive pulmonary disease or asthma requiring regular medication
• Baseline peripheral oxygen saturation below 92% on room air
• Significant cardiovascular instability
• Severe hepatic or renal dysfunction
• Active infection or systemic inflammatory disease
• Use of systemic corticosteroids or immunosuppressive therapy
• Pregnancy
• Inability to provide informed consent
• Anticipated difficult airway
• Expected need for postoperative mechanical ventilation