ORI-Guided FiO₂ Titration in Prone Spine Surgery: Impact on Postoperative Atelectasis Assessed by Lung Ultrasound

Atelectasis is a frequent pulmonary complication after general anesthesia, often triggered by preoxygenation and intraoperative hyperoxia. High inspiratory oxygen fractions (FiO₂) can promote absorption atelectasis, ventilation-perfusion mismatch, hemodynamic alterations, and oxidative injury. This study evaluates the effect of two intraoperative oxygen management strategies-oxygen reserve index (ORI)-guided FiO₂ titration versus fixed 50% FiO₂-on postoperative atelectasis in patients undergoing thoracolumbar spine surgery under general anesthesia. Atelectasis severity will be assessed using lung ultrasonography (LUS), scored across 12 thoracic regions (0-3 per region, total 0-36), while respiratory function changes will be examined via preoperative and 24-hour postoperative spirometry (FVC, FEV₁, FEV₁/FVC). Because postoperative spirometry may be influenced by pain, Numeric Rating Scale (NRS) scores will be recorded to help distinguish true restrictive patterns from pain-limited respiratory effort. The study aims to determine whether ORI-guided FiO₂ titration can reduce postoperative atelectasis and improve respiratory outcomes compared with a fixed FiO₂ approach.

Inclusion Criteria: 1. Adults aged 18 to 80 years 2. Patients with an ASA physical status of I, II, or III 3. Individuals with a body mass index (BMI) between 18 and 35 kg/m² Exclusion Criteria: 1. History of or active upper or lower respiratory tract infection within the past month 2. Pulmonary emphysematous/bullous disease or COPD 3. Pre-existing significant atelectasis or consolidation (Preoperative LUS showing a score of 3 consolidation or ≥2 regions with a score ≥2) 4. Severe obstructive sleep apnea requiring CPAP therapy 5. NYHA class III-IV heart failure, EF \35 kg/m² 8. Severe anemia (Hb \18 g/dL) 9. Non-diagnostic or unclear preoperative lung ultrasound images 10. Preoperative SpO₂ ≤ 94% 11. Inability to apply the sensor due to finger deformity, or inadequate signal caused by digital hypoperfusion