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.
Adults aged 18 to 80 years
Patients with an ASA physical status of I, II, or III
Individuals with a body mass index (BMI) between 18 and 35 kg/m²
History of or active upper or lower respiratory tract infection within the past month
Pulmonary emphysematous/bullous disease or COPD
Pre-existing significant atelectasis or consolidation (Preoperative LUS showing a score of 3 consolidation or ≥2 regions with a score ≥2)
Severe obstructive sleep apnea requiring CPAP therapy
Parallel
Titrated Oxygen
Procedure/SurgeryThis intervention is distinguished by the use of real-time Oxygen Reserve Index (ORI) monitoring to guide individualized intraoperative FiO₂ titration. Unlike fixed-FiO₂ strategies commonly used in anesthesia practice, this protocol continuously adjusts FiO₂ based on ORI values measured with the Masimo Rad-97 device. FiO₂ is increased or decreased in increments of 0.05 according to predefined ORI thresholds to maintain patients within a targeted normoxemic range. The intervention is entirely noninvasive and integrates standardized lung ultrasound (LUS) assessments and spirometry to evaluate postoperative aeration loss and respiratory function. This dynamic, physiology-based oxygen management approach differentiates the intervention from routine fixed-oxygen administration used in other clinical studies.
Fixed oxygen
Procedure/SurgeryThis intervention uses a standard, non-individualized oxygen administration approach in which FiO₂ is maintained at a constant 50% throughout the entire surgical procedure. After preoxygenation with 80% FiO₂ for 3 minutes, the FiO₂ is set at 0.50 immediately after intubation and is not modified in response to patient physiology or ORI measurements. PEEP is fixed at 5 cmH₂O, and a standardized alveolar recruitment maneuver is applied at the beginning of surgery. This fixed-FiO₂ strategy differs from the ORI-guided titration group by avoiding dynamic oxygen adjustments and reflects conventional intraoperative oxygen management commonly used in clinical practice.
Change in Total Lung Ultrasound (LUS) Score
The primary outcome of the study is the change in the total Lung Ultrasound (LUS) score obtained using a standardized 12-zone lung ultrasound protocol. Each hemithorax was evaluated in six regions-anterior, lateral, and posterior lines, each divided into superior and inferior zones-resulting in a total of 12 assessed areas. Each zone was scored from 0 to 3 based on the degree of aeration, yielding a total score ranging from 0 to 36, with higher scores indicating greater aeration loss and atelectasis. Accordingly, the difference between the preoperative LUS score and the LUS score measured at 30 minutes after extubation was defined as the primary endpoint of the study.
Change in Forced Vital Capacity (FVC)
Spirometry is performed preoperatively and repeated at 24 hours postoperatively. Forced Vital Capacity (FVC) is defined as the total volume of air that can be forcibly exhaled from the lungs after a maximal inhalation.
Change in Forced Expiratory Volume in 1 Second (FEV1)
Spirometry is performed preoperatively and repeated at 24 hours postoperatively. FEV1 is defined as the volume of air exhaled during the first second of a forced expiration.
Change in FEV1/FVC Ratio
Spirometry is performed preoperatively and repeated at 24 hours postoperatively. The ratio is calculated by dividing the Forced Expiratory Volume in 1 Second (FEV1) by the Forced Vital Capacity (FVC). The result is multiplied by 100 and expressed as a percentage.
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