ORI-Guided Oxygen Therapy During One-Lung Ventilation

High inspired oxygen concentrations (FiO₂) are commonly administered during general anesthesia to prevent hypoxemia. However, excessive oxygen administration may result in hyperoxemia, which has been associated with impaired hypoxic pulmonary vasoconstriction, increased oxidative stress, ventilation-perfusion mismatch, and postoperative pulmonary complications. During one-lung ventilation (OLV) for thoracic surgery, higher FiO₂ is often required because of increased intrapulmonary shunting, making hyperoxemia a frequent occurrence. The Oxygen Reserve Index (ORI) is a noninvasive pulse oximetry-derived parameter that reflects moderate hyperoxemia (PaO₂ approximately 100-200 mmHg) and may facilitate more precise oxygen titration than pulse oximetry alone.

Inclusion Criteria: * Adults aged ≥19 years * Scheduled for elective lung surgery requiring one-lung ventilation * Written informed consent Exclusion Criteria: * Severe pulmonary hypertension. * Left ventricular systolic dysfunction. Withdrawal Criteria: * The participant or legally authorized representative requests withdrawal from the study. * An adverse event occurs that precludes continued participation in the study. * The planned surgery or study procedures are not performed (e.g., ORI monitoring is not applied or arterial blood gas analysis is not performed). * Perfusion Index is less than 2 during the study. * A major violation of the inclusion or exclusion criteria is identified after enrollment. * The participant fails to comply with the study protocol, potentially affecting the validity of the study outcomes. * Continued participation is considered not to be in the participant's best interest. * In the investigator's judgment, any other condition arises that makes continued participation inappropriate.