Individualized Inspired Oxygen Fraction Titration During Lung Surgery (iOXY-LUNG)

The goal of this clinical trial is to determine whether individualized oxygen adjustment during lung surgery lowers the risk of major complications. The study will include adults undergoing planned surgery on one lung that requires more than one hour of one-lung ventilation. One-lung ventilation means that only one lung is ventilated during part of the operation. The main question is: Does individualized oxygen adjustment, compared with continuous 100% oxygen, lower the risk of death or major complications within 30 days after surgery? Researchers will enroll 628 participants at three hospitals in China. Participants will be randomly assigned to two groups: * Individualized inspired oxygen titration group: The anesthesiologist will adjust the oxygen concentration according to blood oxygen saturation, measured continuously using a pulse oximeter. * Pure oxygen group: The anesthesiologist will maintain 100% oxygen from the start of general anesthesia until removal of the tracheal tube. Both groups will receive 100% oxygen before one-lung ventilation begins. In the individualized group, oxygen adjustment will continue after ventilation of both lungs resumes. Before removal of the tracheal tube, the anesthesiologist may raise the oxygen concentration for safety. Both groups will receive treatment if blood oxygen levels become too low. Researchers will assess participants during hospitalization and through 30 days after surgery. Follow-up after discharge will take place by telephone or outpatient assessment. Researchers will compare deaths and major complications affecting the lungs, heart, brain, or kidneys. They will also assess recovery and safety.

Inclusion Criteria: * Able and willing to provide written informed consent. * Age 18 years or older. * Scheduled for elective unilateral lung surgery requiring one-lung ventilation, with an anticipated one-lung ventilation duration of more than 1 hour. * American Society of Anesthesiologists (ASA) physical status I-III. Exclusion Criteria: * Pregnancy or lactation. * History of thoracic surgery. * New York Heart Association class III-IV heart failure or Canadian Cardiovascular Society class III-IV coronary artery disease. * Acute cardiovascular or cerebrovascular disease within the preceding 6 months or renal insufficiency requiring dialysis. * Intracranial injury or tumor. * Psychiatric illness, cognitive impairment, communication or language difficulties, or other circumstances expected to prevent follow-up or data collection. * Participation in another interventional trial.