Effect of Inspired Oxygen Concentration on Postoperative Atelectasis After VATS Lobectomy

• Low inspired oxygen concentration (FiO₂=50%) during one-lung ventilation (Procedure): Ventilation with initial FiO₂=50% during one-lung ventilation, combined with individualized PEEP titration. Oxygen concentration is dynamically adjusted based on SpO₂; ventilation duration at each FiO₂ level and total oxygen exposure burden are recorded.
• High inspired oxygen concentration (FiO₂=100%) during one-lung ventilaion (Procedure): Ventilation with FiO₂=100% throughout one-lung ventilation, combined with individualized PEEP titration (decremental PEEP titration selecting the highest PEEP corresponding to the lowest driving pressure).

Primary outcomes

• Non-operated lung atelectasis volume percentage [CT scans were performed at 60 ± 10 minutes after tracheal extubation to assess the volume ratio of atelectasis in the contralateral lung.]: Chest CT at 60±10 minutes after tracheal extubation

Secondary outcomes

• Incidence of postoperative pulmonary complications [Postoperative days 1-3]: PPC defined as Melbourne Postoperative Pulmonary Complication score ≥4
• QoR-15 quality of recovery score [Postoperative days 1-3]: 15-item Quality of Recovery questionnaire score
• Arterial blood gas analysis (oxygenation index) [Multiple time points: (1) preoperative preparation room; (2) 5 minutes after two-lung ventilation at induction; (3) 5 minutes after one-lung ventilation start; (4) 1 hour after one-lung ventilation; (5) 10 minutes after tracheal extubation]: PaO₂/FiO₂ ratio, PaO₂, PaCO₂, and pH at five predefined time points
• Intraoperative oxygen saturation [Intraoperative (during one lung ventilation)]: Oxygen saturation (pulse oxygen)
• Oxygen concentration exposure burden [Intraoperative (during one lung ventilation)]: Sum of FiO₂ × time; incidence and frequency of FiO₂ increase
• Incidence of intraoperative adverse events [Intraoperative (from induction to emergence)]: Incidence of intraoperative adverse events including hypoxemia (SpO₂ < 90%), hypotension (MAP decreased > 20% from baseline for > 3 minutes), new-onset arrhythmia, and cerebral oxygen desaturation (rSO₂ < 50% or > 20% decrease from baseline)
• Oxidative stress marker (MDA) [1 hour after one lung ventilation]: Arterial blood malondialdehyde (MDA) level at 1 hour after one lung ventilation
• Postoperative renal function (serum creatinine and eGFR) [Postoperative days 1 and 3]: Serum creatinine (SCr) and estimated glomerular filtration rate (eGFR) to assess postoperative acute kidney injury

Sex: All, ages: 18 Years to 65 Years

Inclusion Criteria:

Age 18-65 years Elective thoracoscopic (VATS) pulmonary lobectomy Anticipated one-lung ventilation duration >1 hour ASA physical status I-III

Exclusion Criteria:

Previous pulmonary surgery (including lobectomy, lung volume reduction surgery, or other lung resection) Pre-existing significant atelectasis (large collapse on preoperative CT) Contraindications to PEEP: intracranial hypertension, bronchopleural fistula, hypovolemic shock, right heart failure, giant bullae, pneumothorax Preoperative continuous oxygen therapy or mechanical ventilation, moderate-severe COPD BMI ≥ 30 kg/m² Ischemic cardiovascular and cerebrovascular diseases, such as myocardial infarction, ischemic stroke, and patients with coronary or cerebrovascular stents Patient refusal to participate

Withdrawal Criteria / Major Protocol Deviations:

Surgery changed to simple wedge resection Severe pleural adhesions (found intraoperatively) One-lung ventilation duration < 50 minutes Intraoperative blood loss > 500 ml Severe hypotension (MAP < 55 mmHg despite high-dose vasopressors) Unexpected non-thoracic surgical procedure Ventilation protocol interrupted (e.g., FiO₂ exposure < 80% of planned time in the low-oxygen group) Postoperative CT not completed or image quality unusable Subject withdrawal of informed consent