BMI-Adjusted PEEP During One-Lung Ventilation in Thoracic Surgery

One-lung ventilation (OLV) is required during many thoracic surgical procedures and is associated with reduced functional residual capacity, atelectasis, ventilation-perfusion mismatch, hypoxemia, and potentially ventilator-induced lung injury. Lung-protective ventilation strategies include low tidal volumes, limitation of airway pressures, and positive end-expiratory pressure (PEEP), but the optimal PEEP level during OLV remains uncertain. Fixed PEEP is simple and reproducible but does not account for individual patient characteristics. Body mass index (BMI) is readily available before anesthesia and is associated with respiratory mechanics, making it a pragmatic candidate for simple PEEP individualization. SIMPLE-PEEP is a prospective, multicenter, pragmatic, open-label, randomized clinical trial including 150 adults undergoing elective pulmonary resection under general anesthesia requiring OLV. Participants will be randomized to either fixed PEEP of 4 cmH2O or BMI-adjusted PEEP calculated as BMI/3 cmH2O. Other key components of lung-protective ventilation will be standardized between groups. The primary outcome is driving pressure during the first 20 minutes of OLV, assessed at 5, 10, and 20 minutes after OLV initiation. Secondary outcomes include respiratory system compliance and other respiratory mechanics, estimated mechanical power, oxygenation, intraoperative hypoxemia and rescue maneuvers, hemodynamic safety, vasopressor requirements, and exploratory postoperative respiratory outcomes. No investigational medicinal product, additional invasive procedure, or study-specific advanced monitoring is required.

Inclusion Criteria: 1. Age 18 years or older. 2. Scheduled thoracic surgery for pulmonary resection requiring general anesthesia and one-lung ventilation. 3. Written informed consent obtained before any study-specific procedure. Exclusion Criteria: 1. Simultaneous participation in another interventional clinical trial that could interfere with the protocol. 2. Severe hemodynamic instability before the start of the procedure, defined as continuous vasopressor infusion or shock of any etiology. 3. Severe restrictive lung disease, defined as total lung capacity \