The complete study protocol (Version 2.3) is available here

• Patient scheduled for open thoracic or video-assisted thoracoscopic surgery under general anesthesia requiring OLV (no emergency surgery)
• BMI < 35 kg/m2
• age ≥ 18 years
• expected duration of surgery > 60 min
• planned lung separation with double lumen tube (DLT, not for study purpose only)
• most of ventilation time during surgery expected to be in OLV

• COPD GOLD grades III and IV, lung fibrosis, documented bullae, severe emphysema, pneumothorax
• uncontrolled asthma
• Heart failure NYHA Grade 3 and 4, Coronary Heart Disease CCS Grade 3 and 4
• previous lung surgery
• documented pulmonary arterial hypertension >25mmHg MPAP at rest or > 40 mmHg syst. (estimated by ultrasound)
• documented or suspected neuromuscular disease (thymoma, myasthenia, myopathies, muscular dystrophies, others)
• planned mechanical ventilation after surgery
• bilateral procedures
• lung separation with other method than DLT (e.g. difficult airway, tracheostomy)
• surgery in prone position
• persistent hemodynamic instability, intractable shock
• intracranial injury or tumor
• enrollment in other interventional study or refusal of informed consent
• pregnancy (excluded by anamnesis and/or laboratory analysis)
• esophagectomy, pleural surgery only, sympathectomy surgery only, chest wall surgery only, mediastinal surgery only, lung transplantation
• presence before induction of anaesthesia of one of the adverse events, listed as postoperative pulmonary complications (aspiration, moderate respiratory failure, infiltrates, pulmonary infection, atelectasis, cardiopulmonary edema, pleural effusion, pneumothorax, pulmonary embolism, purulent pleuritis, lung hemorrhage)
• documented preoperative hypercapnia > 45mmHg (6kPa)