Effects of Oxygen Supply After Lung Isolation in Thoracic Surgery

The goal of this randomized clinical trial is to compare a liberal versus restrictive oxygen supply (fraction of inspired oxygen, FiO2) strategy in patients scheduled for thoracic surgery requiring one-lung ventilation during lung isolation. The primary and secondary outcome parameters are: * oxygenation of the blood after 30 minutes of one-lung ventilation, assessed by PaO2/FiO2 ratio * time to lung collapse after start of one-lung ventilation Participants in the control goup will receive an oxygen content of 100% before lung isolation, which will be subsequently decreased to achieve normoxia or mild hyperoxia (PaO2 of 75-120 mmHg). The intervention group will receive the previous, during two-lung ventilation set, oxygen content and after lung isolation oxygen supply will be increased to secure adequate oxygenation of the blood (PaO2 75-120 mmHg) during one-lung ventilation. The investigators hypothesize, that a higher fraction of inspired oxygen may impede hypoxic pulmonary vasoconstriction of the collapsed lung and thus decrease overall oxygenation performance during one-lung ventilation. Secondary endpoint will be the time to lung collapse, as a lower fraction of inspired oxygen and thus a higher nitrogen content may impede lung collapse.