The 'AIR-test', a method wherein inspiratory oxygen concentration is reduced to 21% and pulse-oximetry hemoglobin saturation (SpO2) is monitored, can be used to demonstrate the presence of an atelectasis-induced alveolar shunt. It remains uncertain whether an intraoperative positive AIR-test is associated with clinical outcomes. It is hypothesized that in a general surgical population, the incidence of postoperative pulmonary complications (PPC) is higher in patients with a positive AIR-test than in patients with a negative AIR-test. The aim of this study is to describe the incidence of PPC in patients with a positive and in patients with a negative AIR-test. Second, the investigators want to describe the incidence of a positive AIR-test and its association with the development of PPC. The investigators also want to evaluate whether mechanical ventilation strategy differs between patients with a positive and negative AIR-test.
The overall objective of this study is to describe the incidence of postoperative pulmonary complications in patients with a positive and negative AIR-test result. Second, the investigators wish to describe the incidence of a positive AIR-test and its association with the development of PPC. In addition, the investigators aim to describe whether mechanical ventilation strategy differs between patients with a positive and negative AIR-test.