PEP (positive expiratory pressure) is routinely given to patients after surgery in order to improve lung function. There is, however, no evidence of effect on lung function, postoperative pneumonia or any other outcome (Guimarães MMF, Tyson AF). The investigators aim to test the immediate effects on oxygen saturation and carbon dioxide. 65 patients will be investigated in RCT design with deep inspirations and expiration using PEP or only deep inspiration with expiration a placebo tube without resistance air. At the end of the study we will also measure the effect of 10x3 very deep inspirations and no expiratory no expiratory resistance. Primary outcome: continuous oxygen saturation from pulse oximetry and transcutaneous carbon dioxide.