Effect of PEP on Oxygen Saturation and Carbon Dioxide After Abdominal Surgery

Positive expiratory pressure( PEP) is routinely given to patients after surgery in order to improve lung function and oxygen saturation. 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 of PEP therapy on oxygen saturation and carbon dioxide after abdominal surgery. 80 patients will be investigated in RCT design with expiration using PEP or with expiration to a sham-PEP, a tube without resistance. At the end of the study we will also measure the effect of 10x3 deep breathing maneuvers without PEP or shamPEP. Primary outcome: Maximum and minimum levels of continuously measured oxygen saturation from pulse oximetry and transcutaneous carbon dioxide partial pressure during the trial.