Background Patients who have undergone thoracic and abdominal surgery receive lung atelectases after surgery. This in turn leads to poorer oxygenation, longer healing time and can contribute to increased risk of complications. In order to counteract atelectasis, patients are instructed by a physiotherapist to take deep inspiratory breaths and expire in a PEP-device (positive expiratory pressure) or incentive spirometry. The method is used routinely at our hospital and the patient breathes against 10-15 cm water resistance. This is repeated 10x3 ie 10 deep breaths and exhalation towards PEP then rest, breath, rest and another 10 breaths. This procedure should be done once an hour after surgery. The idea is that this will widen alveoli and fill atelectases with air, thus increasing the oxygen uptake, lowering the carbon dioxide level, and reducing the risk of postoperative complications.