The study aims at investigate whether low oxygen therapy during anesthesia improves oxygen partial pressure and lung function in the postoperative period after abdominal surgery. 200 patients scheduled for abdominal surgery will be randomized (1:1) to goal directed low oxygen concentration during and after anesthesia vs. fixed high oxygen concentration. Arterial oxygen partial pressure is the primary outcome and lung function a secondary explanatory outcome.

Postoperative hypoxia is a most common complication after major abdominal surgery. This study aims at investigate whether goal-directed low oxygen therapy during anesthesia improves oxygen partial pressure and lung function in the postoperative period after abdominal surgery.

200 adult patients scheduled for major abdominal cancer surgery lasting for more than 2 hours will be included after signed informed consent. Patients will then be randomized to either goal directed low oxygen or high oxygen during anesthesia and in the postoperative period.

Patients who are randomized to goal directed low oxygen will be given oxygen before the induction of anesthesia, with increasing fraction of inspired oxygen (FiO2) from 0.25 to 0.30 to 0.35 and so on. After intubation, the FiO2 is set to 0.25 to achieve a target saturation of 94-96%. Supplementary oxygen after surgery will be given with the same targets and with as little oxygen as necessary, Patients who are randomized to high oxygen will be given FiO2 of 1.0 before induction until end-tidal oxygen concentrations of 0.80 occur. The FiO2 will be reduced to 0.35 during anesthesia, followed by an increase in FiO2 to 0.80 during 5 minutes before extubating the patient, followed by FiO2 0.40 for at least thirty minutes after anesthesia. Oxgen will then be given at 3 liters a minute with a oxygen saturation goal of 98%.

Arterial blood gases, lung function measurements including diffusion capacity will be taken on the day before surgery. Blood gases will be taken during the first and second day after surgery and lung function tests during the second day after surgery. Blood gases and lung function will also be obtained at three months after surgery.

Inclusion Criteria:

• Being scheduled for a major abdominal cancer surgery lasting for more than 2 hours.
• Having a condition within American Society of Anesthesia Class 1-3.

Exclusion Criteria:

• Being at risk for a difficult intubation during anesthesia in the form of Mallampati score 3-4, or having a previous documentation of difficult intubation.
• Decline participation

Depends on what is allowed according to Swedish Ethical authority.