Aim: To investigate the effect of high intra- and postoperative oxygen concentration (80%, as opposed to normally 30%) on surgical wound infection and pulmonary complications after abdominal surgery.

Background: Surgical wound infection is a common and serious complication. Tissue oxygen tension is often low after surgery and the resistance against infection depends on this factor through bacterial killing by neutrophils. Oxygen is a substrate in this reaction, and it is hypothesized that by increasing the arterial oxygen tension, the risk of surgical wound infection is reduced. Previous studies to test this hypothesis have shown entirely different results. Hence, the clinical decision between high and normal oxygen concentration is still controversial.

Primary hypothesis of study: Use of 80% oxygen decreases the incidence of surgical wound infection after abdominal surgery.

Secondary objectives: To investigate the effect 80% oxygen on pulmonary complications (atelectasis, pneumonia, respiratory insufficiency), second operation, mortality and length of postoperative hospitalization and admission to intensive care unit after abdominal surgery.

Inclusion Criteria:

• Age 18 years or older.
• Laparotomy, acute or elective. In case of gynaecological surgery only if malignancy is suspected (defined as risk of ovarian malignancy index >200 or a specimen with atypical or neoplastic cells).

Exclusion Criteria:

• Other surgery within 30 days (except surgery in local anaesthesia).
• Chemotherapy within 3 months.
• Inability to give informed consent.
• Inability to keep oxygen saturation above 90% without supplemental oxygen (measured preoperatively by pulse oximetry).