The effect of supplemental oxygen on surgical site infections was already investigated in several studies before. Although, oxygen is one of the most used medical therapy in hospitalized patients, the influence on the cardiovascular system is still unknown. Available data indicate beneficial effects of supplemental oxygen on cardiovascular function. Because, no evidence exists concerning the perioperative period, it is our objective to investigate supplemental oxygen in cardiac risk patients undergoing major abdominal surgery. Due to the significant reduction of BNP by inhibiting sympathetic nerve activity we hypothesize that supplemental oxygen have beneficial effects in perioperative BNP release in cardiac risk patients undergoing major abdominal surgery.

Inclusion Criteria:

Patients over 45 years on age, which fulfill 1 or more of the following 4 criteria undergoing non-cardiac surgery:

1. History of coronary artery disease
2. History of peripheral arterial disease
3. History of stroke OR
4. Any of 3 of 7 A) Age ≥ 70 years B) Undergoing major surgery C) History of congestive heart failure D) History of transient ischemic attack E) Diabetes and currently taking an oral hypoglycemic agent or insulin F) History of Hypertension

Further inclusion criteria are:

1. Written informed consent
2. Elective major abdominal open surgery or laparoscopically assisted procedures scheduled to take over two hours done under general anesthesia (colorectal, urology, gynecology, liver and pancreatic surgery)

Exclusion Criteria:

1. Symptoms of infection or sepsis
2. Preoperative inotropic therapy
3. Patients under ICU treatment
4. Oxygen dependent patients
5. History of severe heart failure and/or ejection fraction < 30%

Participants don´t know the randomized oxygen concentration. The postoperative follow up will be performed by a blinded research fellow.