This study evaluates the use and effects of supplementary oxygen in surgical and medical wards on patients admitted to a hospital in the capital region of Denmark. The population will be divided in to three groups according to their oxygenation status. The main outcome will be 30-day mortality, with secondary outcomes being Length of stay, 30-day admission to ICU, 30-day reoperations, 30-day readmission, and peak values within 30-days of C-reactive protein, S-Creatinine, Troponin.

Inclusion Criteria:

• Admission date between 1st of January 2014 to 29th of December 2014 on a hospital in the capital region of Denmark
• Age ≥18
• Unique (first) admission in database for either:
• Hip fracture requiring surgery
• Chronic obstructive pulmonary disease in exacerbation
• Acute mycardial infarction
• Open abdominal surgery

Exclusion Criteria:

• No data on saturation within 48 hours after
• Admission (Medical patients)
• Discharge from the post anaesthesia care unit (Surgical patients)
• No data on primary outcome (30-day mortality)

The study is made up of four main population groups, each group having their specific vulnerabilities, thus making the main outcome (30-day mortality) more likely to occur than in the background population.

The four groups are:

1. Patients undergoing laparotomy (open abdominal surgery)
2. Patients undergoing orthopedic surgery due to hip fracture
3. Patients admitted to hospital due to chronic obstructive pulmonary disease in exacerbation
4. Patients admitted to hospital with acute mycardial infarction