Several studies show how patients with hyperoxia after cardiac arrest has increased mortality, but the association of hyperoxia before cardiac arrest and myocardial damage has never been investigated. Neither has the association between hyperoxia after cardiac arrest and myocardial injury.

Our research hypothesis is that hyperoxia before cardiac arrest aggravates myocardial damage, secondly we wish to analyze the association between hyperoxia after cardiac arrest and myocardial injury.

The exposure variables is oxygenation within 48 hours before and 48 hours after cardiac arrest, our primary outcome is myocardial damage and will be measured as peak troponin within 30 days after cardiac arrest.

Inclusion Criteria:

• 18 years or older
• With a record of ICD-10 diagnosis of cardiac arrest in 2014, admitted to a hospital in the Capital Region of Denmark.
• First recorded cardiac arrest in 2014
• Admitted to ICU
• Serum troponin measured within 7 days after cardiac arrest

Exclusion Criteria:

• Out of hospital cardiac arrest, OHCA
• In of hospital cardiac arrest, IHCA, but with no registered saturation before cardiac arrest.

Patients with in hospital cardiac arrest, who had return of spontaneus circulaiton and was then admitted to ICU in a hospital in the Capital Region of Denmark.