For the primary endpoint we hypothesized that withholding oxygen may influence myocardial injury by 20%.20, 21 Assuming a mean peak cTnI level of 75 ± 35 mcg/L,22 for a
statistical power of 90% and a probability of a type I error of 0.01 using a 2-sided test, a sample
size of 326 (163 in each group) was calculated. This sample was increased to allow for the
positive predictive value of prehospital diagnosis of STEMI to be