ENO2 and cardiac arrest: Although statistically there was no difference in the NSE and protein S-100 levels between the two groups, a higher NSE levels were reported in patients who received 1FiO2 and did not undergo therapeutic hypothermia.44 There is some evidence suggesting that O2 may not improve outcomes after MI and even worsen the outcome, increasing the risk of neurological injury after cardiac arrest and return of spontaneous circulation (ROSC).