The following is a summary of “Oxygen targets and 6-month outcome after out of hospital cardiac arrest: a pre-planned sub-analysis of the targeted hypothermia versus targeted normothermia after Out-of-Hospital Cardiac Arrest (TTM2) trial,” published in the October 2022 issue of Critical Care by Robba, et al.

It’s not clear what the best oxygen levels are for people who have been brought back from cardiac arrest. The main goal of this study was to describe the values of partial pressure of oxygen (PaO2) and the times when hypoxemia and hyperoxemia happened in out-of-hospital cardiac arrest (OHCA) patients during the first 72 hours of mechanical ventilation. The second goal was to figure out how PaO2 affected the patients. Targeted hypothermia versus targeted normothermia after the OHCA (TTM2) trial: secondary analysis that was planned ahead of time. After the randomization, arterial blood gas values were taken every 4 hours for the first 32 hours and then every 8 hours until day 3. PaO2 less than 60 mmHg was used to describe hypoxemia, and PaO2 greater than 300 mmHg was used to describe severe hyperoxemia. At 6 months, data on deaths and poor neurological outcomes (as measured by the modified Rankin scale) were collected.

The study looked at data from 1,418 patients. The average age of the patients was 64±14 years, and 292 of them, or 20.6%, were women. About 24.9% of the patients had at least 1 episode of low oxygen levels, and 7.6% had at least 1 episode of high oxygen levels that were too high. Both low and high oxygen levels were linked to death at 6 months but not to a bad neurological outcome. The best cutoff point for hypoxemia was 69 mmHg (RR=1.009, 95% CI=0.93–1.09) and the best cutoff point for hyperoxemia was 195 mmHg (RR=1.006, 95% CI=0.95–1.06).

The area under the curve (PaO2-AUC) for hyperoxemia was linked to death in a way that was statistically significant (P=0.003). Hypoxemia and hyperoxemia are linked to death within 6 months in OHCA patients. The timing of exposure to high levels of oxygen causes this effect. For this group of patients, the level of oxygen should be carefully adjusted.