Effects of very early hyperoxemia on neurologic outcome after out-of-hospital cardiac arrest: A secondary analysis of the TTM-2 trial

PURPOSE: Hyperoxemia is common in patients resuscitated after out-of-hospital cardiac arrest (OHCA) admitted to the intensive care unit (ICU) and may increase the risk of mortality. However, the effect of hyperoxemia on functional outcome, specifically related to the timing of exposure to hyperoxemia, remains unclear.

METHODS: The secondary analysis of the Target Temperature Management 2 (TTM-2) randomized trial. The primary aim was to identify the best cut-off of partial arterial pressure of oxygen (PaO2) to predict poor functional outcome within the first 24 h from admission, with this period further separated into 'very early' (0-4 h), 'early' (8-24 h), and 'late' (28-72 h) periods. Hyperoxemia was defined as the highest PaO2 recorded during each period. Poor functional outcome was defined as a 6 months modified Rankin Score (mRS) of 4 to 6.

RESULTS: A total of 1,631 patients were analysed for the 'very early' and 'early' periods, and 1,591 in the 'late period'. In a multivariate logistic regression model, a PaO2 above 245 mmHg during the very early phase was independently associated with a higher probability of poor functional outcome (Odds Ratio, OR = 1.63, 95 % Confidence Interval, CI 1.08-2.44, p = 0.019). No significant associations were found for the later periods.

CONCLUSIONS: Very early hyperoxemia after ICU admission is associated with higher risk of poor functional outcome after OHCA. Avoiding hyperoxia in the initial hours after resuscitation should be considered.