Supranormal arterial oxygen tension only during the first six hours after cardiac arrest is associated with unfavourable outcomes.

BACKGROUND: Multiple studies have investigated the association between hyperoxaemia following cardiac arrest (CA) and unfavourable outcomes; however, they have yielded inconsistent results. Most previous studies quantified oxygen exposure without considering its timing or duration. We investigated the relationship between unfavourable outcomes and supranormal arterial oxygen tension (PaO2 ), commonly defined as PaO2  > 100 mmHg, at specific time intervals within 24 h following CA.

METHODS: This retrospective observational study included 838 adult non-traumatic patients with CA. The first 24 h following CA were divided into four 6-h time intervals, and the first 6-h period was further divided into three 2-h segments. Multivariable logistic regression analyses were conducted to assess associations of the highest PaO2 and time-weighted average PaO2 (TWA-PaO2 ) values at each time interval with unfavourable outcomes at hospital discharge (cerebral performance categories 3-5).

RESULTS: The highest PaO2 (p = .028) and TWA-PaO2 (p = .022) values during the 0-6-h time interval were significantly associated with unfavourable outcomes, whereas those at time intervals beyond 6 h were not. The association was the strongest at supranormal PaO2 values within the 0-2-h time interval, becoming significant at PaO2 values ≥ 150 mmHg. During the first 6 h, longer time spent at ≥150 mmHg of PaO2 was associated with an increased risk of unfavourable outcomes (p = .038). The results were consistent across several sensitivity analyses.

CONCLUSION: Supranormal PaO2 during but not after the first 6 h following cardiac arrest was independently associated with unfavourable outcomes.