While a meta-analysis suggested that liberal oxygen therapy in hospitalized patients can be harmful, testing conservative oxygenation strategies seemed logical, especially after cardiac arrest, when the brain is most sensitive to oxidative stress. While subsequent randomized trials in critically ill patients did not demonstrate benefits to conservative oxygenation strategies, patients with cardiac arrest were underrepresented.
To address this gap, investigators identified more than 1800 unresponsive adults on mechanical ventilation after out-of-hospital or in-hospital cardiac arrest, with return of spontaneous circulation (ROSC) averaging 25 minutes after arrest. They were randomized to conservative oxygen therapy (target O2 saturation, 90−95%) or liberal oxygen (minimum FiO2 of 0.3, with no upper limit to O2 saturation). The primary outcome was survival with a favorable functional outcome at 180 days.
Key Results
- On average, patients in the liberal-oxygen group had O2 saturation at or above 97% about half the time (vs. about 20% of the time in the conservative-oxygen group).
- The primary outcome and all secondary outcomes, including mortality, were similar at 180 days.
Comments
This trial suggests that in out-of-hospital cardiac arrest with delayed ROSC, neither conservative nor liberal oxygen strategies offer outcome advantages. Looking at the totality of the evidence and recent guidelines, my post-cardiac arrest practice remains grounded in common sense: Avoid hypoxemia, avoid over-oxygenation, and stay in the middle ground (oxygen saturations, 90−98%).