BACKGROUND: In patients who are unresponsive after resuscitation from cardiac arrest, limiting oxygen exposure to that necessary to achieve acceptable oxygenation may increase the likelihood of survival with a favorable functional outcome.
METHODS: We randomly assigned unresponsive adults receiving mechanical ventilation in the intensive care unit (ICU) after cardiac arrest to conservative or liberal oxygen therapy. In the two groups, the default lower limit of arterial oxygen saturation as measured by pulse oximetry (Spo2) was 90%. In the conservative-oxygen group, the alarm for the upper limit of the Spo2 was set at 95%, and the fraction of inspired oxygen (Fio2) was decreased to 0.21 provided that the Spo2 was above the lower limit. In the liberal-oxygen group, there were no measures limiting the upper Spo2, but the minimum Fio2 permitted during mechanical ventilation was 0.3. The primary outcome was survival with a favorable functional outcome at 180 days, assessed with the Extended Glasgow Outcome Scale (GOS-E). Levels on the GOS-E range from 1 (death) to 8 ("upper good recovery"). We defined survival with a favorable functional outcome as a GOS-E level of 5 ("lower moderate disability") or higher.
RESULTS: A total of 1840 patients were recruited from 53 ICUs in Australia, New Zealand, and Ireland, with 882 assigned to conservative oxygen therapy and 958 assigned to liberal oxygen therapy. A favorable functional outcome at 180 days was observed for 313 of 819 patients (38.2%) in the conservative-oxygen group and 353 of 890 patients (39.7%) in the liberal-oxygen group (relative risk, 0.97; 95% confidence interval, 0.87 to 1.09; P = 0.65). No adverse events were reported.
CONCLUSIONS: Among unresponsive adults undergoing mechanical ventilation in the ICU after a cardiac arrest, the percentage who survived with a favorable functional outcome was not higher with conservative oxygen therapy than with liberal oxygen therapy. (Funded by the Health Research Council of New Zealand and others; LOGICAL Australian New Zealand Clinical Trials Registry number, ACTRN12621000518864.).
| Discipline Area | Score |
|---|---|
| Hospital Doctor/Hospitalists |  |
| Internal Medicine | |
| Intensivist/Critical Care | |
| Cardiology |  |
| Respirology/Pulmonology | |
The results can be widely applied.
Relevant for critical care doctors.
Oxygen *might* a not be good for us. Studies of patients with stroke and MI suggest that saturations over 96% might increase mortality. Two prior trials suggested a benefit for people with cardiac arrest with conservative oxygen use. It would figure that limiting higher saturations in someone who had a cardiac arrest and all of the brain injury that follows that there might be some improvement in outcomes. This trial stopped anyone from getting below 90% but in the conservative group, alarms would go off for saturations over 95%. This was a very large trial that appears to answer the question that conservative oxygen probably does not improve good neurologic outcomes. I do note there was no attempt to control for skin tone, which can throw off pulse oximetry and may be an important limitation. This would be important to any of my colleagues who attempt to prevent hyperoxemia. It may not be worth the effort.
In patients unresponsive and mechanically ventilated after cardiac arrest, this study found that a conservative oxygenation strategy did not differ from a liberal strategy for functional outcome at 180 days, mortality, or other outcomes. Although prior RCTs have somewhat variable results, most have shown no effect as this study confirms.
Interesting study, although I'm not sure about the comparators. Makes intuitive sense that there would be little difference.
