Suspected MI and Normal Oxygen Saturation? Don't Bother with Supplemental Oxygen

In 2015, the Air Versus Oxygen in Myocardial Infarction trial showed that supplemental oxygen conferred no benefit (and perhaps some harm) in patients with ST-segment elevation myocardial infarction (MI; NEJM JW Emerg Med Aug 2015 and Circulation 2015;131:2143). However, it has remained unclear whether this conclusion holds for patients with non–ST-segment elevation MI, so many of us have continued to use supplemental oxygen in such patients (despite normal oxygen saturations). To clarify the issue, researchers in Sweden conducted a registry-based, randomized, controlled trial.

They enrolled 6629 patients ≥30 years of age who presented to emergency medical services, emergency departments, coronary care units, or catheterization laboratories with symptoms of chest pain or shortness of breath, oxygen saturations ≥90%, and either elevated troponin levels or ischemic electrocardiographic changes. Patients were randomized to ambient air or oxygen delivered via facemask at 6 L/minute for 6 to 12 hours. The primary outcome was all-cause mortality at 1 year; secondary outcomes included all-cause mortality at 30 days and MI rehospitalization at 30 days and 1 year.

All patients were included in the intention-to-treat primary analysis, and 94% were included in the per-protocol secondary analyses. There were no significant differences between the oxygen and air groups in all-cause mortality at 1 year (5.0% and 5.1%), death at 30 days (2.2% and 2.0%), or MI rehospitalization at 30 days (1.4% and 0.9%) and 1 year (3.8% and 3.3%).