Supplemental Oxygen During STEMI Might Increase Myocardial Injury
Clinical question: Does routine oxygen supplementation in patients with STEMI increase myocardial injury?
Background: Because of physiologic and clinical studies conducted before the era of acute coronary intervention, supplemental oxygen routinely is administered to patients with STEMI, regardless of oxygen saturation; however, recent studies have shown possible adverse effects of oxygen, including increased reperfusion injury and increased adverse outcomes in small clinical trials.
Study design: Multicenter, prospective, randomized, controlled trial (RCT).
Setting: Nine metropolitan hospitals.
Synopsis: This multicenter study included 441 patients with STEMI who were 18 years or older and were randomized by paramedics to receive either 8 L/min of oxygen or no supplemental oxygen. All patients then received protocolized care. The primary endpoint of myocardial infarct size, determined by mean peak of creatine kinase, was significantly increased in the oxygen group compared to the no oxygen group (1948 vs. 1543 U/L; means ratio, 1.27; 95% confidence interval, 1.04-1.52; P=0.01). There were nonsignificant increases of secondary endpoints in the oxygen group, including rate of recurrent myocardial infarction (5.5% vs. 0.9%; P=0.006), frequency of arrhythmia (40.4% vs. 31.4%; P=0.05), and size of infarct on six-month cardiac MRI (n=139; 20.3 vs. 13.1 g; P=0.04).
This study has several limitations: It was powered to detect differences in biomarkers (not clinical endpoints) and the treatment was not blinded to paramedics, patients, or cardiology teams.
Bottom line: Supplemental oxygen administration in patients with STEMI might increase infarct size and lead to poorer clinical outcomes; however, larger clinical trials are warranted.
Citation: Stub D, Smith K, Bernard S, et al. Air versus oxygen in ST-segment-elevation myocardial infarction. Circulation. 2015;131(24):2143-2150.