Oxygen therapy has been historically considered a mainstay of treatment in patients suffering suspected acute myocardial infarction (AMI). Recent data suggests that oxygen therapy during AMI may actually have deleterious effects, possibly via coronary vasoconstriction and increased free radical concentration leading to reperfusion injury. However, trials evaluating specific clinical outcomes have been lacking. This study sought to evaluate outcome differences in patients who received routine supplemental oxygen compared with those maintained on ambient air during treatment for suspected AMI. The multicenter, open-label, randomized, controlled trial included Swedish citizens 30 years of age or older, with baseline oxygen saturation of 90 percent or greater, electrocardiogram findings consistent with AMI or elevated troponin, and symptoms of AMI for less than six hours. Patients in the oxygen group received supplemental oxygen via open facemask at 6 liters per minute for 6 to 12 hours. Primary outcome was death from any cause at one year. Secondary outcomes were death from any cause at 30 days, as well as rehospitalization with AMI, rehospitalization with heart failure, and cardiovascular death. After randomization, hazard ratios were calculated for 3014 subjects in the oxygen group and 3212 subjects in the ambient air group. In evaluation of the primary end point, there was no difference between patients who received oxygen when compared with those assigned to the ambient air group (hazard ratio, 0.97; 95% confidence interval (CI) 0.79-1.21). Similarly, there was no significant difference between the groups with regards to secondary outcomes of all-cause mortality, rehospitalization with MI, or a composite of these two measures at either 30 days or one year. The authors concluded that there was no mortality benefit for the routine use of supplemental oxygen in patients with suspected AMI who are not hypoxic. Comment: This study is the first to evaluate a primary clinical outcome related to the use of oxygen as a treatment for AMI in patients without hypoxemia. While this study was a high quality randomized controlled trial, the investigators were not able to reach their desired power level. By excluding patients with hypoxemia and altered mental status (due to inability to consent), there were large numbers of patients with AMI symptoms where oxygen therapy outcomes could not be determined. While the routine administration of oxygen for AMI appears to be without benefit at this point, more research is indicated to determine harm or benefit in a broader context. Of note, the AVOID trial, which previously demonstrated harm in use of oxygen with these patients, included subjects with higher presenting oxygen saturations and administered oxygen at 8 liters per minute. This could be interpreted as need for further investigation to evaluate the potential for harm in the subgroup of patients with a higher baseline oxygen saturation.
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