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Oxygen Therapy in Suspected Acute Myocardial Infarction

November 7, 2017

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In this RCT, patients suspected of acute myocardial infarction (AMI) with O2 saturations >/=90% were randomized to receive supplemental oxygen vs ambient air.  There was no statistically significant difference between patients in death from any cause at 1 year.

Why does this matter?
Oxygen therapy in myocardial infarction makes sense. There is a mismatch between the myocardial oxygen demand and the ability of the body to supply it. Historically, there have been multiple smaller studies that showed a possible harm attributed to treatment with oxygen with saturations >90%. Most recently, the AVOID trial showed a statistically significant increase in recurrent MI, arrhythmia, and myocardial infarct size at 6 months in the oxygen group. A recent updated Cochrane review did not show a statistically significant difference in all-cause mortality.

DETO2X-SWEDEHEART investigators win the award for the best name
This was a large, multi-center, randomized clinical trial which utilized the national Swedish registry. They enrolled a total of 6629 patients with suspected MI and oxygen saturations >/= 90% and randomly assigned them to supplemental O2 (6L via open-face mask) vs ambient air. The primary outcome was death from any cause at 1 year. This differed from the AVOID trial which looked primarily at myocardial infarct size. There was no clear evidence to whether this translated into patient-centered outcomes.

An important point to note, this study also differed from the AVOID trial in that they enrolled patients with suspected MI, whereas the AVOID trial looked patients with STEMI diagnosed on paramedic 12-lead. In this trial, only 44.5% of patients were diagnosed with STEMI. This could account for the lower than estimated mortality rate (5% vs 14.4%). While this would lower the power, there was almost no difference in the two groups in terms of death at 1 year (5% vs 5.1%). Therefore, it is unlikely that a larger study would have detected a difference (thanks Jin Han).

Ultimately, I will continue to avoid utilizing oxygen in non-hypoxemic patients (>/= 90% O2 saturation) as there does not seem to be a benefit and may have possible harm as shown by previous studies. This is in line with the European Society of Cardiology 2017 Guidelines for STEMI management.

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What are your thoughts?