Oxygen Therapy in Suspected Acute Myocardial Infarction
Selected in The New England Journal of Medicine by D. Milasinovic
Hofmann R, James SK, Jernberg T, Lindahl B, Erlinge D, Witt N, Arefalk G, Frick M, Alfredsson J, Nilsson L, Ravn-Fischer A, Omerovic E, Kellerth T, Sparv D, Ekelund U, Linder R, Ekström M, Lauermann J, Haaga U., Pernow J, Östlund O, Herlitz J, and Svensson L.
August 28, 2017 DOI: 10.1056/NEJMoa1706222
LinkRead the abstract
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Why this study – the rationale/objective?
Despite its clinical use, the effect of routine oxygen therapy on clinical outcomes in AMI patients is unclear. Previous data even signaled a potential harm, in terms of a larger enzymatic infarct size in oxygen-treated patients.
How was it executed – the methodology?
- Registry-based (SWEDEHEART) randomization (1:1) of 6629 patients with suspected AMI and baseline oxygen saturation ≥90% to either 6 liters per minute of supplemental oxygen for 6-12 hours, through an open mask, or ambient air.
- Primary endpoint was all-cause death at one year in the intention-to-treat population.
What is the main result?
- Median oxygen saturation was 99% after oxygen treatment (median treatment duration 11.6 hours) vs. 97% in the control group (ambient air), but hypoxemia (oxygen saturation <90%) occurred less frequently in the group on oxygen treatment (1.9% vs. 7.7%, p<0.001).
- At 1 year, all-cause mortality was similar (5.0% in the oxygen-treated vs. 5.1% in the ambient-air group, p=0.8), as was re-hospitalization due to MI (3.8% vs. 3.3%, respectively, p=0.3). Similarly, there were no differences in clinical outcomes between the groups at 30 days.
- No difference was observed in the median peak values of high-sensitivity Troponin T (946.5 ng/L in patients on oxygen treatment vs. 983.0 ng/L in patients on ambient air, p=0.97).
Critical reading and the relevace for clinical practice
Recognizing the fact that this seems to have been by far the largest randomized clinical study on the effect of oxygen therapy in AMI, there are at least two observations that perhaps ought not be overlooked when interpreting the overall study results. First, of the enrolled patients (n=6629), MI was the final diagnosis in 5010, and only 2952 (44.5%) had a STEMI. Second, whereas the study’s sample size calculation presupposed the one-year mortality rate of approx. 14%, the actually observed mortality was 5%. Both of the aforementioned points may suggest a relatively high inclusion of lower-risk patients that potentially could have diluted the effect of oxygen therapy in higher-risk AMI patients.
Nevertheless, the fact that the registry-based design makes the mortality gap transparent (higher mortality rate in AMI patients entered into the same registry, but not part of the randomized study), seems to add to the precision of the study’s conclusion – no apparent clinical benefit of oxygen therapy in normoxemic patients with suspected AMI.