NEW YORK (Reuters Health) – Despite its widespread use, there is no conclusive evidence that oxygen therapy benefits patients with acute myocardial infarction (AMI), according to a paper in the Cochrane Database of Systematic Reviews for June 16.

In fact, the data suggest that oxygen may actually do more harm than good.

Lead author Dr. Juan B. Cabello from Hospital General Universitario de Alicante, Spain, and his associates note that international guidelines for AMI often advocate oxygen therapy. It is believed to improve oxygenation of the ischemic myocardium and reduce pain, infarct size, and mortality.

However, it’s also biologically plausible that oxygen may be harmful, they say. Possible detrimental effects include reduced coronary artery blood flow, increased vascular resistance, reduced cardiac output, and reperfusion injury from increased oxygen free radicals.

Their literature review turned up three randomized controlled trials (n = 387) comparing oxygen 4-6 L/min with air anytime during the first 24 hours after symptom onset.

Only two trials had data for mortality. Among patients with confirmed AMI, 10 deaths occurred among 138 patients given oxygen and 3 among 156 given air. This yielded a relative mortality risk of 3.03 with oxygen therapy; however, this did not reach statistical significance and could be a chance occurrence, the researchers say.

Two studies had data on opiate analgesia as a proxy for pain. On this measure, there was no significant difference between the oxygen and air groups.

Dr. Cabello’s team points out that the data are surprisingly sparse, of poor quality, and pre-date advances in reperfusion techniques and trial methods.

“The need to clarify this uncertainty is urgent,” they conclude. To that end, they have submitted a proposal for a randomized controlled trial in the UK of oxygen during AMI in the pre-hospital setting.

“It is truly amazing how we, as cardiologists, have been employing this treatment without solid evidence,” Dr. Cabello says in a Cochrane Library press release.

Reference:

http://www.mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD007160/frame.html

The Cochrane Library 2010;6.