Wednesday, August 11, 2010

Routine oxygen administration in acute MI: a trend toward harm?

Yes, according to a recent Cochrane review.

Main results
Three trials involving 387 patients were included and 14 deaths occurred. The pooled RR of death was 2.88 (95% CI 0.88 to 9.39) in an intention-to-treat analysis and 3.03 (95% CI 0.93 to 9.83) in patients with confirmed AMI. While suggestive of harm, the small number of deaths recorded meant that this could be a chance occurrence. Pain was measured by analgesic use. The pooled RR for the use of analgesics was 0.97 (95% CI 0.78 to 1.20).

Authors' conclusions
There is no conclusive evidence from randomised controlled trials to support the routine use of inhaled oxygen in patients with acute AMI. A definitive randomised controlled trial is urgently required given the mismatch between trial evidence suggestive of possible harm from routine oxygen use and recommendations for its use in clinical practice guidelines.

Last year Richard Conti wrote a thoughtful editorial expressing similar concerns:

I must admit that when I see a patient with an uncomplicated myocardial infarction receiving supplemental oxygen whose oxygen saturation is 95%, I usually ask the housestaff and nurses why this patient is receiving oxygen. Most of the time the answer is, ‘‘Well, that’s the way it has always been done,’’ or the nursing staff thinks these patients need oxygen.

Another answer relates to guideline recommendations by the ACC that supplemental oxygen in the first 6 hours of an acute uncomplicated myocardial infarction is okay.5 The level of evidence for this recommendation is C (based on expert opinion, case studies, and ‘‘Standard of Care,’’ (ie, the ‘‘Book of Common Wisdom’’). As far as I am concerned, that is not good enough.

He points out that oxygen may cause coronary vasoconstriction and acknowledges that it should be used in hypoxemic patients.

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