This is a bit of “Not quite evidence as its not published yet,” but was presented at the American Heart Association Scientific Sessions this past week.
In the AVOID (Air Versus Oxygen In ST-elevation MyocarDial Infarction) trial, STEMI patients were assigned either to oxygen at 8L mask (318 patients) vs no oxygen unless under 94%, and titrated to get to that level via mask (320 patients). Oxygenation was initiated via EMS. Once in the hospital and STEMI confirmed, PCI was initiated and those receiving oxygen continued to do so in the cath lab. Baseline characteristics of the two groups were similar.
I’m not sure I agree with their primary endpoints being remotely useful (peak CK and troponin at 72 hours). Troponin I was similar, CK tended to be lower in the no O2 group. For secondary outcomes, there was an increase in the rate of recurrent MI in the oxygen group compared to the no-oxygen group, (5.5% vs 0.9%), and an increased frequency of significant arrhythmia (40.4% vs 31.4% – though I’m uncertain of their definition of “significant arrhythmia” and whether or not its clinically significant). At 6 months, there was no mortality difference between the groups (3.8% vs 5.9%; P = .32), however, those who received oxygen had increased myocardial infarct size on cardiac magnetic resonance, tended to have higher rates of recurrent MI (7.6% vs 3.6%; P =.07) and major adverse cerebrovascular or cardiovascular events (death, stroke, or MI) (21.9% vs 15.4%; P = .08).
So, should we kick the cannulas to the curb? Unfortunately, the primary outcomes are a bit strange using lab values rather than recurrent MI or mortality at 6 months. They used 8L facemasks and maintained them throughout catheterization, whereas we’ve typically maintained a 2L nasal cannula. This is a prime example of something that does not help, might cause harm, and increases cost without much benefit.