Supplemental Oxygen in Acute MI

September 2017

Vignette

You’re working a shift in TCC one morning when EMS brings in a patient are with chest pain and a “possible” STEMI. They wheel the patient in transfer him to the stretcher, at which time you notice that the patient is not on oxygen. Remembering from medical school that everyone gets ABCs, IV, O2, and monitor (especially with chest pain and a possible MI), you ask the paramedics why the patient isn’t on oxygen.

The paramedic points out that the patient’s oxygen saturation is 96% and according to their protocols, written by their Medical Directors, they are not supposed to place a chest pain patient on oxygen when the SpO2 is greater than 92% (unless the patient appears to be in respiratory distress). Questioning this, you bring up the question to Dr. Svancerek who curses and turns to Dr. Levine, who handily supplies you with articles (which were thankfully saved on his iPad) given to him by Dr. Gilmore. However, still being leery of the reasoning behind this logic (and that of ACLS updates), you suggest performing a search on the literature to really find the answer.

You find a journal club on this topic from 2012, but note in the bottom line that the evidence was poor at that time, and that while there was little evidence that oxygen provided benefit in patients with MI, there was also no evidence that oxygen caused any harm. Wondering if there has been any new evidence since this journal club, you perform your own search of the literature…

PICO Question
Population: Prehospital or emergency department patients with acute myocardial infarction “normal” oxygen saturation.
Intervention: Supplemental oxygen administration.
Comparison: Room air
Outcome: Mortality, length of stay, functional status, presence of clinically significant cardiac dysfunction.

Search Strategy
After choosing one obscure article from the 2012 journal club (Ukholkina 2009), PubMed was searched using the terms “oxygen” AND “myocardial infarction,” limited to clinical trials published within the last 5 years (http://tinyurl.com/yargaoz6). This resulted in 57 articles, from which the two most relevant were chosen. Additionally, the Cochrane Database of Systematic Reviews was searched to identify the most recent review of this topic to include as the fourth article.

Articles

Article 1: Stub D, Smith K, Bernard S, Nehme Z, Stephenson M, Bray JE, Cameron P, Barger B, Ellims AH, Taylor AJ, Meredith IT, Kaye DM; AVOID Investigators. Air Versus Oxygen in ST-Segment-Elevation Myocardial Infarction. Circulation. 2015 Jun16;131(24):2143-50.
ANSWER KEY

Article 2: Cabello JB, Burls A, Emparanza JI, Bayliss SE, Quinn T. Oxygen therapy for acute myocardial infarction. Cochrane Database Syst Rev. 2016 Dec19;12:CD007160.
ANSWER KEY

Article 3: Hofmann R, James SK, Jernberg T, et al; DETO2X–SWEDEHEART Investigators. Oxygen Therapy in Suspected Acute Myocardial Infarction. N Engl J Med. 2017 Aug 28.
ANSWER KEY

Article 4: Ukholkina GB, Kostyanov IY, Kuchkina NV, et al. Oxygen therapy in combination with endovascular reperfusion during the Airst hours of acute myocardial infarction: clinical and laboratory Aindings. International Journal of Interventional Cardioangiology 2009;9:45-51.
ANSWER KEY

Bottom Line

Several studies in recent years have suggested a harmful effect from excess oxygen therapy in a variety of conditions, including postcardiac arrest syndrome, sepsis, and stroke. While early guidelines for the management of patients with suspected myocardial infarction went so far as to suggest that all such patients receive supplemental oxygen, regardless of oxygen saturation levels (1990 ACC/AHA Guidelines), no actual evidence was used to support this recommendation.

The earliest and only blinded randomized controlled trial evaluating the effect of supplemental oxygen on outcomes in patients with myocardial infarction pre-dated many current management strategies, including routine revascularization, antithrombotic therapy, and glycoprotein iib/iiia inhibitor use (Rawles 1976). Since then, several additional studies have been conducted; unfortunately, none of these has been blinded. We sought to evaluate some of these studies and look at any high quality meta-analyses to further elucidate the benefit or harm of oxygen in MI in the era of revascularization.

Of the three trials evaluated, all were prospective but none were randomized. None of these observational studies found any difference in mortality between those patients treated with oxygen and those treated with room air. One study found an increase in peak CK levels in the oxygen group, but no difference in peak troponin I levels, which was the primary outcome (Stub 2015). The more recent DETO2X-SWEDEHEART study found no difference in any of the measured outcomes, including one-year mortality and rehospitalization with MI (Hofman 2017) Furthermore, a Cochrane review of this topic, published in 2016, found no difference in mortality, cardiac failure, recurrent infarction, or measures of infarct size (Cabello 2016).

While this evidence does not suggest any benefit from supplemental oxygen in patients with suspected MI, a couple of key outcome measures are lacking from the identified studies. In particular, none of the studies evaluated the effect of oxygen on long-term cardiac function, or, better yet, on the resulting quality of life, such as that measured by the Chronic Heart Failure Questionnaire. Despite this omission, there is no current evidence to support the routine use of oxygen in MI, and hence the most recent ACC/AHA guidelines only recommend supplemental oxygen for patients with “arterial oxygen saturation less than 90%, respiratory distress, or other high-risk features of hypoxemia”.