Oxygen has long been considered the mother’s milk of medicine, particularly in EMS.
The first thing many patients get on arrival of EMS responders is a nonrebreather oxygen mask over their face cranked at 15 lpm whether they are hypoxic or not.
The thinking is it can’t hurt and can only help.
But check out the conclusion of a recent article in the noted British medical journal Heart, Routine use of oxygen in the treatment of myocardial infarction: systematic review, which examined the only randomized placebo-controlled trials of oxygen therapy in MI.
Conclusion: The limited evidence that does exist suggests that the routine use of high-flow oxygen in uncomplicated MI may result in a greater infarct size and possibly increase the risk of mortality.
The authors postulate that high flow oxygen may vasoconstrict the coronary arteries as well as possibly causing increased reperfusion injury.
In an accompanying editorial, Challenging doctors’ lifelong habits may be good for their patients: oxygen therapy in acute myocardial infarction, the editorial writers begin with the following observation:
“Medical history is filled with widely applied therapeutic habits that replicate longstanding practices based upon theories that have no true scientific background.” They note “the extraordinary discrepancy between the high incidence of myocardial infarction, affecting millions of people each year, and the paucity of scientific data on one of its most widely used methods of treatment.”
“The case against routine use of oxygen therapy which is presented in the paper from Wijesinghe et al is barely sufficient to formally rule out this technique; it should rather be considered, as the authors state in their conclusion, an incentive to design future trials to assess whether this treatment as used in contemporary practice (ie, guided by arterial oxygen saturation monitoring) is truly useful.”
And in a September 2009 article Systematic review of studies of the effect of hyperoxia on coronary blood flow in the American Heart Journal, the authors of the previous article are at it again. This time, in a literature review looking specifically at coronary blood flow and oxygen, they conclude :
CONCLUSIONS: Hyperoxia from high-concentration oxygen therapy causes a marked reduction in coronary blood flow and myocardial oxygen consumption. These physiologic effects may have the potential to cause harm and are relevant to the use of high-concentration oxygen therapy in the treatment of cardiac and other disorders.
Bryan Bledsoe, the noted EMS physician and educator, wrote a article in March of this year that also questioned the routine use of oxygen by EMS in The Oxygen Myth. He summarizes research on the use of oxygen in stroke, cardiac arrest, MI, trauma, and neonates, and concludes:
“If the patient’s oxygen saturation and ventilation are adequate, supplemental oxygen is probably not required. ”
American Heart Association
Here’s what the American Heart Association has to say about 02 and MI in the chapter Stabilization of the Patient With Acute Coronary Syndromes, which explains the science behind their 2005 guidelines.
EMS providers may administer oxygen to all patients. If the patient is hypoxemic, providers should titrate therapy based on monitoring of oxyhemoglobin saturation (Class I).
Administer oxygen to all patients with overt pulmonary congestion or arterial oxygen saturation _90% (Class I). It is also reasonable to administer supplementary oxygen to all patients with ACS for the first 6 hours of therapy (Class IIa). Supplementary oxygen limited ischemic myocardial injury in animals, and oxygen therapy in patients with STEMI reduced the amount of ST-segment elevation. Although a human trial of supplementary oxygen versus room air failed to show a long-term benefit of supplementary oxygen therapy for patients with MI, short-term oxygen administration is beneficial for the patient with unrecognized hypoxemia or unstable pulmonary function.
My regional oxygen guidelines are confusing. In our appendix, the indication for oxygen is listed as:
Indications: Any hypoxic patient or patient who may have increased oxygen demands for any reason.
Dose: Patient dependent 1 liter/minute via Nasal Prongs to 100% via rebreather face mask.
Under Acute Coronary Syndrome, it says the following:
Oxygen: Oxygen Therapy (90-100%)
Is that 90%-100% referring to the patient’s oxygen saturation or that they should be given a 90-100% mixture of oxygen?
I sit on the protocol committee and would vote for the saturation interpretation, but it needs to be made clearer.
While we should all continue to follow our own EMS systems current medical guidelines, we may consider that in the future, we may talk about the old days when we gave everyone oxygen.
The comment section of my recent STEMI Redux post produded a discussion about the use of high-flow oxygen in the setting of an MI, thus spuring this post.
I previously addressed the issue of changing views on oxygen in a December 2007 post titled Oxygen).