Oxygen Heresy

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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.

Journal Review

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.”

Their conclusion:

“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

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).

And

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.

Regional Guidelines

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.

The Future

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).

7 Comments

  • EMT says:

    Silly Peter. We can’t have anyone THINKING. They should stick to 30 year-old protocols, like mine that say “Administer OXYGEN at the highest concentration tolerated” and the end of every. Single. Protocol.

  • Eric says:

    About time EMS based treatment on SCIENCE instead of “we’ve always done it that way…although it’s depressing how much of what I “knew” is no longer valid…

  • Paramedic Pete says:

    I think that I first heard of respiratory alkolosis about 12 years ago. A crew who had an ACS patient on a NRB mask, getting tore a new one by an ED Doc for doing what they thought was right. Great way of teaching Dr.
    I think we have already moved along this path with strokes and I imagine there is a similar process taking place here. It doesn’t surprise me that too much O2 can cause negative effects, just like any therapy. The important thing to remember though that both brain and heart tissue are acutely sensitive to anoxic injury. Around every stroke or heart attack there is an amount of tissue which is not yet dead. Too much oxygen can indeed make the injury worse. The key then is goldilocks therapy, not too much or too little but just the right amount for each indivdual patient. This should avoid aterial spasm but mitigate the effects of the ischaemic injury and hopefully improve outcomes.
    I’d like to see the study that looks for the best care for strokes, MI’s, Trauma etc. I imagine titrated oxygen for individual patients is the answer but we won’t know until a proper study is done. One thing I’m afraid of, is throwing out the baby with the bathwater. Having been around a while you see things go around in circles. A healthy dose of sceptiscism should be applied to any new dramatic change in therapy, to make sure we don’t do more harm than good.
    Just a few ideas, Pete.

  • Matt says:

    I hear (no science that I’m going to cite, though) that in Europe, folks have been having much better results recuscitating (BVM, I think) with room air as opposed to 100 percent oxygen.

  • medicscribe says:

    Thanks for all the comments. I agree Europe is ahead of us on the 02 issue. I read somewhere and will try to find it where they don’t use it routinely on STEMIs, only if the patient is hypoxic.

    I also agreed, we definitely need a large scale randomized study looking at 02. The problem is there isn’t a lot of money to be made proving oxygen is overused. All the big studies are funded by drug companies or medical device makers trying to prove their products make a difference.

  • totwtytr says:

    I’ve been on this subject for several years. Or my co workers and medical control staff would say I’ve been ranting about this subject for years.

    We use way too much oxygen. If studies show that we ventilate cardiac arrest patients too rapidly with oxygen, then on strategy might be to decrease the amount of oxygen we use when we ventilate.

    We know that Oxygen not only doesn’t help, but might be harmful to stroke patients, yet most EMTs still persist in giving high concentration Oxygen to them. I’ve developed quite a reputation among the BLS crews for arriving on scenes and directing them to switch out from a non rebreather to a cannula. To the point that some of them are using cannulas routinely now. Plus, I don’t see nurses taking patients off cannulas as I do NRB.

    A lot of the responsibility for this falls on system medical directors and training staff who maintain what I call the “Chicken Soup” approach to some medications. “Can’t hurt, might help.” is the thought process here. Only it can hurt. That and the 1994 revision of the BLS curriculum that determined that BLS (and by extension ALS) patients were too dumb to know how much oxygen a patient might need.

    Yes it’s counter intuitive to not give Oxygen. After all it’s something we are taught to do almost from Day One of EMT training. One of the hardest things to do in medicine, and probably most fields, is unlearn old untruths and replace them with new ones.

    Here, http://tinyurl.com/yeq8h3n is a blog post on the subject I put up in January.

    Good post.

    • medicscribe says:

      Thanks for the link. Great article. It will be interesting to see whether or not this growing research reaches the street in a meaningful way.

      Peter

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