Tuesday, April 19, 2011

ECMO and logic: Absence of Evidence is not Evidence of Absence

I have been interested in ECMO for adults with cardiorespiratory failure since the late 1990s during the Hantavirus cardiopulmonary syndrome endemic in New Mexico, when I was a house officer at the University of New Mexico. Nobody knows for sure if our use of AV ECMO there saved any lives, but we all certainly suspected that it did. There were simply too many patients too close to death who survived. It made an impression.

I have since practiced in other centers where ECMO was occasionally used, and I had the privilege of writing a book chapter on ECMO for adult respiratory failure in the interim.

But alas, I now live in the Salt Lake Valley where, for reasons as cultural as they are scientific, ECMO is taboo. The main reason for this is, I think, an over-reliance on outdated data, along with too much confidence in and loyalty to, locally generated data.

And this is sad, because this valley was hit with another epidemic two years ago - the H1N1 epidemic, which caused the most severe ARDS I have seen since the Hanta days in New Mexico. To my knowledge, no patients in the Salt Lake Valley received ECMO for refractory hypoxemia in H1N1 disease.

Thus I read with interest the Pro Con debate in Chest a few months back, and revisited in the correspondence of the current issue of Chest, which was led by some of the local thought leaders (and those who believe that, short of incontrovertible evidence, ECMO should remain taboo and outright disparaged) - See: http://chestjournal.chestpubs.org/content/139/4/965.1.citation and associated content.

It was an entertaining and incisive exchange between a gentleman in Singapore with recent ECMO experience in H1N1 disease, and our local thought leaders, themselves led by Dr. Alan Morris. I leave it to interested readers to read the actual exchange, as it is too short to merit a summary here. My only comment is that I am particularly fond of the Popper quote, taken from The Logic of Scientific Discovery: "If you insist on strict proof (or disproof) in the empirical sciences, you will never benefit from experience and never learn from it how wrong you are." Poignant.

I will add my own perhaps Petty insight into the illogical and dare I say hypocritical local taboo on ECMO. ECMO detractors would be well-advised to peruse the first Chapter in Martin Tobin's Principles and Practice of Mechanical Ventilation called "HISTORICAL PERSPECTIVE ON THE DEVELOPMENT OF MECHANICAL VENTILATION". As it turns out, mechanical ventilation for most diseases, and particularly for ARDS, was developed empirically and iteratively during the better part of the last century, and none of that process was guided, until the last 20 years or so, by the kind of evidence that Morris considers both sacrosanct and compulsory. Indeed, Morris, each time he uses mechanical ventilation for ARDS, is using a therapy which is unproved to the standard that he himself requires. And indeed, the decision to initiate mechanical ventilation for a patient with respiratory failure remains one of the most opaque areas in our specialty. There is no standard. Nobody knows who should be intubated and ventilated, and exactly when - it is totally based on gestalt, is difficult to learn or to teach, and is not even addressed in studies of ARDS. Patients must be intubated and mechanically ventilated for entry to an ARDS trial, but there are no criteria which must be met on how, when, and why they were intubated. It's just as big a quagmire as the one Morris describes for ECMO.

And much as he, and all of us, will not stand by idly and allow a spontaneously breathing patient with ARDS to remain hypoxemic with unacceptable gas exchange, those of us with experience with ECMO, an open mind, equipoise, and freedom from rigid dogma will not stand by idly and watch a ventilated patient remain hypoxemic with unacceptable gas exchange for lack of ECMO.

It is the same thing. Exactly the same thing.

1 comment:

  1. Several thoughts have come in the form of e-mails about this post.

    One, from one of the Gods of ARDS, reinforced the need for RCTs to allow determination of cost-effectiveness of therapies and to better determine which patients may benefit from them, thereby limiting use of this expensive resource to those most likely to receive benefit.

    This reminded me of transplantation medicine, especially lung, which also has not been tested in any RCT, and which is likely not cost effective any more than ECMO would be. Both are done in tertiary/quaternary centers and consume massive resources.

    I was also reminded of the report in JAMA in late 2010 (see: http://jama.ama-assn.org/content/304/22/2521.abstract?sid=e2fc78a9-f4f0-450e-947c-3b418f3a37b2 )
    which describes the use of ECMO for a patient with staphylococcal disease. In spite of making a prolonged recovery as reported in the article, I understand that this patient ultimately succumbed to his disease.
    I did not mean in any way to suggest in the post that we should not endeavor to further evaluate the efficacy or effectiveness of ECMO in these patients. I also am fully aware of the shortcomings of the CESAR trial. I am simply trying to point out that the absence of evidence of efficacy does not dissuade me from using this therapy in a desperate situation if I have nothing else to offer.
    Whether society should allow me to use costly options in the absence of evidence of efficacy (or evidence of limited efficacy, such as biologics for advanced cancer) is yet another question, and one I would probably answer in the negative. But in the current environment, I do not begrudge others from trying unproven therapies such as this, or HFOV, etc, until society decides to constrain spending in medicine. I agree that this would be a good place to start.


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