Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

How Not to Respond to Negative Research – Addendum

ResearchBlogging.org

Also posted over at Paramedicine 101 (now at EMS Blogs) and at Research Blogging. Go check out the rest of the excellent material at these sites. There is a new research podcast specifically for EMS – EMS Research Podcast. On episode 2 we discuss several topics, including the research on the RAD-57 non-invasive monitor.

In How Not to Respond to Negative Research, I forgot to address one of the more important problems with the response of Dr. Michael O’Reilly.

Because the study used the same type of device and sensor and evaluated patients similar to those in previous studies, the differences in results were likely due to different methods by the investigators. The possible reasons for the discrepancy between the results reported in this study include multiple items addressed in the directions for use of the device and sensor, including:

•inappropriate finger positioning in the sensor

•inappropriately sized sensor for the subject’s finger

•timing of SpCO and COHb measurements not being exactly simultaneous

•increased methemoglobin level (which can be ruled out by measuring noninvasive methemoglobin levels [SpMet] with the Rad-57)

    •patient motion

    •external light interference

    •device or sensor malfunction (there were many zero readings by Rad57 in which HbCO was considerably higher, which could be due to device malfunction and may indicate a need for service)[1]

Dr. O’Reilly is telling us that the RAD-57 is too difficult to use in the ED (Emergency Department), but miraculously acquires accuracy and reliability at a fire scene.

timing of SpCO and COHb measurements not being exactly simultaneous

Exactly simultaneous?

Exactly?

Does carboxyhemoglobin vary that much that a few seconds later, the HbCO is wildly different?

If that is the case, why buy a machine that will only give us a snap shot of a rapidly fluctuating and unreliable number?

Is there any reason to believe that carboxyhemoglobin changes that rapidly and unpredictably?

No.

Three RAD devices and training in their use were supplied by Masimo Corporation for the duration of the study. Clinicians underwent training in use of the RAD device before study initiation. Measurement of RAD carboxyhemoglobin was performed simultaneously with sampling of arterial or venous blood for laboratory determination of carboxyhemoglobin level.[2]

Simultaneously, but not exactly simultaneously?

Dr. O’Reilly is creating the impression that this is a difference. Should we believe that, in the ED, the levels of carboxyhemoglobin are rising dramatically between the application of the RAD-57 and the simultaneous drawing of blood, just because the word exact was not used?

The big problem with the RAD-57 was that it missed over half of the significantly elevated carboxyhemoglobin levels – some while indicating a carboxyhemoglobin level of zero. Did patients have a zero carboxyhemoglobin level one minute and a significantly elevated carboxyhemoglobin level the next minute?

Dr. O’Reilly seems to be indicating that carboxyhemoglobin operates on the same principle of uncertainty as Scrödinger’s Cat, but with a free random number generator.

There are several problems with researching EMS equipment in the much more stable environment of the ED.

The ED environment has much less variability than the EMS environment.

If vasoconstriction is a problem, the warmer ED is much less likely to produce vasoconstriction than being out in the cold, which is often where the RAD-57 will be used.

The people using the equipment are generally paying much more attention to what they are doing, if only because they have to document compliance with study protocols.

As stated in the study, the participants are often trained by the people most familiar with the equipment – not somebody who read a package insert, or watched a video, or was once trained by someone from the manufacturer.

Compared with use in the EMS environment, the ED environment can be seen as much closer to the ideal testing environment.

Is Dr. Reilly complaining that Masimo provides bad training on the use of the RAD-57?

If our device does not work in your hands, it’s your fault.

It is always a pleasure to deal with someone who stands behind a product and is looking out for the patients assessed/treated with that product.

Dr. Michael O’Reilly, who is Executive Vice President of Masimo Corporation, an officer of the corporation, and holds stock options in Masimo[1], is not that person.

The RAD-57 may have some role in identifying elevated carboxyhemoglobin levels, but so far nobody can tell what that role is. As I pointed out earlier

Less than half of the patients with elevated COHb were correctly identified.

If we screen a fire fighter for COHb, then we need to keep that fire fighter out of the fire.

Should anyone ever use a low RAD-57 reading to justify returning a fire fighter to a fire?

No.

Footnotes:

[1] Performance of the Rad-57 pulse co-oximeter compared with standard laboratory carboxyhemoglobin measurement.
O’Reilly M.
Ann Emerg Med. 2010 Oct;56(4):442-4; author reply 444-5. No abstract available.
PMID: 20868919 [PubMed – indexed for MEDLINE]

Free Full Text of letter and author reply from Ann Emerg Med with links to Free Full Text PDF download

[2] Performance of the RAD-57 pulse CO-oximeter compared with standard laboratory carboxyhemoglobin measurement.
Touger M, Birnbaum A, Wang J, Chou K, Pearson D, Bijur P.
Ann Emerg Med. 2010 Oct;56(4):382-8. Epub 2010 Jun 3.
PMID: 20605259 [PubMed – indexed for MEDLINE]

Free Full Text Article from Ann Emerg Med with links to Free Full Text PDF download

O’Reilly M (2010). Performance of the Rad-57 pulse co-oximeter compared with standard laboratory carboxyhemoglobin measurement. Annals of emergency medicine, 56 (4) PMID: 20868919

Touger, M., Birnbaum, A., Wang, J., Chou, K., Pearson, D., & Bijur, P. (2010). Performance of the RAD-57 Pulse Co-Oximeter Compared With Standard Laboratory Carboxyhemoglobin Measurement Annals of Emergency Medicine, 56 (4), 382-388 DOI: 10.1016/j.annemergmed.2010.03.041

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