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

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The RAD-57 Pulse Co-Oximeter – Does It Work – Part I

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.

Non-invasive monitoring for CO (Carbon Monoxide) toxicity seems to be the hot topic right now. Annals of Emergency Medicine has made its main paper, from October, on the RAD-57 non-invasive monitor free for everyone. The Doctor’s Channel has a brief video on the RAD-57 paper. The Poison Review has a brief print review of the RAD-57 paper. JEMS (Journal of EMS) has an entire supplement devoted to CO toxicity. On the EMS Research Podcast, we debate this for a while.

So, does the Masimo RAD-57 non-invasive monitor work?

First, is there a need for some kind of non-invasive monitor?

Symptoms of carbon monoxide poisoning are nonspecific and include headache, fatigue, malaise, confusion, nausea, dizziness, visual disturbances, chest pain, shortness of breath, loss of consciousness, and seizures. Although carboxyhemoglobin levels are inconsistently related to the degree of toxicity, in the absence of a clear history, detection in the blood may be the only means of confirming suspected exposure.1[1]

Many of these can be described as flu-like symptoms. Another problem is hypochondria. When people are told that they have been exposed to something, they frequently imagine symptoms. At the other end of the spectrum, we have fire fighters wanting to go back in to fight a fire and denying that they have any symptoms. with such a diverse mix of presentations, it would be nice to have something more portable and less invasive than a hospital laboratory.

If the RAD-57 can do this, that would be a great thing for fire departments, for EMS, and for patients.

Demonstration of adequate agreement between measurements made with the RAD device and standard laboratory measurement is essential before this noninvasive method of carbon monoxide detection can appropriately be substituted for arterial or venous measurement in clinical care.[1]

Essential?

Is there any other method of assessing the validity of the non-invasive measurements of CO levels?

Not yet.

Measurement was obtained with the RAD by clipping the appropriate (adult or pediatric) probe onto the digit for a period of approximately 15 seconds and reading the carboxyhemoglobin value from the handheld device screen. Immediately after this measurement, the device was removed from the finger, replaced on the same finger, and allowed to recalibrate, and a repeated carboxyhemoglobin level was recorded from the device. Arterial or venous blood was obtained with the first RAD measurement and sent to the hospital laboratory in a heparinized syringe for direct measurement of whole blood carboxyhemoglobin, using co-oximetry (Siemens Rapidlab 1200 blood gas analyzer). Clinicians were asked to record whether the RAD measurement was technically difficult and whether the low signal quality indicator on the device was illuminated for each subject.[1]

That seems reasonable.

Let’s skip to the results.

A nice chart, but what does it mean?

The numbers on the left are the RAD-57 readings, while the numbers on the bottom are the laboratory readings. The readings should be the same. The laboratory readings are considered to be accurate. The difference between the laboratory value, or real COHb (carboxyhemoglobin – CO in the blood), and the RAD-57 value is the way inaccuracy is determined. The gray diagonal line in the middle should be about where all of the results end up, if the readings agree (if the RAD-57 is accurate).

For example, 5% from the RAD-57 (draw a horizontal line from 5 on the left) and 5% from the laboratory (draw a vertical line from 5 on the bottom), we would put a dot on the line where the two lines meet. If we take away all the lines and leave the dots, we have this chart of all 120 patient readings.

Two more examples are taken from Table 3. Laboratory and RAD COHb values(laboratory value ≥15% COHb and RAD value <15% COHb). I use the first two.

Zero% from the RAD-57 (draw a horizontal line from 0 on the left) and 19.8% from the laboratory (draw a vertical line from 19.8 [round off to 20] on the bottom), we would put a dot on the line where the two lines meet.

Zero% from the RAD-57 (draw a horizontal line from 0 on the left) and 35.2% from the laboratory (draw a vertical line from 35.2 [round off to 35] on the bottom), we would put a dot on the line where the two lines meet.

Since very few of the dots are going to be exactly on the line, we include a range of acceptable variance. I changed the gray line to a thick red line and put a thin red line on each side, parallel to the thick red line. This allows the number to be higher or lower by 5, for a total range of 10 around the laboratory reading.

This really does not make clear where the problems are likely to be. If the RAD-57 gives a false high reading and we take somebody to the hospital, that is an inconvenience, but it is not likely to lead to a bad medical outcome. The problems are when the RAD-57 gives false low readings that encourage EMS to tell the patients that there is no problem. If these patients do not receive treatment, there may be problems. The chart below shows that area. I drew a line to indicate that the upper left corner that would be included in the allowable variance range.

Even more potentially dangerous may be the patients with RAD-57 readings that are below 5, while their laboratory readings are more than 10. Do we really think that some EMS personnel will not look at these low numbers and tell patients that they have nothing to worry about?

Then there is the problem of all of the zero readings on the RAD-57. Everybody in this study was being evaluated for suspected carbon monoxide poisoning. There does not appear to have been any zero laboratory reading when the RAD-57 had a non-zero reading. There are a bunch of very low laboratory readings, but the only zero laboratory reading(s) coincide with a RAD-57 zero reading(s).

The RAD-57 zero readings are in the Pet Rock™ Area. I could run some wires and a fancy probe to a Pet Rock™. I would obtain the same result the RAD-57 did for all of these patients, who had laboratory readings of up to 35.2.

Lab   =   35.2

RAD-57   =   0

Pet Rock™   =   0

That’s not even close enough for government work.

The Pet Rock™ doesn’t need batteries or maintenance.

Is the RAD-57 that difficult to use properly?

Or

Is the RAD-57 that inaccurate?

Or

Is the RAD-57 both inaccurate and difficult to use?

Or

Something else?

Those are a lot of zeros that should not be zeros.

Continued in The RAD-57 Pulse Co-Oximeter – Does It Work – Part II and in How Not to Respond to Negative Research as well as in How Not to Respond to Negative Research – Addendum.

Footnotes:

[1] 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

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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Comments

  1. Interesting piece and analysis. I look forward to part II. I have been looking at this device for 3 years now and waiting for the field experiences to make a purchase decision. Interestingly enough, my informal collection of user data indicates that the RAD57 is either despised or revered, depending on the user. There don’t seem to be many folks in the middle, except that some who think the device is great are also quick to admit that it throws some erroneous readings from time to time.
    From the research, it sounds to me like a ‘no-go’ however, the field provider in me thinks that it does provide another tool that can give SOME additional information, provided you are treating a patient, and not the device. Taking together ALL the aspects of your assessment, and adding the input from the RAD57 might give a better overall picture.
    A patient who had their CO alarm go off in the house where the Fire Department found elevated levels of CO, and who shows a carboxyhemoglobin level of 18% might be a good candidate for a BGA.
    I’d be interested to hear if you have any hands on experience with the device.
    Another nice piece.
    Upstart indeed!
    UU

    • UnlimitedHours,

      Interesting piece and analysis. I look forward to part II.

      Thank you.

      Part II is here.

      Interestingly enough, my informal collection of user data indicates that the RAD57 is either despised or revered, depending on the user. There don’t seem to be many folks in the middle, except that some who think the device is great are also quick to admit that it throws some erroneous readings from time to time.

      All attributes of a religion. Maybe there is some sort of chant that needs to accompany use of the RAD-57 to improve results.

      From the research, it sounds to me like a ‘no-go’ however, the field provider in me thinks that it does provide another tool that can give SOME additional information, provided you are treating a patient, and not the device. Taking together ALL the aspects of your assessment, and adding the input from the RAD57 might give a better overall picture.

      It might, but one of the limitations of the study is that it did not match the symptoms with the readings. On the other hand, the authors did explain in the very first paragraph –

      Symptoms of carbon monoxide poisoning are nonspecific and include headache, fatigue, malaise, confusion, nausea, dizziness, visual disturbances, chest pain, shortness of breath, loss of consciousness, and seizures. Although carboxyhemoglobin levels are inconsistently related to the degree of toxicity, in the absence of a clear history, detection in the blood may be the only means of confirming suspected exposure. 1

      If the RAD-57 indicates that the level is high, that is probably correct.

      If the RAD-57 indicates that the level is low, or zero, that is useless information.

      I could be just as accurate flipping a coin.

      Heads = High COHb.

      Tails = Low COHb.

      Coin flip accuracy = 50%.

      RAD-57 accuracy = 48%.

      A patient who had their CO alarm go off in the house where the Fire Department found elevated levels of CO, and who shows a carboxyhemoglobin level of 18% might be a good candidate for a BGA.

      I think that the way we need to look at this is something that might be useful with further development. If we use this device on people, we may find some asymptomatic people with high COHb by using the RAD-57.

      If we use the Rad-57 on any symptomatic patient, we have to encourage the patient to go to the hospital.

      If the reading is high, we encourage them to go.

      If the reading is low, we don’t know anything more than we did without the RAD-57. We still need to encourage the person to go to the hospital.

      According to this study, a low reading on the RAD-57 is useless, but potentially harmful.

      I’d be interested to hear if you have any hands on experience with the device.

      I have not used the RAD-57.

      Another nice piece.
      Upstart indeed!

      Thank you. 🙂

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  2. […] Pulse Co-Oximeter – Does It Work – Part II Wed, 17 Nov 2010 06:30:11 +0000 By Rogue Medic Leave a Comment […]

  3. […] from The RAD-57 Pulse Co-Oximeter – Does It Work – Part I and later to be continued in How Not to Respond to Negative Research. More on the use of the RAD-57 […]

  4. […] from The RAD-57 Pulse Co-Oximeter – Does It Work – Part I and from The RAD-57 Pulse Co-Oximeter – Does It Work – Part II. More on the use of the […]

  5. […] The RAD-57 Pulse Co-Oximeter – Does It Work – Part I Fri, 12 Nov 2010 […]

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