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Accuracy of Noninvasive Multiwave Pulse Oximetry Compared With Carboxyhemoglobin From Blood Gas Analysis in Unselected Emergency Department Patients


ResearchBlogging.org
Also posted over at Paramedicine 101 (now at EMS Blogs) and at Research Blogging. Go check out the excellent material at these sites.

The Masimo RAD-57 non-invasive CO monitor is promoted as an accurate way to identify patients at risk of life-threatening complications of CO poisoning. CO (Carbon monOxide) is a significant cause of poisoning in the US, with hundreds of fatalities each year.

Masimo claims that their RAD-57 is able to accurately measure blood levels of CO without any complicated lab equipment. If it works, the RAD-57 might save some lives. Unfortunately, the research that has not been funded by Masimo does not support a decision to buy a RAD-57 until after they improve the device.

Suspicion of CO poisoning is very important in identifying CO poisoning. One study was conducted at a burn center among patients already suspected of having CO exposure.

The RAD device correctly identified 11 of 23 patients with laboratory values greater than or equal to 15% carboxyhemoglobin (sensitivity 48%; 95% CI 27% to 69%).[1]

A coin flip is going to be just as accurate as a test that identifies only 48% of the affected patients.

 

The RAD-57 was shooting at fish in a barrel and still missed most of the time.

 

Dr. Michael O’Reilly (Executive Vice President of Masimo Corporation) has claimed that those researchers, who are not on the Masimo payroll, are biased against his device.[2]

What does he understand about science, objectivity, or controlling for biases?

Nothing comes to mind.

[youtube]JFvujknrBuE[/youtube]

Even some people who are not on the Masimo payroll have suggested that the RAD-57 might be useful and that the next study (quoted below) would confirm the usefulness of the RAD-57.

Compared with the large population used for the calculation of bias and precision, the number of patients actually found to be poisoned was small, especially in the group of poisoned smokers. Therefore, the opportunity for false-negative results was limited. Because a false-negative reading could have serious medical consequences, this device should be tested in a much larger number of poisoned patients to confirm the generalizability of our stated cutoff values.[3]

This does not contradict the first study.

What is the problem?

Symptoms of CO poisoning are nonspecific, ranging from mild headache, nausea, confusion, and dizziness to end-organ injury such as myocardial infarction,6 stroke,7 and death. [8] and [9] Diagnosis is therefore difficult and relies on clinical suspicion and confirmation by measurement of carboxyhemoglobin (COHb), using either venous or arterial10 blood gas analysis. However, COHb analyzers are not ubiquitously available.11 As a result, many victims of CO poisoning might be overlooked and misdiagnosed. [12] and [13] [3]

Suspicion of illness/exposure is the most important part of identification.

If we examine patients without considering suspicion, does the RAD-57 improve identification?

Maybe, but this study is not capable of testing that hypothesis.

These are only patients who are going to have ABGs (Arterial Blood Gas measurements) regardless of what the RAD-57 shows. We don’t know how many of the patients who did not have ABGs, or did not have ABGs within one hour of RAD-57 measurement, actually had CO poisoning.

Blood gas analysis (arterial or venous) (Table 1) was performed later as a standard procedure in our ED on discretion of the treating physician for a variety of clinical reasons.[3]

If the patient had a low reading on the RAD-57 and did not have an ABG, should we conclude that the unmeasured carboxyhemoglobin level was also low?

Of course not.

31% of patients who had ABGs were excluded because there was more than one hour between RAD-57 measurement and ABG measurement. How many of these patients were presenting as unstable and had the RAD-57 measurement omitted? How many of these patients were presenting as very stable and had the RAD-57 measurement over an hour before the ABG?

We do not know.

How many of the 17 patients in the documented sample had life-threatening symptoms?

We do not know.

Maybe all 17.

Maybe zero.

How many of the 17 patients in the documented sample had only minor symptoms?

We do not know.

Maybe all 17.

Maybe zero.

This kind of information is not included in the study.

What was the basis of diagnosis of CO poisoning?

The diagnosis of CO poisoning was based on increased COHb levels and clinical symptoms consistent with poisoning, including headache, vomiting, abdominal pain, and loss of consciousness.[3]

Identifying 16 out of the 17 patients in the 1,578 patient sample is impressive, but when we limit the patients to those with symptoms suggesting CO poisoning, we lose any possible value of the non-invasive screening.

 

These are the patients who are going to have blood drawn to assess for CO poisoning regardless whether anyone uses a RAD-57.

 

There is no benefit to RAD-57 screening in this setting.

What about using the RAD-57 in 1,017 EMS patients, regardless of the reason for the 911 call?

Of the 11 patients with a SpCO >15%, 10 were transported to a hospital for which the investigators had institutional review board (IRB) approval to review the patient’ s medical record. Of those 10, none had confirmatory venous carboxyhemoglobin levels. The two patients with an SpCO level of 21% did have a repeat SpCO documented at triage upon arrival to the emergency department. Their repeat levels were 8% and 2%. None of the 10 patients with levels >15% ultimately were diagnosed with and treated for carbon monoxide exposure or toxicity.[4]

The same idea, just not limited to patients chosen by having ABGs measured within one hour of RAD-57 measurement.

The result is very different.

None of the patients with elevated RAD-57 measurements had carboxyhemoglobin measured by drawing blood.

None of the patients with CO poisoning (according to the RAD-57) were treated for CO poisoning.

Is the RAD-57 reliable for determining if a patient should not go to the hospital?

Absolutely not.

What is the target audience of RAD-57 marketing?

Firefighters.

What is the patient population studied?

Patients already being treated in the hospital. They may include firefighters, but there is nothing in the study to indicate if there are any firefighters in the sample.

Quick and easy-to-use—requires no user calibration and does not require patient cooperation or consciousness.[5]

Dr. Michael O’Reilly (Executive Vice President of Masimo Corporation) had a bunch of excuses for the study that did not agree with the research paid for by Masimo. One excuse was that incorrect use of the RAD-57 interfered with results, even though Masimo trained the people using the RAD-57. Would Dr. O’Reilly have mentioned this if the study had produced the results he wanted?


Image credit.
Trust me. I am here to serve you.

Keep Firefighters Safe From CO Poisoning

> Have CO levels tested on the scene with the Masimo Rad-57.

• Just because firefighters don’t feel like they have CO poisoning doesn’t mean that they don’t have unsafe levels of carboxyhemoglobin (SpCO) in their bloodstream.

• That’s why rehab guidelines support the use of on-scene CO testing.6 To be safe, have SpCO levels tested with a Masimo Rad-57 before going back into the fire and during overhaul, even if firefighters think they’re okay.

> Get prompt on-scene treatment.

• Recognition is the key to immediate on-scene treatment. With early recognition, treatment for CO poisoning can begin immediately, which significantly reduces both immediate and long-term health risks.[6]

To be safe, have SpCO levels tested with a Masimo Rad-57 before going back into the fire and during overhaul, even if firefighters think they’re okay.

Masimo is providing very bad advice. Is Masimo trying to kill firefighters?

And if the RAD-57 does not detect CO poisoning, is that any reason to allow a firefighter to go back into a fire?

Absolutely not.

 

The RAD-57 should NEVER be used to screen asymptomatic people for CO poisoning.

 

The RAD-57 should NEVER be used to rule out CO poisoning.

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

[2] 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

[3] Accuracy of noninvasive multiwave pulse oximetry compared with carboxyhemoglobin from blood gas analysis in unselected emergency department patients.
Roth D, Herkner H, Schreiber W, Hubmann N, Gamper G, Laggner AN, Havel C.
Ann Emerg Med. 2011 Jul;58(1):74-9. Epub 2011 Apr 2.
PMID: 21459480 [PubMed – indexed for MEDLINE]

Annals of Emergency Medicine podcast
Podcast Download in MP3 Format

Late entry – 02/23/2012 @ 15:18 – I originally did not include the link to the abstract. The link is now included.

[4] Non-invasive carboxyhemoglobin monitoring: screening emergency medical services patients for carbon monoxide exposure.
Nilson D, Partridge R, Suner S, Jay G.
Prehosp Disaster Med. 2010 May-Jun;25(3):253-6.
PMID: 20586019 [PubMed – indexed for MEDLINE]

Free Full Text PDF Download from Prehosp Disaster Med.

[5] RAD-57
Masimo
Product information page

[6] RAD-57 for Fire/EMS
Masimo
Product information page

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

O’Reilly, M. (2010). Performance of the Rad-57 Pulse Co-Oximeter Compared With Standard Laboratory Carboxyhemoglobin Measurement Annals of Emergency Medicine, 56 (4), 442-444 DOI: 10.1016/j.annemergmed.2010.08.016

Nilson D, Partridge R, Suner S, & Jay G (2010). Non-invasive carboxyhemoglobin monitoring: screening emergency medical services patients for carbon monoxide exposure. Prehospital and disaster medicine, 25 (3), 253-6 PMID: 20586019

Roth, D., Herkner, H., Schreiber, W., Hubmann, N., Gamper, G., Laggner, A., & Havel, C. (2011). Accuracy of Noninvasive Multiwave Pulse Oximetry Compared With Carboxyhemoglobin From Blood Gas Analysis in Unselected Emergency Department Patients Annals of Emergency Medicine, 58 (1), 74-79 DOI: 10.1016/j.annemergmed.2010.12.024

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