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Bernhard

When to believe the pulse oxymeter, when not?

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Dwaynes post on another topic made me think again (thank you) about two recent calls, where we used four different pulse oxymeters.

Call#1: >80 y/o male, felt to the floor, 4 x oriented, some bruises on the head, nothing else, pulse and BP pretty OK (don't remember, but nothing special). The initial SpO2 reading was 60%! However no indications for a real need of oxygene from general patient appearance. Totally awake, sat on the bench, normal breathing, no record of lung or breathing problems, no acute indications for additional O2 other than the pulse oxy reading. The pulse oxymeter was one of those finger clips, we use in our staff transporter (just happened to be nearby the scene as it was dispatched, so I did first responding). The finger clip fitted well, reading didn't change after resetting and re-applying, it had fresh batteries and usually gives good readings when tested. It is licensed for professional use as well. Despite this, according to the perfect patient state I gave no oxygene. The reading on the responding ambulances pulse oxymeter (other brand, hand held - no finger clip) was perfect in the 95% range, as expected.

Call#2: On a patient ~70 y/o male suffering from "something with the heart" (totally unspecific) I attached the SpO2 sensor of our LP12, but couldn't get a decent signal. After fiddling some seconds, I re-attached to our hand held pulse ox (other brand) and it instantly got a signal of >90% and a pulse of 70/min. That seems very reasonable according to the patients general appearance. Then from the 3-lead ECG we got a first A-fib diagnosis, from the immedeate following 12-lead it was a clear additional left branch block. BTW, heart frequency was 140 and pressure 150/0 (zero!) - nice exact cook book view of a "half pulse" palpation and on the critical edge of a compensated heart failure (patient just walked up to the bath room in the first floor and sat there fully oriented). In this scenario I blame the LP12 pulse ox for not getting any signal (just some bleeps, but no measurement) where the other still was able to. On the same finger. Would like to have thought of additionally attach the other pulse ox on another finger, but that was not the time and patient to experiment.

I since then feel I can't trust our pulse oxymeters any more...(they all are well known brands and licensed for professional use plus checked regularly according to manual). Sure I'm somewhat able by myself to see if a patient really needs oxygene and I always take general patient appearance in count (first half of my EMS life there was no such thing as a pulse ox!), but with todays doctrine to not force SpO2 over 95% - my own senses ability simply are not that exact on every %...

So I have following questions:

  1. How do YOU really know to trust your SpO2 readings?
  2. Dwayne states in the mentioned posting, that "to many times people are/were suffering, and/or dying because providers didn't treat them because the pulse ox said that they didn't need to." How comes this? Beside true application errors (including deflective finger nails), the only real false-high reading of pulse ox I know is a CO poisoning. All other problems would give no reading (no signal) or false-low readings - how can this lead to provider's not giving oxygene? In my case#1 I decided so because of the general apperance (and was correct), a less imaginative provider may have given O2, because of low reading, but most probably this wouldn't have done any harm.
  3. Do we really need pulse oxymeters or the SpO2 value (if we can't trust it anyway)?

Would like to hear your thoughts (I will share mine later), thanks!

(P.S.: I will check all our four oxymeters on one test person soon, just getting curious)

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I agree with you. Incorrect reading tend to be low (affected mostly by issues in the finger - cold hands, poor circulation, etc.). Sometimes, moving the sensor to an earlobe or a toe helps. I have seen patients compensating extremely well for chronically low PO2 (long term COPDrs for example) where low SPO2 readings are correct and have had these readings dismissed by providers.

A low SPO2 reading is one of my indicators to absolutely put the patient on end tidal canula. If corresponding ETCO2 is low, then it is a strong impetus to give em some Os. Conversly, high ETCO2 with low SPO2 becomes a balancing act.

Like every other device that assists in evaluation, the SPO2 reading is just one piece of the bigger picture.

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  1. How do YOU really know to trust your SpO2 readings?
  2. Dwayne states in the mentioned posting, that "to many times people are/were suffering, and/or dying because providers didn't treat them because the pulse ox said that they didn't need to." How comes this? Beside true application errors (including deflective finger nails), the only real false-high reading of pulse ox I know is a CO poisoning. All other problems would give no reading (no signal) or false-low readings - how can this lead to provider's not giving oxygene? In my case#1 I decided so because of the general apperance (and was correct), a less imaginative provider may have given O2, because of low reading, but most probably this wouldn't have done any harm.
  3. Do we really need pulse oxymeters or the SpO2 value (if we can't trust it anyway)?

Great questions.

1. As long as there is no reason to suspect CO and the patient doesn't have any obscure conditions that could impact SpO2 (e.g. methemoglobinemia), I trust my SpO2 when there is a good waveform. Rarely will I consider an SpO2 reading without viewing the waveform. It is a bit of a pain on the Zolls to need to go into manual mode to see this, but I think the extra information is worth the button presses. In my anecdotal experience, I do not recall ever seeing an SpO2 reading that seemed unreliable when there was a good waveform.

2. Given a properly functioning SpO2 monitor and a good waveform, I do not believe that it would be likely to get erroneously high SpO2 readings, with the obvious exception of CO poisoning (which isn't really erroneous since the hemoglobin is saturated). Without a waveform to help judge the reliability of the reading, it may be possible to get an erroneously high reading, but my experience has been similar to yours, Bernhard, in that I have only seen erroneously low readings. I certainly do not have experience with all devices or in all situations though, so Dwayne's experience could have been different.

On a related note, there was a comment made on a different forum that you wouldn't want to be the medic who withholds oxygen from a cyanotic patient just because their SpO2 is high. Sounds like a good statement to make, but when you stop to think about it, it really is not likely that we will ever see a patient like this (of course, excluding SpO2 malfunctions). The only thing we could come up with where a patient may be cyanotic with an erroneously high SpO2 reading was methemoglobinemia. These patients will often have an erroneously low reading if they have with mild methemoglobinemia and an unreliable high reading if they have high-level methemoglobinemia. There did not seem to be anything else that would normally lead to a cyanotic patient (who was actually in need of oxygen) having a high SpO2.

3. As you probably gather from my answers to the previous questions, I trust SpO2 more than some of my colleagues. Do not take this trust for SpO2 as an over-reliance on it though as it is still just one assessment of many that we should be doing when considering a patient's respiratory function. We certainly do need SpO2, but in my opinion we should only be using SpO2 monitors that display a waveform.

As one final note, it seems that the 2010 ECC guidelines are putting a bit of weight in SpO2 readings in the reccomendation for titrating oxygen based on SpO2 in ACS patients (http://circ.ahajournals.org/content/122/18_suppl_3/S787.full).

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You should not be allowed to use a pulse-oximeter until you have run at least 100 respiratory calls, and have assessed all of those properly with just your ears, eyes, and brain. You should be able to approximate a pulse-ox reading without using it, then use the pulse-ox to prove your estimation. You will be a far better clinician if you follow that advice.

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The SPO2 reading is just one component of the patient assessment. Only one indicator in a long list of signs and symptoms. If the Oximetry reading agrees with the signs and symptoms all is well. If it disagrees then a differential assessment must be done to determine the reason for inconsistency.

As a EMT-B I find Pulse Oximetry to be a very useful tool although it really doesn't influence my treatment that much. At our level we pretty much give everyone a little O2 except when otherwise contraindicated.

You should not be allowed to use a pulse-oximeter until you have run at least 100 respiratory calls, and have assessed all of those properly with just your ears, eyes, and brain. You should be able to approximate a pulse-ox reading without using it, then use the pulse-ox to prove your estimation. You will be a far better clinician if you follow that advice.

Running 100 respiratory calls will definitely make you a better clinician considering you do the proper workup and have a good feedback system but saying that the only way to learn to use oximetry is by running calls indicates that you think we all are idiots and incapable of learning through didactical training.

Also denying a patient the luxury of available Pulse Oximetry while you are still on your "learning calls" would not be fair to them and would be inconsistent with the best healthcare practices.

Edited by DFIB

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As one final note, it seems that the 2010 ECC guidelines are putting a bit of weight in SpO2 readings in the reccomendation for titrating oxygen based on SpO2 in ACS patients (http://circ.ahajourn...ppl_3/S787.full).

Exactly, since we are stepping back from the old "O2 can`t hurt"-attitude, SpO2 measuring is even more important.

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You should not be allowed to use a pulse-oximeter until you have run at least 100 respiratory calls, and have assessed all of those properly with just your ears, eyes, and brain. You should be able to approximate a pulse-ox reading without using it, then use the pulse-ox to prove your estimation. You will be a far better clinician if you follow that advice.

Should you run 100 diabetic calls before measuring a patient's blood sugar as part of your assessment?

Should you run 100 cardiac calls before using an ECG as part of your assessment?

I can agree with that idea for something like not using an automatic BP cuff until you've run many calls without ever using one. Whether it is automatic or manual, it is essentially the same assessment and you can get the same information either way. But the use of SpO2 (and the two other examples above) is different because these are assessing things that we cannot assess without the special tools. Yes, you can do a thorough respiratory assessment, but no matter how good a clinician you are, you cannot measure someone's SpO2 without an SpO2 monitor.

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So I have following questions:

  1. How do YOU really know to trust your SpO2 readings?
  2. Dwayne states in the mentioned posting, that "to many times people are/were suffering, and/or dying because providers didn't treat them because the pulse ox said that they didn't need to." How comes this? Beside true application errors (including deflective finger nails), the only real false-high reading of pulse ox I know is a CO poisoning. All other problems would give no reading (no signal) or false-low readings - how can this lead to provider's not giving oxygene? In my case#1 I decided so because of the general apperance (and was correct), a less imaginative provider may have given O2, because of low reading, but most probably this wouldn't have done any harm.
  3. Do we really need pulse oxymeters or the SpO2 value (if we can't trust it anyway)?

Would like to hear your thoughts (I will share mine later), thanks!

(P.S.: I will check all our four oxymeters on one test person soon, just getting curious)

1. Displayed pulse matches manually measured pulse. Clinical correlation. If there's a waveform on the pulse ox, then the waveform is regular and not hitting the upper or lower limits.

2. Lack of clinical correlation. "Oh, look, the patient is struggling to breath, but hey, there is an SpO2 of 99%, so I guess they don't need oxygen." In general, I think most erroneous use of SpO2 readings is user error either in misinterpreting a reading or using the device in a way where they reduce the chance of figuring out that the reading is bad (i.e. not verifying the pulse rate).

3. What other point of care testing can we use to titrate treatment, or do we just go with a NRB for everyone?

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(Edit: Sorry for the redundancies, I was posting the same time as the other. Bernhard, I swear to God that if you didn't make the sedom, small grammatical error I would never know that English isn't your first language. Also, thanks for taking me to task on this Brother...though I know that wasn't your intent, it feels so good to know that you all are paying attention and not allowing me to be a bigger idiot than absolutely necessary.)

You know, it seems that I've spent the last week following myself around after getting contrary opinions saying something to the effect, "Hell...It looks like I didn't know what I was talking about." I have sort of a love/hate relationship with this task..

I developed part of my opinion from a while back when someone posted some articles about people dying from CO2 poisoning. It seems like, though I can't find it now, that several people died in a relatively small area because they were picked up by basic crews who believed them to have the flu, or to be drunk or hung over, but in fact had gas leaks in their furnaces or issues with their wood burning heating units. The SPO2 showed 100% so they weren't treated well and some of them died. Again, I can't remember exactly, but it was something like that. As well, the treatment that the crews delivered likely had almost nothing to do with their morbidity/mortality.

And I think we write off CO2 to quickly. I can raise my SPO2 by 5-7 points by having a smoke. It doesn't take long, and it lasts for a while. We had a bunch of gym rat medics when I was in Afg that hated that I smoked . I used to make them crazy when they'd start of a lecture as I'd run outside, smoke like a demon, and then go back inside and challenge them to compare SPO2/vitals. Thanks goodness it never occurred to them that smoking might have be the reason for a falsely elevated reading as opposed to me simply being healthier than they were. Of course I've probably traded the joy of tormenting them for about 20 years of my life.

I got really sick when on the oil spill in LA, skin hurt, joints ached, headache, N/V, seemed to have a hard time catching my breath, developing over about a week or so. I assumed it was a flu. One of the other medics finally stepped up and did a half assed assessment, put on the pulse ox and it showed 100%. He said, "Hmmm...Lungs are clear, SPO2 is good, so you're oxygenating great...so that's not it." As soon as I saw the SPO2 reading I was able to put it together with the other symptoms and tore the trailer I was living in apart. It was one of the really cheap FEMA trailers, and discovered that the exhaust for the water heater was located directly below the scoop for the exhaust for the stove, funneling the exhaust back into the trailer.

I sealed it closed, spent every spare minute sitting in the trailer on a non rebreather, and began to feel better after about a day, and after 4-5 days my SPO2 had returned to around 96% which I knew was about right for me at sea level. (I was shocked by how long it took!!) Had I been in the care of the other medic solely I may have died in the poisoned trailer before he figured out that I wasn't really doing so well.

I have a real issue with giving people tools that they don't understand, so probably I let that cloud my comments. I've rarely seen in the hospital where most question their machines at all, leading me to believe that they are more reliable than I have come to believe.

Also, the pulse ox rarely tells me anything that I didn't already know, though at times it's comforting if it helps to validate what I thought. It's just so rare that I put it on and go, "Holy shit! What the hells going on here!" that I probably don't have the respect for it that I should. I was Googling for arguments to make my point and my point is tough to make. But what is easy is to find a gazillion articles, many of them in medical journals, that crow about how SPO2 changed the face of medicine, or comments to the like.

So, maybe I'm off in the ditch again. If the pulse oxs that people are using are giving low readings for the most part, instead of high, then maybe there is no damage at all other than to the assessment quality of the basic, and as shown above, medic providers that learn to lean on them.

One caveat. Should anyone find that there is a huge number of CO2 issues in the country, much higher than I intuit, then I go back to my previous argument and you all can go and screw yourselves... :-)

Dwayne

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(Edit: Sorry for the redundancies, I was posting the same time as the other. Bernhard, I swear to God that if you didn't make the sedom, small grammatical error I would never know that English isn't your first language. Also, thanks for taking me to task on this Brother...though I know that wasn't your intent, it feels so good to know that you all are paying attention and not allowing me to be a bigger idiot than absolutely necessary.)

You know, it seems that I've spent the last week following myself around after getting contrary opinions saying something to the effect, "Hell...It looks like I didn't know what I was talking about." I have sort of a love/hate relationship with this task..

I developed part of my opinion from a while back when someone posted some articles about people dying from CO2 poisoning. It seems like, though I can't find it now, that several people died in a relatively small area because they were picked up by basic crews who believed them to have the flu, or to be drunk or hung over, but in fact had gas leaks in their furnaces or issues with their wood burning heating units. The SPO2 showed 100% so they weren't treated well and some of them died. Again, I can't remember exactly, but it was something like that. As well, the treatment that the crews delivered likely had almost nothing to do with their morbidity/mortality.

And I think we write off CO2 to quickly. I can raise my SPO2 by 5-7 points by having a smoke. It doesn't take long, and it lasts for a while. We had a bunch of gym rat medics when I was in Afg that hated that I smoked . I used to make them crazy when they'd start of a lecture as I'd run outside, smoke like a demon, and then go back inside and challenge them to compare SPO2/vitals. Thanks goodness it never occurred to them that smoking might have be the reason for a falsely elevated reading as opposed to me simply being healthier than they were. Of course I've probably traded the joy of tormenting them for about 20 years of my life.

I got really sick when on the oil spill in LA, skin hurt, joints ached, headache, N/V, seemed to have a hard time catching my breath, developing over about a week or so. I assumed it was a flu. One of the other medics finally stepped up and did a half assed assessment, put on the pulse ox and it showed 100%. He said, "Hmmm...Lungs are clear, SPO2 is good, so you're oxygenating great...so that's not it." As soon as I saw the SPO2 reading I was able to put it together with the other symptoms and tore the trailer I was living in apart. It was one of the really cheap FEMA trailers, and discovered that the exhaust for the water heater was located directly below the scoop for the exhaust for the stove, funneling the exhaust back into the trailer.

I sealed it closed, spent every spare minute sitting in the trailer on a non rebreather, and began to feel better after about a day, and after 4-5 days my SPO2 had returned to around 96% which I knew was about right for me at sea level. (I was shocked by how long it took!!) Had I been in the care of the other medic solely I may have died in the poisoned trailer before he figured out that I wasn't really doing so well.

I have a real issue with giving people tools that they don't understand, so probably I let that cloud my comments. I've rarely seen in the hospital where most question their machines at all, leading me to believe that they are more reliable than I have come to believe.

Also, the pulse ox rarely tells me anything that I didn't already know, though at times it's comforting if it helps to validate what I thought. It's just so rare that I put it on and go, "Holy shit! What the hells going on here!" that I probably don't have the respect for it that I should. I was Googling for arguments to make my point and my point is tough to make. But what is easy is to find a gazillion articles, many of them in medical journals, that crow about how SPO2 changed the face of medicine, or comments to the like.

So, maybe I'm off in the ditch again. If the pulse oxs that people are using are giving low readings for the most part, instead of high, then maybe there is no damage at all other than to the assessment quality of the basic, and as shown above, medic providers that learn to lean on them.

One caveat. Should anyone find that there is a huge number of CO2 issues in the country, much higher than I intuit, then I go back to my previous argument and you all can go and screw yourselves... :-)

Dwayne

For me, any SPO2 reading of 100% will always be suspect of a false reading. You are fortunate to be alive amigo. Another couple of days and you would not be posting on The City. Your medic buddy might do better in another line of work. Maby you should look him up and give him a smack for every neuron you lost. :)

How low was you SPO2 really at that time? Did you ever get an acurate reading?

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