Don't let a 6% differential reading in your SpO2 levels confuse you

General Discussion on any topic relating to CPAP and/or Sleep Apnea.
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GearChange
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Don't let a 6% differential reading in your SpO2 levels confuse you

Post by GearChange » Wed Dec 22, 2021 1:08 pm

If like me, you are concerned about your oxygen saturation level in parallel to your CPAP therapy, then you are most likely using some kind of a reasonably priced Oximeter which you perhaps purchased online.
In my case I have accumulated a whole collection of under $150 Oximeters over the years, however I have come to a point that I can't trust any of them to provide an "accurate" reading of my SpO2.
Picture attached was taken earlier today when I placed 2 oximeters from the same manufacturer on the same finger, only to find that the difference between the two readings averaged 6% (fluctuating between 2% all the way up to as much as 10%).
This much discrepancy between two instruments made by the same manufacturer who most likely uses the same electronics circuitry in both devices, can only indicate that neither of them has been "calibrated" correctly at the factory and since there is no way that the user can calibrate them either, readings from either device should not be taken seriously.
Of course the best way to Oximetry in conjunction with CPAP, is to use oximetry kits that are specifically designed to interface directly with the CPAP device. However oximetry kits for Resmed can run up to over $1K in price and for a DS it could go as high at $600 which means that if insurance won't cover it, it is a pretty heavy load on most pocketbooks.

How about your Oximetry device(s)? Do you have ones that you can rely on? What do you recommend?
PXL_20211222_064427255.PORTRAIT_2_ccexpress (1).jpeg
Even though I have had extensive experience with the use and functionality of several types of different PAP machines,no information in my posts should be put in practice unless cleared by your own medical practitioner first.

Thumper1947
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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by Thumper1947 » Wed Dec 22, 2021 4:09 pm

I have the wellue ring and I also have standard pulse oximeter. Several times I have compared them, and I just did it again and got the same result. The ring read 98, the pulse oximeter read 97. Each time I have done it, the results were either in agreement, or within plus or minus 1. Have you done several tests? Maybe just a bad reading.
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GearChange
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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by GearChange » Wed Dec 22, 2021 5:41 pm

Thumper1947 wrote:
Wed Dec 22, 2021 4:09 pm
I have the wellue ring and I also have standard pulse oximeter. Several times I have compared them, and I just did it again and got the same result. The ring read 98, the pulse oximeter read 97. Each time I have done it, the results were either in agreement, or within plus or minus 1. Have you done several tests? Maybe just a bad reading.
Thumper
Very lucky. Sounds like you have two well calibrated units. I wish these things could be made so customers can calibrate them.
Even though I have had extensive experience with the use and functionality of several types of different PAP machines,no information in my posts should be put in practice unless cleared by your own medical practitioner first.

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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by chunkyfrog » Wed Dec 22, 2021 8:10 pm

I brought my Dr. Talbot's <$27 pulse ox to a medical appointment.
The nurse was happy to compare it to the professional model she used on me.
Exact match.
I bought it at Target.

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MMcG
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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by MMcG » Thu Dec 23, 2021 4:09 am

Maybe you just didn't leave them on long enough to settle. Most of these things need at least a minute to give reliable readings. Or you may just be unlucky that one of them is faulty.

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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by SleepyCPAP » Thu Dec 23, 2021 10:08 am

Maybe you just didn't leave them on long enough to settle. Most of these things need at least a minute to give reliable readings. Or you may just be unlucky that one of them is faulty.
I didn’t realize this until recently. A nurse told me this. My CMS 50D+ finger pulse/ox needs that warmup time, and may give instant readings that are wrong. The O2Ring has it built in, and just shows dashes at first. Both my units agree within 1/2 point with the one at the doctor’s office. I find my O2Ring to be very good in overnight sleep recording, not quite consistent if I’m out for a walk.

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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by lars_the_bear » Thu Dec 23, 2021 11:39 am

I became a bit obsessive about Sp02 when I was recovering from pneumonia (and later Covid). I have a drawer-full of meters, ranging from the cheapo eBay things, to an expensive ambulance unit. Oh, and a watch.

I find that at any instant in time, their readings can differ by 3-4 percentage points. I haven't seen any two read six percentage points apart in the steady state, but...

When I was unwell with Covid, and my SpO2 was falling by five points every time I tried to walk upstairs, I found (because I really am this much of a geek) that different units I was using at the same time would show SpO2 rising and falling at different rates. My ambulance one, for example, seems to average over a much longer period than the cheap units, so its values change much more slowly. So during fluctuations, I probably could see differences of more than a couple of percentage points -- at least for a half minute or so. But at rest, all the units seemed to converge.

FWIW, when not calibrated my hospital pulse-ox unit is only claimed to have an accuracy of +/- two percentage points. So I guess that two good-quality oximeters could differ by four percentage points if you were unlucky, and they hadn't been calibrated.

Anyway, I think if I saw two units reading six percentage points apart in the steady state, I would tend to think that one of them was faulty; or perhaps I had grubby fingernails or odd peripheral blood circulation. Something not quite kosher, anyway.

Although I can't prove this, I would expect that most pulse-ox units, even cheap ones, and even without calibration, would show changes in SpO2 with reasonable precision, and that's what I tend to be concerned about.

Best wishes
Lars.
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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by lars_the_bear » Thu Dec 23, 2021 11:42 am

Incidentally, is there an (affordable) oxygen saturation meter that can record a whole night? And save the data in some way that I can understand? Mine does record, but can only send the results to a proprietary data printer, which I don't have, and probably couldn't afford even if I wanted one.

Best wishes
Lars.
ResMed S9 AutoSet / Hoffrichter standard full face

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Pugsy
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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by Pugsy » Thu Dec 23, 2021 11:51 am

lars_the_bear wrote:
Thu Dec 23, 2021 11:42 am
Incidentally, is there an (affordable) oxygen saturation meter that can record a whole night? And save the data in some way that I can understand? Mine does record, but can only send the results to a proprietary data printer, which I don't have, and probably couldn't afford even if I wanted one.

Best wishes
Lars.
Sure there are such devices...from around $50 to close to 200 depending on how fancy and how many features you want to play with and even compatible with OSCAR software.

Cheapest is likely the CMS D 50 + (note the plus is critical).
They are called overnight recording pulse oximeters and found on Amazon or EBay easily.

From OSCAR
Oximetry Wizard

Data from the following pulse oximeters can be imported via OSCAR's Oximetry Wizard:

Contec CMS-50D+, CMS-50-E, CMS-50E
Contec CMS-50F, CMS-50H, CMS-50I (v3.7 firmware or later)
Pulox PO-200/300/400/500

Note: Contec CMS-50F -- the newer version 2 hardware uses a new USB protocol which the OSCAR team has not yet reverse engineered, so currently you need to use the new (Windows-only) Contec software to read the data and create a data file, which apparently uses the same format as the older models. This has not been verified just yet.

The Pulse Ox CMS50F Version 2.0.0 hardware requires the Smart Device Assistant V3.1.0.1. The software can be downloaded at http://www.dlsoftw.com with index code: 01GS4016.

The software's default SpO2 data storage folder in Windows 10 is C:\users\user name\AppData\Local\VirtualStore\Program Files (x86)\Smart Device Assistant v3.1.0\Data. I copy CMS50F SpO2 data files from the default Smart Device Data folder to a new root directory folder named C:\SpO2_Data. Oscar will import the SpO2 data files directly from the C:\SpO2_Data folder. You must first have Oscar import your machine's sleep data file from your SD Card prior to importing the corresponding SpO2 data file from the same time frame.
Manual Import

Beginning in OSCAR 1.1.0, the following pulse oximeters are imported via OSCAR's Data > Import Viatom Data... menu. See Viatom File Import for how to download and import their data files.

Viatom/Wellue SleepU
Viatom/Wellue O2Ring

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Grumpy48
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Re: Don't let a 6% differential reading in your SpO2 levels confuse you

Post by Grumpy48 » Thu Dec 23, 2021 2:32 pm

I bought a Wellue O2Ring in December 2019 as I suspected an apnea issue. I brought one of the charts from the O2Ring's software to my doctor and he agreed that a sleep study was in order. It's easy to check the previous nights O2 from the O2Ring and I do this daily along with a quick check of DreamMapper (Dream Station2) and Fitbit sleep data while having morning coffee. I did once upload the O2Ring data into Oscar when I had the original Dream Station, so if you use Oscar the O2Ring is doable in Oscar.
I've not compared the O2Ring to a clip-on O2 oximeter I have, but might as a comparison.

December 2019 before CPAP
Image

Dec 2021 with CPAP
Image

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