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Pulse Oximetry
More and more of us are buying pulse oximeters, despite the fact that the majority of the sleep clinics in the UK seem to want to keep their patients in blissful ignorance of their actual sleep patterns.
However those of us who want to learn more about their sleep patterns face the problem that we are not trained in how to interpret the results given by these oximeters. My understanding from research data is that the results from pulse oximeters correlate very closely with full polysomnography. If that is right, oximeter users should be able to use their results to indicate accurately whether the pressure they are using is properly controlling their OSA.
To start this discussion I would like to pose the following questions, which are based on my own oximeter (CMS50F). Obviously there may be some other machines which give more, or better, information. If so, details here would greatly assist other users and potential users.
1. What is Basal SpO2(%) and is it significant?
2. My oximeter is pre-set with a "Desaturation Criteria Level" of 88%. What is the significance of this figure, and should I alter it up or down?
3.How low should the "Average low Sp02 %" be, before it is considered abnormal?
4. Is the "Average low Sp02 % < 88%" more, or less, important than the overall average?
5. My oximeter results show %Sp02 levels, and number of events, in bands of 5 i.e. 99-95, 94 - 90 and so on , with the number of events in each band. Should we be aiming not to go below 90 at all, or is the threshold level lower?
6. Is the time in each band significant, and if so what should we look for to show good OSA control?
7. Which overnight pulse levels are considered abnormal?
8. Can the oximeter results be converted into AHIs and if so how?
My apologies for setting out formal questions in this way, but I hope that Rock, and other members, will be able to give expert guidance on these points and others, to assist us all.
We would all benefit if we could understand :
a) the default settings to use
b) which readings indicate good OSA control
c) which readings are considered abnormal / undesirable
Views: 7366
Replies to This Discussion
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Permalink Reply by John Hedley on
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Hi Rock, Judy and TF
Thanks for the info
I am not sure how Judy's details of the Respironics definition of apnea/hypopnea actually link to these reports. You will see the threshold figure of 88%, which is the default figure for my oximeter.
Should I, for example, watch the total events, time in events, events < 88%, time under 88% etc
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Permalink Reply by Tigers Fan on
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Hi John
Looks like you went for a pee at 04.40 both nights.
I'm surprised at 2.1 events with a pulse line like those - I'd expect higher.
What action,if any, did you take based on those results? As I remember, you have the same machine as me. I'd try a 0.5cm increase and assess the effect.
By what process did you publish the charts in the forum? I've got as far as making a .pdf file of the results but have yet to find an easy way to convert that into a .jpg so I can upload to a photo server.
John Hedley said:Hi Rock, Judy and TF
I set out below two sample reports from the manufacturer of my oximeter.
and:
I am sorry that the images are small, but if you click them you see a larger image.
I would be very interested in your views as to the important markers to watch on these reports. I am afraid that my own reports are very different!
TF - are these the same reports as those produced by your oximeter please?
Incidentally the software also produces a detailed file print but I have not added a sample here because it runs to several pages.
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Quote: baseline breathing is taken at rest on room air. For most people this would be above 95%.
Now I know why nurses rush at me with oxygen tubes every time I walk past a hospital! Mine is 94% but they want 97% or above and tut! tut! me for having smoked until twenty-odd years ago.
Thanks for the definitions, Judy. Do you know the connection between SpO2 events and AHI?
TF
Judy said:The following are Resmed definitions for their PAP devices:
Apnea is the temporary absence or cessation of breathing. An apnea is scored when there is reduction in breathing by 75% of the baseline breathing for at least 10 seconds.
A hypopnea is an episode of shallow or slow breathing during sleep. A hypopnea is scored when there is a reduction in breathing by 50% of baseline breathing for 10 seconds or more.
Oxygen Desaturation Index The mean value of the number of drops in oxygen saturation per hour
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* baseline breathing is taken at rest on room air. For most people this would be above 95%. I have COPD, my baseline breathing at rest on room air is usually 91%-92%.
When hospitalized, it seems to vary whether 88% or 90% is the low 02 saturation level indicating the need for the addition of supplemental oxygen.
Professional Oximetry
Oximeters usually define a desaturation event as a decrease of saturation by 4 or more. Compare that to Resmed's definition of apnea and hypopnea.
The event durations usually have to be w/in 3 minutes to qualify and event onset is definied as a decrease in Sp02 by 4 or more.
Pulse range is also usually identified and reported.
The professional oximetry reports to qualify for insurance coverage include reporting High, Low and Average Or Mean pulse and High, Low and Average or Mean Sp02 as well as Start and Stop time, Event duration, Low Sp02, Highest pulse and Time to high pulse.
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Hi TF
Thanks. These are NOT my reports - they are sample reports produced by the manufacturer. Mine are very different, and not so good!
I too had problems, and needed help from Kath and Mike re the images. Eventually I saved the image by dumping a copy into Paint and saving as a.jpg. Then on the forum I used the image button (top left, second in), and browsed to the jpg on my pc. The only problem is that the resulting image is very small - I have not yet worked out how to solve that one!
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Sorry, John - I entirely missed the text beneath your charts!
Ah! so those are not your results! Yes - they are exactly the same format as mine. I can only make sense of the long, several page report - where I can sort out the dips from the levels, compare to loo break, etc. The compressed chart in the summary report is entirely too - well - compressed for me.
These posts are growing out of control, are they not, with the endless repitition of who said what every time someone replies? Is there a way round this?
TF
Tigers Fan said:Hi John
Looks like you went for a pee at 04.40 both nights.
I'm surprised at 2.1 events with a pulse line like those - I'd expect higher.
What action,if any, did you take based on those results? As I remember, you have the same machine as me. I'd try a 0.5cm increase and assess the effect.
By what process did you publish the charts in the forum? I've got as far as making a .pdf file of the results but have yet to find an easy way to convert that into a .jpg so I can upload to a photo server.
John Hedley said:Hi Rock, Judy and TF
I set out below two sample reports from the manufacturer of my oximeter.
I would be very interested in your views as to the important markers to watch on these reports. I am afraid that my own reports are very different!
TF - are these the same reports as those produced by your oximeter please?
Incidentally the software also produces a detailed file print but I have not added a sample here because it runs to several pages.
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Hi TF
I know exactly what you mean. I now use the bottom box (Reply to discussion) rather than the "reply" above it. The latter repeats the last post. The former does not. Cheers.
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Here are some stolen charts.
A night of two parts - what is wrong?
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I would be very interested to hear Rock and Judy's views on how this report should be interpreted please
TF - which settings did you use to import the jpg and get them full size please - much better than my amateurish effort!
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Like I said - I stole them!
I'm working on converting the oximeter output to a .pdf - done - and then the .pdf into a .jpg - not done. The trick about size has to be saving full-sized copies at the .jpg stage.
The interpretation is easy - he fell asleep without his mask on, woke up (surprise. surprise!) and then wore his mask for the rest of the night.
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The difference is in the interpretation of a desaturation by the oximeter and the interpretation of an apnea by the PAP device.
You can have an apnea that does NOT meet the oximeter's definition of a desaturation. Thus an oximeter reading is NOT sufficient to DX obstructive sleep apnea.
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If this works, I'll tell you how, John. Here goes ......
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Hi Judy
We are not trying to DX (?) - diagnose? - OSA with a pulse oximeter. Our Consultant did that for us - we know we have OSA. The same consultant then dispensed really basic machines - they blow and they record only the time they were blowing, nothing else. In case you are in the States, "compliance" here is four hours usage per night - this is the key to being able to drive, operate machinery, etc.
So, with no clue as to the effectiveness of our therapy, we sought a tool to give us an indication - and the oximeter does that very nicely. I refer to it as a toy and an indicatoir elsewhere.
Clearly, there is a correlation between oximeter and CPAP events - just a matter of comparing the definitions of the two.
TF
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