How to interpret Oximeter data

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Condoragio

How to interpret Oximeter data

Post by Condoragio » Tue Nov 25, 2014 4:19 am

I have been diagnosed with OSA and supplied with a CPAP machine. This was following a test which, I was told, showed that I actually stopped breathing much more frequently for half the night than was normal. The consultant thought the reason it was for only half the night was that I probably changed my position during the night. In order to check this, I have bought a pulse oximeter (Contec CMS50E). My plan was to compare the readings when wearing the CPAP machine for the night with readings obtained when not wearing the machine but, instead, wearing a backpack to stop me from sleeping on my back. But how I do I interpret the readings from the oximeter? Specifically, how do I convert data provided by the oximeter into 'number of times stopped breathing'? I hope someone can help.

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ChicagoGranny
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Re: How to interpret Oximeter data

Post by ChicagoGranny » Tue Nov 25, 2014 6:42 am

First you need to get a copy of your sleep study summary. Look at what position you were sleeping in during the part of the night when you had no apneas. During this time check how many minutes you were in each sleep stage.

Particularly look at how many minutes you were in REM and whether there were any breathing events in REM. The REM stage is the most difficult stage for airway collapse. If you had no apneas during a long REM stage (20 minutes or longer) it is a good indication. You may be able to treat your condition by avoiding backsleeping. Sleep on your side or stomach.

Sleep pulse-oximetry studies yield false negatives for sleep-disordered breathing. If you see your O2 level dropping significantly below normal frequently or for long periods, you probably have a true positive for sleep-disordered breathing. If you see no oxygen desaturation, you cannot assume a true negative.

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Julie
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Re: How to interpret Oximeter data

Post by Julie » Tue Nov 25, 2014 6:50 am

And if you weren't told, the 'normal' levels would be from 88-90 and up. Any drops below that (for however long they may be) are considered to be problems, so info about levels is as important as the time involved.

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ChicagoGranny
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Re: How to interpret Oximeter data

Post by ChicagoGranny » Tue Nov 25, 2014 7:02 am

Julie wrote:Any drops below that
Julie, Tell him about motion artifacts.

OKCSleepDoc
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Re: How to interpret Oximeter data

Post by OKCSleepDoc » Tue Nov 25, 2014 8:06 am

To some degree I would say that while I appreciate you wanting to make the comparison, it is not exactly "apples to apples". As a Sleep Physician, there are a few points I would like to make about how we score a sleep study:

1. Apneas are scored when there is a 90% drop in flow for 10 seconds. Note: There is no desaturation requirement.

2. Depending on if you have medicare or not, and where you had your sleep study done, hypopneas have a variety of criteria with which they can be scored, one of which is a desaturation criteria with 30% drop in baseline flow.

The reason I am mentioning this is, you could probably use the Oximetry data to get a good idea of what your ODI is and compare that to your ODI on your sleep study (ODI stands for Oxygen Desaturation Index i.e. the number of times your oxygen level dropped during a certain period of time). However beyond that, oximetry is not likely to give you a "number of times stopped breathing" because the only way to really get that number would be to monitor your respiratory flow (which usually would be either a home or in lab sleep study, but even these are not really apples to apples in comparing to each other). Rather than comment on why your breathing "could have been worse" for half the night, there are probably more specific answers one could provide if you looked at your sleep study or the hypnogram.

I hope that helps to some degree.

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ChicagoGranny
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Re: How to interpret Oximeter data

Post by ChicagoGranny » Tue Nov 25, 2014 8:35 am

OKCSleepDoc wrote: there are probably more specific answers one could provide if you looked at your sleep study or the hypnogram.
Why are your colleagues, as a general rule, so lax in looking into the detail and recommending positional therapy when it is appropriate?

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Re: How to interpret Oximeter data

Post by mossytreesprite » Tue Nov 25, 2014 1:56 pm

Something to be aware of, as I also have a CMS50E, is that if it slips slightly off your finger, you could wind up with oxygen readings in the 50% range that aren't truly in the 50% range. My oxygen dipped to 62% in my first sleep study, so I wanted to monitor myself and when I first saw it hit 53% after using the CMS50E, I kind of freaked out until I realized that it was really just an error. It was still dipping to the 70s even with CPAP, but I've switched to ASV now and doing great. But back to the topic at hand - these are tips based on my experience with this oximeter, so they may not be everyone's experience, but what I've found that worked is (1) the oximeter didn't reliably collect an entire night of data accurately until I hooked it up with my computer, downloaded the SPO2 software, and linked the CMS50E to the program, after that it worked quite well, and (2) I use some paper medical tape (like the kind you use to hold gauze in place) to secure the oximeter to my finger at night, that has prevented the false data I was getting previously. I know that some people don't have any trouble with the oximeter staying in place, but I did, so I thought I'd share. I would also place it on my finger, start the recording, and start the CPAP at the same time so I can sync it in Sleepyhead - it's pretty easy to analyze desaturation events when the readings are synced, but I wouldn't be able to comment on what to do without the CPAP. Hopefully you're not having trouble with the oximeter, but I thought I'd put my 2 cents in just in case.
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Re: How to interpret Oximeter data

Post by HoseCrusher » Tue Nov 25, 2014 2:23 pm

Everyone agrees that you need oxygen in your blood to be healthy and alive.

Everyone also agrees that if you stop breathing long enough your oxygen levels will fall.

Oxymetry does a reasonably good job of measuring the oxygen levels and you get a correlation with your heat rate. This can provide some valuable insight but it doesn't tell the whole story.

The sleep people have found that you can have sleep disordered breathing without oxygen desaturations. This is where the problem comes in.

Wearing a pulse oximeter while sleeping and reviewing the data will tell you something but it isn't the whole story. If you experience desaturations you probably have problems but if you don't experience any desaturations that doesn't mean that you don't have sleep disordered breathing problems.

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Re: How to interpret Oximeter data

Post by Lycidas » Wed Nov 26, 2014 6:32 am

Many thanks to you all for your advice. I am in the UK and receiving treatment from a local hospital. I appreciate that the pulse oximeter I used will not give the kind of date collected in a sleep clinic, but a pulse oximeter is what the hospital used for the diagnosis of OSA. So my data are at least comparable with theirs. In response to ChicagoGranny: Thank you. I did indeed have a problem keeping the oximeter in place. My solution was to pull a sock over my hand and wrist, which seems to work.
I would welcome comments on the results of my comparison of oximeter readings when using the CPAP machine and when wearing a backpack instead. Here are the numbers from the SpO2 report - in each case the number when wearing the backpack is shown first and then (in brackets) the number wearing the CPAP machine:
Total events (Drop in SpO2 by at least 4% for a minimum duration of 10 seconds): 39 (35) / Time in events (minutes): 39.4 (35) / Average event duration (secs): 60.6 (70. / Index (1/hr): 4.3 (5. / % Artefact: 23.3 (0.2) / Adjusted index (1/hr): 5.6 (5..
Basal SpO2 (%): 93.5 (94. / Time (minutes) < 88%: 4.8 (1.3) / Events < 88%: 5 (0)/Minimum SpO2 (%): 84 (86) /Average low SpO2: 91.1 (92.7) / Average low SpO2 < 88%: 86.4 (n/a)
To my untutored eye, most (though not all) the numbers in brackets (i.e. using the CPAP machine) seem a bit better than the backpack numbers, but they are not hugely different. I suppose the most important question is: Is the difference big enough to warrant permanent use of the machine?

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Re: How to interpret Oximeter data

Post by ChicagoGranny » Wed Nov 26, 2014 7:29 am

Lycidas wrote:Total events 39 (35)
What period of time does this cover? How long did you sleep?

Lycidas wrote:I suppose the most important question is: Is the difference big enough to warrant permanent use of the machine?
This is not an appropriate question at this point. Your machine settings and your CPAP process must first be optimized. Many of us have optimized our CPAP process to the point that we are getting less than one event per hour average (AHI < 1.0) or, for instance, less than 8 events in 8 hours of sleep.

So your backpack/CPAP comparison may look very different if you take the time and effort to optimize your CPAP process. As for the backpack, I assume it is already optimized, meaning it did not allow you to roll onto your back at anytime while asleep.

To optimize your CPAP process, you will need a data-capable machine. Fill out your equipment profile so we know what you are using and we will try to help you optimize your CPAP therapy.

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Re: How to interpret Oximeter data

Post by Lycidas » Wed Nov 26, 2014 11:44 am

Thanks ChicagoGranny. I slept for about 6 hours on both occasions, but when wearing the backpack, the oximeter was actually recording for 9 hours because I did not turn it off when I got up. If recording time is used as the denominator for the averages, the backpack readings may be false. But I suspect the denominator is the time with it on the finger. I did not (to judge from how I felt the next day) have enough sleep on either occasion. I believe my machine is supposed to be optimized. I was first given a machine that, I was told, would enable the clinician to establish the correct pressure for me. When I returned that machine I was given another, set at whatever pressure the first machine had shown was necessary to keep my airway open. I assume that by 'event' you mean drop in SpO2 by at least 4% for at leas 10 seconds, rather than drops of below 88%. The technician told me that to stop breathing around 5 times a night is normal, but I do not know which of the 'events' corresponds to stopping breathing. The label on the CPAP machine says 'ResMed IP21'. The number S9 also appears on it. The backpack I used is quite big, and does not let me get on to my back. It is good of you to take the time to advise me.

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Re: How to interpret Oximeter data

Post by Pugsy » Wed Nov 26, 2014 12:22 pm

Lycidas wrote:The label on the CPAP machine says 'ResMed IP21'. The number S9 also appears on it.
What other words do you see on the machine up by the on/off button?
Escape?
Escape Auto?
Elite?
Autoset?
maybe VPAP something?

In the UK they normally do apap trial for a couple of weeks and then figure out a pressure and then dispense a basic no frills cpap machine that doesn't collect any data to evaluate beyond hours of use.
The model name (choices I listed above) will let us know which type you have.
The Escape offers zero useful data beyond hours of use.
The Escape Auto at least offers generic AHI but that is all so it is severely limited in how it might help you.
If you got lucky and have the Elite or AutoSet or one of the VPAPs there is a lot of data that can be used to evaluate your therapy effectiveness.

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Re: How to interpret Oximeter data

Post by Lycidas » Wed Nov 26, 2014 12:33 pm

Above the switch it says 'Escape' and below it 'EPR'. The technician did tell me that this machine cost much less than the first, because the first one was capable of doing more.