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Sleep Test done. What is hypoxemia?
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RockABye Offline

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Post: #1
Sleep Test done. What is hypoxemia?
First time poster, but I've been reading the forum for a few months. My sleep study was done a week ago. It felt like I didn't sleep at all during the night, but the tech told me she got plenty of data, so obviously I did. I usually fall asleep with no problem, but it took a long time for me to fall asleep. I won't go into all the details because it's probably no different than what everyone else here has been through in their own sleep study. I had a lousy night, and felt like I'd been through the wringer when the night was over! But at least my tech was wonderful and explained everything very well.

The doctor's office called and said the diagnosis is "moderate obstructive sleep apnea and nocturnal hypoxemia with snoring and excessive daytime sleepiness." The sleep apnea wasn't a huge surprise, but the nocturnal hypoxemia was. The nurse said it meant that my oxygen level was too low while I was sleeping, but I thought that was part of sleep apnea, so I'm a little confused. I remembered that within the first hour of the sleep study, the tech came in and said she needed to check my pulse/ox monitor. She took it off my finger, checked it on her own, then put it back on me and I heard her murmur to herself that it was working correctly. In light of the diagnosis, I assume that the pulse/ox reading was low and that prompted her to verify that it was on my finger correctly and working right. Later in the night, she also came in to adjust the staps around my chest and waist. I looked up "nocturnal hypoxemia" on the internet and some of the links were about hypoxemia in people with COPD, chronic bronchitis and emphysema. I don't have any of those ailments and I don't smoke (never have). I have a book on sleep apnea and there's nothing in it about hypoxemia. Is this just a normal part of OSA or something separate? I'm scheduled to come in for the 2nd sleep study on the 22nd to find the proper pressure setting for the CPAP and then the doctor will write the prescription for the machine.

I received the sleep study report in the mail and it was in a narrative format. I thought it would be in a table format with more information that mine seemed to contain. Here's the info from the "Summary" part of the report. I tried to put it in a more readable format:

Total sleep time of 244.5 minutes and a sleep efficiency of 55.9%. The patient's sleep latency was 31.0 minutes.

There was a total of 8.8% REM sleep with the REM latency of 135.5 minutes.
Stages:
Stage 1 - 16.2%
Stage 2 - 64.6%
Stage 3 & 4 - 10.4%

The patient was noted to have snoring during the study.

Respiratory Analysis demonstrated 71 hypopneas, with an Apnea-hypopnea index (AHI) of 17.4.
The patient spent 48.6% of total sleep time in the supine position, with a supine AHI of 27.6, versus a non-supine AHI of 4.5.
The REM AHI was 86.5, versus non-REM AHI of 10.8.
The lowest desaturation was 82%. The total time spent with an O2 saturation less than 88% was 113.1 minutes.
Periodic leg movements were noted, with a PLM index of 5.5.

As per AASM guidelines, a patient must have two hours of sleep and an AHI of >40, or an AHI of >20 if they have co-morbidities, to have a split night study. This patient was not placed on PAP therapy. She had an AHI of 10.8 with 150 minutes of sleep at the 3:00 AM cutoff time.

PVCs were noted by technician.

Impression:
1) Moderate Obstructive Sleep Apnea Syndrome with oxygen desaturations.
2) Snoring
3) Nocturnal hypoxemia
4) Mild periodic limb movements of sleep, without significant related arousals.
5) Delayed sleep onset with increased WASO resulting in reduced sleep efficiency.
------

Does this mean I only had hypopneas and no apnea events? I don't really understand all the different percentages for the various AHIs. I'm particularly interested in information about the hypoxemia and what this means in relation to sleep apnea. Are the PVCs anything to worry about, or will those most likely go away with CPAP treatment? Thanks for any help you can give me in understanding some of this while I wait for the next study in 2 weeks.
11-12-2013 11:03 PM
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Tez62 Offline

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Post: #2
RE: Sleep Test done. What is hypoxemia?
RockABye, welcome officially, here is a definition of Nocturnal Hypoxemia - Nocturnal hypoxia is a drop in oxygen in the blood when sleeping. It's associated with sleep apnea, but also with hypoxic chronic bronchitis pulmonary hypertension and emphysema. Sleep apnea can be due to airway obstruction or of central origin. It causes reduced oxygen, often dangerously, and arousal from sleep, leading to daytime fatigue
To answer your second question, everyone is different but CPAP help and treat most of the issues. If not, you may need to have them looked into more. I also have PLMD periodic limb movement disorder and CPAP has helped me with that, I was prescribed meds to treat it but I wanted to see what CPAP did for me first. I used to kick and move and sometimes my body would jolt me 6 inches off the bed, now I hardly even move. When CPAP is working correctly, you should not snore as your airway is kept open. In theory, if your OSA is treated that is causing the oxygen desats, CPAP should also treat that. Good luck and please keep asking questions.
11-12-2013 11:16 PM
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mdh235 Offline

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Post: #3
RE: Sleep Test done. What is hypoxemia?
(11-12-2013 11:03 PM)RockABye Wrote:  The lowest desaturation was 82%. The total time spent with an O2 saturation less than 88% was 113.1 minutes.

I'm surprised they didn't put you on oxygen for the rest of the night after the tech confirmed your O2 meter was working properly.
11-13-2013 12:09 AM
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robysue Offline
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Post: #4
RE: Sleep Test done. What is hypoxemia?
(11-12-2013 11:03 PM)RockABye Wrote:  (quoting sleep study)Total sleep time of 244.5 minutes and a sleep efficiency of 55.9%. The patient's sleep latency was 31.0 minutes.

There was a total of 8.8% REM sleep with the REM latency of 135.5 minutes.
Stages:
Stage 1 - 16.2%
Stage 2 - 64.6%
Stage 3 & 4 - 10.4%

The patient was noted to have snoring during the study.

Respiratory Analysis demonstrated 71 hypopneas, with an Apnea-hypopnea index (AHI) of 17.4.
The patient spent 48.6% of total sleep time in the supine position, with a supine AHI of 27.6, versus a non-supine AHI of 4.5.
The REM AHI was 86.5, versus non-REM AHI of 10.8.
The lowest desaturation was 82%. The total time spent with an O2 saturation less than 88% was 113.1 minutes.
Periodic leg movements were noted, with a PLM index of 5.5.


As per AASM guidelines, a patient must have two hours of sleep and an AHI of >40, or an AHI of >20 if they have co-morbidities, to have a split night study. This patient was not placed on PAP therapy. She had an AHI of 10.8 with 150 minutes of sleep at the 3:00 AM cutoff time.

PVCs were noted by technician.

Impression:
1) Moderate Obstructive Sleep Apnea Syndrome with oxygen desaturations.
2) Snoring
3) Nocturnal hypoxemia
4) Mild periodic limb movements of sleep, without significant related arousals.
5) Delayed sleep onset with increased WASO resulting in reduced sleep efficiency.

You specifically ask:
Quote:Does this mean I only had hypopneas and no apnea events?
Yes, you only had hypopneas and no apneas. But your hypopneas were very severe given the amount of O2 desaturation going on. OSA does NOT require the presence of apneas to be diagnosed---there are some people in the sleep medicine community who are beginning to use the acronym OSAH syndrome to stress that hypopneas are just as bad as apneas.

A hypopnea occurs when your airway has collapsed to the point where you are no longer getting enough air through the airway. Yes, some air is getting in, but the problem is not enough air is getting in. And this can lead to some pretty bad O2 desats in some people (like you) or repeated EEG arouasals (like me).


Quote:I don't really understand all the different percentages for the various AHIs.
Each AHI is computed in the same basic way---you take the number of events scored (during that type of sleep) and divide by the amount of time spent in that type of sleep. Things become confusing when you spend less than an hour in a given kind of sleep. Here's a break down of the individual AHIs in your sleep test.

Overall AHI = (total number of events)/(total sleep in HOURS)

You had 71 hypopneas scored in 244.5 minutes of sleep. 244.5 minutes of sleep = 4.075 hours of sleep. So your overall AHI for the study is: 71/4.075 = 17.4 because it's traditional to round the AHI to one decimal place.



Supine AHI = (the number of events scored during supine sleep)/(the time spent in supine sleep).

Since your supine AHI is much greater than your non-supine AHI, that means one of two things:

1) Your OSA may be strongly positional---i.e. it's much worse when you sleep on your back.

AND/OR

2) You spent very, very little time sleeping on your back (as in maybe no more than 15 minutes for the entire night), but you had a cluster of events while you were on your back. When you have less than an hour of supine sleep, the supine AHI is best interpreted as a prediction---it is an estimate of how many events you would likely have in one hour of sleeping on your back.

The summary data does not include how much time you spent on your back so it is impossible to tell whether 1) or 2) is more likely the case from you r post.


REM AHI = (the number of events scored during REM sleep)/(the time spent in REM sleep).

Since your REM AHI is much, much greater than your REM-supine AHI, that means one of two things:

1) Your OSA may be strongly related to sleep stage---i.e. it's much worse in REM. (This is NOT uncommon.)

AND/OR

2) You spent very, very little time sleeping in REM, but you had a cluster of events while you in REM. When you have less than an hour of REM sleep, the REM AHI is best interpreted as a prediction---it is an estimate of how many events you would likely have in one hour of REM sleep.

In your case, I think it means BOTH of these things happened. We have enough data from the summary to figure out exactly how the REM AHi was computed

Your sleep test summary says that you spent 8.8% of your sleep time in REM sleep. We can use that to figure out exactly how many of your 71 hypopneas actually occurred during REM sleep.

First: We figure out how much REM sleep you got:

You had 244.5 minutes of SLEEP and 8.8% of that was REM sleep. Hence you got

0.088 * 244.5 = 21.5 minutes of REM = 0.359 hours of REM sleep.

Next: We figure out how many hypopneas were scored during REM sleep. Your REM AHI = 86.5. So we know that

86.5 = (number of events in REM)/(0.359 hours of REM sleep)

Hence (number of events in REM) = 86.5 * 0.359 = 31.. In other words, 31 of your 71 hypopneas were scored during the 21.5 minutes of REM sleep. And 40 hypopneas were scored during the remaining 3.716 hours of Non-REM sleep. Hence, your Non-REM AHI equals 40/3.716 = 10.76 = 10.8 (because AHI is rounded to 1 decimal place).


Quote:I'm particularly interested in information about the hypoxemia and what this means in relation to sleep apnea.
I think the hypoxemia is noted separately from the OSA to call attention to it. Some hypoxemia (low oxygen levels) are typical in OSA patients because many of the experience a 4+ O2 desat with every hypopnea. And each hypopnea has to last at least 10 seconds long. You had 71 hypopneas during the night. So we know that you were not breathing well for at least 710 seconds during the night, and 710 seconds is not quite 12 minutes. So it wouldn't be all that unusual to see a time "time with O2 < 88%" listed as about 8-15 minutes on a sleep study like yours.

But your O2 saturation levels were less than 88% for 113.1 minutes. . Even we make a gross assumption that all of your hypopneas lasted 40 seconds or so, we'd still only account for about 48-50 minutes of really bad breathing and low oxygen levels. (And remember that about 40% of your hyponeas were scored during the 21.5 minutes of REM) So the fact that your O2 levels were so low for so long out side of times that can easily be directly tied to a specific hypopnea is a concern.

It may mean that you just take a very long time to reoxygenate after a hypopnea occurs. It may mean that you've got some super long hypopnneas. Or it may mean that you've simply got a problem with maintaining night time O2 levels in addition to the OSA. You need to talk to a doctor about the significance of this finding on the sleep test.


Quote:Are the PVCs anything to worry about, or will those most likely go away with CPAP treatment? Thanks for any help you can give me in understanding some of this while I wait for the next study in 2 weeks.
Since PVCs are heart arrythmias, I think you should ask the doctor about them. My impression is that they may be caused by the OSA and in that case they should resolve with CPAP. But they may be significant by themselves.

Since you are concerned about your report, you might want to call the sleep doc's office and see if they keep a cancellation list and if they do, get your name on it. That might allow you to be seen a bit sooner than your current appointment.
(This post was last modified: 11-13-2013 09:22 AM by robysue.)
11-13-2013 09:12 AM
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trish6hundred Offline

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Post: #5
RE: Sleep Test done. What is hypoxemia?
Hi RockABye,
WELCOME! to the forum.!
What others have said so far.
Hang in there for more responses to your post and good luck to you with your next sleep study.

trish6hundred
11-13-2013 10:05 AM
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skyler Offline

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Post: #6
RE: Sleep Test done. What is hypoxemia?
Hi, welcome. I am one of those people whose O2 levels do not drop during the night when I have apneas.
11-13-2013 11:26 AM
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RockABye Offline

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Post: #7
RE: Sleep Test done. What is hypoxemia?
Thanks to all of you for the explanations.

Robysue, I especially appreciate all the information in your post. I think I finally understand some of the numbers. I admit I had to study it long and hard to fully grasp it all (the fuzzy OSA thinking), but it finally makes sense. Thanks so much for the time you spent to on such a thoughtful and informative post!

RB
11-14-2013 11:59 PM
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Peter_C Offline

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Post: #8
RE: Sleep Test done. What is hypoxemia?
(11-13-2013 12:09 AM)mdh235 Wrote:  
(11-12-2013 11:03 PM)RockABye Wrote:  The lowest desaturation was 82%. The total time spent with an O2 saturation less than 88% was 113.1 minutes.

I'm surprised they didn't put you on oxygen for the rest of the night after the tech confirmed your O2 meter was working properly.

At the time of my different studies, they stated they do not add O2 unless/until we go below 60, as the purpose of the study is to see how bad we are. I know I spent +2hrs in smurf-zone during my first study (example).

*I* am not a DOCTOR or any type of Health Care Professional. My thoughts/suggestions/ideas are strictly only my opinions.

"Only two defining forces have ever offered to die for you. Jesus Christ and the American Soldier. One died for your Soul, the other for your Freedom."
11-20-2013 01:34 PM
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mdh235 Offline

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Post: #9
RE: Sleep Test done. What is hypoxemia?
(11-20-2013 01:34 PM)Peter_C Wrote:  At the time of my different studies, they stated they do not add O2 unless/until we go below 60, as the purpose of the study is to see how bad we are. I know I spent +2hrs in smurf-zone during my first study (example).

Not me. As soon as I hit 86% they had the tubes up my nose for the rest of the night.
11-20-2013 02:28 PM
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RockABye Offline

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Post: #10
RE: Sleep Test done. What is hypoxemia?
Friday night I have my second sleep study for the titration. I hope I fall asleep quicker this time! Usually I'm out within a couple of minutes of hitting the pillow, but at the sleep study it was 35 minutes before I could go to sleep. I was just too keyed up! With next week being Thanksgiving week, I'm a little concerned that I won't get the prescription for the CPAP machine next week. Hopefully the Doc doesn't take the week off! Smile I am Sooooooo looking forward to feeling better!! My sister took to it like a duck to water, so I'm hopeful that I will too. Cool

Thanks so much for everyone's help and support!
11-20-2013 10:41 PM
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