SpO2 as an indicator for CPAP

[Jim Bronson]

Is it true that sleep studies mainly determine the need for CPAP use by measuring Sp02 level? If a patient were to self-measure their level without using a CPAP, and it remains consistently between 95-100 throughout the night, every night, then wouldn't that be a conclusive indicator that CPAP therapy is not needed? He/she could do that easily without a doctor and very inexpensively.

I ask because during my sleep studies (2), I was wired with several sensors, including those that detect leg movement, pulse, respiration, snoring, and probably some others. If Sp02 is the gold standard to indicate CPAP therapy, then why the other tests? I'm guessing that some loud snorers don't have SA, because their airways are never blocked enough - and thus low AHI - to cause low SpO2 levels.

Just some musings of an idle mind.....

[PaulaO2]

No, not at all. They use all sorts of stuff. Respiration rate, chest movement, body movement, brain waves, etc etc. It is the combination of stuff that is used to determine a diagnosis.

An oximeter can be used later for followup tests, especially when the patient has a brick for a machine and there's no way to track therapy usefulness, but that's done with the CPAP in use.

And not everyone's oxygen levels decrease with each event. It is ideal to stay above 92% when asleep.

If you are looking for a reason to not use your CPAP, just look to the data on it. Are you having events? What is your AHI? But to further exercise that idle mind of yours , you could do a little experiment. Your profile says your pressure is 9. Turn it down some. Say to 7 if you can stand the low air feeling. Use it and wear the oximeter. Look at the data the next morning. Granted, it's just one night, but it might reveal a few things. If nothing different happened, try a few more nights.

If you do it, let us know what happened.

Are they saying you need another sleep test? There's no reason to. You have a data capable machine. Show them the dataz.

[DariaVader]

people who rouse easier than others may never have low O₂. They may wake up just enough to breathe all night and never get refreshing sleep

[Jim Bronson]

No, the sleep doc is not recommending a new test, nor am I seeking a reason not to use CPAP. I don't currently use an recording oximeter, so I don't know what my sleep oxygen levels are. I have a simple unit, so I know that my levels while awake are 97-98. When I have some time, I'll look up the sleep study reports to find what my levels were then.

During my first appointment, the doc pointed out the health risks of having a low SpO2 while asleep, and I certainly accept that. I also accept that holding the airway open under pressure with CPAP allows more life-giving oxygen into the organs in patients who would otherwise suffer high AHI numbers and thus lower SpO2 numbers. My thinking is that the endgame of the therapy is to maintain high SpO2 levels during sleep, as would be present in someone without sleep apnea. High AHI numbers would suggest that Sp02 numbers are lower than normal even in the absence of direct readings.

In my case, my sleep disorder is not exclusively SA, but also insomnia, so my treatment is more complex than it would be with SA alone. Therefore I have not seen the remarkable turnaround in daytime sleepiness that those with SA only experience. I don't plan to give up CPAP unless my sleep doc tells me I can, and he would only do so if another sleep study revealed a remission in symptoms, and I don't see how that is possible. My near-term goal now regarding CPAP is to tweak the therapy so that it is repeatable with low AHI, no large leaks, and minimum arousals. As for the insomnia, I'm still not finding long-term relief, but I'll keep on trying.

[DocWils]

One "cure" for insomnia is CPAP - it becomes a learned behaviour (remember Pavlov?) - you start to associate putting on the mask with sleepiness, and pretty soon, you will notice you can lie in bed all night wide awake without the mask, but put it on and you will sleep - a mild and interesting side effect of the device. It takes time, but it actually works, and that is coming from an insomniac.

But the best cure for insomnia remains learning to calm the mind before bed - mindfulness, meditation, whatever - don't use your computer for at least an hour before bed, don't drink coffee after 5, put off the TV at least an hour before sleeping, develop bed time rituals to get you in the right frame of mind. Add to that the wearing of the mask and you will start to find a new rhythm, but it will not happen over night, or over a few weeks - it will take several months to a year for the mind and body to adapt to the new behaviour.

[Jim Bronson]

Thanks for the reply DocWils. It is interesting that you mentioned my only sleep hygiene crime - watching TV and using the computer immediately before bedtime. I occasionally have a dream about the last show that I watched. Maybe I would sleep better without the stimulation these activities produce.

Another point is that sleep studies don't monitor brain chemistry (melatonin and serotonin for example), and thus can't present a complete picture of the of the exact reasons for irregular sleep that aren't related to SA.

After almost a year of CPAP use, I'm used to it to the extent that I don't dread using it. However it hasn't been the godsend solution that I was hoping for.

[DocWils]

TVs and computers produce a blue light which wakens you and makes your body think it is daytime, messing up your normal rhythm. That is why you shouldn't use it before bed - give a good hour or more between, and dim the lights a bit as well, to give body a chance to realise that it is evening and time to put out the nighty-night chemistry your brain and body need to get to sleep (how's THAT for avoiding confusing medical jargon?).

Brain chemistry testing that you mention is normally only available in lab situations, using regular blood draws or spit samples, so it doesn't effectively reflect real world situations. However, EEG readings give good indications of the chemistry, especially when tied into bp, pulse and movement readings, and this can be done, to some extent, in home testing, although usually only with rudimentary EEG, three lead and ear lead testing, that sort of thing, and it produces hellish amounts of noise to sift through, so is usually avoided unless absolutely necessary. Most sleep labs won't have that equipment for home use at hand, even.

Start by cleaning up your sleep hygiene and see where it takes you..... also, remember that caffeine (coffee, chocolate, a lot of other stuff) up to five hours before bed time can delay sleep onset by 40 minutes or more.

[Jim Bronson]

Thanks again DocWils. I notice there's a program available called f.lux that reduces the blue light from monitors in the evening. It may be worth a try.

[DocWils]

I have that program, but I must emphasise that that is not enough - you need to get away from the screens well before bed time, an hour at least, two or more is ideal.

[Jim Bronson]

OK I'll do it, but I may have discontinuation side-effects. (: