90 percent pressure vs mean and average

Hi everyone,
I’m new to the site and a new CPAP user. I’m impressed with how knowledgeable folks are on this forum. I have a question about comparing the pressures on the data readout. I’m on a DreamStation auto CPAP. If I wanted to change to a fixed pressure, which pressure reading is most useful to determine the pressure I need -the 90 percent, mean, or average pressure? Thanks for your help!

The 90% pressure number just means you were at OR BELOW that pressure for 90% of the night. People often either don't know or forget about the "or below" part. It is NOT a pressure where you spent 90% of the night. It is NOT necessarily where a person would set the machine if they wanted to use a fixed pressure.
90% numbers are easily skewed by relatively short periods of time at a higher number.
Now sometimes if there never is much change in the pressure over the night the 90% number might be a good choice for a fixed pressure setting....but it's not the gospel and certainly wouldn't be the optimal setting for everyone.
Maybe long term average of a 90% number might be close...like 6 months of numbers to average out.

If I was going to do a fixed setting I would start with the median pressure average or better yet the overall average pressure and watch the data closely to see if I might need a little more. Watch for clustering of obstructive events which would mean more pressure is needed. The 90% number might be used if it is within 1 or 2 % points of the average but I sometimes have seen a 90% pressure of 18 but the overall average was 10. The 90% number get skewed high because of maybe 30 minutes in REM sleep where I need 18 cm pressure.
I sure wouldn't want to use 18 all night long just to deal with the 20% of the night that I might be in REM.
So it depends on just how close the 90% number is to the overall average number.

If during a normal night, you have an average pressure range of say 8-12. You determine that you want a fixed pressure of 10......part of the night your pressure will be too low to stop events and part of the night your pressure will be higher than needed. You have an auto machine...why not determine your best pressure range and use it?

First note. The below assumes that you’re using OSCAR (formerly SleepyHead) or an equivalent tool!
Second note: This is not qualified medical advice, it’s just “general” advice.


As a rule of thumb, I would say to set the max pressure to the machine max unless one or more of the following occur:

1. Annoying leaks or discomfort are occurring associated with the higher pressure. Remember that your machine will compensate for most leaks. Therefore, you can ignore leaks unless you find them annoying or if they are so excessive that your machine is unable to compensate.
2. Central (or “Clear Airway”) events are occurring at the higher pressures. If they seem to occur equally at the lower pressures, this might not be the issue.


The min pressure is a little more difficult. If you had a proper sleep study, you probably have a prescription. By default, this should be your min unless you’re experiencing issues. If you did not have a proper sleep study, of if the pressure from the study does not seem to be correct, you might need to tinker. Remember that even a proper sleep study is just one night and might not be a “typical” night.


If you need to adjust the min pressure, here are some general guidelines:
1. If you feel like there’s “not enough” ai coming from the hose, you might want to raise the pressure.
2. If you feel like there’s “too much” air coming through the hose, you might want to increase the ramp time, decrease the initial ramp pressure, and/or reduce the min pressure. Remember that for newbies, “too much” pressure might an adjustment issue rather than a truly excessive flow.
3. If you’re experiencing obstructive events or hypopneas, you might want to raise the pressure. If you’re experiencing central or “clear airway” events even at the lowest pressures try lowering it (if that doesn’t help, then this probably isn’t your problem).
4. If you find that you’re spending a lot of time at a higher pressure, try raising your pressure to that point.

5. Ignore D.H.

6. Listen to Pugsy and LSAT.

JPB

Why if someone asks a question about fixed pressure do they get a lecture on auto adjusting pressures?

Can't people just answer a simple question? Maybe the OP has a good reason for wanting to try fixed pressure for some reason.

Crazytired wrote: ↑

Wed Jul 31, 2019 9:08 am

Hi everyone,
I’m new to the site and a new CPAP user. I’m impressed with how knowledgeable folks are on this forum. I have a question about comparing the pressures on the data readout. I’m on a DreamStation auto CPAP. If I wanted to change to a fixed pressure, which pressure reading is most useful to determine the pressure I need -the 90 percent, mean, or average pressure? Thanks for your help!

The 90% number is just a statistic, best thought of as a Max number with any short term spikes cut off... It really means *nothing*, but people that aren't competent to read a nightly pressure graph have seized on it as a crutch to guess at a fixed pressure.

Like pugsy says, the right way to determine a fixed pressure is to examine the pressure trace... And keep monitoring your ahi, since needs change.

Pugsy wrote: ↑

Wed Jul 31, 2019 11:37 am

Why if someone asks a question about fixed pressure do they get a lecture on auto adjusting pressures?

Can't people just answer a simple question? Maybe the OP has a good reason for wanting to try fixed pressure for some reason.

Cuz, some folks don't read the question before answering?

palerider wrote: ↑

Wed Jul 31, 2019 2:26 pm

Pugsy wrote: ↑

Wed Jul 31, 2019 11:37 am

Why if someone asks a question about fixed pressure do they get a lecture on auto adjusting pressures?

Can't people just answer a simple question? Maybe the OP has a good reason for wanting to try fixed pressure for some reason.

Cu, some folks don't read the question before answering?

Obviously.
It continually amazes me how often I see a question get asked and the response doesn't answer the question at all.
People go assuming all sorts of stuff instead of just answering the frigging question.
Some people like fixed pressures better and they sleep better and they don't always have wild swings in the pressure.
Hell, I have seen some pressure graphs in auto mode with the settings 7 min and max 20 and the damn thing never goes above 8 cm night after night after night. They just don't ever seem to have whatever it might be to cause a pressure increase.
People forget the YMMV thing when someone wants to do something that others think is the wrong thing to do without knowing any facts at all. They forget that we tell people to try different stuff if they maybe still aren't feeling like they think they should or want to.
Maybe someone wants to try fixed just to be trying something different for whatever reason....and that's fine.
They will either realize it wasn't a good experiment or they may find out it was a good experiment.

Geez....let people experiment if they want to. Might work out good and it might not but either way they learn from it.
Anytime anything is learned by any experiment...it's not a total waste of time.

Just answer the friggin question ....what's so hard about KISS?

Lets let D.H. address that in his own words:

by D.H.



We definitely need more detail to tell you anything meaningful. Somebody suggested several possibilities, all of which are possible causes. However, she was flying blind since there's not much information. The pressure could be too high or too low, so you can't assume anything.

When he puts that way who can argue?

Thank you for all the responses and the different perspectives. Even though I was inquiring about a fixed pressure, I learned a lot more about the auto mode from DH. I like this forum - it gets lively!

I noticed a while back that if my machine auto adjusted to 16 or higher, I started swallowing air. So I set my max pressure to 15.6. Later, I noticed that for the vast majority of nights, my pressure was in the 14's. Long story short, I kept narrowing the range until it seemd silly to start at 13.6 and max at 15.6 -- a whopping 2 cmH20 range... At that point, it just made sense to pick a pressure and set it to CPAP mode.

I actually didn't pay much attention to the calculated metrics, I just clicked through a couple of months worth of Oscar "Pressure" graphs and it was fairly easy to spot where the machine consistently adjusted to and I picked that pressure. I've been on CPAP mode since. No more air swallowing, leaks are reduced, don't wake up with air blowing out of my mouth, AHI has stabilized for the most part. I'm happy with it.

I have not had to adjust the pressure either -- I think that points more to a lucky pressure choice. Or, perhaps as long as you get the pressure *close*, it's good enough. Maybe for me, my airway is "reasonably" happy as long as I'm within 1 or 2cmH20. At least for me, I don't know that my pressure needs to be exact within a 0.2cmH20 tolerance.

But I'm a garden variety idiot and just because something worked for me, that's no guarantee it will work for anyone else. However, the biggest thing to remember is that you are in control of it. You can change it right back to auto if it doesn't work out. And don't be afraid to bump your CPAP pressure up or down and make mid-course corrections. You don't have to get it perfect on the first night. The (arguably) second biggest thing to remember is that, as long as you can use Oscar and have access to this forum, you have an ad-hoc support system to help you figure it out if needed.

I think you will be just fine. Good luck with it!
-JD

Thanks JD. I’m would like to use OSCAR but I’ve not been able to access it. I think I need step by step instructions. Not sure what I’m doing wrong...

Crazytired wrote: ↑

Fri Aug 02, 2019 2:29 pm

Thanks JD. I’m would like to use OSCAR but I’ve not been able to access it. I think I need step by step instructions. Not sure what I’m doing wrong...

could you explain just where the problem lies? maybe if you went through it, step by step, while writing it down, we could get you through it.

it really IS a helpful tool to have to hand. so if you have the patience to try it, we have the patience to get you going.

good luck!