Please Help...? Right pressure with automatic CPAP

I've got a question...

My Dr. told me to set the pressure of my CPAP between 6 and 20, so when I checked my apneas during the night I saw that the pressure always reached a max of 14 during some episodes. Then, I noticed that when I hold my breath, the CPAP takes quite some time to really increase the pressure, so I thought that maybe it'll be a good idea to set the minimun pressure (instead of 6) at 14, given the fact that some times it reaches that pressure.
Is it a good or maybe a really bad idea???

Thanks,

Luis Felipe.

It does take the machines a while to respond and you are correct that the wide open pressure range starting at 4 is too low--you will have more apneas while your pressure is always trying to "catch up" to the events.

But 14 is probably too high if you don't need 14 all the time. You may find that you get some pressure induced centrals, and it may be an uncomfortable if not needed.

Do you know what your titrated pressure was? Generally, a good rule of thumb is 2 cm below and 3 cm above the titrated pressure. Some people prefer the bottom number to be the titrated pressure and go up from there.

Above all, you need to be checking the data to see what's going on with those pressure changes, to make sure you're not solving one problem to create another.

If the changing pressures are waking you it might be a good idea to narrow the range. Do you have the software or just taking the numbers off the machine? Do you know the AHI? Obviously a minimum pressure of 6 is too low so you might try tweaking the minimum 1-2cms and watch the data. It's really important to have software.

Janknitz wrote:It does take the machines a while to respond and you are correct that the wide open pressure range starting at 4 is too low--you will have more apneas while your pressure is always trying to "catch up" to the events.

But 14 is probably too high if you don't need 14 all the time. You may find that you get some pressure induced centrals, and it may be an uncomfortable if not needed.

Do you know what your titrated pressure was? Generally, a good rule of thumb is 2 cm below and 3 cm above the titrated pressure. Some people prefer the bottom number to be the titrated pressure and go up from there.

Above all, you need to be checking the data to see what's going on with those pressure changes, to make sure you're not solving one problem to create another.

What are "pressure induced centrals"?

Centrals, or "clear airway" apneas can occur sometimes when the pressure is too high--they are not caused by an obstruction, but you stop breathing anyway. This is something you can see on software--I'm not sure if the ResMed machines show it on the onboard screen but the Philips Respironics machines definitely do not.

Typically what you will see if you don't have the software is that the AHI will actually go UP when you increase the pressure.

lfmoy wrote:I've got a question...

My Dr. told me to set the pressure of my CPAP between 6 and 20, so when I checked my apneas during the night I saw that the pressure always reached a max of 14 during some episodes. Then, I noticed that when I hold my breath, the CPAP takes quite some time to really increase the pressure, so I thought that maybe it'll be a good idea to set the minimun pressure (instead of 6) at 14, given the fact that some times it reaches that pressure.
Is it a good or maybe a really bad idea???

Thanks,

Luis Felipe.

I think I'd try a range of 10 - 20 first....if it were me. But you do have the right general idea. The minimum pressure is the important one to set "right" with an autopap. A minimum of 10, 11, or 12 might work just fine -- allowing the autopap to do its job quite effectively.

If you don't have leak problems, then leaving the max at 20 is fine while you work on tweaking the minimum pressure to try to prevent most apneas right from the get-go.

Results: 1st night with Auto A-Flex (topic started by TSSleepy)
Two nights graphs posted using pressure range 4 - 20 and 10 - 20
viewtopic.php?p=348963#p348963

November 2008 Just got an APAP (topic started by turbosnore)
viewtopic.php?p=319619#p319619

October 2008 Turning off Aflex and Cflex (topic started by DoriC)
viewtopic.php?p=307265#p307265

September 2008 New Guy - Need Help w/Settings (topic started by alanhj13)
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Wulfman, DreamStalker, and ozij explain why autopaps make changes slowly.
December 2008 Why adjust APAP. Isn't it auto? (topic started by oxygenium65)
viewtopic.php?p=323218#p323218

Well, actually what I did was set the minimum at 14... and it's been almost 2 years. Is there any "bad" consecuences if you set your minimum pressure higher than you probably need? I mean, what if you don't use your cpap one night... given the fact that you've been using all that pressure to sleep, is it possible that your apneas will be a lot worse than before?

Thanks,

Luis Felipe.

lfmoy wrote:Well, actually what I did was set the minimum at 14... and it's been almost 2 years. Is there any "bad" consecuences if you set your minimum pressure higher than you probably need? I mean, what if you don't use your cpap one night... given the fact that you've been using all that pressure to sleep, is it possible that your apneas will be a lot worse than before?

Thanks,

Luis Felipe.

I'm not a doctor, but I really don't think there are any "bad" consequences for most people if the minimum pressure is set higher than what's probably needed to keep the airway open.

You'll hear warnings about "HIGH PRESSURES CAN CAUSE CENTRALS!!!" Central apneas happen when the brain simply doesn't send a timely signal to "breathe now." The brain finally does send a signal to end a central apnea, in the same way the brain finally does send a signal to end an obstructive apnea.

Regarding concern about "pressure induced centrals"

viewtopic.php?t=14225
Page 2

The phenomena of pressure-induced central apneas is tossed around far too freely. The vast majority of people do not get centrals because of ultra-therapeutic CPAP levels. BiLevel, Pressure Support (PSV) and Proportional Assist (PAV) Ventilation are another matter. You need some mechanism to drive the pCO2 below the sleeping apneic threshold, and plain old CPAP rarely is able to do that. OK, if you wanna argue that CPAP increases base lung volume (Functional Residual Capacity)(FRC), and since that increases gas exchange, some people can generate centrals that way, fine. But it's not as many as you might think.
SAG

SAG ("StillAnotherGuest") is also "deltadave", "Muffy" and "NotMuffy" on cpaptalk, and was "sleepydave" on another board long ago and far away.

lfmoy wrote: when I checked my apneas during the night I saw that the pressure always reached a max of 14 during some episodes.

The way you described what you've seen on your data at times, I don't think there would be anything wrong with your setting the minimum pressure at 14, if that's what you want to do. After all, your doctor was already willing to allow the machine to go all the way to 20, if need be. So, setting 14 (instead of 6 or some other number) as your minimum pressure should be ok for you.

lfmoy wrote:I mean, what if you don't use your cpap one night... given the fact that you've been using all that pressure to sleep, is it possible that your apneas will be a lot worse than before?

I don't think so. I'd think the propensity of your airway to collapse is going to be what it is... whether you've been using "just enough pressure" to prevent most of them, or have been using "more pressure" to try to prevent all of them.

If anything, it may be possible that a person's airway "collapsibility" might not be quite as bad on a single night without CPAP (following good effective nightly CPAP treatment for several weeks) as it would have been if the person had never used CPAP...ever. A few people on this forum have said that when they were going back to a sleep lab for another study or another titration, and had been using CPAP regularly for quite some time, the lab (doctor, presumably) told them to not use their CPAP for several nights before coming in. I don't think many labs suggest doing that, however.

Thank you so much, Restedgal!

Are we talking about setting the ramp, or setting the limits of the auto?

If you always reached a maxof 14 IPAP, setting the machine that way seems reasonable. I don't think holding your breath is a reliable way to check the response of a machine. There are those that say it takes the machine longer to reach the needed pressure, 14 in your case, when the minimum IPAP is set for 6. I think the idea of pressure induced centrals is overstated. I know some people have complex, or central sleep apnea, but setting the machine IPAP to 20 is hardly likely to get you into trouble (paraphrasing my RT), if you have plain OSA.

lfmoy wrote:Well, actually what I did was set the minimum at 14... and it's been almost 2 years. Is there any "bad" consecuences if you set your minimum pressure higher than you probably need?

If you aren't already in the hospital, the bad is usually limited to ruining your sleep. But if that's happening, it is bad enough.

You want your minimum high enough to prevent most obstructive events. If you have a lot of centrals, it's possible your pressure is too high. The S8 can't tell whether or not your airway is clear, so you'll have to look at your graphs and make some educated guesses.

If you keep having events as the pressure drops below a certain threshold, set the minimum pressure just above that.

If you have events at the maximum pressure, it could be that they are pressure-induced centrals, or that the pressure is waking you up (check the leak rate), or that the S8 correctly interpreted previous events and raised your pressure, but needs to go higher to keep your airway open.

If you post your data, you'll probably get some good suggestions.