APAP 90% creep

Has anyone noticed or can explain why when you use an APAP with a wide range then after a few days you set your minimum pressure to what your 90% average was. Then you go a few more days and now your 90% is higher than the last. the 90% keeps increasing as you increase your minimum pressure. I have a PR 1 if that is relevant. Thanks

With a low minimum pressure, it may never get to where it needs to be to respond to the events......and then drops back down to the minimum again. Since it takes so long and never get there, the 90% pressure is naturally going to be lower. That's why it's so important, when using an APAP in APAP mode, to have the minimum pressure set to the point where it eliminates almost all of the events.......like where you would set it for CPAP pressure. Then if it NEEDS to go higher for some straggler events, it can respond faster.


Den

What Den said and also ...

For APAP use, a good rule of thumb for setting range to find optimal pressure is to use your titrated pressure and subtract no more than 1 or 2 cm for lower setting. For higher setting, you can leave wide-open IF you are certain your PSG lab study did not show you sensitive to centrals. To be safe however, setting upper limit to 2 or 3 cm above titration pressure should work and then if your data shows you are constantly bumping up against your upper limit then raise it again by another cm. or two. Once your data is showing that you are rarely bumping up against the upper limit or not at all, collect data for a couple of weeks without changing settings and you can use the average 90% value for that period to reset back to CPAP if you prefer CPAP mode.

It may be an iterative process but most importantly to remember is that all this assumes that mask leaks are completely under control ... otherwise you just end up chasing leaks and eventually have to go back to square one, not pass go, and not collect optimal AHI values.

Yes, of course. The 90% pressure is the pressure that the machine needs to raise to, from the minimum, 90% of the time. So if your minimum pressure eliminates many of your apneas, the machine never even notices those, and only counts the ones that *weren't* eliminated.

Den hits the nail on the head, here.