Auto BiPAP, pressure support, and lowering AHI

[cwsanfor]

At 19.5/15 on an Auto BiPAP I have several instances where I get an apnea when IPAP is at the maximum limit, but EPAP is still at it's usual 15, or lower limit.



My pressure support (PS) set to 4.5, the max for this IPAP/EPAP combo. I guess that if IPAP is at max (19.5), there's some sort of narrowing of the airway going on, and that it would be useful to narrow the PS to 4.0 or 3.5, so that when I have an IPAP of 19.5, it will drag the EPAP up some.

Rested Gal tends to advocate a wide open PS, dsm not so much. Do I understand the principles here? Is it reasonable to expect faster or better EPAP/apnea response with a "leashed" PS, in this case?

Thanks.

Comments.

[Snoredog]

I don't think you are going to improve on that AHI with any change of settings.

IPAP is certainly doing its job, you only had 2 Hypopnea and those appear to be "onset" events (there was a "break" immediately before them), so I would ignore them.

BASED UPON your current pressure settings, you basically disable any PS setting. Your IPAP=20 and your EPAP=15, so any PS setting isn't being used.

Minimum PS = 2 hard coded by the machine. The maximum spread you have is 5 cm (based upon max & min settings), for PS to work you would need your IPAP and EPAP spread farther apart. I think you had problems in the past setting your IPAP=25, so I don't recommend doing that, you also had a few train wrecks at lower EPAP so I would leave things where you are at.

If you wanted to see "more" movement possibly on the lower side, you would set PS Max=3 (range is 3-8), then your IPAP could be pulled down as HI's disappear and since EPAP is taking care of OA's it would pull EPAP down by using the lower PS=3 setting. Right now you have PS=4.5, that makes sense it is 4.5 cm higher than EPAP meaning EPAP is "pulling" IPAP down from 20 cm to 19.5 based upon that PS=4.5 setting. If PS=3 it would have pulled IPAP down to 18.0 cm. If there were no events to drive it back up, it should continue to drop until it gets to the PS Minimum=2. Those pressures will never run into each other, there will always be a 2 cm PS cushion between them.

If you had OA (apnea or snore) events it could still drive up your EPAP all the way to 18 cm (with current PS=4.5 setting). But you are correct if you set your PS=3, it would/should have pulled up EPAP sooner possibly not needing the highest IPAP seen.

But look at therapy hour 7, there you had the OA and the machine drove up EPAP to take care of it, while the IPAP and EPAP appear to meet on the graph, I bet it pushed IPAP on up past its 20 cm maximum.

EPAP still does most of the work of splinting the airway even though it is exhale.

If you open your mouth (w/nasal mask) and let the pressure escape where the airway deflates/collapses that it pressure maintained by EPAP.

It is akin to checking the air pressure on a bicycle tire, there is enough air to hold the bike up but when you push on the tire it may need more air.

Basically with the setting used on your machine it is like being on Bilevel, but it appears to be working so I would leave it.

You do have a problem with "on-set" events, usually after you wake during mid-night, doesn't seem to be a problem at all when you first start therapy.

Those "FL" are always interesting, you have to wonder why they show up at 20 cm pressure.

[cwsanfor]

Thanks, Snoredog.

A small matter: the charting in EP makes it look like I'm at 20/15: actually I'm set to 19.5/15.

Any different views from sag, RG, dsm, anyone? I'm interested in a range of opinions, if they're available. Thanks in advance.

I was thinking that a Max PS less than the range between IPAP and EPAP would "pull" the EPAP up when IPAP is at 19.5, rather than "pull" the IPAP down when EPAP is at 15, where mine tends to stay. I need to read up on that ...

[Snoredog]

well if you look at your "FL"s they are what drove up your IPAP pressure throughout the night.

If you look at the Minutes at Pressure (MaP) for EPAP it basically stayed there at 15 the whole night even when that OA was seen, IPAP moved up but EPAP stayed at 15 (or 14.9).

So if you consider the current settings;

when you first turn On the machine EPAP will be at 15 cm, IPAP will be 2 cm higher at 17 cm. So if you are using a PS=4.5 setting there won't be much drag or pull movement of EPAP from the floor setting (only .5 cm) if it is to be "pulled" up by the PS max setting because it is too high. Since there is only a 5 cm spread "allowed" and it is at 4.5 it doesn't have much room to move up (2 cm).

Is there anything wrong with that picture? Not really, EPAP of 15 shows it pretty much takes care of ALL OA's seen, that is also why it didn't respond to that last OA, everything else in the form of a OA was taken care of prior to that last OA so the machine didn't seen any "pattern" to use and respond to.

That is what I call pressure "masking" the event, sure it preemptively eliminates them but it also hides those events that the machine may use and store in memory to trigger a response higher down the road.

But you are splitting hairs, your AHI looks fine.

[StillAnotherGuest]

Well, you have 2 areas of about 20 minutes where IPAP has effectively hit ceiling, and essentially the last 2 hours of the record. Areas like that either suggest a pressure that could be sub-optimal, or some really precise titrating there.

As noted in the original transition to AutoBiPAP:

A Year Already?



there may be as many as 4 sets of pressure requirements:

NREM sleep in the lateral position
REM sleep in the lateral position
NREM sleep in the supine position
REM sleep in the supine position

And we really don't know what supine REM pressure requirements are based on the sleep study. It can be inferred, tho, that they are substantial.

So if those IPAP max areas are REM, and you got there because of a successful Poptimal search (as opposed to those event-free very short IPAP bursts, which may suggest a less fruitful Poptimal patrol), then one must wonder if IPAP (or, as you suggest, EPAP) is truly optimal.

However, the rule of thumb tends to be chase only apnea events with EPAP, and attack everything else with IPAP.

Which also begs the question, "Is EPAP too high?" Based on titration results, as long as you're lateral, your pressure requirements don't appear to be that much.

Applying the 4W Philosophy, however, if everything is going well, why pull the bottom can out of the bean display?
SAG