Tweaking Bilevel

[ahuman]

What do you suggest to try to improve each of the issues below? It would be helpful to understand possible tweaks to address each issue alone and then also in combination. These are all with a Dreamwear nasal mask. 

Machine not adjusting pressure in response to flow rate issues
Can this be fixed or is this an example of an algorithm problem and why some prefer fixed pressure settings? 
Zoomed: https://lh3.googleusercontent.com/drive-...1600-rw-v1 
Full: https://lh3.googleusercontent.com/drive-...1600-rw-v1
 
Kinks at the top of flow rate curve
Zoomed: https://lh3.googleusercontent.com/drive-...1600-rw-v1
Full: https://lh3.googleusercontent.com/drive-...1600-rw-v1

Pressure increasing to max of range, but that is not enough
This isn’t common, but links provide an example. Is it better to increase EPAP or let this happen occasionally? Or is there something else going on I should try to fix? Or is this an algorithm issue?
Zoomed: https://lh3.googleusercontent.com/drive-...1600-rw-v1
Full: https://lh3.googleusercontent.com/drive-...1600-rw-v1

Flow rate curve shape is more square
Is this due to flow limitations or the pressure not being setup to avoid rather than respond to flow limitations? While the overall flow limitations for the night are low, can reducing flow limitations be improved?
Zoomed: https://lh3.googleusercontent.com/drive-...1600-rw-v1
Full: https://lh3.googleusercontent.com/drive-...1600-rw-v1

Thanks.

[PeaceLoveAndPizza]

The machine is working as expected, no worries there.

Note that flow limitations may be enough to flatten the top of the flow rate curve, but not be enough to trigger the FL indicator. I have asked ResMed a few times how much of a flow limitation is required to increment the count, but so far no answer. Does not matter in the long run as we can still see what is going on, but it would be nice to know.

Try increasing pressure support to 4.4 and see how things look. 

EPAP min 8
IPAP max 15
PS 4.4

We can review after a few nights and see how things look.

[ahuman]

My sense was to increase PS so I'll give that a try. Other than focusing on adjusting one setting at a time, is there a reason you suggest leaving IPAP and EPAP as they are? I wondered about increasing those slightly even though there are few apneas or hypopneas.

[PeaceLoveAndPizza]

We may need to bump up IPAP and EPAP a bit, but let’s see how you respond to a slight increase in pressure support first.

[ahuman]

Below is a recent night. I'm getting more centrals and I don't see much reduction in flow limitations. What should I try next? 

https://lh3.googleusercontent.com/drive-...1600-rw-v1

[PeaceLoveAndPizza]

It looks pretty danged good to me. Flow limitations are minimal, tidal volume is good, I:E ratio is good, the only pressure increase was caused by a leak. Still some arousals, but nothing major.

If you want to tweak further, try this:

EPAP min 8.4
IPAP max 14.4
PS 4

Similar to before but with a bit more pressure on exhale and a little lower PS. We are right around an optimal pressure for you, so slowly bumping up by 0.2 every few nights may help in reducing the remaining arousals. If you hit a point where things go off the rails, then work backward until they settle down.

Keep in mind every night is different, so changing things too often is an exercise in frustration.

[ahuman]

I'm still working to improve flow rate curve shape and reduce the number of arousals. Any suggestions as to what adjustments to try? I'm pondering increasing EPAP a little so EPAP and EPAP + PS are closer to 95% values. I also wonder about lowering PS a tad along with increasing EPAP?

https://lh3.googleusercontent.com/drive-...1600-rw-v1

[Sleeptechmaster]

Try a pressure support of 6 to increase comfort and ease of ventilation. 16 max ipap 10 max epap.

[ahuman]

Can you explain more about why you suggest trying PS 6? That seems a big jump from PS 4.

[Sleeptechmaster]

It will increased comfort, you exert less energy exhaling so you have more energy during the day, you can expel CO2 easier, increase oxygen levels, reduced mask leak. When you increase pressure support you keep the EPAP at the pressure where events are controlled and increase the IPAP pressure. The increased pressure feels less severe due the the greater difference in exhale pressure. Helps you use the greater pressures that bilevel has avaliable. One of the benefits of bilevel is that it's maximum ipap is actually 25 to 30 (not that you would need that) but people would not be able to breathe out against that high of pressure.
Typical reasons for the switch from cpap to bilevel is intolerance to cpap pressure, higher pressure needs, need for higher oxygen levels like COPD.