School Me - EPR (EPAP) & Flow Limitations

[Sleeprider]

Very good explanation Geer1. I think it's safe to say this forum is filled with engineers and scientists rather than doctors.

[Coffee Man]

Many doctors have strong backgrounds in science...just sayin’

[Geer1]

Very good explanation Geer1.  I think it's safe to say this forum is filled with engineers and scientists rather than doctors.

Was my mechanical engineering background that obvious lol.

There are only two ways to increase flow. 

1) Decrease pressure loss by removing obstructions, using larger pipes etc. There are the odd surgery options, cervical collar, mouthpiece etc that attempt to do this. EPAP also acts in this way.
2) Increase pressure differential. Can't easily do that on the body but you can do it on the CPAP supplied air in the form of EPR/PS.

[Sleeprider]

I have calculated flows from ducts and stacks to lab hoods and supplied air PPE. I knew exactly where you were coming from.

[70sSanO]

Having recently drunk the Dr. Krakow kool-aid, I am going to bring this subject back up with a few observations and questions.

Dr. Krakow has called CPAP a traumatic experience and has used a term Expiratory Pressure Intolerance to describe people who fight against the CPAP pressure when exhaling. He states this intolerance leads to RERAs or Flow Limitations. In the past I have thought pressure, pressure, and more pressure can fix any sort of obstruction or limitation, but there are just too many people who can't handle the therapy. If what Dr. Krakow says is correct, that intolerance is primarily on the expiratory leg of the breathing cycle and not the inspiratory side.

One slide I saw in a presentation stated that the goal was to aggressively treat RERA breathing events without triggering expiratory pressure intolerance. I can understand why some people are traumatized by CPAP and never come back if they struggle to exhale against high pressure; especially if they are fighting it by just using their nose. It must feel like trying to blow up a balloon through your nose.

If all this is correct, would not the goal be to reduce the EPAP to the lowest possible level, (within reason but definitely to single digits), for comfort and then rely on the ability of sophisticated BiLevel/Vauto to ramp up the pressure support to combat any apnea or limitation event after end of expiration?

I realize that everyone is different in what therapy is required, and I don't want to oversimplify things, and I really don't want anyone to change what he/she is doing that works, but it makes me wonder if a high EPAP of 10, 12, or more might cause more fight than fix.

John

[slowriter]

If all this is correct, would not the goal be to reduce the EPAP to the lowest possible level, (within reason but definitely to single digits), for comfort and then rely on the ability of sophisticated BiLevel/Vauto to ramp up the pressure support to combat any apnea or limitation event after end of expiration?

Yes, with three caveats:

1. There's one wrinkle with the Resmed bilevel: (unlike with the Dreamstation alternative) PS is fixed*, so if the machine is raising IPAP to address flow limitations, it's also simultaneously raising EPAP. I self-titrate on the VAuto by seeking to minimize those pressure swings, so that IPAP and EPAP is pretty stable even on the auto mode. 
   
2. You don't really lower the EPAP for comfort. You raise it from the minimum until it resolves obstructive events, and no more.
   
3. If the min EPAP + the max PS that does not introduce central apneas does not resolve hypopneas and RERAs, you would have to raise the min EPAP to ensure the IPAP was high enough.
   

* I'm hoping Resmed addresses this limitation in the next iteration of their auto bilevel.

[70sSanO]

Yes, with three caveats:

1. There's one wrinkle with the Resmed bilevel: (unlike with the Dreamstation alternative) PS is fixed
   
2. You don't really lower the EPAP for comfort. You raise it from the minimum until it resolves obstructive events, and no more.
   
3. If the min EPAP + the max PS that does not introduce central apneas does not resolve hypopneas and RERAs, you would have to raise the min EPAP to ensure the IPAP was high enough.
   

Agree with all of this.

I was not aware that Resmed VAuto did not have a Min/Max EPAP and a Min/Max PS.

Having an EPAP Min/Max of 5/8 and a PS of 2-15 would cover everything up to a 23 IPAP without taking EPAP past 10 worst case.

But in a less extreme situation it would be possible to run an EPAP fixed at 5 and PS at 2-10.  I’ve never been a fan of wide open settings and Webster hasn’t created the words to convince me otherwise.

John

[slowriter]

To be clear, variable PS is a theoretical benefit; I don't know how much practical benefit it has. I certainly wouldn't get a DS over a VAuto just to get that feature.

[70sSanO]

All I know is from my ASV, which is a different animal, but has no IPAP settings, per se. It only has EPAP (fixed or range) and Min/Max PS.

Right or wrong, I assumed variable PS was a benefit.

John

[Sleeprider]

Variable PS on a bilevel, as implemented in the Philips machine seems like a good idea, but the implementation is poor without the ASV algorithm. I have used the PRS1 BiPAP Auto, and the variable PS moves in a relatively small range. PS on that machine seems to move higher in response to hypopnea, but Philips does not have effective flow limitation detection, so it could be better. The fixed PS on the Resmed machines works equally well once it is tuned in, and I have actually found variable PS is not very useful when coaching Philips users. As ASV is a different animal, and for most users, I don't think a minimum nd mximum PS range is very effective. We're not treating centrals or periodic breathing with a BiPAP S or Auto. FWIW the hardware is the same, but the ASV firmware costs a lot more. I don't expect that to change soon.