[split] Confusion over PS equation (Discussion)

[Rubicon]

In trying to understand how PS relates to EPAP/IPAP...

I looked a little bit into transitional/sleep onset apnea. 

Wat?  Did I just miss the elevator?

Oh well, throwing something out there to try to drive my post count up.

IMO defining an EPAP:IPAP Gradient as Pressure Support is incorrect.  Confusion exists because you're mixing machine parameters (EPAP:IPAP) with a machine mode (PS)

Better understanding my be had by looking at the mode EPAP:IPAP parameters live in, namely Bilevel Positive Airway Pressure.  In this mode, when a breath is called for, the system pressurizes to set IPAP, resulting in a square waveform, and whatever the volume the patient gets during that time, good luck.  Inspiration is terminated by pre-set time or cessation of inspiratory flow.

OTOH, PS is provided for a portion of the patient breath, usually ~75% based on peak flow.

In machines with Auto Modes, pressures change in response to respiratory events.  Setting start points and limits for EPAP:IPAP define the window that PS is allowed to operate in.

Consequently, labelling the EPAP:IPAP Gradient (or for that matter, EPR) as being Pressure Support is incorrect.  It's Bilevel.

[Gideon]

Now I'm confused.
I've never seen a machine mode called PS, and PS doesn't exist? Because it's called BiLevel?

I'm sorry,
The common definition for the rest of us is PS is simply the difference between inhale and exhale or IPaP and EPAP.

A BiLevel adds PS to the EPAP where a CPAP subtracts EPR from pressure (IPaP)

[Rubicon]

Now I'm confused.  
I've never seen a machine mode called PS, and PS doesn't exist?  Because it's called BiLevel?

I'm sorry,
The common definition for the rest of us is PS is simply the difference between inhale and exhale or IPaP and EPAP.  

Yeah, kinda pulls the bottom can out of the soup display, don't it?

[Gideon]

I try hard to not confuse the OP but you can go ahead and set your BiLevel to 4, I'll stick with PS.

[Rubicon]

And actually, if you research the original exposé of EPR on September 11 2005 by the legendary poster deltadave on The Other Forum, you'll note that he too identified it as bilevel, and not pressure support:

"My point still remains that if EPR is carried throughout the expiratory cycle to the point of inspiration, then the only possible trigger could be negative inspiratory pressure at a now-subtherapeutic level. This would mean that the only time the patient would see his prescribed pressure would be during the inspiratory phase. A whole new EPAP has been established, and call it BiPAP, Bilevel, or whatever, but by definition, it's not CPAP. And if you aren't at therapeutic CPAP level prior to inspiration, some people are going to have an issue with that."

[Gideon]

Would you please stop confusing the OP.

[Rubicon]

I try hard to not confuse the OP but you can go ahead and set your BiLevel to 4, I'll stick with PS.

Thanks but I don't actually use a machine, but if I did, and I had a little excess chemoresponsiveness that would potentially lead to CompSAS I'd probably go with proportional assist ventilation rather than any of this stuff.

[Rubicon]

Would you please stop confusing the OP.

I would be happy to further explain any of these concepts to the OP upon request.

But let's let him decide, OK?

[Geer1]

Clearly you think you know more than everyone else including the doctors, researchers and equipment manufacturers that all refer to pressure support as being the difference between IPAP and EPAP. Please get your facts straight especially if you are going to be aggressive like this.

For example maybe you should inform Resmed they don't know anything about pressure support or positive airway pressure equipment. 

https://www.resmed.com/en-us/healthcare-...-10-vauto/

"The device works by adjusting the baseline pressure to hold the airway open while maintaining a fixed pressure support."

Pressure support (PS) also known as pressure support level is not a machine mode, it is a the level of support provided by a ventilation machine and it is equal to driving pressure - PEEP which are the equivalents to a PAP machine IPAP - EPAP.

Pressure support ventilation on the other hand is the mode of ventilation (not a bilevel operating mode) that many bilevel PAP device uses.

Bilevel is a type of machine and it just means the machine has two pressure levels (IPAP and EPAP). Bilevel is not the difference between IPAP and EPAP. The difference is PS.

Your reference to a random internet poster is somewhat correct in saying that EPR is not by definition CPAP (constant positive airway pressure) because constant pressure is no longer held. He does not say anything about PS but what he infers is the exact same thing we said, EPR effectively acts the same way as PS and machines with it should be in some ways considered a bilevel because they have two pressure levels...

I haven't seen this defined or explained anywhere (otherwise I would link to it) but my belief is that the FDA or some other governing body has or had some sort of specification that machines that provide pressure support ventilation are considered bilevel machines and that they require extra steps to get a prescription for because of the potential dangers associated with over ventilation if using poor settings. Equipment manufacturers knew that low levels of PS are advantageous if not required in some cases (primarily for comfort reasons) and they searched out loopholes to allow this feature to be included on their basic CPAP and APAP machines. They came up with the idea that they would call the pressure difference something other than pressure support (EPR in the case of Resmed and Flex in the case of PR) and that this difference in pressure would in theory provide expiratory benefits by being subtracted from the set pressure rather than be considered to act primarily as inspiratory pressure support. In order to avoid concerns of over ventilation they limited the pressure difference to under 3 cm and then I am guessing they performed some sort of study to prove how this new EPR/Flex function can be advantageous to basic apnea cases. This combination of renaming variables, changing the way the machine is set up (setting IPAP and EPR instead of EPAP and PS) and limiting PS was enough to create a loophole the regulatory body would allow these features to be included without requiring extra prescription requirements. 

Anyone that has used a Resmed autoset and a Resmed vauto and looked at data in detail realizes that the pressure waveform and equipment operation is almost identical (although vauto adds some timing controls to fine tune waveform shape). The only difference in these machines is the variables names and how you set up the machine as well as limitations on PS/EPR amount. I can all but guarantee this is because of some stupid regulatory regulatory requirement as it is the only thing that makes sense to explain why these pressure differences aren't called PS and why these basic machines are set up stupidly by setting IPAP and EPR when setting EPAP + EPR (PS) makes much more sense from a treatment point of view (since EPAP, not IPAP, is what combats obstructive apnea).

[SarcasticDave94]

I suppose these are interesting observations and opinions, but to me there's no real weight to them if you don't have any working knowledge by not using a PAP yourself. I've also not seen PS mode on the BPAP I've had in the past, and certainly not on the ASV.