Pressure Support Question

[MrIvanDrago]

I saw this in a post from the past, "Far from getting expiration relief, the patient is actually getting LESS than his prescribed EPAP pressure (7 instead of 10) and a healthy dose of pressure support (3.0) that he may not need and which may actually cause him problems."


Why would a pressure support of 3.0 cause problems? What type of problem would you typically experience with unneeded pressure support?

[WhyMe]

EPR and pressure support are different, but often confused, terms.  If you set your APAP machine for a minimum pressure of 10 (with an EPR of 0), you get 10cm h2o of pressure, both when you inhale and when you exhale.  That is the pressure you have determined is the lowest needed to keep your airway open at all times.  If you set the EPR to 3, you lower the pressure you are getting during exhale from 10 to 7, resulting in too low a pressure, and an increased chance for an event (this is, I think, the answer to your question).

On the other hand, with bilevel treatment, you set the minimum pressure (10 in the example), and the pressure support increases the pressure for inhalation (to 13 if you used a PS of 3), so your therapy never drops below the minimum you had determined you needed to keep your airways open.

If you use a regular APAP with EPR, you really need to raise the minimum pressure by the amount of EPR to make sure you get enough pressure.  EPR lowers the minimum pressure to make exhalation easier, while PS (which I think you only get in bilevel machines or ventilators) increases the pressure higher than the minimum to increase tidal volume, encourage inhalation or get past flow limitations making inhalation easier.

Sleeprider described the benefits and drawbacks in an earlier post.

[PeaceLoveAndPizza]

Why would a pressure support of 3.0 cause problems? What type of problem would you typically experience with unneeded pressure support?

Too much (or little) pressure support, whether EPR or PS on Vauto, can create different issues for people. For me, if I have PS < 4 I get CA’s, but if I have it > 4 I get CA’s. For others, there is no end of problems too little or too much PS can cause, like too little or too much pressure. 

Everyone’s pressure needs are different. We need to see as much data as is available to help them find what works as best it can.

[MrIvanDrago]

Too much (or little) pressure support, whether EPR or PS on Vauto, can create different issues for people. For me, if I have PS < 4 I get CA’s, but if I have it > 4 I get CA’s. For others, there is no end of problems too little or too much PS can cause, like too little or too much pressure. 

Everyone’s pressure needs are different. We need to see as much data as is available to help them find what works as best it can.

So you use trigger settings to high? Very high? Or normal?

[PeaceLoveAndPizza]

I currently have it on very high. When I wear the Evora FFM and use medium my AHI is 2-3, high is 1-2, very high < 1. 

With pillows it is almost the same, although I do drop my pressure from 8-12 to 7-11 as I seem to need less pressure with them. No idea why…

[CPAPfriend]

There's a subtle detectable difference in FL between the two nights, where the higher PS resulted in less FL. That said, in both cases it's n=1 data, so we can't exactly slam the gavel. FL is a bit of an enigma, and there is even a measurable degree of FL within the general population (no SDB, no complaints, no symptoms people). The most common cohort is FL for about 5% of the night, and some researchers have suggested that FL beyond 30% of the night could be used as a threshold for screening for SDB patients. So, to your question whether the flow limitation or residual obstruction is still disturbing your sleep, the answer is that we cannot know but also that both suggestions are reasonable: that is, it could be contributing or it could not. Arousal threshold between patients is something often overlooked but now well-established, and so the question is whether or not even a little bit of airway resistance is problematic for you. Once patients start getting woken up around 15 times per hour, they start to get really sleepy, though this is an average, and by "waking up" I mean EEG arousal signatures.

[SingleH]

Hi CPAPfriend,


In regards to the 5% and 30% figures you mentioned for flow limits, I wanted to understand how this correlates to the Med, 95 and 99.5% figures in Oscar.

What is an acceptable or preferable Flow limit figure in Oscar, I dont understand how the percentages correlate to the one figure. When I look in Oscar there are always flow limits shown, but the Med is always 0.0 and the 99.5% is somewhere between 0.10 and 0.20 on a PS of 6.6 to 8 and goes upto about 0.45 on PS of 5. Are these these good figures or bad?

Thanks in advance.