Leak rate vrs time in large leak

I've been doing cpap setups for near 20 years but still don;t totally understand the signifigance of "Leak Rate" and "Time in Large Leak". If your leak rate is high but your time in large leak is low, lets say 5 or 6 minutes, which is more significant. Please educate a RT....

rjjayrt wrote:I've been doing cpap setups for near 20 years but still don;t totally understand the signifigance of "Leak Rate" and "Time in Large Leak". If your leak rate is high but your time in large leak is low, lets say 5 or 6 minutes, which is more significant. Please educate a RT....

It is just a method Respironics decided to use to present statistical information to someone who does not know statistics.

What is important is how it might be tied to the rest of the data.

For example, if you have a leak rate that is below 35 liters per hour (the general cutoff people seem to like to use), it tells you that your AVERAGE was less than 35. Let's look at two different example sets of data:

[ 0, 0, 0, 70, 70, 70 ]

[ 30, 30, 30, 40, 40, 40 ]

Both numbers would give us an AVERAGE of 35. Which of the two would be more effective? The second of course, though there is more air leaking through out the time of use, it is closer to the average.

So, with one number, how should a equipment manufacturer show you that you are getting less effective therapy that you should?

Respironics decided to reasonably call those bad leak conditions "Large Leaks". It's how they let us know that though the average might be good for that 5 or 6 minutes, the therapy was not effective.

Now let's assume you also look at the data and see a periodicity to it. That is, every 60 to 120 minutes it repeats. In fact at the same time the apneas increase. I bet you would assume it was during REM sleep this occurred. It makes sense. When we are in REM sleep our bodies relax even more. So, the mask probably also leaks more then. But, a large leak that coincides with an apnea in REM sleep is probably an avoidable apnea, which we did not avoid.

So, in this instance, who cares what the AVERAGE leak rate is. The large leak is probably cutting short our time in REM sleep.

But if there was only one event of Large Leak and it is not associated with other activities, it might just indicate we rolled over onto the mask during the night. In that case, 5 to 6 minutes out of 8 hours is nothing. So, in that instance, who cares about the Large Leak rate, as long as the AVERAGE leak rate is acceptable.

This is, of course, why I recommend people use the software to SEE how all the data relates. It's amazing what you can SEE that numbers alone do not tell you.

Hope that helps.

My personal experience has been with Respironics (Legacy model) machines, so that will be where I'm coming from in my interpretation.

As you know, each mask has it's own "Vent Flow Rate" which is a known/anticipated liters per minute (LPM). Anything above that is essentially "leakage".
With a CPAP machine that has leak compensation, somewhere around the 70 t0 80 LPM range, the machine can't keep up with providing the fixed pressure and declares it to be a "Large Leak". With an APAP, it will keep increasing pressure until it hits the maximum pressure the machine is set to.......or until the Large Leak ends.

In my opinion, it's important to turn Off the "Auto Off" feature in the machine's setup because even during a Large Leak, it'll keep blowing air and keep treating the patient/user. If "Auto Off" is turned On, then the machine will turn itself off at some point. (we want it to keep blowing air)

I don't consider a Large Leak (especially if it's of a shorter duration) to be as significant as seriously high (jagged leak lines) during the rest of the night.........assuming that during the rest of the night the normal leak line is somewhere nearer the "Vent Flow Rate". Visually......a Large Leak resembling a skyscraper sticking out of the Kansas prairie would not be as bad as a leak line looking like the Rocky Mountains or some stock market graphs over the last couple of years.
The first one gets back to "normal" after a short duration, but the latter indicates the probability of some serious seal problems with the mask.
From my own therapy reports, I occasionally get some "skyscrapers". I know that for the largest percentage of the night, my leak line is "good", but for some short duration, the mask gets dislodged and then at another point is back in place. I can go for months without having any and then I may get a couple of nights in a row when I do. I also never know that I've had them until I look at my reports in the morning......so, I'm guessing they may occur during REM.

From what I've seen on the forum, serious leak problems occur with APAP machines set to ranges. Typically, the user does not adjust the mask to the highest pressure that may be encountered during the night. Consequently, if the mask is adjusted for a pressure of, let's say, 8 cm. and the maximum pressure is wide open......and the person starts leaking, it can become a "runaway".

From my own experience with similar machines, there can be a difference in how each machine records/reports information, too. I have five machines with four different firmware levels......and they all report different "numbers".
With my mask and pressure, I should see an "Average Leak" (Vent Flow Rate) around 40 LPM. With my oldest machine (firmware v 2.5), the norm is about 44 - 45. With the newest (firmware v 2.8.), it reports a rate in the low 30's. Most of the others are somewhere in between.......upper 30's to low 40's.
So, when someone says they're getting an average leak rate in the vicinity of 50 with a similar setup, I try to assure them not to worry about it. If the typical leak line is reasonably flat, that's what's important.......in my opinion.

Hope that helps.


Den

Well if the large leak rate resulted in a 5 to 6 minute apnea, I would asy the large leak rate would be way more significant.

What Den said, look at the nightly leak plots and if they look like jagged mountains and valleys, that is not a good thing. If the plots look like a zipper pattern or flat line, that is a good thing.

DreamStalker wrote:Well if the large leak rate resulted in a 5 to 6 minute apnea, I would asy the large leak rate would be way more significant.

What Den said, look at the nightly leak plots and if they look like jagged mountains and valleys, that is not a good thing. If the plots look like a zipper pattern or flat line, that is a good thing.

But, you won't know if the apnea occurred because the machine suspends event recording at some level of LPM (during a Large Leak)......except for snores......it ALWAYS records snores......


Den

Wulfman wrote:

DreamStalker wrote:Well if the large leak rate resulted in a 5 to 6 minute apnea, I would asy the large leak rate would be way more significant.

What Den said, look at the nightly leak plots and if they look like jagged mountains and valleys, that is not a good thing. If the plots look like a zipper pattern or flat line, that is a good thing.

But, you won't know if the apnea occurred because the machine suspends event recording at some level of LPM (during a Large Leak)......except for snores......it ALWAYS records snores......


Den

Well someone would know once they discovered that everything is flat lined after the large leak occurred.

I understand leaks and leak rates for masks, what I want to understand is the measurement "time in large leak. Example, patient is wearing a profile lite nasal mask and has a leak rate of 57 and the amount of time in large leak equals 6 minutes. Patient is very difficult to fit a mask due to abnormal facial features and personal likes and dislikes. Previous mask was a FFM with a leak rate of 100 and time in large leak equaled 1 hour and 38 minutes. Considering that we've reduced the leak to 57 and the time in large leak to 6 minutes, should I be happy with the time in large leak of 6 minutes and live with the leak rate or should I continue to address the leak rate. (at this point we've tried 6 different masks, including nasal, FFM, pillows and hybrid). Guess I'm looking for a consult.. I know that pressures are important also but due to lenght of time it take to explain lets assume were making progress on pressures and that even if I totally fixed the mask issue I'd still have high AHI's to deal with. (Suboptimal titration study due to patient hysterics and pressure issues, just changed patient to bipap auto to address that concern) So consult away, pleaseee..... I will admit that this is my most difficult patient in over 20 years and I'm close to lost................

rjjayrt wrote:I understand leaks and leak rates for masks, what I want to understand is the measurement "time in large leak. Example, patient is wearing a profile lite nasal mask and has a leak rate of 57 and the amount of time in large leak equals 6 minutes. Patient is very difficult to fit a mask due to abnormal facial features and personal likes and dislikes. Previous mask was a FFM with a leak rate of 100 and time in large leak equaled 1 hour and 38 minutes. Considering that we've reduced the leak to 57 and the time in large leak to 6 minutes, should I be happy with the time in large leak of 6 minutes and live with the leak rate or should I continue to address the leak rate. (at this point we've tried 6 different masks, including nasal, FFM, pillows and hybrid). Guess I'm looking for a consult.. I know that pressures are important also but due to lenght of time it take to explain lets assume were making progress on pressures and that even if I totally fixed the mask issue I'd still have high AHI's to deal with. (Suboptimal titration study due to patient hysterics and pressure issues, just changed patient to bipap auto to address that concern) So consult away, pleaseee..... I will admit that this is my most difficult patient in over 20 years and I'm close to lost................

This is probably from a Respironics unit, since you are using whole numbers. The rate is in liters per hour. As you note, 57 is still WAY above a good number. But then again 57 is approaching 1/2 of what it was before. And againg the time is improved. Down from 1 hour 38 minutes to just 6 minutes.

Clearly 57 won't allow the mask to deliver fully effective therapy - as you note. But in this case, the lower overall leak rate would seem to be more important. Fortunately, it also seems to correlate with a lower Large Leak value. But as others note, the lower overall value means more here.

At this point, if this mask fits correctly, it might be time to try to "strap down" the mask to see if a firmer seal is possible. And I suspect (due to the facial features ... and I bet sensitive skin) something like the Pad A Cheek may be needed to make the tighter mask straps bearable for the patient.

By the way, I have EXACTLY this type of problem with my ASV unit. When I have a bad day and need to constantly remind myself to breathe (while awake), my machine apparently ends up swinging the pressure from a low value (8cm H2O) to a very high value (about 23cm H2O). When it must compensate for a lot of breathing problems, I end up with "Very Poor" mask fit on the ResMed VPAP Adapt SV unit. And I sleep poorly as a result. When I have fewer problems, I end up with "Good" or "Excellent" mask fit.

Why do I mention that? Well, as you might imagine, I feel much better if the mask fit is better. I suspect that would be true for most everyone. So, improving the overall leak rate should be your first line of attack. That will probably make the most difference.

Anyway, that's my two cents. Hope it helps.

rjjayrt wrote:I understand leaks and leak rates for masks, what I want to understand is the measurement "time in large leak. Example, patient is wearing a profile lite nasal mask and has a leak rate of 57 and the amount of time in large leak equals 6 minutes. Patient is very difficult to fit a mask due to abnormal facial features and personal likes and dislikes. Previous mask was a FFM with a leak rate of 100 and time in large leak equaled 1 hour and 38 minutes. Considering that we've reduced the leak to 57 and the time in large leak to 6 minutes, should I be happy with the time in large leak of 6 minutes and live with the leak rate or should I continue to address the leak rate. (at this point we've tried 6 different masks, including nasal, FFM, pillows and hybrid). Guess I'm looking for a consult.. I know that pressures are important also but due to lenght of time it take to explain lets assume were making progress on pressures and that even if I totally fixed the mask issue I'd still have high AHI's to deal with. (Suboptimal titration study due to patient hysterics and pressure issues, just changed patient to bipap auto to address that concern) So consult away, pleaseee..... I will admit that this is my most difficult patient in over 20 years and I'm close to lost................

Can I ask what brands and which specific masks you have tried with this user?

Also, under what surroundings were the masks checked for leaks, etc.......at home or in your office?

The Profile Lite is a PR brand. If all of the rest of your masks (with maybe the exception of the hybrid) are PR masks, that could be one reason. As much as I am into full face masks, I couldn't tolerate a Comfortfull 2 longer than three nights......I HAD to have my UMFF back.

If the surroundings were at the user's home, another possibility could be the bed pillow. "Standard" bed pillows (for the most part) aren't worth a darn with this therapy.


Den

Just adding another 02.c worth.

Based on personal observation, on my Bipap Auto SV, when I see a large black bar above the leak data, I know there has been a real problem. If that line persists for much of the night or night to night, self will typically start to feel daytime drowsiness within a couple of days.

Am sure the black line, is registering time in large leak.

When this 1st happened self ignored it as was sure was having a good sleep & all the other data looked ok. But within 3 days was experiencing the dreaded drowsiness.

These days will look more for the black bar & react. If there is no black bar but lots of leak scoring, Will still try to sort out what it is but not with the same sense of urgency that comes from seeing excessive black bars in the data.

DSM

rjjayrt wrote:...tried 6 different masks, including nasal, FFM, pillows and hybrid)...

I hate to sound like a salesperson for the RespCare Hybrid, but with the 3 sizes of both oral cushions and pillows, pillows that can be set at 2 heights, and 2 mask straps as well as an over-the-head strap, I have a hard time thinking that it couldn't be fitted for this person. The Libery is much less adjustable and fits very, very differently.

BTW, while the Medium pillows are supposed to work for me based on the fitting guide, they leaked a lot and I need the Large. This was also true of my beloved former mask, the Respironics OptiLife pillow mask; with the Mediums, I just wasn't getting enough air, that sensation disappeared when I went to the Large pillows. If I hadn't started losing therapy air, I'd still be wearing the OptiLife.

I have tried the ultra mirage II nasal mask, respironics profile lite nasal mask, F&P 431 FFM, Resmed Quattro, Hybrid, and respironics comfort lite 2 (where applicable I used a respironics premium chin strap)

Here are a few of the key items that stuck out for me.

Significant mask leak issues.
Pressure requirements are higher than normal.
Patient has abnormal facial features.
Patient experienced hysteria during titration.

All of these key points do indeed make for most difficulty. All of these issues are interrelated.

Obviously the mask selection is signifcantly influenced by the "abnormal" facial features. Could you elaborate on what you mean by abnormal? This would help guide to at least the right type of mask nasal vs. FF vs. pillow vs. other. Was the hysteria related to mask (ie. claustrophobia) or something totally different?

The sleep tech told me that the "hysterics" seemed related to pressure changes and frustration. Patient has sunken cheeks, narrow lower jaw and short span from bridge of nose to lower jaw. To make matters worse his primary MD doesn't know much about sleep therapy and the patient refuses to see sleep specialist in followup. So I'm caught between a rock and a hard place. The primary is relying on me to "fix the problem". I think i'm pretty versed in sleep therapy but this one is confounding me to no end

How about something like one of these?

https://www.cpap.com/productpage/purita ... rface.html

https://www.cpap.com/productpage/aeiome ... rface.html


Den