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Unread post  Post subject: Large leak vs Leak rate  |  Posted: Sat Oct 03, 2020 5:00 pm

Joined: Fri Oct 02, 2020 4:46 pm
Posts: 10

My machine is a Philips Respironics REMstar Auto (System One) AutoCPAP. Oscar has a category (visible on pie chart) for Large Leak - mine is always zero. However in the statistics box there are 2 categories - one for leak rate and the other is for total leaks and for me, these are always high. I understand that there are supposed to be these small leaks as the masks have them built into them to blow off CO2, but since my nightly values for these 2 categories are always different (sometimes drastically different) I'm concerned that there may be a problem. How does the machine know the leak rate for whatever mask I'm using since I haven't told it and does it make a difference? I assume that the different masks have different leak rates and what's an acceptable/expected leak rate for each type of mask is an unknown to me. I looked this up on the internet and while there is lots of information and parameters for Large leak rates, there is almost nothing for the acceptability for the small leaks.

Unread post  Post subject: Re: Large leak vs Leak rate  |  Posted: Sat Oct 03, 2020 6:04 pm
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Joined: Mon Apr 27, 2020 1:06 am
Posts: 170
Location: Australia
PAP Mask: Resmed Airtouch F20
PAP Machine: Resmed S9 VPAP Adapt
Humidifier: Resmed H5i
Pressure Setting: Min EPAP: 8.0 Max EPAP: 11.0 PS Min: 3.0 PS Max: 8.0

There is a setting in your machine to tell it the type of mask you're using. I don't know how it works on a Philips - you'll have to read the manual.

Masks intentionally leak to flush out exhaled CO2 (as you noted above). But when the leak gets above that pre-determined level, then the leakage isn't doing you much good - but neither is it doing you much harm unless it gets big enough that the machine has trouble coping. On Resmed machines, the "red line" is when the unintentional leak exceeds 24 L/sec. At this point the machine starts to have trouble maintaining adequate pressure and flow, and may also have trouble diagnosing and treating apneas.

Philips machines aren't so clear-cut, but as a rule of thumb, when the lower of the two lines on the leak graph gets above 25 or 30 then you need to think about correcting the leak.

The other issue, which can happen even with quite small leaks is that they can disturb your sleep, by blowing in your eyes or making "face farts". So independent of the numbers, if the leaks are disturbing you, then you need to look for a better seal.

Regards from Australia

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Unread post  Post subject: Re: Large leak vs Leak rate  |  Posted: Sat Oct 03, 2020 7:53 pm
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Joined: Wed Aug 02, 2017 8:01 pm
Posts: 2142
PAP Mask: Bleep/DreamPort nasal mask
PAP Machine: ResMed AirCurve 10 VAuto

Respironics machines report total leak which is the mask's expected vent rate (also called intentional leak) plus any excess leak.

ResMed machines report excess leak only so we can't use ResMed leak numbers to compare to Respironics machines.

Respironics machines have a much wider latitude where they say they can compensate for excess leak. They can and will handle more than even 35 excess leak and not run into trouble.

On the OSCAR software you will see 2 leak lines. The top line is total leak which will always seem high because it includes the intentional vent rate.
The bottom leak line is a close approximation of excess leak only but it's not 100% set in stone because with Respironics machines the red line where large leak territory begins will vary with the mask and with the pressures used throughout the night. It's not the gospel because it was just too difficult to write code for something that varies all the time. It's close though.

Respironics machines don't have a mask type choice like ResMed machines but they do have something called a Resistance setting choice....this does NOT impact the leak numbers though. It's not a factor when figuring excess leak.

I once asked a Respironics software tech how the machine figures excess leak when there are so many unknowns and I was told that at the beginning of the night the machine assumes no leaks and sets a baseline with the pressure used at that time and then auto adjusts and calculates leaks based on what was used at the beginning of the night. It uses a generic vent rate for whatever pressure is being used in the calculations.
Sort of an overall average vent rate between all masks at whatever pressure is being used. The higher the pressure the higher the vent rate.

I used a Respironics machine for years...both the M Series and a System auto adjusting mode. Minimum of 10 cm and no ramp.
Nasal pillows with a vent rate of about 25 at 10 cm. I didn't hit large leak territory until I hit 90 L/min total leak....which means I could have upwards of 65 L/min excess leak before the machine called it a large leak. Respironics machines have a much larger range before they will call excess leak a large leak. ResMed machines have a much more conservative number...of 24 L/min so you can't really use their excess leak number unless you just want to be ultra conservative.

Leak numbers are confusing and there's nothing you can do about them or need to do as long as the machine isn't flagging Large Leaks up on the events graph.

Now any leak, no matter if big or little, wakes you up you need to work on it because it is messing with your sleep.

Don't worry about the numbers....just look on the events graph and the LL line near the top and if you don't see LL flagging that amounts to much....shrug your shoulders and move on.

I may have to rise but I refuse to shine.

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