Need Technical Help

Can someone explain to me what's happening with the two masks I use given the following information? When I use my full face mask, I get high leak readings 40-60 cm with the 95 percentile pressure reading of around 8 L/m where the maximum possible set on my machine is 10 L/m. When I use my hybrid mask, I get much better leak readings, 10-20 cm, but the 95 percentile pressure reading goes up to 9.8 L/m consistently. Also, given that information, which mask appears to work better dealing with apnea events?

What machine do you have?

That would let us know if these are unintentional or total leak rates.

If it records efficacy data, you can look at it to see exactly what's going on.

If you're taking the mask off while the machine is running, and the hybrid mask allows a higher airflow that would explain the higher maximum leak. If it also leaks less when you're actually wearing it that would explain its better average leak readings.

I use a Resmed S9 CPAP machine and I don't take the mask off while the machine is running. If it does record efficacy data, I don't know what I'm looking for. Any help would be appreciated.

O wrote:I use a Resmed S9 CPAP machine and I don't take the mask off while the machine is running. If it does record efficacy data, I don't know what I'm looking for. Any help would be appreciated.

Do you have the owner's manual that came with the machine?

Where are the leak numbers coming from? The machine's LCD? If so, can you tell us what the AHI, AI, and CAI numbers look like for both masks. Those numbers are the efficacy data. Also when you look at the data on the screen each morning do you typically see Mr. Green Smiley Face or Mr. Red Frowny Face when using the FFM?

Since you are using an S9, the leak numbers are unintentional leak rates. Leak rates are measured in Liters per minute (L/min). Think of the CPAP sit up---your machine's blower unit, the hose, the mask, your nose (and mouth) and your upper airway as
a "semi-closed system" that is slightly pressurized. Semi-closed means that the system is designed to leak air at a certain rate so that you do not rebreathe CO2. To maintain pressure, the blower unit is constantly pumping the same amount of air into the system as is being lost through the venting. The unintentional leak rate is the air that's being lost that is above and beyond the intended leak rate. And an unintentional leak rate of one L/min means that each minute the machine is being run, one liter of air is being lost unintentionally. And you can think of a liter of air as the amount of air inside of an empty one-liter Coke bottle.

I'll assume that the leak numbers are coming off the S9's LCD. In that case, the leak numbers are the so-called 95% leak rates. In other words, for 95% of the time the S9 was running, your unintentional leak rate was AT or BELOW the number that shows up on the screen. It also means that your unintentional leak rate was AT or ABOVE the leak number on the screen for 5% of the time the machine was running. With the FFM you say the leak numbers range from 40 to 60 L/min. On a night where the leak number is 60, that means that for 95% of the night with leaks AT or BELOW 60.0 L/min and 5% of the night AT or ABOVE 60.0 L/min. And how much is 5% of the night? Well, 5% of one hour is three minutes. So you can get an idea of an upper bound on how long your worst leaks (the ones above the 95% leak figure) lasted by multiplying the usage (in hours) by three minutes/hour. For example, if your machine was running for 7.3 hours and the 95% leak figure is 60.0, that means your leak rate was AT or ABOVE 60.0 L/min for a total of (7.3 hours)*(3 minutes/hour) = 21.9 minutes And keep in mind that an unintentional leak rate of 60 L/min means you are losing 40-60 one-liter Coke bottles of air every minute when you use the FFM during the 5% of the time with the highest leak rates. And quite probably you are losing large amounts of air during the rest of the night.

And this is a problem for many reasons: Comfort is one---leaks at that high of a rate are bound to be uncomfortable and hence disturbing to your sleep. But just as important, leaks at this magnitude are roughly 2--3 times greater than 24 L/min, which is the maximum unintentional leak rate that the Resmed engineers believe the machine is capable of compensating for. When unintentional leak rates exceed 24 L/min for any length of time, the machine just cannot cope with the leak by increasing the airflow into the system in order to maintain the desired pressure. And this could be why your 95% pressure numbers are lower with the leaky FFM than they are with the less leaky hybrid mask: When the huge leaks hit, the semi-closed system is actually LOSING pressure instead of maintaining it.

The solution? Unless there's a reason you don't want to use the hybrid mask, I'd say give up on the FFM and use the hybrid. Working on dealing with any small leaks that wake you up when you are using the hybrid will be much easier than taming that out of control FFM.

There should be a word on the case to the upper left of the 'on' button as you are looking down at the display:
What does it say? Hopefully, It will say Elite or Autoset; in which case you will be able to get more information.
Others may be able to direct you to the Clinician's manual--so you can access efficacy data and the comfort controls.

Thanks for all the assistance. I think I understand what's going on now.