Questions about leak

Hello all - question concerning leak rate. I know that less leak is desirable, but how much is too much?

For example, last night my numbers were 6.2 hours on the machine, with an AHI of 0.6 and a green smiley for my mask fit which seems good, but the leak was 15.6L/min, which seems like a lot. I've been on the CPAP since about mid April, but its only in the last 6 or 8 weeks that I've actually been able to use it regularly and haven't yet got into the habit of tracking my numbers carefully.

Other details: my machine is a ResMed s9 Elite, I'm using a full face mask (not sure which kind), my pressure is 20 (prescribed pressure is actually 22 but the machine doesn't go that high). I set the humidity to max (6), and have the heat completely off.

I also have mustache and goatee; the doc said because of that I'd have more leak than someone who is clean shaven.

Is that too much leak? or is leak not that big a deal? Should I focus on usage and AHI more?

Thanks in advance for the insight!

Hiya and welcome!

I have the S9 as well, and found out that it automatically subtracts an "allowed leak" rate from the number it shows you. So the numbers you're seeing are above and beyond what the S9 thinks you should see with your mask type. The red line in the ResScan software is set to 24 Lpm, showing that anything over that (on a ResMed machine) can interfere with therapy. That would indicate that the 15Lpm is still within OK limits, but not good. Mr. Frowny (the unhappy face) only shows up if you're over the red line for a significant portion of the night, so it's useless for anything but fitting the mask =)

You may need to adjust your mask a bit to reduce the leak rate, and that takes some time and patience. Search this forum for "mask fitting" and you'll find TONS of tips though, so hang in there.

Personally, I had to shave the goatee (but kept the moustache) to get a good fit on my Mirage Quattro full face mask, but many in the forum have been able to get the leak rate down without shaving, so don't give up!

Naznarreb wrote:Hello all - question concerning leak rate. I know that less leak is desirable, but how much is too much?

For example, last night my numbers were 6.2 hours on the machine, with an AHI of 0.6 and a green smiley for my mask fit which seems good, but the leak was 15.6L/min, which seems like a lot. I've been on the CPAP since about mid April, but its only in the last 6 or 8 weeks that I've actually been able to use it regularly and haven't yet got into the habit of tracking my numbers carefully.

Other details: my machine is a ResMed s9 Elite, I'm using a full face mask (not sure which kind), my pressure is 20 (prescribed pressure is actually 22 but the machine doesn't go that high). I set the humidity to max (6), and have the heat completely off.

I also have mustache and goatee; the doc said because of that I'd have more leak than someone who is clean shaven.

Is that too much leak? or is leak not that big a deal? Should I focus on usage and AHI more?

Thanks in advance for the insight!

Hi, and welcome aboard.

Talon covered the leak issue. Basically, on a ResMed machine, you want the leak rate to be as close to zero as possible.

FYI, if the heat is off on the humidifier, it doesn't matter what the setting is. The setting applies to the level of heat being applied to the water (to create more humidity).

My question: If your prescribed pressure is 22cms, why do you have a machine that only goes up to 20?

Naznarreb wrote: For example, last night my numbers were 6.2 hours on the machine, with an AHI of 0.6 and a green smiley for my mask fit which seems good, but the leak was 15.6L/min, which seems like a lot. I've been on the CPAP since about mid April, but its only in the last 6 or 8 weeks that I've actually been able to use it regularly and haven't yet got into the habit of tracking my numbers carefully.

I'll assume that the 15.6 L/min figure is from the S9's Detailed Sleep Quality Report on the machine's LCD.

In that case: The number represents the 95% UNINTENTIONAL Leak Rate for the night. As others have pointed out, the Resmed machines subtract off the intentional leak rate for the mask before reporting the leak figures. But it's also important to understand exactly what a 95% unintentional leak rate actually measures.

The basic mathematical meaning of the figure is this: For 95% of the time the machine was running overnight, your unintentional leak rate was LESS THAN or EQUAL to 15.6 L/min, which is well under the scary RedLine in ResScan that indicates the size of the leak is big enough to possibly affect the quality of the therapy and the quality of the data. That also means that for 5% of the time the machine was running, your unintentional leak rate was GREATER THAN or EQUAL to 15.6L/min.

And how long were you leaking at a rate of more than 15.6 L/min? Well, 5% of one hour equals three minutes. Since your machine ran for 6.2 hours, that means that you were leaking at a rate GREATER THAN 15.6 L/min for no more than 3*6.2 = 18.6 minutes. So at most you had a leak that was potentially large enough to affect the data (from the Resmed engineers' point of view) for less than 20 minutes out of the whole night. Sine 6.2 hours is 6 hours and 12 minutes, that means that your leak was LESS THAN or EQUAL to 15.6 L/min for about 5 hours and 55 minutes (5:55) Probably not enough to worry about in the sense of compromised therapy or compromised data.

But---that's not the whole story and the answer to your question, Is that too much leak?, is more complicated. To really answer the question you need to look at your leak data in ResScan. And to see why, let's consider two distinctly different scenarios, both of which result a 95% Leak Rate of 15.6L/min. To fully understand the arithmetic, you need to be aware that 6.2 hours is the same as 6 hours and 12 minutes.

Scenario One: For 5:45 (5.75 hours) your mask was very well sealed and the S9 could detect no unintentional leak. But for the remaining 27 minutes you somehow nudged the mask a bit in your sleep and it sprang a leak that was right around or a bit above 15.6 L/min for about 20 minutes of the full leak. Because the 18.6 minutes with the HIGHEST leak rates all had leaks ABOVE or EQUAL to 15.6 L/min, the 95% leak figure is reported as 15.6 L/min. And Mr. Green Smiley Face still shows up because your 75% leak rate is 0.0 L/min or something very close to 0.0. Hardly a disaster of a night leak-wise unless that 20 minute leak woke you up and disturbed your sleep.

Scenario Two: For about 6 hours your unintentional leak rate was bouncing between 15.0 L/min and 15.6 L/min. During the remaining 18.6 minutes, you developed a very severe leak with a leak rate of 40 L/min for about 10 minutes. Because the 18.6 minutes with the HIGHEST leak rates all had leaks ABOVE or EQUAL to 15.6 L/min, the 95% leak figure is reported as 15.6 L/min. And note that Mr. Green Smiley Face still shows up because your 75% leak rate is roughly 15.6 L/min, which is below the magic 24 L/min level where Mr. Red Frowny Face pays you a visit instead of Mr. Green Smiley Face. And while technically the Resmed engineers believe the S9 is capable of handling this much leak all night long without seriously compromising your therapy or the recorded data, the real question is How well can you sleep with an unintentional leak rate that's roughly 15.0 L/min or more all night long?. It seems quite likely that prolonged unintentional leaks at this level will adversely affect the overall quality of your sleep even if it doesn't directly affect the quality of the therapy or the data.

The only way to tell if your particular night's data is closer to Scenario One or closer to Scenario Two or somewhere in the middle is to look at the data in ResScan. If you look at the detailed data, the leak graph will quickly tell you the difference between the two scenarios. If you look at the summary data, the median leak rate together with the 95% leak rate give a pretty good picture of which scenario is closer to what happened. If the median rate is very low, that indicates whatever leaks that happened close to the value of the 95% leak rate were NOT happening all night long. But if the median leak rate and the 95% leak rate are close to each other, that indicates you were leaking at a rate around that 95% rate for at least half the night.

Is that too much leak? or is leak not that big a deal? Should I focus on usage and AHI more?

My honest advice? If the leaks aren't disrupting your sleep too much and the leak line doesn't look too bad (subjectively), then I'd not worry a whole lot about the leak. But if I felt like I wasn't sleeping very well OR if the leak line shows a lot of leaking at this level, then I'd start chasing the leaks down.

But worry about your AHI? Not if last night's AHI = 0.6 is typical. That means you only had a grand total of 4 apneas+hypopneas all night long. You don't need to worry about trying to make that AHI into a perfect 0.0.

Good post, robysue from Buffalo, NY. It taught me something and I have a completely different machine.

jimnsc wrote:Good post, robysue from Buffalo, NY. It taught me something and I have a completely different machine.

Always good info from Robysue! However, remember that only the ResMed devices seem to take "expected leak" into account when coming up with the leak number on the display. So if you're seeing 15 Lpm on other machines, that's not actually all that bad =)

Talon makes an excellent point. The other machines on the market do report TOTAL leak, which is defined as:

TOTAL leak rate = INTENTIONAL leak rate + UNINTENTIONAL leak rate.

To interpret leak figures on other machines, you need to consult the user manual of the mask you're using. It will have a table or graph somewhere in the guide that will show the INTENTIONAL or EXPECTED leak rate for the mask at various pressures. The better user manuals will also report a margin of error as well in that INTENTIONAL leak rate. On a machine that reports TOTAL leak rates, you want your TOTAL leak rate to be (roughly) equal to the INTENTIONAL leak rate (plus or minus the margin of error) for your mask at your pressure. And a flattish leak line in the graph is better than a bumpy one.

Many machines report 90% leak rates. They work similar to 95% leak rates: If you are using a machine that reports 90% TOTAL LEAK rates and your leak rate figure is 25L/min, that means your TOTAL leak rate was LESS THAN or EQUAL to 25 L/min for 90% of the night. And hence your TOTAL leak rate was GREATER THAN or EQUAL to 25 L/min for 10% of the night. And 10% of one hour is six minutes. And so on.

TalonNYC wrote: I have the S9 as well, and found out that it automatically subtracts an "allowed leak" rate from the number it shows you. So the numbers you're seeing are above and beyond what the S9 thinks you should see with your mask type. The red line in the ResScan software is set to 24 Lpm, showing that anything over that (on a ResMed machine) can interfere with therapy. That would indicate that the 15Lpm is still within OK limits, but not good. Mr. Frowny (the unhappy face) only shows up if you're over the red line for a significant portion of the night, so it's useless for anything but fitting the mask =)

Burried deep in the documentation somewhere is this fact: Mr. Red Frowny Face shows up if your 75% UNINTENTIONAL leak rate is AT or ABOVE 24 L/min. That means your leak rate needs to be GREATER THAN or EQUAL to 24 L/min for 25% of the night for Mr. Red Frowny Face to show up in the morning. And of course, 25% of one hour is 15 minutes. So if your machine runs for 6.2 hours, that means the UNINTENTIONAL leak rate has to be GREATER THAN or EQUAL to 24 L/min for at least 15*6.2 = 93 minutes (about an hour an a half) for the whole night. It doesn't need to be one 93 minute leak at that level to trigger Mr. Red Frowny Face: Eight 12-minute long LARGE leaks over the course of the night would be enough to trigger Mr. Red Frowny Face if the total run time is 6.2 hours.