Thank you so much!!!! I can't believe the tech didn't do this--or think to do this. I would hope that she knows she is supposed to do this!  I have to imagine that the pressure would be different for nasal vs full-face, so maybe I just wasn't getting the pressure I though I was.



This site and the people on it are WONDERFUL, so THANK YOU!!!!!!

The mask setting doesn't affect the therapy pressure.  The setting only affects what the machine DISPLAYS for your leak rate.  The actual leak is still whatever it is and the pressure is still whatever it is, only the displayed leak amount is affected by the setting.

As I mentioned before, this is supposed to take the guesswork out of finding out if your leak rate is excessive.  Instead I find this very unhelpful.  Resmed assumes some amount of leak on ALL the mask settings (and a different amount on each setting!), so it is impossible without a calculation to find out how much your leak rate REALLY is, unless you just happen to be using the exact specific mask that the machine has a setting for.

So it's a little more complex, but not impossible, to find out if your leak rate is excessive.  

This may seem complicated, but if you arm yourself with three pieces of information, it is not as hard as it may appear.  The trick is getting the information (see last part of this post).

Here's a hypothetical example which should illustrate how to make the calculation.  Recall that I do NOT know any of your numbers so this is NOT a calculation of YOUR situation!

Let's pretend you have been prescribed a pressure of 10 cmH2O and your mask manufacturer says your mask has a normal 'leak' rate (e.g. port exhaust) of 40 liters per minute (L/m) at pressure 10.

Now let's pretend the mask setting you have on the Resmed, whatever it is doesn't matter, we just need to know that it assumes at pressure 10 you'll have a normal leak rate of 0.3 L/s (note that is liters per second, not liters per minute.  Take care when comparing numbers).  That means what the machine is actually displaying for your leak rate, is OVER AND ABOVE that figure.

So here is our hypothetical situation and the subsequent calculation:

Mask leak at pressure 10, is 'normal' or 'expected' to be 40 L/m or .66 L/s
Resmed assumes at pressure 10 your mask will leak 18 L/m or .3 L/s
Your Resmed displays .5 L/s is your leak rate

What does that mean?

That means .3  (machine assumption) + .5 (machine display) = .8 L/s or 48 L/m total leak.  Your leak rate is 8 liters per minute (.13 L/s) more than what is normal for your mask at pressure 10.

Now you have to ask, is that excessive?

This is somewhat subjective.  My DME and doctor feel anything over 10-15% of expected leak, is excessive.  For our hypothetical mask with expected leak of 40 L/m at pressure 10, the maximum allowed overage is 6 L/m, so in our hypothetical situation the leak rate displayed as .5 L/s is in fact excessive and could be compromising your therapy's effectiveness.

Here's what you need to know, to do the calculation for yourself:

1.  The expected leak for your mask at your pressure.
2.  The 'assumed' or subtracted leak amount at your pressure and mask setting on the machine
3.  The displayed amount of leak on the machine

The manufacturer's website for your mask should have a spec sheet available with a chart or table indicating expected leak at various pressures.  Look up your specific pressure in the chart or table to find out how much your mask is expected to leak at that pressure.  Note whether that is in L/m or L/s so you can convert if necessary.

You will probably have to call or email Resmed to get information about what the machine is subtracting from the display, at your mask setting and pressure setting.  I haven't found the figures published online anywhere as of yet.  (If anyone knows where this is published, please let me know.)

You can make your calculation, and then you can determine if your displayed leak rate is actually too high.

A high leak rate can be caused by leaks around the mask (e.g. mask not sealing well), if using a nasal mask it can be from mouth breathing.  Another indication leaks could be too high is an AHI > 5.

Blessings,
--pseudonym

I just tried to take a nap with the machine on the new setting, and I have to say the pressure does feel greater. For what it's worth, although set at 7, before it was registering actual pressure at 6.2. Since changing the mask setting, it now says 7.2. ???

Will let you know after another night.

thanks again!

The machine does try to compensate for leaking as best it can so you will see pressure variations at all settings.

Bottom line is to check the leak and the AHI.  If the AHI is routinely above 5 in an adult, and leaking has been corrected, it is time to see the doctor again.

Blessings,
--pseudonym

Pseudonym,

Nice description of the calculations. I just want to add one thing. Since some people may not know how to convert units (L/m to/from L/s):

If you have L/m, divide by 60 to get L/s.
If you have L/s, multiply by 60 to get L/m.


_________________
Respironics Auto M Series, Pressure: 12 cm
Fisher & Paykel Opus 360 Nasal Pillows
My Sleep Blog

@HeirloomGardener

Thanks for that addition!

Blessings,
--pseudonym

So last night, things seemed a little better.

Leak .14
AI .4
AHI 6.2

I'm still getting hypopneas, but the apneas are close to gone. But yes, my overall ahi is still too high.  

I have to say, though, I am still waking up at least five times during the night. I am always tempted to take the mask off, but have kept it on. The on thing that is improved, that forces me to keep it on is that each night that I have, I eliminate my morning headache. THAT is a godsend. I just wish I could stay asleep. I don't know if it's possible for it to be the apneas that are still waking me up?

I've heard that the elite overreports hypnopeas, so I wouldn't be too concerned as long as your apneas are still low. It may take a while to relearn to not wake up at night.  I know it was months before I could sleep consisently for 4 hours without an awakening, and at least a year before I could make it for 5.  I'm down to just one potty break a night now, and there are many times when I sleep straight through for 7 hours or more.  It amazes me everytime that I do that.  I come from an apnea prone family, there was always someone roaming the house in the middle of the night, I always thought it strange when I when on sleep overs and I was the only one up at 2 in the morning.  Virginia


_________________
Resmed elite , 17, mirage quattro ff . 25 + years of untreated OSA

Check out the leak factor for your mask and as .14 may be excessive.  The mask leaking intermittently may be arousing you enough to wake you up.  Hypopneas CAN be as arousing as apneas, and while they may be over-reported by a Resmed machine, it is still important to get them under control.

And Virginia is exactly right, you have learned a HABIT of waking up.  The CPAP will take care of the original cause of disturbance but now you must address the habit.  As Virginia pointed out, this can take some time.  Relax and don't concern yourself if it continues to happen.  Concentrate on removing causes such as mask leaks and working with your doctor to keep your AHI down.

If you aren't doing this already, do follow "good sleep hygiene" practices.  Here's is a good link, or google up Standord, Mayo, etc.:

http://www.sleepdex.org/tips.htm


Clock watching in particular can actualy TRAIN you to wake up and look at the clock.  So don't do it.  Turn the clock away, and if you wake up just leave the mask on and go back to sleep without knowing what time it is.  

If you are awake for more than 20 minutes, get out of bed and go do something else (relaxing!) until you feel sleepy enough to go back to bed.  For CPAP users with a partner, this may be difficult.  Although Good Sleep Hygiene cautions against watching TV or reading in bed, this can still work if disturbing a partner is in the equation.  If I wake up and don't feel like I can be sleepy soon, I have a reading light and *boring* book at the ready.

Blessings,
--pseudonym

LAst night was good. AHI of 2.3, AI of .4. I still catch myself in the occasional snore. My question is why it says the pressure is at 6 on the efficacy data, when it's set for 7. A question of a leak? The epr of 3?

I'm back! Spent a week at Mayo Clinic in MN (12 hour drive one way so another 2 days going and coming). Getting an evaluation of the Crohn's disease and the simple ovarian cyst. No surprise, surgery is recommended. I'm not having enough symptoms yet for me to agree to the surgery. However, had a good consult w/a wonderfu gyn onco surgeon and w/a colorectal surgeon.

According to the Quattro literature you can use either the Mir Ful or the Standard mask setting. The Standard mask selection allows for mask vent rate of .4 L/s or 24 L/M at 8 cms set pressure.

Resmed's EPR works in 1 cm increments so EPR of 3 reduces exhalation pressure by 3 cms, EPR of 2 by 2 cms and EPR of 1 by 1 cm. With a set pressure of 7 and EPR of 3 your exhalation pressure is only 4 cms. Very few people can breathe comfortably at 4 cms w/a CPAP mask of any kind on. Try changing your EPR to 2 or even 1. For that matter, w/a set pressure of 7 cms you might even do better turning EPR entirely. Try each setting for one week before deciding which works best for you.

Assuming that we spend half the night exhaling and half the night inhaling if you had 0 leaks your reported pressure would STILL be UNDER your set pressure. Keep in mind the Elite reports the pressure and leak at or below which you spent 95% of the night.

Keep in mind that the Ramp feature starts out at 4 cms and builds up in .5 cms increments over the set time to your set pressure of 7 cms. Ramp is going to lower your reported 95% pressure as well.

On the other hand, these newer CPAPs compensate quite nicely for mask and mouth leaks and raise the pressure accordingly over your set pressure as needed. That, too, has an effect on your reported 95% pressure.

The key is how you feel each morning and what your AI is. The other data has value for tweaking your therapy needs but the AI and how you feel remain the key.


_________________
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.
Resmed VPAP Auto. Humidaire 3i, Simplicity & Micro masks, ResScan 3.4, S8 ResLink, Embla oximeter.

I understand the calcs for leakage at a single pressure.  What about calcs for somebody bipaping?  Say at 8/12.  The expected leak rate for my mask is 32/41 (lpm).  I would imagine that you would need to average the leak rate since you don't know how much time you spend at which pressure.  Or, I could be all wrong!  Thanks - Philomath, a small town in western Oregon

Ha! I just started on a bi-level the 25th of March. And I have the software and cable reader as well. Matter of fact I was on straight CPAP therapy for 18 months before being switched to a bi-level. And I had the software when I was using the Elite and Vantage.

Don't ask ME to explain all this bi-level data and workings!!!! Its still all Greek to me! I'm on EPAP 8cms and IPAP 13 cms. I'm averaging 10.8 cms for the 95th percentile, 10.2 cms for the median and 11 cms for the maximum pressures. My guess is that the bi-level's internal software calculates the numbers based on combined pressures and leaks.


_________________
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.
Resmed VPAP Auto. Humidaire 3i, Simplicity & Micro masks, ResScan 3.4, S8 ResLink, Embla oximeter.