How DO mask leaks affect therapy?

[FormerFed]

Can someone give some insight about mask leaks? I get it that they compromise my therapy, but not exactly sure that I understand to what extent.

I get it that air leaks translate into less air pressure available for my airway which, then, does not get as strong an “assist” from the ResMed as it needs, and the reduced pressure may be too low to stop as many apneas as my proper pressure would stop.

However, if I do have apneas or hypopneas at the same time I’m having mask leaks, are the leaks ever keeping my ResMed from detecting the apneas or hypopneas?

This is key to whether I give up my comfy, but squiggly, DreamWear nasal mask. My AHI numbers seem to indicate that therapy is working very well for me, but, maybe not so much if mask leaks ever cause numbers to be falsely low. Side-sleeping seems to cause leaks all the time for me, my 95th percentile is usually in the 30’s. I rarely, though, see ResMed’s frownie face – 7 times in the 93 days I’ve been on CPAP. My AHI is usually quite low – roughly 2/5 of these nights I have had no events; otherwise, 1/5 of the time the AHI is 0.1, 1/5 it’s 0.2, 1/5 it’s 0.3-0.6. I also monitor my oxygen saturation and it has been consistently staying in the mid 90’s – began to rise and level off in this neighborhood pretty much since the day I started the therapy. I can’t use the way I feel as an indicator – I felt pretty well and never did have any apnea symptoms before I started CPAP. I came into this because I was found to have Atrial Fibrillation (paroxysmal, and happily episodes are low-drama and relatively short). My doctor wanted me screened for apnea, the sleep study found I had an AHI of 6, the sleep specialist said I should be on CPAP, so now I am. It does not seem to have had a marked effect on the AF yet, but it also doesn’t seem to be getting worse, so I’m happy to hope improvement is on the way but needs longer than 93 days to start showing.

A bad allergy night brought up a whole new question, also. I had an irritated nose which eventually just closed up totally not long after I had put on the CPAP and hit the hay. I collected pillows to sleep sitting up, maybe head off apneas if I couldn't get air thru the nasal mask, but kept the mask and air on in case the nose calmed down. Eventually my nose did open up and I went on to have a normal, albeit sitting-up, CPAP night’s sleep. The next day I looked at my data and saw many, long apneas during the 20 minutes that I was mouth-breathing before my nose cleared enough for me to relax and go to sleep. One was recorded as 46 seconds long!

Not only am I really sure I wasn't sleeping because of the t.v. show that was on at the time, but I also know for nearly all this time that my nose was completely blocked - there was no sensation at all of air coming back to my mouth from the ResMed strapped to my nose until my nose started to open up after I'd been sitting up for a while.

So, could the ResMed even detect any apneas if it was completely blocked from my airway? Were all these “apneas” on my ResScan report possibly my faithful friend ResMed simply trying to make sense of what it was/wasn't sensing? My oximeter recorded my oxygen saturation was very good that night except for the beginning of the night when I was trying to tough it out with the nasal mask though my nose was closing up on me.

Thanks to anyone with enough patience to have read through all this – any and all insights will be very much appreciated!

[justMongo]

The machine can make up for leaks up to a certain point. The machines tries to maintain a constant pressure (hence the name, continuous positive airway pressure). Resmed reports unintentional leaks. Those leaks not caused by the mask vents which are required to flush exhaled air from the mask and tube.

Leaks up to 24 Liters per minute can be compensated for by speeding up the blower to move more air volume (flow) to maintain therapy pressure. After that, all bets are off. Therapy pressure is compromised; and event detection is questionable.

Forget the smiley face, you can be doing terrible and still get a smiley.

AF and sleep apnea often occur together -- so, it's somewhat common practice to screen an AF patient for SA.
You are fortunate that you have short runs of AF. Many people cannot be controlled; and they live with it; usually with a blood thinner.

[PaytonA]

In my case, I was hospitalized with Afib and after a bunch of testing my cardiologist was quite certain the Afib had been brought on by sleep apnea. I went for a sleep test and sure enough - sleep apnea.

To add a little to Mongo's comments. The machine does compensate for leaks up to 24 liters/minute by speeding up to maintain the continuous pressure. Leakage rates higher than 24 l/min can exceed the capability of the machine to maintain the pressure and definitely make event detection and differentiation extremely questionable.

If your nose is plugged up at bedtime, nasal rinse should open it up enough to get you started on the CPAP. Then the CPAP will probably keep your nose splinted open as well as the rest of your airway for the rest of the night. If you are mouth breathing due to congestion, the CPAP will not know what the heck is going on unless you are using a full face mask. The CPAP can not detect breath that goes in or out of the mouth unless it is captured by a full face mask.

Best Regards,

PaytonA

[DeepBreathing]

Just adding to what Mongo and Payton have said... The red frowny face indicates your leaks were above the 24 L/min threshold for at least 30% of the night. This is a pretty low bar, and if you're getting this more than very occasionally then your leaks are out of control.

The good news is that with an untreated AHI of 6, your apnea is very mild, extremely borderline in fact. A sleep test on another night might even show you don't have a clinical level of apnea, though your aFib would indicate there is a problem.

[vsheline]

Hi FormerFed,

Looks like your A10 AutoSet is set on fixed pressure of 10?

You are doing really great at your present settings, but you might want to consider turning on the AutoSet therapy mode, with Min Pressure of 8 and Max Pressure of perhaps 12, to see what pressures the AutoSet algorithm would come up with.

Personally, I would trust the AHI your machine is reporting even when fairly large unintended leaking is ocurring. (Unintended Leak is leaking other than the intended leaking through the mask vent holes.)

During periods of large leak, the higher the pressure, the harder it will be for the machine to accurately maintain a target mask pressure, especially if we are using a long hose or the popular narrow hose, instead of a 6 foot long fat hose.

Even during periods of very high Unintended Leak (say, between 30 to 50 Liters per minute) I think the machine would still do a good job maintaining a moderate mask pressure of 10, unless the Hose Type setting is not correctly set, making it impossible for the machine to correctly calculate how much pressure is being dropped across the hose.

What rapidly falls apart above Unintended Leak of 20 is fine detail in the Flow waveform needed to detect Flow Limitation and acurrately perform the AutoSet algorithm. (The "Flow" waveform shows the estimated rate of air entering/exiting our airway and lungs.)

If the fine detail in the Flow waveform is washed out by too much Unintended Leak, the AutoSet algorithm would likely miss signs of partial obstruction and would not maintain the pressure high enough to avoid Flow Limitation and hypopneas and apneas, resulting in poor sleep quality if in auto-adjusting therapy mode. Also, the reported Tidal Volume and Minute Volume will be inaccurately low. (The Tidal Volume is the estimated volume of air breathed per breath, and the Minute Volume is the estimated volume of air breathed per minute.)

But even at its highest pressure setting of 20, for Unintended Leak below 30 the ResMed AutoSet still trusts the fine detail of the Flow waveform enough that it will attempt to distinguish central apneas from obstructive apneas. For Unintended Leak above 30 the machine does not bother to try, and all such apneas will be marked as type Unclassified Apnea (UA).

But I think the machine would still do a fairly good job of reporting UA which occur during periods of unintended Leak up to perhaps 50 or somewhat higher.

Take care,
--- Vaughn

[PaytonA]

I think that the exact results of leakage depend on what type of leakage it is and what type of machine it is. It is a totally different dynamic, if one has mouth leakage/breathing versus leakage that is just at the mask seals. Many of us adhere to the most conservative numbers just to be on the safe side.

My personal experience was when I made the first major reduction in mouth leakage, my AHI went up significantly for a reasonably long period of time.

Best Regards,

PaytonA

[vsheline]

It is a totally different dynamic, if one has mouth leakage/breathing versus leakage that is just at the mask seals.

Yes, that makes sense.

In my own case, since starting on CPAP I've been always using Full Face Masks, with no mouth leaking. So my personal experience does not include mouth leaking.