The manufacturers call it an "anti-asphyxiation valve" or "anti-asphyxia" valve as well as a "non-rebreathing" valve. The purpose is to prevent asphyxiation.avi123 wrote: Archangel, I think that you make a bit of a fuss about this issue. To start with, it is not called anti-asphyxiation valves but non-rebreathing valves.
http://www.resmed.com/us/assets/documen ... er_eng.pdf
https://www.cpap.com/productpage/resmed ... masks.html
No, the vent holes in a nasal mask are sized to leak enough air out to flush out the CO2 when the mask is under pressure. If the CPAP machine is not running, there is very little pressure in the mask. Your exhaled air will go down the hose and through the machine and you will be rebreathing the same air you exhaled. The manufacturers will tell you that the vents don't leak enough air out if the pressure is below 4 cmH2O.avi123 wrote: You would not get asphyxiated during power stoppage b/c CPAP masks have intentional leak holes. But you would breathe air a bit higher with CO2.
Unplug the hose from your machine, put on your mask, and exhale into the mask. Try to feel air flowing out through the mask vent. You won't feel much, if any airflow. The rest of the air is going down the hose and being rebreathed.
That is why every full face, hybrid, and oral mask has an anti-asphyxia valve in it. You can call it
"non-rebreather" if you want, but the function is the same. If the CPAP machine quits, you breathe fresh air directly into the mask, not in and out through the hose and CPAP machine.
Will you die without an anti-asphyxia valve on a full face mask if there's a power failure? Maybe most of us will wake up before that happens. However, every mask manufacturer puts an anti-asphyxia valve in their full face, hybrid, and oral mask. I suspect the FDA requires it.
There will also be some mixing of fresh air with stale air as the air flows back and forth down the tube and in and out of the back of the machine. You'll get low CO2. Will it get low enough to cause death from asphyxiation? I can't say for sure. The mask manufacturers don't seem to be willing to risk it. Even if it doesn't kill you from hypoxia, we know low O2/high CO2 is dangerous. Would the O2/CO2 levels be bad enough to cause heart attack, stroke, etc.?
I know that in theory, I'll automatically breathe through my mouth if my CPAP machine shuts down and I've got a nasal mask. I might still do quite a bit of rebreathing of bad air before my reflexes make me open my mouth. I might even inhale spent air for most of the night, only occasionally struggling and opening my mouth for a few gasps of air before closing my mouth again. This might be especially bad if I'm using a chin strap. Why risk an unnecessary night of hypoxia/CO2 poisoning if I don't have to?avi123 wrote:
About your question: Does anyone make an anti-asphyxiation valve that fits between the mask and the hose? That way, you'd get fresh air with a nasal mask even if the power goes off. Why if you use a nasal mask can't you just open your mouth to breathe in such cases?
I'm not as convinced as everyone seems to be that you'll open your mouth if the machine shuts down. Yes, if your nose clogs up during the night, you'll open your mouth when your lungs can't pull in any air through your nose. However, will you necessarily open your mouth if you're continuing to inhale and exhale through your nose, but the CO2 gradually rises as the O2 drops? How low will your O2 levels have to get before this happens? Will your mouth stay open once your O2 level rises and you get a good breath of fresh air?
Those people who tape their mouth could benefit, too. For them, a nasal mask is essentially a full face mask without an anti-asphyxia valve.
