almost killed myself with full face mask

[archangle]

Our drive to breath is based almost entirely on our CO2 saturation. If you are rebreathing, your CO2 saturation will go up in proportion to your O2 saturation going doing. The normal physiological response to this is to initially increase your respiration rate, and then to induce a sense of panic. It is unlikely you would kill yourself in this situation as you would be unable to resist the urge to tear off your mask.

It is however, a situation to be avoided, as it could be a very quick path to CPAP induced insomnia. I hope you are OK now.

Most people will wake up, but it's not a 100% sure thing. At some point, the low O2 level will cause you to lose consciousness. Google "confined space" for some horror stories in industrial settings. The idea of "losing consciousness" in your sleep is a little wonky, but I think the idea is valid. i.e. with a low enough O2 level, you might not be able to wake up, even if you don't outright suffocate. Add in a higher level of danger if the patient is on meds or alcohol, or has certain medical conditions.

Even if the anti-asphyxia valve doesn't open, there's still a little fresh air because of the exhalation vent. It won't leak as much air as it does in normal use because there's little pressure in the mask, but a small amount of air leaks out due to the resistance of airflow through the machine even when it's turned off. Also, a little fresh air will get in from mixing of fresh air coming in through the back of the machine, but it's got to mix in a fairly long path in the hose and machine, so it will be pretty stale. i.e. I'm not 100% sure you'd die even without the anti-asphyxia valve, but it's best to avoid it.

[KillingMe]

always do this:

1. turn on machine,
2. put mask on.

3. take mask off
4. turn off machine

This would not work for me. With my high pressure setting, it would be difficult to properly put on the mask due to the windstorm.

I forgot how long I lying in bed and all in a sudden I felt dizzy, I immediately remove the mask,and looked that oximeter, 56% oxygen saturation.

I doubt this was from rebreathing. It sounds like you fell asleep and had some long apnea clusters.

[Janknitz]

I find that auto-on for my machine doesn't work in a full face mask like the Quattro UNLESS I manually block the anti-asphyxia valve. Then there's enough pressure differential to trigger the auto on. I suppose a deep, hard breath would work, too, but I find it easier just to put my finger over the valve for a second. On the other hand, the auto-on is overly touchy with nasal and nasal pillow masks, so that often the machine turns on while I'm still fiddling with the straps (darn that snap on the Wisp--it's hard to connect!).

I find I'm not hearing the "on" beep from my machine consistently anymore (I'm sure it's not quieter, just that I'm so used to it now, or perhaps some hearing loss), and if I don't move my finger off the valve as the air rushes in from the machine, there's a weird "sucking" sensation on my mask.