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Inhaling exhaled CO2 gases
#11
RE: Inhaling exhaled CO2 gases
(11-22-2012, 10:31 PM)archangle Wrote: You don't have to worry about rebreathing CO2 as long as you're using standard CPAP equipment in proper working order.

First, realize that you exhale Carbon Dioxide, CO2, not Carbon Monoxide, CO. Carbon MONoxide is the stuff that kills you if you have a car exhaust leak. A fair number of people confuse the two. There is no Carbon Monoxide involved in CPAP. (Except whatever pollution is in the air you breathe even without CPAP.)

Long before CPAP was thought of, we figured out the hazards of rebreathing CO2 from using ventilators. The physics of the situation are very well understood, safe levels were established, and CPAP equipment was designed to have a large safety margin.

The minimum pressure most machines will produce is 4 cmH2O. The exhaust holes are designed such that they leak out enough air at that pressure that they will clear out the exhaled air enough to prevent the build up of CO2 and depletion of O2 to harmful levels. Unless the exhaust air holes are plugged, or the machine is producing less than 4 cmH2O, you won't get enough rebreathing to be harmful.

By the way, the hazard to rebreathing air is not so much from high CO2, as it is from low O2.

Also, the effect of rebreathing some of your exhaled air is much the same as having apnea. In either case, O2 has a hard time getting into your lungs and CO2 has a hard time getting out.

Enough for one post. Time to stop to let my keyboard breathe for a bit.

Thanks Arch, I did mean carbon dioxide. my bad.
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#12
RE: Inhaling exhaled CO2 gases
(11-22-2012, 11:14 PM)bryank1 Wrote: Thanks Arch, I did mean carbon dioxide. my bad.

No, you didn't mention "monoxide." I did, just because you wouldn't be the first to confuse the two.

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#13
RE: Inhaling exhaled CO2 gases
The topic is about the danger of re breathing CO2 not CO.
And regular CPAP machines do not address that problem.
The CO2 has to be removed chemically by canister filtering or with a valve controlled by exhaling.
If you do not have any of these features you are re breathing CO2 and that is not good for you.
Period.
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#14
RE: Inhaling exhaled CO2 gases
Hi CO2 danger - Welcome
Please note this thread has been inactive for 5 years . . . well, actually 4 years and 10 months.
Crimson Nape
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#15
RE: Inhaling exhaled CO2 gases
A healthy person exhales 6 to 8 liters per minute and the mask(s) vent out 19 liters per minute at a pressure of 3 cmH2O. This data corresponds to both a nasal and full face mask from Resmed. According to this data and if one does the math, one cannot physically rebreathe their own air with a working mask and even with the new QuietAir elbow because exhaled air is getting expelled at more than twice the rate even with the lowest pressure of 3 cmH2O.


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#16
RE: Inhaling exhaled CO2 gases
Stumbled upon this ancient thread but see some value in it.

@zonk/crimson nape
"As with all masks comes with a warning ... some re-breathing may occur at low pressures"

I found that an interesting statement, in the light of trying to find my own safest low pressures. Presumably fixed pressure is meant here. How would that apply to EPR or bilevel pressure?

@joshua1
I find those graphs interesting, again applicable only to fixed pressure? Hence the minimum pressure of 4cm set by most machines.

At least one member on this board has modified her mask P10 to allow more venting.

If i want to minimise risk of rebreathing which is best,
Increase the EPAP or the IPAP or both?

Pity this thread has not enjoyed more discussion.

Some of the pieces of the puzzle are slowly coming together. 
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#17
RE: Inhaling exhaled CO2 gases
Just to confuse things even more, there are cases where several of us have recommended increasing the amount of CO2 that is rebreathed. Look up EERS.
This is used to increase the drive to breathe when too much CO2 has been flushed from the system and this results in central apnea/hypopnea. It is not for use with 'normal' obstructive apnea.
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#18
RE: Inhaling exhaled CO2 gases
This is a very old discussion, but I just want to add my experience for any future explorer.

Yes rebreathing CO2 is possible. At least I had the symptoms of it. It always happens to me while using F&P masks at lower pressures, for some reason. But it happened, it's real.
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