Issues about using a mask without the anti-asphixia valve??

[archangle]

Could that happen if you have external O2 bleeding in at the connection where the airhose attaches to the cpap machine? I have 4 ltrs comming in at that point.

You have a full face mask with an anti-asphyxia vent, so you shouldn't have an asphyxiation problem anyway.

If you have an oxygen concentrator, it should shut down too if it's a power failure. Are you on bottled oxygen? I guess the CPAP could quit for other reasons than a power outage and the concentrator keeps going.

Assuming your AA vent was blocked, and the O2 continued to flow, I presume 4 liters/minute would give you an air quality that's pretty good. Heck, without the CPAP machine blowing "competing" air into your mask, you might actually have higher O2 than you get with the CPAP running. You wouldn't have any CPAP pressure, so your apnea would be back.

I know that too much oxygen can be a medical problem. I don't know how bad the problem could get if your CPAP quits and O2 keeps going. Your CPAP/O2 setting is designed to give you the right mix of O2 when the machine is blowing, not when the O2 is going and the machine isn't.

Now to throw in even more doom and gloom, there are all kinds of "death and destruction" warnings about hooking O2 up to a CPAP machine. You're warned to turn the O2 off before turning off the CPAP. Repironics says this in one of their manuals:

"When using oxygen with this system, turn the device on before turning on the oxygen. Turn the oxygen off before turning the device off. This will prevent oxygen accumulation in the device. Explanation of the Warning: When the device is not in operation and the oxygen flow is left on, oxygen delivered into the tubing may accumulate within the device’s enclosure. Oxygen accumulated in the device enclosure will create a risk of fire."

"When using oxygen with this system, a Respironics Pressure Valve must be placed in-line with the patient circuit between the device and the oxygen source. The pressure valve helps prevent the backflow of oxygen from the patient circuit into the device when the unit is off. Failure to use the pressure valve could result in a fire hazard."


I presume the "pressure valve" is a safety thing to keep O2 from backing up into the machine if the machine goes off and the O2 is left on. This probably changes the physics of the situation if your anti-asphyxia valve fails.

In your case, Roger2, I think too many things have to fail at once for a real problem to happen. I would be sure to turn off the O2 if the machine ever quits, and to not use the mask if you ever decide the anti-asphyxia vent has failed.

[avi123]

Toni, here is a warning from Resmed:

CPAP or bilevel systems are intended to be used with
special masks with connectors which have vent holes or separate exhalation devices to
allow continuous flow of air out of the mask. When the CPAP or bilevel device is turned
on and functioning properly, new air from the flow generator flushes the exhaled air out
through the mask exhalation port. However, when the CPAP or bilevel device is not
operating, enough fresh air may not be provided through the mask, and exhaled air may
be rebreathed. Rebreathing of exhaled air for longer than several minutes can in some
circumstances lead to suffocation. This warning applies to most models of CPAP or
bilevel systems.

**************************************

However, as long long as the intentional vent holes in a mask exist, and are not blocked, then, IMO, real asphyxiation is small in case of machine stoppage, b/c the vent holes allow enough air to survive on. An adult person normally breathe 0.5 liter per cycle at a rate of 12 to 16 cycles per minute. Multiplying the two gives a flow rate of 6 to 8 liters per min. See in the following table of pressure vs flow, of a simple full face mask, that there is a safety factor of 3 times to supply the needed air even at a low attempted respiration pressure of 4 cm H2O, even with no anti-rebreathing valve. So there is NO danger of asphyxiation but of rebreathing. When you continue to breathe when the machine is stopped and there no anti- rebreathing valve then some of the air comes in thru the humidifier and thru the hose and some from the vent holes. The 6' hose would comprise a dead space and contain rebreathed air which would be added to the stale air inside the mask, but as Resmed mentioned above you should be able to take it for several minutes.

Pressure vs. Flow of a Resmed FF mask:

Pressure..............Flow
(cm H2O).............(L/min)
4........................ 22
8........................ 32
12....................... 41
16....................... 48
20........................54

[archangle]

A confined space is an area big enough to get into that is not designed for occupancy. There is a difference between entering a confined space and entering your bedroom.

Don't be silly. We're not talking about the air in the bedroom. We're talking about the "confined space" of your mask, the inside of your hose, and the inside of the CPAP machine.

No one's going to exhaust the O2 supply in their bedroom.

Continuous re-breathing air can cause problems and it is not clear if the vents in the various masks allow enough air exchange to contribute to re-breathing.

Since there's very little air pressure in the mask if the machine shuts down, I don't think much air will go out the exhalation vent.

What I think is more significant is that there will be some mixing of fresh and stale air in the hose. As you exhale, stale air goes down the hose. As you inhale, fresh air comes in the back of the machine. At some point, the stale and fresh air will meet and some mixing will occur, so some CO2 will get out, and some O2 will get in. I don't have any good way to figure out how bad the air at the mask would get in this situation.

Apparently the FDA and the mask manufacturers think it IS a problem. Hence the term "anti-asphyxia."

Having recently experienced a power outage I can tell you that I immediately noticed the change in the feel of the mask and woke up. Usually there is air blowing into the mask and it tends to float on your face. When the power goes out, the mask sucks into your face with each breath and becomes more uncomfortable to wear.

I think the change in mask fit would wake most people up, but there is always the exception.

You would think you'd wake up, but people sleep through 120 second obstructive apneas. Try holding your nose and mouth closed for 2 minutes. It's hard to conceive that an apnea doesn't wake you up long before even one minute has passed.

[archangle]

However, as long long as the intentional vent holes in a mask exist, and are not blocked, then, IMO, real asphyxiation is small in case of machine stoppage, b/c the vent holes allow enough air to survive on. An adult person normally breathe 0.5 liter per cycle at a rate of 12 to 16 cycles per minute. Multiplying the two gives a flow rate of 6 to 8 liters per min. See in the following table of pressure vs flow, of a simple full face mask, that there is a safety factor of 3 times to supply the needed air even at a low attempted respiration pressure of 4 cm H2O, even with no anti-rebreathing valve.

Pressure vs. Flow of a Resmed FF mask:

Pressure..............Flow
(cm H2O).............(L/min)
4........................ 22
8........................ 32
12....................... 41
16....................... 48
20........................54

avi, I think you're assuming you get the 22 L/min flow rate through the holes in the mask because you can easily suck or blow 4 cmH2O pressure.

You are considering the case where the hose is blocked and no airflow comes through the CPAP machine.

With the CPAP machine unplugged, air flows fairly freely through the CPAP machine. When you inhale and exhale, most of the air will be going though the CPAP machine, not in and out through the exhalation vent.

Hooked up to the CPAP machine, you will not have anywhere near 4 cmH2O in the mask. The airflow through the exhalation port will not be anywhere near 22 L/minute.

Use a mask without an anti-asphyxiation vent, hook it up to an unplugged machine and try to inhale. You can inhale pretty easily. Then plug the hose connection with your thumb and try to breath through the exhalation vent. You need a LOT more effort.

Yes, there is SOME air drag. You will get SOME airflow through the exhaust vent. The "experts" don't assume it's enough air flow. They all warn of asphyxiation.

[Roger2]

If you have an oxygen concentrator, it should shut down too if it's a power failure. Are you on bottled oxygen? ............

I know that too much oxygen can be a medical problem.

"When using oxygen with this system, turn the device on before turning on the oxygen. Turn the oxygen off before turning the device off. This will prevent oxygen accumulation in the device. Explanation of the Warning: When the device is not in operation and the oxygen flow is left on, oxygen delivered into the tubing may accumulate within the device’s enclosure. Oxygen accumulated in the device enclosure will create a risk of fire."

I use a concentrator at home and hooked into the cpap but liquid O2 away from home. My sleep doctor told me to use 4ltrs into the cpap hose per the sleep study. Normally when I am not engaged in any activity I use 3.5 ltr flow and up to 8ltr when active like vacuuming the floors or exercising at the gym.

As for turning the O2 on and off, it appears I have been doing that completely backwards. Good thing I asked before I got myself into some real problems. I have been on external O2 for over ten years and seem to have become somewhat complacent about proper use. Thanks.

Roger

[HoseCrusher]

I am using a Swift FX mask. I ran a test putting the mask on with the machine shut off. My pulse oximeter showed that my O2 levels dropped from 97% to 82% in about 2 minutes. I was relaxed and reclining but not asleep. I have to think that if I were sleeping the results would be similar.

I repeated the test 5 times with similar results each time. Also, as my O2 levels dropped, my heart rate increased.

From this I conclude that if the power goes out and you are using a Swift FX mask you should either take it off or breathe through your mouth.

[archangle]

I am using a Swift FX mask. I ran a test putting the mask on with the machine shut off. My pulse oximeter showed that my O2 levels dropped from 97% to 82% in about 2 minutes. I was relaxed and reclining but not asleep. I have to think that if I were sleeping the results would be similar.

I repeated the test 5 times with similar results each time. Also, as my O2 levels dropped, my heart rate increased.

From this I conclude that if the power goes out and you are using a Swift FX mask you should either take it off or breathe through your mouth.

Let me recommend that people NOT try this experiment unless someone is watching you. The big thing they always tried to drill into our heads in the confined space lectures was that with O2 deprivation, you could slip into unconsciousness without ever realizing anything was wrong. Even if you were deliberately thinking about being sure you're OK, you would get confused and not notice the symptoms of O2 deprivation.

Yes, they were trying to scare the heck out of us, but there's probably some truth in it.

[avi123]

Yes, they were trying to scare the heck out of us, but there's probably some truth in it.

My impression is that you're trying that too with your many posts about possibility of asphyxiation.


Comment:

Those mfg that need the money badly i.e for increasing business, call it ANTIASPYXIATION valve.
Others who are less aggressive call it NONREBREATING valve.
Those who need the money least call it ENTRAINMENT valve.

[archangle]

Yes, they were trying to scare the heck out of us, but there's probably some truth in it.

My impression is that you're trying that too with your many posts about possibility of asphyxiation.

For some strange reason, I hate to see people kill themselves in easily preventable ways because they weren't warned. Or because someone else did something stupid a few times and got away with it.

Maybe it's a character flaw of mine.

[chunkyfrog]

I slept almost an entire night with my machine off with a full face mask--(With anti-asphy valve.)
No seriously bad effects. (I woke up STILL tired.)
Now I always check the exhaust flow to confirm it's on.
My tape scheme allows a little space I can breathe through.

[TonioGT]

Thanks to everybody for your interest, advice and wisdom in your posts. I apologize for posting until now, actually this is my first post ever in any forum, so I thought I might gets replies by email (probably I could, but I don't know how to set it up, it is in my to do list), and secondly, I have been traveling to Colombia and México, and preparing for those trips.

I intend to summarize what I learned from many people who wrote so dilligently, trying not to go into detail.

First, as archangel pointed out, when the CPAP machine is not pumping air, the air coming in mixes with the air coming out from the lungs, making the air mix more rich in carbon dioxide. This could be dangerous, because you might not be able to notice it. As time passes the air mix wouldn't have enough oxygen to keep you functioning normally, and you might take your mask off, because your instinct might turn an internal alarm and force you to act, but there is a chance we can't neglect of this not happening. Then it is like going climbing to high altitudes and breathing air with less oxygen than the air you normally breath. As avi123 posted, main risk is suffocation, but there is also risk of asphyxia. Depending on the person and the circumstances, these risks might have from low to high impact, from headaches and tiredness (more probably) to death (less probably).

So, the anti-asphyxia valve is a safety control that mitigates those risks. Not using it is exposing yourself to those risks.

Second, there was a second issue that concerned Roger2, who uses an oxygen supply device as part of his therapy. archangle pointed out that it adds another risks which might be the topic for another interesting discussion.

Third, there might be the slight risk that the anti-asphyxia valve won't work. This risk might be mitigated using a device such like DorisC kindly mentioned. This device emits an alarm to wake you up in case there is a power failure, and also, it has a LED light to illuminate in case it is needed.

Fourth, I agree with archangle, that if you are experimenting with the anti-asphixia valve or breathing without the machine pumping air, do it taking the precaution that all the time there is someone watching you. Better if you don't try at all.

Fifth, thanks to all the posts, I started using again the anti-asphyxia valve, especially that I travel recently to a Palenque, in México, an archaeological Mayan site in the jungle, and stayed in a hotel with electricity. Since it is rainy season, when heavy rain, raccoons or other animals might climb utility poles, suffer electrocution and cause a power failure. This didn't happen, but I was prepared though.

Now when I set the mask and the air pressure goes up, I try to adjust the valve so it doesn't make too much noise. It still distracts me a little bit, it takes a little while to get used to it, but I fall sleep anyway. An also, it still leaks a little, but it is not that much.

At the end, I accept this as part of my therapy and my life.

[kempo]

Is there a case that we can point to where a person died from asphyxiation because the power went out while using their cpap?.

I would like to here about it.

[archangle]

Is there a case that we can point to where a person died from asphyxiation because the power went out while using their cpap?.

I would like to here about it.

No coroner in the USA is going to bother to investigate such a death. They're public officials with what they consider to be inadequate budgets. They're either politicians or political appointees. They're only interested in cases of foul play or newsworthy things that are going to hurt others.

Once he decides it wasn't murder, he's going to be looking for the easiest way to fill in his paperwork.

In order to suffocate from a failed CPAP machine, you'd have to have a full face mask with a failed anti-asphyxia valve or someone who taped their mouth.

The junior assistant to the deputy coroner is going to see someone who's so sick they were on breathing equipment who died in their sleep. To make the connection, he'd have to understand CPAP, understand anti-asphyxia valves, and realize the CPAP had failed during the night. Then his first thought would be that the victim died from a heart attack, stroke, etc. because his throat collapsed without CPAP. How is he going to distinguish dying from rebreathing his exhaled air from dying because his apnea cut off his airflow.

Presumably, there is medical documentation of the deceased having a condition that could kill him without CPAP. Do you really think a public official is going to look any deeper to find out the details of why an apneac died without CPAP?

If he says it was caused by asphyxiation due to mouth taping or a removed anti-asphyxia valve, the family is going to be upset for him telling them dad died from stupidity. Or he's going to be dragged into a lawsuit if there's some way to blame the manufacturer.

The easiest way for him to "do his job" is to simply say he died of complications of sleep apnea.

[kempo]

So the answer is NO!

Makes me wana go out and buy an extra roll of tape

[archangle]

So the answer is NO!

Makes me wana go out and buy an extra roll of tape

Please do. And be sure to leave instructions for your next of kin to post here if you're found dead some morning with tape over your mouth.

You could be our first proof.