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RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - Apnea Infant - 06-02-2019
If you could, I think it is useful getting your words to the right size and re-posting. I would be keen to read it without having to enlarge my eyes outa its socket to comprehend the sentences.
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - mdmarmd - 06-02-2019
ASSUMPTION AIRFIT P10 PASSED RIGOROUS CLINICAL TESTING TO GAIN FDA APPROVAL--WRONG!
For context, I am adding some snippets from the two long threads regarding P10 obstruction. The point of restating these posts is to underscore the fact that most of us assumed that there must have been precise engineering and a scientifically rigorous process that led to the certification of the AirFit P10 and it’s release to the market. We also assume that a medical device that could seriously jeopardize one’s health would be subject to heightened scrutiny. (skip if not interested):
AshSF: Moisture is not retained in the P10 mesh…Even if some water is lodged in there, it will be easily pushed/evaporated by incoming air from the machine. If that were not the case, and the water was indeed blocking the vent, it would be a major design flaw (since Resmed has to account for rainout conditions). It would also expose Resmed to lawsuits of angry, dazed & zombie PAPers complaining of CO2 rebreathing.
OpalRose: Also have to wonder if there were a real problem with this mask, wouldn't ResMed have pulled it by now? It is one of the most popular masks out there.
TyroneShoes: I honestly don't think the vent is blocked, and I honestly don't think anything can actually get on the vent and solidify and block it.
…I think it is just designed really cleverly, to not put out a concentrated stream of air, but to disperse it. They have to have designed it to exhaust CO2 properly, or they would be liable for a class-action lawsuit. There is no chance that they designed a medical device so nonchalantly that it would work that improperly and risk CO2 rebreathing.
…But it would be ludicrous for it to be designed without proper venting, or to be designed so that something could get in the holes and block the air.
…Physics works, and this is a good example of talented designers who know what they are doing addressing the annoying air stream issue of previous designs. They did it so well that it is hard to even realize that the venting is working. The did it so well that we now have a 12-page conspiracy theory thread about it. I consider that a testament to how well it was designed.
PaytonA: …Lets not deify the Resmed designers quite yet.
Sleeprider: …I think a lot of you are trying to fix what is not broken. Yes, the diffuser has a fair amount of resistance on exhale when you block the tube, but that is not how you sleep. It passes plenty of air with the machine on to purge the hose and avoid rebreathing, and exhale pressure is never more than what you have your machine setup to deliver.
… A cold room will make condensation at the vent more likely. I don't consider any of this a defect in design, but more awareness of avoiding moisture on the vent is probably a good idea.
AshSF: This thread refused to get settled one way or the other. I was initially in the first camp which asserts that the vents are blocked. But after some research and experiments, I have moved to the other camp which assert that there is nothing wrong with the mask.
Seems that most people who suspect something wrong with the P10 are running Resmed machines. Since Resmed doesn't show 'Intentional leak rate', it's hard to convince them that the mask is venting properly.
alby_c: I know how the mask performed when I first got it, and for some months after - it was great. The diffuser worked well, I could breathe, I could just feel the exhaust, but I could feel it.
Then it blocked. I could not breath out. I finally understood people who said they felt a mask was smothering them as I had not experienced that before. I could feel nothing from the vents etc. It blocked up. It was not like this to begin with. It is substantially altered in its performance.
Saying I am dreaming an issue is not helpful, nor accurate. I really liked this mask and want to figure out how to get it working again without doing it violence.
palerider: the p10 and the swift fx and swift lt, (I couldn't find an lx) all vent at exactly the same rate when new (check the charts in the back of the manuals.)
BadGoodDeb: My lungs disagree with their vent chart.
palerider: your (probably) imprecise interpretation of the measurements from your wet, squidgy, floppy, gloopy meatbags not agreeing with scientific measurements isn't really much of a surprise
euquiq: The only mask that I learnt to hate is the P10. I sincerely think that Resmed guys did not think as hard as they should have on this mesh design.
herbm: Also note that the odds of your being able to "improve" one of these very carefully designed masks with pin holes are very, very close to NIL.
…High humidity and/or a cold room can easily cause condensation in the hose -- the water is condensing and collecting in the HOSE, not in the mask (to a virtual certainty.)… The film I am hypothesizing is something cohesive enough it doesn't wash off trivially so it would be more than JUST moisture.
chris61: Today I called the Dutch supplier and the representative admitted that the blocked vents was a more common heard complaint of the P10....
Cuppa: I suspect it will only be a matter of time before Resmed sees fit to change the design, (to what otherwise is a great mask)
HULK: So, with a diffuser such as this, the air volume and pressure become critical factors. Due to the shape and design of the vent holes, as the volume and pressure increase the back-pressure increases at a greater rate. This occurs due to turbulence as the air is forced through the vent holes faster than they want to allow.
...This is easily tested by blocking the hose and breathing out slowly a lung-full of air. It is reasonably easy. Do the same and breath out quickly. There is a lot of resistance.
...Block the exhaust vents on the mask (just put fingers over them) on the exhale and compare the back pressure to when using the mask with the vents uncovered. If it is about the same or less, the back pressure in the supply tube is less than the back pressure from the vents so some (or all?) of your exhaled breath will be going down the supply tube, i.e. re-breathing.
...Whatever the result of the debate above it is a simple fact, in a system where there is no non-return valve, to avoid expiration going back down the tube and being re-breathed, the pressure provided by the CPAP machine must be always higher than the back pressure from the mask vent.
...So, getting the pressure balance correct is problematic?
The dangers of Hypercapnia (Carbon Dioxide Poisoning) are well known and researched...
...Consequently, I assume that RESMED has put considerable time and research into preventing this happening?
...While I applaud RESMED for engineering such fine equipment… I am concerned about the absence of information they are providing to Consumers, Physicians and Technicians...
...Should there be monitoring and measuring in place to ensure re-breathing is not occurring?
...If it is the EPR allowing the pressure in the supply tube to drop below the back pressure of the mask vents, should there be a warning about using it with masks that have no non-return valve in the supply line?
ajack: G'day, I understand your concern and it looks like you read/misunderstood some scarey stuff, but we as a group here have thousand of man years under the belt. cpap increases o2, decreases co2. There is no rebreathing risk because of the venting when enough volume is being moved.
HULK: In chewing through all this data i cannot reconcile the basic observation "I noted that there was venting out of the P10 Most when breathing in but either very little or none, when breathing out!"
TBMx: if you would suffer Hypercapnia you would start to hyperventilate ... your respiratory rate hovers around 13 - which is like 10 miles away from that…nd be assured: there is no such thing as negative flow back in the machine. You might be "strong" enough while awake (or at least believe that you can breath forcefully enough to do that - but I doubt anyone is stronger than the turbines in the machines) but not during sleep - you would simply open your mouth to exhale. (and you would do the very same thing before starting to hyperventilate through your nose - except you did some crazy stuff to not be able to open your mouth)
DaveResmedP10: HULK I found exactly the same issue with my new P10 and I believe you are totally correct about rebreathing CO2 concerns.
It took a few nights to figure out what was going on. By the last night of use I was a mess, woke up several times breathing fast and heavy like I was running up hill. Mouth breathed for a while, things normalised and I would go back to sleep. Felt progressively more drugged during the day and my head was swimmy. Changed back to my old FX mask and things are improving.
I really like the comfort aspect of the mask so have been trying to figure out whats going on, searching online etc and your CO2 info really struck a chord. Oddly, yours is only the second post I have found anywhere online where someone talks about concerns that the P10 is not venting enough.
I have contacted the retailer and Resmed about it mostly to ask if it could be a manufacturing fault because the vast majority of comment online is all good. Resmed say 'no such probelm exists, never had a manufacturing fault, you need to get used to it or change masks'.
bonjour: I disagree with modifying any part of the air delivery system, including the mask. The mask is engineered to deliver air and vent a certain amount of air to prevent CO2 rebreathing
PaytonA: What would be the problem with more air venting than the "engineered" rate. The only danger that I see is getting to too much venting for the machine to handle when inhalation is added to it.
PaytonA: First, putting holes or slits in the vent diffuser may sound like a baaaad thing since someone probably spent a fair amount of time engineering those vent diffusers. The fact of the matter is that increasing the vent rate should have no negative effect on anyone's treatment efficacy with a Resmed machine unless you increase the venting so much that the machine can not keep up.
bonjour: Air in the system is designed to be balanced at some point and it must be balanced from 3cm H2O to 25cm H2O, the full range of pressures used for cpap treatment. This includes air delivered to the mouth/nose and the air vented. You can over vent which could result in the inability to deliver adequate air to the mouth/nose. Also you could under vent resulting in too much CO2 rebreathing…Without a solid method of knowing how to measure this balance I cannot recommend encouraging anyone to make alterations.
PaytonA: What do you mean "balanced'? This is an open ended dynamic system and as long as you have at least enough venting then the person is safe. Since one would be increasing the venting from what is "engineered" to be safe, one would still be safe. It would be difficult to vent so much air that the machine could not keep up by just modifying the P10 diffuser with pin pricks or small cuts and one would feel it if the machine could not keep up. We have a number of people that use this kind of modification and they are still on the forum…I do not promote modifying the vents but I think that too much emphasis has been placed on the "danger" of modifying the F10 vents.
PsychoMike: HeyHulk, I'm another with extensive SCUBA, SCBA, AvOx and RPE experience. I find that the CPAP machines are most akin to a PAPR set-up. The PAPRs don't need the oral-nasal cup in them due to the constant flow of air (just like a CPAP). The increased dead air space and normal exhalation should not result in excessive build-up of CO2, assuming the diffusive vents are working properly.
You are correct that you can breathe out and feel the results of the excess backpressure (the vents can only clear so much in a fixed amount of time), but don't forget that they are constantly venting and the machine is constantly pushing air through them...it would take extraordinary circumstances for it to lead to a hypercapnia event (i.e. blocked vents). HULK: The scary thing was when waking, noting the pressure was low and feeling as though I had been re-breathing. I would cover the exhaust vents by putting my fingers over the vents when breathing out. There was no difference in breathing back pressure with them covered or un-covered! So it was quite clear, that the path of least resistance was back down the tube. Re above, some theory to consider and questions for those who know a lot more about this stuff than I: When sleeping, what is the pressure of exhaust breath? The pressure back down the delivery tube is Exhaust breath pressure - Mask Vent back pressure. Is this pressure back down the supply tube sensed by the S9 so, it will wind itself back to meet the minimum pressure? Hence, making it quite easy to blow back against the CPAP pump?
PaytonA: The nasal and nasal pillow masks do have their own anti-asphyxiation valve. It is called.......your mouth. Sorry I could not resist. The logic is that if your machine quits operating while you are asleep you will open your mouth to prevent asphyxiation. Since the fullface mask seals off both the mouth and nose it was felt that they needed their own method for preventing inadvertant asphyxiation.
HULK: I agree with PaytonA, there is an anti-asphyxia valve - i.e. your mouth.
So, as a nose breather, perhaps this is why I had incidents of opening my mouth?...Don't we all have a natural mechanism that when there is no or poor quality air through the nose, we instinctively/subconsciously go the back-up i.e. mouth?...As the appliance used to manage the mouth opening was a chin strap (just one of the number of commercially available ones specifically for this purpose), did this make the issue worse be limiting the ability to open my mouth? Of note, it was suggested that strips off tape could be placed across my lips! I believe this could be highly dangerous as the anti-asphyxia valve is your mouth.
PsychoMike: Yes, there is more dead air space volume so you do re-breathes some additional volume of exhaled air when using CPAP. However, unlike a snorkel, the effective dead air space volume is far lower than the amount of volume in the tubing due to the constant air flow from the blower of the CPAP unit itself. In other words, it's not like you're breathing through a 6' hose and, hence, re-breathing 6' of exhaled air....but yes, there will be some minor additional re-breathing of exhaled air for ALL CPAP masks. Again, the effective increase in re-breathing volume would be quite minor (probably less than that of a snorkel, TBH). I'm not sure why you were having an issue with the pillows mask (unless there was an issue with the exhaust ports)…
HULK: TBXx's comment.... "but I doubt anyone is stronger than the turbines in the machines" intrigued me?...I would have thought this to be the case?...To be sure, I thought I would test it by blocking my nose and mouth breathing directly onto the delivery tube. Pressure 6, no EPR…I was surprised at how easy it was!
DaveResmedP10: In the case of the P10 nasal pillows mask and CO2 poisoning we have to consider several factors particular to the P10. It has a mesh vent with hundreds of tiny micro sized holes. This is a big departure from other vents I have seen that have a lot less and larger holes. The frictional forces are proportional to the surface area the air has to pass over. Logic dictates then that the P10 has greater frictional value than other vent types with fewer but larger holes. My observations/tests have proven with normal light breathing the P10 can vent sufficient exhaust air. However, although the mask is continuously venting, its not enough in all circumstances. Even the manual states ‘some rebreathing may occur’. What is the value of 'some', at what point, for how long and how often!!?? If you get into a state where you start to breathe heavier it does not vent all exhausted air. Additionally the micro sized holes are easily restricted or blocked by moisture. Whether you haven’t dried it properly, have condensation in your tubes, cough, sneeze or just blow out hard you can block up the tiny holes with moisture. The effect lasts a long time. Its surprisingly hard to clear moisture from this vent design.
…Where exhaust air is rebreathed a feedback loop can ensue.
If you are breathing air with higher CO2 levels than 400 ppm your body automatically makes you breathe faster and deeper to compensate. The exhale pressure inside the mask will increase as you blow out more volume faster. The vent flow rate is not proportional so the amount you blow back down the tube increases and so the proportion of air at 50,000 ppm you rebreathe increases. This new level of CO2 is additional to the amount your body produces and therefore the level of CO2 on your next exhale is higher again, stepping up with every cycle.
The effort required to breathe harder increases your bodies CO2 output therefore up goes the level of CO2 you are exhausting and so rebreathing… away it goes again and a negative feedback loop ensues.
Some comments have been made that you have safety features called your mouth and waking up. With low level CO2 poisoning neither of these may apply, especially when one of the symptoms of CO2 poisoning is sleepiness. As a nose breather mouth breathing is not automatic for me…I think we should be demanding more information from the manufacturers. Vent rates at given pressures and clear warnings as to the risks of CO2 where when and how - if only for the small percentage of users that are at risk.
SnoringInOregon: That 23 liters of air is going somewhere…It could be leaking before it gets to my pillows. In the dreamstation itself or in the hoses to the P10 mask. Or in the P10 mask ahead of the pillows and vents. I haven't detected such a leak…It could be leaking right at my nostrils. I don't think so. I'd notice something like that…I could be exhaling it through my mouth. No, I'd notice that too. I have no problems keeping my mouth closed while sleeping…There's only one place left for those 23 liters per minute. They're flowing out of the vents in the 10 mask. Where else could the air be going?...claim (and this is the only possibly dubious statement here) that this rate of air flow is more than sufficient to rapidly clear any and all of my exhaled CO2.
DaveResmedP10: As a separate issue regarding the technology, how much can we rely on the data. How precise is the reporting. We are relying on it to making some pretty important decisions. Do the units have a flow sensor or just making calculations based on current draw of the motor. It’s one thing to use data to inform choices and improve sleep experience its totally another to use the data as precise risk assessment.
(BTW: In my view, many of these comments leveraged off a basic assumption that there was a rigorous certification process. I believe other comments reflected “pseudo science” where extrapolations made from givens were extended to unknowns. One of the most obvious was the use of published bench tests results on flow rates to disprove concerns that vents could obstruct, that back flow could occur or that CO2 could rise significantly. In essence you are using a circular argument that high flow proves that vents can’t obstruct, when high flow is predicated on non-obstructed vents. An analogy that comes to mind is arguing that a stream carrying pollution into a river had inconsequential risks because the high volume of water and rapid flow in the river would effectively dilute and flush out the pollutants. That might be right…unless you dam the river: Then the flow rates of the river no longer apply since the river has effectively been converted to a lake. Now, concentration of contaminants from the stream will not only rise in the river, but also begin to flow upstream.)
FDA APPROVAL…OR NOT
I gained some additional insights in my conversation with the Harvard professor of sleep medicine that I mentioned earlier. For one, he did a “back of the napkin” calculation regarding the effect of high inspired CO2 on alveolar O2:
Dr: "I just did a little calculation depending on how high the person's PCO2 gets, during the time that they are breathing at 40,000 parts per million or 45,000 parts per million, you're inspired O2 at that time is probably like in the fifties could be in the 50s or anywhere between 50 and 60 or a little lower depending on how...so the longer it, the longer the PO2 in your blood is going to be falling, um, as the CO2 rises, and your blood rises. But at the same time, um, the inspired O2 is, is getting lower as well because the CO2 is rising so the PO2, could be in the, in the 50s or lower depending on how long the person is breathing with the elevated CO2, which is not good for you…"
510(k) CLEARANCE:
The second, more interesting bit of information conveyed by this Harvard sleep doctor was that ResMed is not actually required to submit completely new clinical testing data to support approval for the release of a new CPAP mask on the US market. They only have to submit, what is called a 510(k) Clearance. Here's our dialogue:
Dr: You don't have to get your mask approved by the FDA.
Me: Oh, I didn’t know that.
Dr: Not really. They don't have to do any special testing on that in order to submit to the FDA. I mean it's like if you have new brand of Kleenex, you don't get it
approved by, I mean, they might have to fill out a little bit of paperwork, but they don't have to, they just have to certify it is just like any other mask
Me: But you do have to get a prescription for it?
Dr: Oh yeah. But that doesn't mean anything.
Me: Now that's rather cynical view of the FDA.
Dr: I mean there are more, there are like 10 or more CPAP manufacturers. I mean they, they have to get their device approved, but the, the approval
processes, they don't have to submit any new data on their device. They just have to certify that it is basically essentially equivalent to what else is out
there on the market and performs identically. So they don't have to do any real fancy testing on this.
Me: That's interesting.
Dr: It's called, that type of approval is called a 510(k). And so it basically, it just basically means the first person had to get some sort of proof. But after that,
people who kind of manufacturer me too-type stuff for this sort of thing, they yeh, it's like these masks or, the hoses or any of that, the amount of testing is
pretty minimal. And for these masks, I'm sure they didn't have to do any testing. I mean they probably did some testing for their own good, to make sure
that it worked, but they didn't, they don't have to ike submit stuff to the FDA. They probably just had to submit some forms saying that hey, we're putting on
a new type of mask. It's kind of like our last version and FDA will say. Okay.
Me: What's kind of weird though, that if you make a product that specifically states in the user manual, if, the vent is obstructed, you can suffocate. that sounds
like a...
Dr: But that wordings in there for all these masks. I mean if you obstruct the valve on the other masks, that will have the same effect.
Me: Right. I know, I know that. But it seems like you as a company would want to take some measures to make sure that it doesn't obstruct by design. Not by
accident. I mean it's one thing if someone tapes over the vent, it's another thing if you're design actually increases risk of that happening.
Dr: Well they probably didn't think much of it. You know, Boeing didn't think much of the software change on the seven 737 Max either so.
“510(k)” is actually a section of the Federal Food, Drug and Cosmetic Act (FD&CA, the Act) from which this process was derived. The process is somewhat analogous to the “generic” drug concept in that Premarket Notification is used to obtain marketing clearance for a device that is “substantially equivalent” in safety and effectiveness to another lawfully marketed device or to a standard recognized by the FDA when used for the same intended purpose(s). Note that the concept allows for technological advancement; the new device does not HAVE to be manufactured from the same materials or perform its intended purpose using the same technology. The new device must exhibit roughly the same safety and effectiveness characteristics as the “predicate” device to which the new one is being compared.
A successful 510(k) submission results in FDA permission to market the new device. The nature of this comparison depends on the device and the degree of risk associated with its use. The comparison may comprise physical or performance characteristics as measured by standardized methods.
Some Premarket Notification submissions are based upon bench testing of the new device and a comparison of the findings with the known performance characteristics of the predicate device.
Because of the nature of the laws underlying this process, a successful submission is deemed to be “cleared.” Clearance of a Premarket Notification submission by CDRH (Center for Devices and Radiological Health) confers permission to market the new device. By legal definition, it is NOT an “approval” process.
Reference: https://www.devicewatch.org/reg/510k.shtml
AIRFIT P10 510(k) CLEARANCE:
I was able to obtain a copy of the 510(k) premarket notification for the AirFit p10 (Swift Air):
[attachment=12463]
[attachment=12464]
[attachment=12465]
This document indicates that the predicants used for the Airfit P10 are the Mirage FX, the Swift FX and the Ultra Mirage ll.
Interestingly, the initial design apparently offered, "two vent options, a traditional multi-hole vent and a new diffused type vent to provide a continuous air leak to flush out and minimize the amount of CO2 re-breathed by the patients. Like the predicate mask, the incorportation of these exhaust vents does not interfere witht he intended performance of the new device."
It makes you wonder if ResMed first considered a Brevida like system with a multi-hole vent, and a snap on diffuser, but settled on a fixed difusser design.
[attachment=12466]
Looking at these three predicant masks, it makes me wonder if the flow dynamics of these are really so similar to that of the AirFit P10 as to not require actual clinical testing to demonstrate adequate venting, especially under rain out conditions. All the others have traditional venting that would not obstruct with water or, if they did, could easily be blown open.
[attachment=12467]
When comparing close up pictures of the simple pore type vents vs. the extremely tight, fine mesh design of the P10, it is hard for me to believe that an engineer who understands the physics of flow dynamics would think these are equivalent regarding air flow and risk of obstruction, especially if wet. Were they tested under prominent rainout conditions?
Importantly, it is a legal requirement that ResMed forward any reports of adverse events to the FDA. It seems that those who have contacted ResMed about these concerns have just had those concerns dismissed. In the future, if anyone does contact ResMed, I would advise them to do it it in writing so there is a paper trail. Page 5 of the 510(k) clearance states:
Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations adminstered by other Federal agencies. You must comly with all the Act's requirements, including, but not limited to: registration and listing (21CFR Part 807); lebeling (21 CFR Part 801); medical device reporting (reportin of medical device-related adverse events) (21 CFR 803)
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - spirilis - 06-02-2019
(05-29-2019, 04:57 AM)spirilis Wrote: Man this thread scared me as I have noticed lately awakening more groggy than my 1st week of therapy (in week 5 right now) and I've cleaned the mask a couple times.
For good measure I soaked the mask in hot water for a few minutes and blew it out with compressed air (seemed to flow OK). But then I figured out how to reach the clinician menu on the Airsense 10 and found EPR set to Full-Time, 2cmH2O, and switched it to Ramp-Only. Woke up this morning a bit sharper than usual.
As a short followup, I think most of the benefit was in my head, as I didn't feel quite as sharp the next day or 2. I spent 3 days with EPR=Ramp Only, one interesting item of note is the first night I had only 1 obstructive and 2 clear-airway apneas, but the following 2 nights I had 0 clear-airway apneas (but 1 RERA per night and several obstructives).
Upon switching back to EPR=Full-Time at setting of 2, for which I've spent 2 nights so far, both nights I had 2 clear-airway apneas.
I'm fairly certain my P10 mask is flowing normal. I've read somewhere (i.e. this is a fuzzy understanding I've developed from my usual reading the firehose of threads & google searched articles) that having the extra support of EPR can induce either ... lower blood CO2 or higher O2 levels? Is it possible the use of EPR induces the occasional central apnea by excessive lowering of blood CO2? (assuming the mask exhausts correctly, which I believe it is)
(Of course this doesn't explain my first night going without EPR, where I had 2 clear-airway apneas anyhow)
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - kingskid - 06-02-2019
Thanks to all of you for your input, and especially for mdmarmd for giving us a lot of food for thought. Before this issue was raised, I never gave the mask vents any thought at all. Just swished the mask in hot soapy water every few months and never brushed the ports. That has changed immediately! Thanks again to all; the kind of info on this website is truly invaluable and who knows...could even save a life someday!
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - Canberragirl - 06-09-2019
Hi again everyone. I need to ask about what I can expect to gain by way of information from an upcoming oximetry test. All responses gratefully received!
The background (and relevance to this thread) is that I was happily using the P10 mask for some time, but then started finding that I was waking up feeling suffocated/heart racing etc. I searched and found this thread which seemed to offer a possible explanation for my symptoms, i.e. excessive rebreathing of CO2 in the mask due to either or both (1) accumulation of hard-to-remove debris in the mesh diffuser and (2) condensation occluding the mesh in cooler weather. Despite threatening earlier in this thread to stab holes in my P10 mask, I haven't done it yet. Instead I've been using the AirFit N20 as a substitute. I definitely don't like it as much -- except that it hasn't been making me feel suffocated, which I feel is a deal breaker. I've also requested to try a F&P Brevida at my next clinic visit, and played around with trying to minimise condensation (with some success but not enough for me to feel safe going back to the P10).
Anyhow, before finding this thread/theory, I had reported the symptoms to my doctor who agreed to arrange an oximetry test. I had become worried that we were in a closed information loop, where the machine would generate data which supposedly proved that its own treatment was working without any independent corroboration (apart from subjective perceptions of being sharper etc -- which may be trustworthy enough for many, but I felt like I needed something more objective). So I wanted to know what my oxygen levels were doing, as an independent source of information about treatment effectiveness. If I understood her logic, my doctor felt that the machine telling us there was no problem (i.e. good AHI) meant there was no problem, but she wanted me to feel safe/comfortable and was happy to reassure me with an O2 test.
Anyway that's the background. So I am now scheduled to borrow the oximetry equipment overnight in the coming week, and I am wondering about what it will be able to tell me. I only get to keep it for one night so I can't compare a night with CPAP to one without, or compare different nights using different masks. (I don't think it's worth swapping masks during one night because different times of night are different anyway. Or am I being too finicky about that?) So I'm going to try the one night using the P10.
If my oxygen levels remain good all night then I will assume either I have been spontaneously cured (extremely unlikely) or that CPAP treatment is working as the machine says it is, despite any suffocating feelings that may occur. (Of course if they don't happen maybe it means I have managed to solve the problem by better cleaning or less condensation -- but how can I be sure it won't come back?And KILL ME?! Sorry, a bit dramatic, but deep down that's what I'm afraid of.)
If my oxygen levels do drop down, while the machine continues to give a low AHI, what inferences might I be able to draw from this?
In particular, I am wondering whether any CO2 rebreathing leading to suffocation symptoms would show up as low oxygen levels. Presumably if too much CO2 is in the tube, replacing the fresh air that should be delivered by the machine, I would expect to see lower oxygen levels in my blood. Low levels of O2 won't prove there is excess CO2 (it could be another reason), but if there *is* excess CO2 to the point of producing my suffocation/heart racing symptoms, that should show up as lower oxygen as well -- right?
Thanks for any thoughts.
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - Sleeprider - 06-09-2019
Rebreathing CO2 due to a plugged vent would result in an increase of CO2 which will cause an increase in the respiratory rate. If this increases and you don't breathe through your mouth, an adrenaline increase would raise the heart-rate and create the "need to get air" response. This would be read on a recording oximetry by a decrease in SpO2 and increase in pulse rate. Your machine data would likely show an increase in respiration rate above your normal levels.
The value of this thread is to understand the mechanisms of the problem and how to prevent it. Moisture or contaminate buildup on the mesh is the root cause, and while a number of people have apparently experienced this, it tends to be among those who clean frequently and do not ensure the mesh is fully dried.
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - mdmarmd - 06-18-2019
Canberragirl
Initially, you said you complained of feeling suffocated/heart racing following an initial period of doing well on the P10. That's important because some patients seem to feel claustrophobic or uncomfortable with the mask on their face and complain of feeling short of breath or "suffocating". So your initial good adjustment would seem to rule out this type of anxiety driven response.
This would fit with the reports of onset of problems after a problem free interval, making one suspicious that dust or water, or both conspired to create this new problem.
"Anyhow, before finding this thread/theory, I had reported the symptoms to my doctor who agreed to arrange an oximetry test."
It seems at that point your sleep doctor was not aware of the concerns regarding possible hypercapnia, and she went the extra mile to reassure you that your dyspnea (sense of shortness of breath) was not a consequence of hypoxemia--hence, ordering the oximeter. (I could be wrong, but I don't think low AHI rules out problems with elevated CO2 at the alveolar level.)
If your oxygen levels remain normal on the oximeter, then it could mean you are not having obstructed vents/hypercapnia as a cause of your distress, or that the level of hypercapnia is not sufficient to displace O2 and show up as desaturation. Unfortunately, you have no way of knowing what your inhaled CO2 levels are.
I would have loved to have measured O2 during the time I was measuring the elevated CO2, but unfortunately both of my recording CMS 50IW oximeters were no longer functioning.
Since then, one of my patients lent me an oximeter that's working, but I'm not sure when I'll get around to measuring inspired CO2 and PO2 concurrently. It's currently over 100 degrees here in CA, and the night air is not cold enough to provoke condensation at this time.
In the discussion with the Harvard sleep doctor above, it seems that inspired CO2 of nearly 40,000 ppm should substantially lower the alveolar PO2. But I tried to get some further information on this from him, and he didn't respond to my inquiry. It sure would be nice if there is any anesthesiologist or pulmonologist out there that can really tell us what the clinical risks/implications of these inspired CO2 levels are. I presented my FDA report to the last sleep doctor I saw. He didn't seem to know what to make of it, but he said he'd try to forward it to his mentor at the renowned Stanford Sleep Medicine Clinic, but I never heard back from him.
So I’ll be quite interested to know if what your oximeter results are. But if your vents are not blocked during that one night, you likely will just have low AHI and normal PO2.
When I get some time, I might just tape the P10 vents closed and watch the capnograph readings as the CO2 has to go up, and I’ll wear the oximeter so I can see if there is a correlation between the high inhaled CO2 and O2 readings on the oximeter.
If I do this, I’ll post the results here.
BTW: I am sure that the P10 can occlude with just condensation. Because I can see the vents under high magnification, I can be certain there is no dust when this has occurred. Personally, if you can’t view the vents under magnification, I think the most reliable way to assure they are clean is with a WaterPik if you have one. I think it’s a fast and better way to clean them than trying to do too much brushing, because this might physically abrade the fibers over time and make them more susceptible to trapping water and dust.
As far as drying the vents after cleaning, if you just squeeze them between a tissue to absorb the surface water, you can then put a foam ear plug into one of the nasal pillow opening to reduce air flow and blow into your supply tube enough to start your CPAP. Then connect your P10 and there should be enough resistance to keep your blower from shutting off. Make sure there is air flow out the vents and after 30-60 minutes your vents should be dry.
But remember, this will not prevent a potential obstruction if there is prominent rainout.
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - Snoring Bear - 06-18-2019
(06-18-2019, 03:49 PM)mdmarmd Wrote: BTW: I am sure that the P10 can occlude with just condensation. Because I can see the vents under high magnification, I can be certain there is no dust when this has occurred. Personally, if you can’t view the vents under magnification, I think the most reliable way to assure they are clean is with a WaterPik if you have one. I think it’s a fast and better way to clean them than trying to do too much brushing, because this might physically abrade the fibers over time and make them more susceptible to trapping water and dust.
As far as drying the vents after cleaning, if you just squeeze them between a tissue to absorb the surface water, you can then put a foam ear plug into one of the nasal pillow opening to reduce air flow and blow into your supply tube enough to start your CPAP. Then connect your P10 and there should be enough resistance to keep your blower from shutting off. Make sure there is air flow out the vents and after 30-60 minutes your vents should be dry.
I don't use any special equipment at all other than a soft bristled tooth brush to clean the vent holes in my p10. That plus warm water and mild soap used on a regular basis seems to do the job just fine. I do clean my pillows and vent piece at least twice a week. I believe most people doing something similar will have satisfactory results. - - If one waits weeks and/or months to clean one's p10 then I suspect one could have trouble. Resmed recommends cleaning the pieces daily. I sure wouldn't take the chance of being too lax on my cleaning schedule.
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - flipflopmedic - 07-15-2019
Thank you for this post!!! I have been using the AirFit P10 for her (it was a better fit) for the past year, recently I have had nights where I feel like I can't get a good breath, almost suffocating, resulting in taking off the CPAP...creating issues for my wife
I will be checking to see if this is the issue I'm having.
RE: EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA - JamesRyan - 07-16-2019
I'm brand new to the cpap club(1 night) and love the p10 but this is very good info to know. How often should I clean the vents so this doesn't happen?
Thank you for the heads up
