Hello Guest, Welcome to Apnea Board !
As a guest, you are limited to certain areas of the board and there are some features you can't use.
To post a message, you must create a free account using a valid email address.

or Create an Account


New Posts   Today's Posts

[Equipment] Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
#1
Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)

From what I have read, plus the advice received from Sleep Physicians and CPAP Technicians, getting acclimatised to CPAP is often a difficult process that everyone goes through and patience, tolerance and perseverance is needed. I am currently going through that process and it is very tough for many reasons.
 
Over the period of a couple of weeks the fatigue increased to a point where, when I got up from a sleep period with the CPAP equipment, I was suffering fatigue like I have never experienced before and sometimes had a headache. It became dangerous to drive and I could not work. I would dispense with the CPAP equipment and go back to bed until lunchtime. I became concerned there was more going on than just acclimatisation?


Equipment: RESMED S9 with H5i Humidifier and P10 Nasal mask
 
I noted that I was waking up during the night with a higher respiration rate. Initially I thought it was just agro with the hose, mask head straps, noise etc. However, I also noted that there was venting out of the P10 Mast when breathing in but either very little or none, when breathing out! When I squeezed the tube on the exhale, it was very hard to breath out, upon releasing the tube it was easy to breath out. This lead me to concerns about re-breathing causing hypercapnia (carbon dioxide poisoning).
 
Being a SCUBA diver/snorkeler/swimmer, trained for work in high CO2 environments, Breathing Apparatus and enclosed spaces, I am both conscious and subconscious alert to the actions of the non-return regulator valves and the volume of the exhaled air which are both positive and often quite noisy.
 
I note that RESMED has decided to:-
1)   dispense with non-return valve(s) and instead use the back pressures of the CPAP and the mask’s diffuser.
2)   use a high-tech mask diffuser to reduce the noise and effect of the flow.
 
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.
 
However, the P10 Manual states:
“The mask contains passive venting to protect against rebreathing. As a result of manufacturing variations, the vent flow rate may vary.”

[img]blob:http://www.apneaboard.com/4f42aa40-3f3a-49d7-b501-a09daf6b0947[/img]
 
A recent Spirometry Test revealed I could exhale up to a rate of 635 litre/min. This is way off this scale.
 
Another test that can be done;
WARNING: - DON’T DO THIS FOR MORE THAN A COUPLE OF BREATHS AS IT WILL CAUSE HYPERCAPNIA (Carbon Dioxide Poisoning).
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. This test also reveals if there is a non-return valve anywhere in the system.


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.
 
I assume that this is going to vary considerably from person to person and be dependent on the stage of sleep?
 
So, getting the pressure balance correct is problematic?
Is this one of the reasons why Sleep Physicians and Technicians don’t like the users adjusting their own machines?
The dangers of Hypercapnia (Carbon Dioxide Poisoning) are well known and researched. I go back to the days of having the regulator on the SCUBA tanks.
Re-breathing is now prevented by having the regulator on the mouthpiece.
Consequently, I assume that RESMED has put considerable time and research into preventing this happening?
 
However, there does not appear to be any advice to Consumers, Physicians or Technicians.
So far, the only advice I have seen is:
P10 – User Guide: “As with all masks, some rebreathing may occur at low CPAP pressures.”


I have emailed RESMED for some tips and advice to get the settings correct, but have not received any response.
 
As the user is locked out of the settings of the machine by the restrictions of the Sleep Physician’s Prescription and the enabling of the ‘S9 essentials’, the Patient is very much in the hands of the Sleep Physician and the Technicians.
 
If there is a risk of Hypercapnia, that needs to be closely monitored and managed. Will the data measuring of the ‘leakage’ during expiration, measure/reveal the level of re-breathing?
 
While I applaud RESMED for engineering such fine equipment. (They certainly did a much better job than the people who put Darth Vader back together!) I am concerned about the absence of information they are providing to Consumers, Physicians and Technicians.
 
In systems where there is no non-return in the supply line, should there be warnings about re-breathing causing Hypercapnia (Carbon Dioxide Poisoning)?
 
Should there be monitoring and measuring in place to ensure re-breathing is not occurring?
 
There was a marked change for the worse when the settings were changed from ‘Auto with EPR on’ to ‘fixed pressure (10) with EPR on’.
 
Currently, we are trialling turning off the EPR (Expiratory Pressure Relief). So far, this has resulted in a dramatic improvement.
 
Is it the solution? I don’t know as, in the absence of information I have tried to work this out from basic theory without access to the massive volumes of research that has been done.
 
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?
 
Has anyone had similar experiences?
 
Do you agree with the above?
Post Reply Post Reply



Donate to Apnea Board  
#2
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
I think there may be a major fallacy in your in your description. To my knowledge there are no non-return valves in any of the masks. The flapper valve in the elbow of all of the full face masks is not one and will not act as a non-return valve. Its function is to allow easy access to breathable air if the power should fail during your sleep. The nasal masks and nasal pillows do not have this feature because the CPAP user  can merely open his/her mouth to get a breath.

Now on the other hand, I have become concerned about just the kind of thing that you are talking about when I was using a nasal mask from Fisher & Paykel called the Zest mask which has the normal vent holes above the nose in the mask. I switched to the Zest Q when I heard about it to avoid blowing my spouse off the bed (or so she said). The Zest Q has the vent on the elbow with a diffuser on the vent. Neither of these masks has a Non-return or an anti asphyxiation valve. After a while I began to notice that I did not feel quite as good with the Zest Q as with the regular Zest mask. I began playing around with the Zest Q and found that if I manually blocked the inlet tube in the elbow I could hardly blow air through the vent, blowing as hard as I could. I tried a brand new diffuser and it was a little better but still not good enough in my mind. I also did not like the vent being in the inlet line instead of in the mask because I feel that the mask does not get the CO2 washed out of it as well as with the vent in the mask. I quit using the Q version of the mask. I later found that I did a lot of mouth breathing or leaking with the nasal mask which is probably why I did not feel worse than I did with the Zest Q.

I am curious where you have seen a valve that you feel is a non-return valve and in what kind of mask. This type of valve is also called a check valve in the US.

Best Regards,

PaytonA

Admin Note:
PaytonA passed away in September 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
Post Reply Post Reply
#3
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Hi PaytonA,

Thanks for you information about masks.

Until using this Nasal mask RESMED P10, my experience is limited to Diving and Breathing Apparatus (confined space, noxious gas and fire rescue units), oxygen therapy masks, which all have non-retun valves (stop or check valves) to prevent re-breathing.

If the full face masks (which I am yet to trial) don't have non-return valves then is this statement valid for full face masks as well as nasal masks with pillows?
'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.'

The point I am to focus on is the question of whether the settings on the CPAP machine are critical to avoid Hypercapnia due to rebreathing or does the design of the Mask and it's integration with the CPAP machine prevent the user suffering the symptoms of Hypercapnia?
Post Reply Post Reply
#4
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
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. This is generally on the forum, advised as 6cm, although 5cm will normally be ok with most masks.

Download the manual for your machine and install the sleepyhead software. keep your min above 6 and that will vent enough for any mask.
get some charts up and ask some questions. Get some advice about how you are going. you will get good advice to what is the best pressure for you to use. you are using 10cm fixed pressure, that may or may not be the best.

now, after telling you not to worry. the P10 needs to be dry when you go to bed, infact a lot don't wash them. the very fine mesh can clog and some actually drill small holes.
http://www.apneaboard.com/forums/Thread-...ed?page=20
new http://www.apneaboard.com/wiki/index.php...re_success
mask fit http://www.apneaboard.com/wiki/index.php...ask_Primer
From machine or charts for auto-cpap, set the min at 'med' median pressure, or 2cm below 90/95%. max at 20cm for now. Forum will help you fine tune settings
Post Reply Post Reply



Donate to Apnea Board  
#5
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Thanks for your feedback.
What was scary, was waking up in the middle of the night with no (or little) venting from the nasal mask vents, my symptoms after the CPAP sleeps and the advice that this was all 'normal' - just acclimatisation!
Plus it was getting worse each day!

I am most particular about cleaning the mask (dismantle it on each cleaning), tubes and humidifier each day.

I check the mask vents are clear when I put it on by disconnecting and blocking the inlet tube, then blowing out (I suppose I get this from the DIVING and BA Training?)

The data printouts I have received form the CPAP supplier don't show how much the delivery pressure is backed off for the EPR, does the sleepyhead software show that?
Post Reply Post Reply
#6
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
yes it will show the pressures, download sleepyhead and post some charts, it is a very good program that will show each breath you breathe and lots of data. The s9 is a good machine, but the 10 is the current model, I hope you got a good discount on it.
also go to ebay and buy an overnight o2 recorder A$60 cms-50f usb cable and software..you know you want to know your o2 levels for peace of mind.

read the thread on the p10 mask I linked
new http://www.apneaboard.com/wiki/index.php...re_success
mask fit http://www.apneaboard.com/wiki/index.php...ask_Primer
From machine or charts for auto-cpap, set the min at 'med' median pressure, or 2cm below 90/95%. max at 20cm for now. Forum will help you fine tune settings
Post Reply Post Reply
#7
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Thanks for the feedback.
S9, H5i and P10 all on loan for trial so keen to build my knowledge ASAP, so I can get back to work and also before I dig deep and buy my own machine.
Initial Data has the Apneas dropping from 24 to between 1.5 and 2, so there appears to be a great result?
The side effects of using the equipment is the issue that needs to be sorted.
Post Reply Post Reply



Donate to Apnea Board  
#8
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
ahi under 2 is working well. you can't modify a loan mask, so I would swap it for another. I use a full face because I mouth breathe, so I can't offer much advice about nasal masks. have a read of some mask threads here, you should get some ideas.

if you don't have private ins and a decent copay, you can buy secondhand in the states and local. don't pay full retail for the trial mob, work a price with them, from what is available online in AU
new http://www.apneaboard.com/wiki/index.php...re_success
mask fit http://www.apneaboard.com/wiki/index.php...ask_Primer
From machine or charts for auto-cpap, set the min at 'med' median pressure, or 2cm below 90/95%. max at 20cm for now. Forum will help you fine tune settings
Post Reply Post Reply
#9
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Here are a couple of Sleepyhead charts.in the first you can see the difference between inhale and exhale pressure from PS (pressure support) or EPR or Flex depending on your machine.  The second demonstrates the ability to see what is happening on a breath by breath basis. My machine is different from yours but you get the idea.

Anyone can look at and change their settings, Go here and learn how. http://www.apneaboard.com/forums/Thread-...P-Pressure  I only suggest to do so from knowledge and not just try randomly and very different settings.  Post your charts here and you will get very good advice.
[Image: kwbZMu8m.png]

[Image: vNQqTcmm.png]
The links in my sig will help you to get started learning all about apnea and it's treatment.
Fred Bonjour - Project Manager and Lead Tester for OSCAR - Open Source CPAP Analysis Reporter 

New to Apnea? Helpful tips to ensure success
Mask Primer
Dealing with a DME
Download SleepyHead
Organize Charts
Attaching Charts

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
Post Reply Post Reply
#10
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Hi HULK,
WELCOME! to the forum.!
Hang in there for more responses to your post and good luck to you with CPAP therapy.
trish6hundred
Post Reply Post Reply



Donate to Apnea Board  


Possibly Related Threads...
Thread Author Replies Views Last Post
Gross EVIDENCE OF AIRFIT P10 VENT OBSTRUCTION CAUSING HYPERCAPNIA mdmarmd 89 3,739 Yesterday, 03:10 PM
Last Post: mdmarmd
  CPAP making my eyes very puffy, drying my hair and skin, causing it to itch Thanos 3 170 03-19-2019, 12:15 PM
Last Post: Mila
  R.E.M. Causing Heavy Eyes?? CPAPUserDave 1 111 03-05-2019, 07:42 PM
Last Post: mesenteria
  Masks causing breakouts gsxr1k 4 180 03-04-2019, 03:36 AM
Last Post: crowtor
  Using my ASV causing breathing problems during the day pmartin12 7 248 02-24-2019, 04:41 PM
Last Post: rnrcpap
  CPAP causing inner ear issues - help needed stephennic 16 1,555 10-29-2018, 01:03 AM
Last Post: Hydrangea
  Blockage behind Adam's Apple causing obstructions? MyronH 5 317 10-04-2018, 03:07 PM
Last Post: crowtor


New Posts   Today's Posts






About Apnea Board

Apnea Board is an educational web site designed to empower Sleep Apnea patients.