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[Diagnosis] They want me to use a CPAP with oxygen concentrator
#41
RE: They want me to use a CPAP with oxygen concentrator
Do not turn up oxygen too high... Mongo.

from: https://www.quora.com/How-long-can-a-pat...saturation

By Gary Larson, MD for 35 years - ER and Radiation Oncology - academic and private practice
Updated May 31

"One warning - incorrect administration of supplemental oxygen to patients with severe COPD can be fatal (I don’t mean gradually, I mean dying right then and there). The other answers given are very good, but unless I missed it somewhere, no one mentioned the danger of increasing the rate of supplemental oxygen beyond a safe level.

Patients with COPD live with a CO2 level in their blood much higher than the average person. Normal values for arterial blood gas are given in the table below. (Note - O2 and CO2 levels given are the “partial pressures” of these gases in the blood - not the same thing as the “percent saturation of hemoglobin” - the measure that is used in the question).

Those of us without COPD live with a CO2 level in our blood very close to 40. This is the main thing that drives our respiration. If we’re not breathing deeply or rapidly enough, CO2 builds up in our blood and this stimulates the respiratory center in our medulla to increase our respiratory rate/depth. As long as we’re breathing well enough to keep our CO2 at the right level, we also put enough oxygen in our blood to saturate our hemoglobin to nearly 100% (and keep the partial pressure of oxygen in our blood at around 80 - 100).

People with severe COPD, don’t get rid of CO2 as well as the rest of us, and may run around with (or more likely sit around with) a CO2 of 60 - 100. Their kidneys adapt to the high CO2 levels and maintain their acid/base balance. This happens over a long period of time - and - gradually, their respiratory center gets used to their blood containing high levels of CO2. (Having high levels of CO2 in the blood is called hypercapnia.) Since their respiratory center stops paying attention to their CO2 level, they lose the “hypercapnic drive” to breath. At this point, they depend on their “hypoxic drive” to breath. When their oxygen level decreases their respiratory center causes their respiratory rate/depth to increase.

By this point, most people are oxygen dependent, receiving two or three liters per minute by nasal prongs. They get enough oxygen (their O2 sats are at least in the mid to high eighties) and everything is OK. If, however, their oxygen is turned up from say two liters per minute to five, they lose their hypoxic drive (their respiratory center doesn’t sense the need for more oxygen, so their respiratory rate slows). As respiration slows, their CO2 goes up - sometimes to a very high level, their kidneys can’t compensate acutely, and they develop respiratory acidosis and die.

Certainly people with COPD may need higher levels of O2 from time to time, but this should only be done in a closely monitored setting.

So the take home message is - don’t turn grandma’s O2 up high to make her more comfortable while you go to wash the dishes, or you might come back to find her dead."

Fair Use of educational material for non-profit purposes.


Admin Note:
JustMongo passed away in August 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
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#42
RE: They want me to use a CPAP with oxygen concentrator
Hi Justmongo,
I can only tell you my experience and what my oximeter tells me. 2LPM gets no change in my oximeter reading.

Larry
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#43
RE: They want me to use a CPAP with oxygen concentrator
Hi Sleep Rider,
Your input matches with my reality. I found the service manual for the Invacare Perfecto2 V I have. At 2LPM, they say the pressure 5 PSI. Based on the manual, I would need 4LPM to overcome the 14PSI at ramp up. I am just a patient. I understand what Justmongo is saying. I also understand what my oximeter is saying. I am hoping the different hose helps.

Larry
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#44
RE: They want me to use a CPAP with oxygen concentrator
(11-11-2016, 08:58 AM)mckee105 Wrote: Hi Sleep Rider,
Your input matches with my reality. I found the service manual for the Invacare Perfecto2 V I have. At 2LPM, they say the pressure 5 PSI. Based on the manual, I would need 4LPM to overcome the 14PSI at ramp up. I am just a patient. I understand what Justmongo is saying. I also understand what my oximeter is saying. I am hoping the different hose helps.

Larry

I'm sorry but you are mixing Apples and Oranges in terms of pressure. Your units are wrong. Your CPAP pressuse is 14 centimeters of water. 14 PSI would blow you up like a car tire. 14 cm-water is 0.2 PSI.

The concentrator tries to be a constant flow device. When set to 2 LPM, it can provide that flow up to a point. That point is 5 PSI by design. That means if you connect a canister to the concentrator, it will flow oxygen into the canister at 2LPM until the internal pressure of the canister reaches 5 PSI. It does not matter if you set the flow to 2LPM or 4 LPM, the dead-head pressure is regulated at 5 PSI max.
Admin Note:
JustMongo passed away in August 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
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#45
RE: They want me to use a CPAP with oxygen concentrator
My input had to do with dilution of the flow that reaches your airway. The CPAP puts out over 3-times your minute volume requirement. In order to deliver 2 Lpm, you would need 5-6 Lpm injected into that airflow, and 2/3 of that would be lost to the exhaust vent. A professional should be able to figure it out, and I'm certainly not qualified to suggest what the correct compensation for CPAP intentional leak is.

As far as pressure, several members have mentioned that the CPAP pressure is measured in centimeters of water pressure. Pounds per square inch (psi). You can do this conversion online http://www.convertunits.com/from/psi/to/cmH2O, and find 14 cm H2O is only 0.2 PSI, so your oxygen generator is easily able to overcome the CPAP pressure, but it is the flow volume that dilutes the oxygen and may require compensation in order to deliver the 2 liters per minute dose.
Sleeprider
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#46
RE: They want me to use a CPAP with oxygen concentrator
Although it is possible to do the percentage of oxygen calculation knowing the mask vent rate at pressure and the supplemental oxygen flow rate, it would not be useful. The rise in PsaO2 cannot be predicted. It's dependent upon the patient's physiology and possible disease factors.

I'm Rx'ed for 2 LPM O2 introduced into my CPAP flow. When I was in the hospital in 2010, they put me on a PAP machine that had to be mounted on a cart. An O2 line was connected to it; and they just dialed in 30% O2 (compared to approximately 20% in normal air.)

I doubt that my 2 LPM results in 30% O2. I also doubt that anyone did a calculation to get the 30% number from my written script.

My personal experience is: I get a bigger PsaO2 boost from the CPAP pressure alone, than I get from the added O2.
Admin Note:
JustMongo passed away in August 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
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#47
RE: They want me to use a CPAP with oxygen concentrator
Justmongo,
Thank you for the clarification.

Larry
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#48
RE: They want me to use a CPAP with oxygen concentrator
I was on Ox first now i have my cpap machine with the ox line attached and it is working well..I saw the Dr. tuesday and he said i was doing well and to continue the way things are....*smile*
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#49
RE: They want me to use a CPAP with oxygen concentrator
(11-11-2016, 05:18 PM)David44142 Wrote: I was on Ox first now i have my cpap machine with the ox line attached and it is working well..I saw the Dr. tuesday and he said i was doing well and  to continue    the way things are....*smile*  
Thanks Mongo, Larry, David & others -
I find this a very interesting conversation because I too have considered the question, "How much O2 am I actually getting with my concentrator set to 2 litres per min. (2 l/m) and its output tapped into my xpap supply line"? Having read the posts to this thread I have determined this to be a vexed question.
Consider this, my doc prescribed supplemental oxygen @ 2 l/m and my xpap machine delivers say, 24 l/m how much oxygen am I actually inspiring? The ratio of  atmospheric air to oxygen is 12:1 does that mean I am getting one sixth of my prescribed supplemental oxygen? Also the output of concentrators is less than 100% so the question really is, "How Much"? And, how much O2 is carried away in the washout?
BTY Some time back I devised a way of interegrating a nasal cannula with my FFM and this worked really well until I got a new mask, a F&P Simplus FFM which I have not yet modified, but am severely temped to do so.
[Image: signature.png]Keep on breathin'
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#50
RE: They want me to use a CPAP with oxygen concentrator
Sorry,
     I don't have the background to answer definitively. I get 8 LPM into my Resmed Autoset. That allows me to get fully saturated. Less then 8 LPH and I can't get to 100%

Larry McKee
mckee105
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