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Thread: Testing for CO2 retention? Critical or Not?

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    RBW Member jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk has a reputation beyond repute jkaterenchuk's Avatar
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    Testing for CO2 retention? Critical or Not?

    I remember reading an article that outlined that one of the initial tests given to CCR diver candidates in a Navy (not sure if it was US or another) involved determining if they were CO2 retainers. If so they were not allowed into the program because of the negative outcome that is possible. Seems this type of testing has not moved over to the general population CCR divers.

    I have been wondering if there is a test to determine if a diver is a CO2 retainer?

    If so what is it called and what does it involve?

    What do the results look like and is there some kind of sliding scale that indicates level of CO2 retention and risk of continued CCR diving?

    Is there a simple home test or list of symptoms to indicate higher than normal CO2 retention that might trigger a CCR diver to seek a detailed test?

    Would it make sense that every CCR diver should be evaluated for CO2 retention as part of the decision to start or continue CCR diving?

    John
    Last edited by jkaterenchuk; 23rd November 2009 at 12:27.

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    Re: Testing for CO2 retention? Critical or Not?

    IMHO, everyone retains/builds up Co2 relative to exercise and WOB... try running up a hill breathing through a straw, you'll get a first hand experience of what I mean... a bit extreme, but pretty much the same deal. I'm guessing the reference you speak of is related specifically to folks who retain co2 more readily than most. I have a hunch that it is more of a killer for average divers than many folks realize.

    g

    Gill Envy

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    Re: Testing for CO2 retention? Critical or Not?

    Without looking stupid, which is easy for me, what exactly is a CO2 retainer? Someone who metabolizes a lot of O2 to CO2 for a given workload?

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    Re: Testing for CO2 retention? Critical or Not?

    Quote Originally Posted by Tienuts  View Original Post
    Without looking stupid, which is easy for me, what exactly is a CO2 retainer? Someone who metabolizes a lot of O2 to CO2 for a given workload?
    Diving Doctor - Diver Magazine September 2001

    CO2 Risk Management Summary
    Last edited by jkaterenchuk; 24th November 2009 at 02:48.

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    Re: Testing for CO2 retention? Critical or Not?

    Quote Originally Posted by jkaterenchuk  View Original Post
    I have been wondering if there is a test to determine if a diver is a CO2 retainer?
    Hello John,

    There has been a lot of talk but nothing definitive.

    I should not really post stuff from this, but one paragraph won't hurt. This is what we had to say about the matter in our soon to be published chapter on gas exchange in hyperbaric environments:

    DOOLETTE DJ, MITCHELL SJ. Gas exchange in hyperbaric environments. In: Wagner PD, Hlastala MP (eds), Handbook of Physiology, Section 3 (Respiration) Volume IV (Gas Exchange). Bethesda, MD., The American Physiological Society, In press, 2009.

    "Because of the potentially deleterious effects of CO2 retention in diving, and the recognized inter-individual variability in the tendency to retain CO2 (described earlier), there has been much interest in the exclusion of candidates with a predilection for ‘CO2 retention’ from diver training. To this end, Lanphier [171] demonstrated that a low ventilatory response to inspired CO2 was predictive of a tendency to retain CO2 during underwater work. However, his attempts to define a selection procedure based on CO2 response testing were frustrated by poor specificity of the test and the difficulty in defining an appropriate ‘cut-off’ threshold in the response. Kerem et al. [152] investigated using the end-breath-hold PCO2 as an indicator of any tendency to CO2 retention under diving conditions, but found it a weak predictor. The desirability of an appropriate screen for a tendency to retain CO2 in diving candidates has subsequently been discussed by others [77, 116] but to date there is no consensus on an appropriate technique."

    77. Elliott DH. Loss of consciousness underwater. In: Diving Accident Management. Proceedings of the 41st Undersea and Hyperbaric Medical Society Workshop, edited by Bennett PB, Moon RE. Bethesda, MD: Undersea and Hyperbaric Medical Society, 1990, p. 301-310

    116. Hashimoto A, Daskalovic I, Reddan WG, Lanphier EH. Detection and modification of CO2 retention in divers. Undersea Biomed Res 8(1), Suppl: 47, 1981

    152. Kerem D, Melamed Y, Moran A. Alveolar PCO2 during rest and exercise in divers and non-divers breathing O2 at 1 atm abs. Undersea Biomed Res 7: 17-26, 1980

    171. Lanphier EH. Nitrogen-oxygen mixture physiology phases 4 and 6 (Research Report 7-58). Washington, DC: Navy Experimental Diving Unit, 1958.

    So, the answer is no, not a reliable one anyway.

    Hope this helps.

    Simon M
    Last edited by Simon Mitchell; 24th November 2009 at 04:23.

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    Re: Testing for CO2 retention? Critical or Not?

    Quote Originally Posted by Simon Mitchell  View Original Post
    Hello John,

    There has been a lot of talk but nothing definitive.

    So, the answer is no, not a reliable one anyway.

    Hope this helps.

    Simon M

    Simon

    Thanks for the posting. Of course it does not answer the question but at least I know that the medical community has not resolved it yet.

    Are you aware of any current testing in which I might consider volunteering as a test subject/diver?

    John

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    Re: Testing for CO2 retention? Critical or Not?

    Quote Originally Posted by jkaterenchuk  View Original Post
    Simon

    Thanks for the posting. Of course it does not answer the question but at least I know that the medical community has not resolved it yet.

    Are you aware of any current testing in which I might consider volunteering as a test subject/diver?

    John
    I thought the answer to your original question was in Sawatzky's article:

    Most people maintain arterial PCO2 at 40 mmHg by increasing respiration, even with heavy exercise and large increases in CO2 production. Some individuals do not. They allow the arterial PCO2 to increase, sometimes as high as 70 mmHg! These individuals are called CO2 retainers and there seem to be more CO2 retainers among divers than in the general population.
    Of course, the implied test would be to measure arterial PCO2, not an easy task. My guess is that someone has done a study to correlate PCO2 in the breath to arterial CO2, but to do that study would require sophisticated equipment. There may be something in the dive science literature.

    Were you looking for something more basic or anecdotal?

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    Re: Testing for CO2 retention? Critical or Not?

    Quote Originally Posted by moribund  View Original Post
    I thought the answer to your original question was in Sawatzky's article:



    Of course, the implied test would be to measure arterial PCO2, not an easy task. My guess is that someone has done a study to correlate PCO2 in the breath to arterial CO2, but to do that study would require sophisticated equipment. There may be something in the dive science literature.

    Were you looking for something more basic or anecdotal?
    I could not find Part II of Sawatzky's article and also found that he has been an expert witness in some cases defending manufacturers. So althought interesting reading I felt the need to seek some additional information.

    Seem a quick and easy answer is not immediately available so additional digging will be needed.

    I also felt that this entire area is not given the profile which it might deserve if as much was known about it compared to hypoxia, hypercapnia and DCS. Is it the missing link explaining some of the past CCR deaths or just a red herring. Food for thought.

    On the personal side I would like to know if I am a CO2 retainer or not. I have a below average low RMV and low HR and rate in the top 5% of my age group when looking at cardio type activities. All of which are great for OC and general fitness but might mean I am a CO2 retainer which might not be so good when diving CCR.

    John

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    Re: Testing for CO2 retention? Critical or Not?

    I believe we see this to some degree in Neurosurgery on an almost daily basis. Do we have any neuro-anesthesiologists or in this bunch who could comment?

    I just know that the ones I work with make regular comments about how you can't rely on expired CO2 to be an indicator of arterial CO2 because of the variable amount of dead space person to person in the lungs. these guys have the really really expensive machines that go ping. They still draw blood gasses very regularly on patients that require a lower than normal CO2 during their surgery (to reduce brain swelling). If there were a good formula, one would think they should not have to do this. The bottom line is that everyone is different. The human body is a complex variable.

    The impression I get from having worked in the surgical theater for about 15 years is that end tidal CO2 just tells you that you have CO2, and your patient is intubated properly. It is indeed an indicator, but not always a good indicator of everything that might be going on with regards to gas exchange. if you really want to know, you draw a blood gas.

    Quote Originally Posted by moribund  View Original Post
    I thought the answer to your original question was in Sawatzky's article:



    Of course, the implied test would be to measure arterial PCO2, not an easy task. My guess is that someone has done a study to correlate PCO2 in the breath to arterial CO2, but to do that study would require sophisticated equipment. There may be something in the dive science literature.

    Were you looking for something more basic or anecdotal?

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    Re: Testing for CO2 retention? Critical or Not?

    Quote Originally Posted by ljj  View Original Post
    I believe we see this to some degree in Neurosurgery on an almost daily basis. Do we have any neuro-anesthesiologists or in this bunch who could comment?

    I just know that the ones I work with make regular comments about how you can't rely on expired CO2 to be an indicator of arterial CO2 because of the variable amount of dead space person to person in the lungs. these guys have the really really expensive machines that go ping. They still draw blood gasses very regularly on patients that require a lower than normal CO2 during their surgery (to reduce brain swelling). If there were a good formula, one would think they should not have to do this. The bottom line is that everyone is different. The human body is a complex variable.

    The impression I get from having worked in the surgical theater for about 15 years is that end tidal CO2 just tells you that you have CO2, and your patient is intubated properly. It is indeed an indicator, but not always a good indicator of everything that might be going on with regards to gas exchange. if you really want to know, you draw a blood gas.


    Thanks LJ for the input. It's always good to have a look at something from different angles as it clarifies things better.


    Regards. Wael

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