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Thread: Relationship of hypercapnia to spO2?

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    RBW Member Scott will become famous soon enough Scott will become famous soon enough Scott will become famous soon enough Scott will become famous soon enough Scott's Avatar
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    FrankenLAR

    Relationship of hypercapnia to spO2?

    Casual thinking going on here..

    What is the relationship to carbon dioxide retention and/or hypercapnia and spO2 as read by a Pulse Oximeter?

    Further, would a reading of Carbon Dioxide Tension be a helpful metric for us?

    I just literally stubled upon a study that used an experimental Pulse Oximeter combined with Carbon Dioxide Tension monitoring ear sensor...

    Study: A Combined Ear Sensor for Pulse Oximetry and Carbon Dioxide Tension Monitoring: Accuracy in Critically Ill Children ? A & A

    (I was looking for a cheap submersible sonar transducer for another of my hair-brained ideas that will probably never be put into use...)


    The idea of using pulse oximeters was opened in a 5 year old thread, to a small extent.. http://www.rebreatherworld.com/rebre...-for-cc-2.html



    So.. what are your thoughts?

    -Scott

  2. #2
    New Member Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell's Avatar
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    Re: Relationship of hypercapnia to spO2?

    Hello Scott,

    Quote Originally Posted by Scott  View Original Post
    What is the relationship to carbon dioxide retention and/or hypercapnia and spO2 as read by a Pulse Oximeter?
    Essentially none. It is quite possible (and indeed frequent during anaesthesia in some contexts) to have a normal arterial oxygen saturation while your arterial PCO2 is very high.

    Quote Originally Posted by Scott  View Original Post
    Further, would a reading of Carbon Dioxide Tension be a helpful metric for us?
    Absolutely. Hugely useful, and there are many threads on this in various places on this site. This is what Alex Deas is attempting to do in the Apocalypse rebreather by using end tidal PCO2 as a surrogate for measuring arterial PCO2. Whether his system works or not is another (long) story. We do the same every day in anaesthesia.

    Quote Originally Posted by Scott  View Original Post
    I just literally stubled upon a study that used an experimental Pulse Oximeter combined with Carbon Dioxide Tension monitoring ear sensor...
    Yes, I have been following this too. The million dollar question is whether the system could be waterproofed and made to work underwater at pressure in cold environments when peripheral circulation shuts down significantly. I have serious doubts about this. For example, even in the operating room, if a patient is cold and peripherally shut down pulse oximeters often do not work very well. There might be ways around this. For example, a small probe can often be placed across the tissue between skin and nostril on the nose. Such a probe might work inside a full face mask (for example).

    Quote Originally Posted by Scott  View Original Post
    (I was looking for a cheap submersible sonar transducer for another of my hair-brained ideas that will probably never be put into use...)
    I don't think it is a hair-bained idea, but as is often the case there are technical difficulties to be overcome.

    Simon M
    Last edited by Simon Mitchell; 27th March 2010 at 21:50.

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    RBW Member Scott will become famous soon enough Scott will become famous soon enough Scott will become famous soon enough Scott will become famous soon enough Scott's Avatar
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    FrankenLAR

    Re: Relationship of hypercapnia to spO2?

    Thank you very much for your reply Dr. Mitchell.

    I now feel justified in the future use of dozens of free time hours on researching transcutaneous pCO2 monitoring. =)

    .....As an aside, I was not referring to this idea as hair-brained.. I was referring to my investigation of the feasibility of a homebuilt Mapper, utilizing Inertial Measurement Unit and peripheral sonar, with additional GPS endpoint acquisition as reference to provide a method to approximate corrections in the compounding error of the dead reckoning. Basically trying to satisfy my curiosities by reinventing the 'wheel' implemented by Stone Aerospace at a price that doesn't require me to sell my arms and legs.. =)

    Warm Regards,

    Scott

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    RBW Member Scott will become famous soon enough Scott will become famous soon enough Scott will become famous soon enough Scott will become famous soon enough Scott's Avatar
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    Re: Relationship of hypercapnia to spO2?

    For anyone interested, I have found another research article that is somewhat more applicable to us. (Tested at 41 bar instead of 1, and tested on mice instead of humans ;) )


    Rubicon Research Repository: Item 123456789/2474

    Title: Transcutaneous measurement of PCO2 at high ambient pressure (41 bar)

    Authors: Furset, K; Aanderud, L; Segadal, K; Tyssebotn, I



    Regards,
    Scott

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    Re: Relationship of hypercapnia to spO2?

    There have been a handful of studies where SpO2 was measured in free divers using a waterproofed pulse oximter

    one paper is here: Continuous pulse oximetry in the breath-hold divin... [Undersea Hyperb Med. 1993] - PubMed result

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