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Thread: Testing for CO2 retention? Critical or Not?

  1. #21
    Monkeywench ljj is just really nice ljj is just really nice ljj is just really nice ljj is just really nice ljj is just really nice ljj is just really nice ljj is just really nice ljj is just really nice ljj is just really nice ljj is just really nice ljj's Avatar
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    Re: Testing for CO2 retention? Critical or Not?

    The patients we see in the OR that seem to have more issues (and issues they watch for) as it was explained to me are some of the following

    history of smoking
    history of reactive airway disease/asthma
    obesity
    age
    idiopathic lung disease
    trauma

    the bottom line though is we can't always tell until the patient is on the table and we are looking at the brain and it's not responding to the hyperventilation they way it should. If we have someone at the head of the bed who's used to doing lots of aneurysm clippings, as SOON (or sometimes before) as the neurosurgeon mentions blowing off some CO2, they send an arterial gas to see if the lungs are doing what they are supposed to. if something 'changes', one of the things they do is send a blood gas to see if something is going on with the lungs.

    this can be a HUGE issue in neurosurgery from a surgical standpoint, as CO2 levels change the blood flow in the brain. it is very difficult for everyone involved when you are standing there looking at a swelling brain and all of the standard methods of care are not working.

    I realize that CCR/sCCR isn't quite as invasive as having surgery with a general anesthetic, but with the exception of the inhaled gases, from the machine at the head of the bed, it is in fact quite similar.

    So again, i think if there were a simple test to accurately predict who was going to be a CO2 retainer and who wasn't, the guys in Neuro would test a number of their cranial patients before surgery so that we could all plan accordingly. Maybe they do and i just don't know about it, which could be entirely likely, but I do pester pester with lots of questions and imagine it would have come out by now :)

    although monitoring CO2 for other systemic reasons is important, I only recollect seeing extreme attention being paid to it (where the surgeon actually asks for it to be kept very low at times) in neuro. (this is part of why there are specialist in the field of anesthesiology... cardiac, neuro, pediatric, etc... different surgeries require different care at the head of the table as well as the person doing the surgery)
    Last edited by ljj; 27th November 2009 at 16:42.

  2. #22
    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: 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
    Hi John,

    Unfortunately no.

    I think Andy provided the best advice:

    Quote Originally Posted by apitkin
    It's a thorny problem that has dogged diving for decades. Probably the best you can do is be aware of it, and try to prevent it by having equipment that minimises work of breathing, use more helium when diving deep and avoid significant physical workload.
    Simon M

  3. #23
    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: Testing for CO2 retention? Critical or Not?

    Quote Originally Posted by Abbo  View Original Post
    So Navies are rejecting people for training because they are judged CO2 retainers.
    Hi Nicholas,

    Just to clear up this misconception.... I am aware of attempts to derive testing procedures (such as the examples I referred to in my earlier post) but I am not aware of any Navies that believe they have a CO2 tolerance test that is sensitive and specific enough for selection of diving candidates.

    Simon M

  4. #24
    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: Testing for CO2 retention? Critical or Not?

    Quote Originally Posted by ljj  View Original Post
    So again, i think if there were a simple test to accurately predict who was going to be a CO2 retainer and who wasn't, the guys in Neuro would test a number of their cranial patients before surgery so that we could all plan accordingly. Maybe they do and i just don't know about it, which could be entirely likely, but I do pester pester with lots of questions and imagine it would have come out by now :)
    Hello LJJ,

    I do a reasonable amount of neuro-anesthesia. I think this is a bit of a red herring in the context of the diving situation. The main reason for validating the end tidal CO2 against an arterial CO2 in neuro cases relates to the explanation Andy gave in his earlier post. In some patients with significant physiological dead space there may be quite a big difference between the end tidal CO2 which we measure breath by breath and the true arterial value; specifically, the true arterial value is higher. As you have pointed out, in neurosurgery a high arterial CO2 is often bad because it causes dilation of cerebral blood vessels and swelling of the brain. It is therefore a common goal to keep the arterial CO2 at normal or low normal (and sometimes even low) levels. If you are going to do this accurately using your end tidal CO2 as a guide to ventilation (remember, more ventilation = lower arterial CO2), then you need to check early in the case (and periodically thereafter) how the end tidal CO2 relates to the true arterial CO2. As you point out, in patients with respiratory disease the difference can often be quite large. For example, if I am ventilating a patient and their end tidal CO2 is 35mmHg but the arterial blood sample shows that the true arterial value is actually 42mmHg, then I know that I probably need to ventilate them down to an end tidal CO2 of 28mmHg to achieve a true arterial value of 35mmHg.

    Its not a matter of predicting "CO2 retention" as such and none of this really has much immediate relevance to CO2 retention in diving.

    Simon M

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