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In-Water Recompression, Revisited

Discussion in 'Diving Medicine' started by Duke Dive Medicine, Jan 20, 2017.

  1. Duke Dive Medicine

    Duke Dive Medicine Medical Moderator Staff Member

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    I don't think anyone ever said it didn't matter, but according to Moon and Gorman in the Bennett and Elliott text, 40-50% of divers with DCS experience complete relief of symptoms even with delays of 24+ hours. This one isn't from the NEDU but maybe it's the one you were thinking of:

    How delay to recompression influences treatment and outcome in recreational divers with mild to moderate neurological decompression sickness in a r... - PubMed - NCBI

    <Editing> found a couple more:

    Risk factors and clinical outcome in military divers with neurological decompression sickness: influence of time to recompression. - PubMed - NCBI

    Delayed treatment of decompression sickness with short, no-air-break tables: review of 140 cases. - PubMed - NCBI

    This shouldn't be interpreted as a mandate to evacuate divers more slowly, but probably explains the Navy's rationale in advising that divers be evacuated to chambers vs performing IWR if the diver can reach a chamber facility within a "reasonable time frame (12-24 hours)."

    Best regards,
    DDM
     
    Last edited: Aug 15, 2017
    Akimbo likes this.
  2. Duke Dive Medicine

    Duke Dive Medicine Medical Moderator Staff Member

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    Si, gracias. As we say (with the greatest respect and affection) in the American South, you are a mess.

    Best regards,
    DDM
     
  3. Kay Dee

    Kay Dee Barracuda

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    And while we are on the subject of Ox-Tox, just for the record (but certainly not for measuring your you know what, but just to state FACTS, not assumptions, re my own 'experiences');

    1) The deepest I have ever been in water on o2 is 9m / 30ft

    2) The shallowest I have personally seen someone show signs of Ox Tox in water, and almost, but not fully, convulse, is 9m / 30ft.

    3) The deepest I have personally seen someone Ox-Tox is at or about 80m / 262ft, when he mistakenly switched regulators to pure (100%) o2 and convulsed and died within a matter of seconds, literally. (So much for breathing off independent doubles and continually swapping regs to 'breathe each cylinder down equally' for ya!)

    BTW, All the above took place in the 90's and both 2 and 3 took place off Miami so to speak. 'Nuff said.

    EDIT; But just in case some folks get the wrong idea about the company I keep (although I couldn't care even one iota what people think of me on here to be brutally honest); no the guy that died @80 was not part of our group, just another diver off the same charter boat at the time, and the guy @9m was a friend of mine and not breathing pure (100%) o2 when the physical signs of Ox Tox began to materialize.
     
    Last edited: Aug 15, 2017
  4. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

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    Sorry for mistyping the name. I had no idea I had done it until reading this. There is an occasional SB poster with that name, and although I knew they were not the same person, I must have subconsciously mixed up the names.
     
  5. Storker

    Storker Divemaster

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    [way off topic]
    That thing reminds me of the one-person chamber that JYC had on the deck of Calypso. I still chuckle over the story of how one of his team had to spend several hours in it while the rest of the crew lunched on lobsters and wine, making sure the poor guy had a good view of the meal.
    [/wot]
     
  6. Kay Dee

    Kay Dee Barracuda

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    Those guys just had to much fun! And they called it 'work'? ;-) Talk about torturing that guy!!
     
  7. Dr Simon Mitchell

    Dr Simon Mitchell Medical Moderator Staff Member

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    Hello,

    As DDM has pointed out, the existing medical literature that purports to address the importance of delay to recompression in determining outcome in DCS is not as supportive of early recompression as one might expect – at first glance. However few, if any studies have addressed this issue properly.

    With one or two exceptions, the studies suffer from one or both of two problems.

    First, unless you carefully stratify patients into different severity categories, then your results will be confounded. For example, if the vast majority of patients in your study have mild DCS then their prognosis is to get better no matter whether you recompress them or not. Under those circumstances you will obviously never show an outcome advantage for early recompression. Similarly, sicker cases with serious symptoms will usually present for recompression earlier (because they cannot ignore their symptoms) than mild cases who may present a day to two after diving. Remember the mild cases tend to get better no matter what you do. So if you compare outcomes for early and delayed recompression without carefully stratifying cases for severity, then you could even show that early recompression is worse, just because the patients getting recompressed early are the sickest ones.

    Second, almost none of the studies in recreational divers have a cohort who were recompressed early enough to be relevant to the potential advantages of IWR (which can be invoked very early). This is obviously true (as Akimbo pointed out) of the study that stratified delay < 48 hours and > 48 hours.

    A third problem, that ALL of the existing studies suffer from is that they are what we call observational. That is, they report results of what happens in the real world. This sort of study will never answer the question we are asking here properly, but this takes us into slightly esoteric realms of experimental methodology, so let’s not go there.

    There a quite a number of studies (some mentioned in this thread) which purport to look at the effect of delay to recompression but virtually all of them suffer from one or other or both of the first two problems that are mentioned above. We review them in our coming IWR review article. Only one (the French one whose abstract was linked to by DDM) actually includes divers who were recompressed early enough to be relevant to IWR but it was very small. They found that the factors most predictive of outcome were the initial symptoms (severe neurological symptoms predicted incomplete recovery). But if you read the paper itself there is a signal that very early recompression was advantageous.

    But that’s it. One study with equivocal support for early recompression. Which leaves us with what people like Akimbo know to be true from having worked in environments where very early recompression is always available: very few divers who develop symptoms in these settings end up with long term problems and the most plausible explanation for this is the access to early recompression. One strong factor supportive of this conclusion is that it passes the “biological plausibility test”. In other words it makes sense based on what we know of the disease process. We (mainly David Doolette who has access to a lot of the original test data gathered in 1000s of US Navy test program dives) have compiled a moderate amount of supportive data showing that almost all cases of DCS presenting early and treated early in these programs get better with no long term problems. That is how David has convinced IRBs that he can use DCS in an outcome measure in studies like the NEDU deep stops study. The subjects will get recompressed immediately and will get better. We will present this in our pending IWR review.

    Simon M
     
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  8. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

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    This may be slightly off topic, but could you comment on what may be a related issue?

    In a thread several years ago, someone posted something written by DAN related to the need to have qualified physicians diagnosing DCS. The problem they were identifying was not the failure to identify and treat DCS; it was misidentifying other maladies and treating them as if they were DCS. In many cases, the other maladies got better with time, as they would have without treatment, and the fact that some of that time was spent in a chamber was taken as confirmation that they had successfully treated a DCS case when in fact nothing of the kind had happened.

    I can speak to this issue personally. A number of years ago, after a weekend of decompression diving in New Mexico, I returned home and experienced a combination of pain and numbness in my hand and arm. I was at first afraid I had DCS, but I did not go to a doctor. The problem was worse the first day, and then it improved over the next couple of days. Then it happened again after a weekend that did not involve diving in any way, so I knew something else was going on. It started happening every dive trip, and I eventually got used to the sequence of pain and numbness followed by slow recovery. Eventually it reached the point that the fingertips on my right hand were perpetually numb.

    I was by then seeking a diagnosis, and that search eventually identified the problem--carpal tunnel syndrome. It was being aggravated by handling all that heavy equipment over the weekend. Once I had the simple surgery needed to correct it, my symptoms vanished, never to return.

    I think it is very possible that if I had gone to a hospital with a less-than-superior--hyperbaric physician, I would have been treated for DCS, and the usual fading of the symptoms during treatment might have been considered confirmation of that diagnosis.
     
    Akimbo likes this.
  9. Miyaru

    Miyaru Tech Instructor

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    I'm not sure if I understand this correctly: is there a plan to deliberately bend divers in a study?
     
  10. Storker

    Storker Divemaster

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    The rather recent NEDU study on deep stops used DCS incidence as the primary parameter.

    They aborted the experiment as soon as they got significant data showing that one of the protocols gave a higher DCS incidence, though.
     

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