DCS incident after wreckdive

[ajduplessis]

This is the logic that 20 years ago pushed all of us to believe that emphasising deep stopping would be the answer. Yes, without question, you can make diagrams like the multideco ones on this thread look more benign with deep stops. You can reduce the peaks in the faster tissues. But there is strong evidence to believe that it is what is going on in the slower tissues (however you define those), whose gas tracking looks a lot less dramatic on these sorts of figures, that is the more important determinant of risk. Even Ross's commentary on the implications of those figures has been very measured and cautious in this thread. In contrast, your appeal to something which seems apparent but which is challenged by virtually all the relevant evidence is another demonstration of your complete inability (or refusal) to comprehend the evidence that has been laid in front of you by multiple studies.

Simon M

yet this guy got bent shooting shallow... or maybe he did not go shallow enough, or quick enough??

 

[Dr Simon Mitchell]

yet this guy got bent shooting shallow.

So what? Divers got bent in the shallow stops arm of the NEDU study too. This is another of your unsophisticated evaluations based on one case, and exactly the sort of logic that led us down the deep stops path 20 years ago. But we don't need to base a decompression strategy on one case . We now have real data from multiple studies that suggest that if we do what you are suggesting, then we end up with more decompression stress and decompression sickness. In those studies, evaluation of the deep stop profiles using similar approaches to Ross's multideco graphs show that the deep stops do exactly what you want them to do; they reduce those peaks in the faster tissues, but we still end up with more problems. That's why, in order to find the truth, we do studies with many subjects instead of drawing simplistic inferences based on a single anecdote.

Another point you are forgetting is that you could evaluate the profiles of 1000s of similar dives that did not result in decompression sickness and they would all look the same. We have no idea of the final "blend" of contributing factors in Miyaru's case, but some of those on Neal's slide from Ross's post may have had an influence.

Simon M

 

[w3dge]

yet this guy got bent shooting shallow... or maybe he did not go shallow enough, or quick enough??

Or maybe he stopped too deep. You're arguing with no reference, and it makes no sense

 

[John the Pom]

It is important to remember that the models used in computers or to derive tables are just that - models. To quote George Box: "All models are wrong but some are useful".

 

[ajduplessis]

So what? Divers got bent in the shallow stops arm of the NEDU study too. This is another of your unsophisticated evaluations based on one case, and exactly the sort of logic that led us down the deep stops path 20 years ago. But we don't need to base a decompression strategy on one case . We now have real data from multiple studies that suggest that if we do what you are suggesting, then we end up with more decompression stress and decompression sickness. In those studies, evaluation of the deep stop profiles using similar approaches to Ross's multideco graphs show that the deep stops do exactly what you want them to do; they reduce those peaks in the faster tissues, but we still end up with more problems. That's why, in order to find the truth, we do studies with many subjects instead of drawing simplistic inferences based on a single anecdote.

Another point you are forgetting is that you could evaluate the profiles of 1000s of similar dives that did not result in decompression sickness and they would all look the same. We have no idea of the final "blend" of contributing factors in Miyaru's case, but some of those on Neal's slide from Ross's post may have had an influence.

Simon M

If the studies where based on actual dive profiles the rest of the worlds do, I might have agreed, but NO. You are quick to point out 1000s of dives without DCI , but in the same breath will not accepts the many more dives successfully completed using others models without DCI.

But if things don't go your way, you will briefly mention divers getting bent using shallow stops and then waffle straight-on about a couple of studies and that other factors could have contributed to this incident, instead of agreeing that different factors and models affect different divers differently. Deep stops like your swallow approach actually works for various divers, there is no "one fits all" approach.

My unsophisticated evaluation is no better than your "We have no idea of the final "blend" of contributing factors in Miyaru's case"

 

[Dr Simon Mitchell]

but in the same breath will not accepts the many more dives successfully completed using others models without DCI.

This is patently untrue. I have acknowledged this fact in many of these on-line debates, and have also suggested that if divers are convinced a bubble model works for them they should probably keep using it.

But this is where your argument does become unsophisticated. You either don't understand the scientific method, or you are so infused with deep stops dogma that you refuse to acknowledge what science is telling us (thus far). Your interpretation seems to be that if a deep stop approach to decompression has prevented DCS for an individual diver then that somehow establishes the deep stop approach as optimal for that diver. Such a conclusion is invalid. The risk of DCS in the diver's deep stop decompressions may indeed be low, and quite possibly acceptably low for that diver; this is a fact that I have acknowledged on many occasions. But every bit of human experiment evidence available suggests that a decompression conducted over the same duration using an approach with less emphasis on deep stops than typically applied by current bubble models will be associated with less decompression stress and an even lower risk of DCS.

The concept that something which appears safe could actually be even safer if done slightly differently within the same decompression time is something that you seem incapable of comprehending. Does that really matter if the deep stops approach seems to be fundamentally working for someone? Maybe not. But if divers are seeking the truth in the universe about decompression safety, then the position I am taking is the one which reflects the current state of our evidence base.

and then waffle straight-on about a couple of studies

You try to be dismissive of the available studies, but the elephant in your room is that the ONLY scientific studies of deep stops in decompression diving all show that current deep stop approaches are less efficient (more risk / decompression stress for the same decompression time) than approaches with less emphasis on deep stops. On what, exactly, do you base your passion for defending deep stops? Where is the hidden treasure trove of evidence that suggests that a deep stop emphasis is the right approach? Or is it just that your instructor told you it was the right way to go and now you are immutably stuck in that paradigm?

...instead of agreeing that different factors and models affect different divers differently. Deep stops like your swallow approach actually works for various divers, there is no "one fits all" approach.

You seem to believe that if deep stops have avoided DCS so far in some divers you know, deep stops must therefore be best for these divers (see my response to this concept above), and this must mean that "different models affect different divers differently". It is absolutely true that different divers have different risk factors for DCS; some of this is accounted for by physiological factors we understand, and some (probably) by factors we don't understand. But the notion that "different divers respond to different decompression models differently" is little more than a construct of convenience on your part. We have no evidence that it is true. And even if it were, the relevant studies involving multiple divers (which we could assume have a cross section of divers in whom "different models affect different divers differenty") have still found a signal that decompression approaches emphasising deep stops are less efficient.

Simon M

 

[Miyaru]

I'm surprised to this gas/bubble discussion coming from a 64m/210ft dive. Yes it's beyond rec limits, but this dive is not deep and long enough to make a significant difference in choice of decompression model. Bubble and gas model will produce the same plan, with one or two minutes difference.

For this dive, the DCS hit was (very likely) determined before the dive. When I look at Neal's slide (the one Ross posted), the factors around predisposition are lighting up. State of hydration - I should have hydrated more. Physical fitness - I should not have unloaded 8 tanks at the compressor station 4 hours prior to this dive. That action might have caused a strain in my shoulder, affecting circulation.
Affecting influences on the dive profile are repetitive and ascent rate, two factors which I can change in the future, but for this dive, the model one chooses is of minor influence, if any at all.

 

[Dr Simon Mitchell]

but this dive is not deep and long enough to make a significant difference in choice of decompression model..

I agree. I was responding to another poster's implication that it was a lack of deep stops that caused your problem.

Simon M

 

[FinnMom]

... I am one of the doctors covering the NZ equivalent of the DAN line you called. If I take a call about a diver and refer them to a hospital, then I always call the hospital, speak personally to the duty consultant emergency physician, and let them know the diver is coming and what I believe needs to happen with them. Communication is the key to smooth management of diving casualties. However, despite best efforts by diving doctors on DAN lines, problems can still occur when divers arrive at hospitals that are not accustomed to seeing divers.

Simon M

Your practise of doing everything possible to see that the patient gets diver-appropriate treatment and ASAP is smart. If DAN made this a standard practise it would not only improve customer service, it might also decrease DAN's treatment costs.

 

[ajduplessis]

I'm surprised to this gas/bubble discussion coming from a 64m/210ft dive. Yes it's beyond rec limits, but this dive is not deep and long enough to make a significant difference in choice of decompression model. Bubble and gas model will produce the same plan, with one or two minutes difference.

Let me refresh those fragile memories, the NEDU study was based on 170ft/30min dive profiles....

I agree. I was responding to another poster's implication that it was a lack of deep stops that caused your problem.
Simon M

The only person implying is you, let me refresh the memories again....

“yet this guy got bent shooting shallow... or maybe he did not go shallow enough, or quick enough??”

I asked an question and the best answer you could muster was ...“We have no idea of the final "blend" of contributing factors in Miyaru's case"

and before you jump to more conclusions, I agree with your answer....