Deep Stops Increases DCS

[ajduplessis]

First, it won't take 12 hours for genuine niggles to show up. Second, the throbbing bone pain is a dead-giveaway IMO. Third, when you go to 20' with a bottle of O2 and your shoulder feels better, congratulations it's a genuine niggle.

Did you read through the NEDU incident report of all 13 cases?

"22 year old active duty male USN diver <add>presented 22hours after<add> participating in <gap> dive (2005-12-08).Patient states he had no problems during or immediatelyfollowing the dive. The patient complained of some knee"cracking" during the evening of the dive <supplied>(2005120900:30)<supplied>, but denied any pain. Patient states thatupon waking at 0630 the morning following the dive (2005-12-09), he noticed a 1/10 right knee pain. The pain wasretropatellar and felt like it was "in the joint". The pain did notradiate, had no relieving or exacerbating factors, and was notreproducible with movement or palpation. The patient playedfootball that morning without difficulty. The patient presented to​

sick-call at 0900 and mentioned his pain to the duty DMO.

 

[Dr. Lecter]

Did you have a point that connected with your earlier post?

 

[ajduplessis]

Did you have a point that connected with your earlier post?

"First, it won't take 12 hours for genuine niggles to show up" Your words, not mine.

 

[UWSojourner]

The divers in our group have done more combined deep dives than the NEDU study utilising VPM-B +2 without incident. We live and dive together for a week at a time, so yes we know when someone has an issue. They dont call it the bends for nothing, you know when someone takes a hit.

Let me ask you this. Those that wake up 12 hours later with a shoulder niggle, how do you know the niggle is not related to sleeping on that shoulder, or workload related while unloading the boat earlier in the day? I have woken up at night with knee pain, shoulder pain or any other pain you can think of, but I was not in the water for a week. Did I have DCS? Of course not. Would my pain reduce taking a chamber ride? Yes! Because chambers are medical devices used to threat and heal many different injuries, not just DCS.

If you report any form of pain/numbness to a chamber operator/doctor and stating you dived even if you have never been in the water, the outcome will be DCS. "Diver:I dived today and have a shoulder niggle. Doc:Take a ride! Do you feel better? Yes! Perfect you had a type 1 hit". Is this a 100% true reflection? No one will ever know for sure, but it becomes a statistical number.

Do I know of divers that have taken hits? Yes! Each and every one of them was due to user error (dehydrated, flu, obese, unfit, wrong gas switches, longer BT than planned, air deco) not the model.

Your response is making my point. Evidence of bubbles large enough to induce pain, rash, etc. are frequently ignored or just self-treated with O2, aspirin, time. I think way more often than we admit, unless the pain is persistent, strong, and urgent enough to require treatment, the tech diver self-treats and chalks it up to *anything* besides evidence of too many bubbles.

I'm not a physician and wouldn't know where to draw the line on each case, but I do know a line is there and if you simply ignore all events of some pain in joints, shoulder, etc., you're ignoring potential signs that your algorithm may need to be dialed back a bit.

 

[boulderjohn]

Fallacy of the single cause - Wikipedia, the free encyclopedia
Post hoc ergo propter hoc - Wikipedia, the free encyclopedia

The problem with using personal anecdotes, even a lot of them, about things like this is that it is too easy to fall into single cause and post hoc thinking. There is an old joke about a man who is constantly snapping his fingers. Asked why he does it, he says it is to keep the elephants away. As proof that it works, he notes that no elephants have come near him while he is snapping his fingers. He assumes that his snapping the fingers is causing the elephants to stay away, when in fact the lack of elephants is the real cause. It is the kind of thinking that leads Polynesians to drop virgins into the craters to prevent volcanic eruptions and Aztecs to perform daily human sacrifices to make the crops grow.

Divers can use vastly different ascent profiles, with everyone coming up OK as long as they are within a certain overall realm of safety that we really don't understand well. Post hoc and single cause thinking identify one aspect of an algorithm and assume that it is the reason for success, when in fact there are other reasons. The identified cause can in fact be a detriment--the algorithm might have done even better without it.

Thus, even if two different alogrithms are working within certain parameters, that does not mean they are equally good. It does not mean that every aspect of the algorithm is valuable. An algorithm can work despite the negative effect of one aspect of it.

The only way to tell if some part of an algorithm is working is to find a way to isolate it from other factors and see how it does. That takes a carefully controlled experiment.

 

[tomfcrist]

Your response is making my point. Evidence of bubbles large enough to induce pain, rash, etc. are frequently ignored or just self-treated with O2, aspirin, time. I think way more often than we admit, unless the pain is persistent, strong, and urgent enough to require treatment, the tech diver self-treats and chalks it up to *anything* besides evidence of too many bubbles.

I'm not a physician and wouldn't know where to draw the line on each case, but I do know a line is there and if you simply ignore all events of some pain in joints, shoulder, etc., you're ignoring potential signs that your algorithm may need to be dialed back a bit.

The exact opposite applies to Navy DMT's. Most that I know will error on the extremely safe side when it comes to DCS. As in "Your elbow hurts? Take a ride." regardless of your attempt to bench press 500lbs last night.

 

[Divetech99]

Gents, are we seeing some changes in deep stops teachings/recommendations across the Certification Agencies (ie GUE, TDI, PADI TecRec, etc) ?

 

[Omisson]

Gents, are we seeing some changes in deep stops teachings/recommendations across the Certification Agencies (ie GUE, TDI, PADI TecRec, etc) ?

I've seen PADI Tec-Rec and DAN program bulletins mentioning the swing in theory - but in not aware of any manuals or standards changes on Deep/AN-DP/Trimix courses.

Others?

 

[Kevrumbo]

Look at the Bottom Mix Gas used in the NEDU Study link -see Post #1 above-- (essentially Deep Air):

This is the simple main practical point IMO/IME, to take away from the study:

Of course you're going to have significant residual inert Nitrogen and potentially on-gas N2 at your deep stop & perhaps even possibly at intermediate deco stops on Eanx50 which may encroach on critical slow tissue M-values as well --if you were using a working bottom mix with a high fractional N2 content to begin with like Air. Plan accordingly, use a computer to track your inert tissue loading (i.g. Shearwater Petrel) and be prepared to extend your 6m depth 100% Oxygen deco profile along with a stand-by IWR contingency protocol.

Aren't you all risking as a result of not performing Deep Stops, or ascending too fast to the first intermediate Eanx50 deco stop --a Fast Tissue type II Neuro DCS?? You should take this into account when deciding to omit Deep Stops: are you willing to risk a rare but possible type II DCS hit for the sake of not late supersaturating/loading your Slow Tissues (per the Conclusion of the NEDU Study)???

The best most prudent compromise to practically apply from the NEDU Study & discussion, is to do the Deep Stops, and extend out the O2 profile at 6m such that you have a surfacing Gradient Factor of 60% or less (per the readout of a Petrel Computer upon surfacing from your O2 deco stop) --to ensure inert gas elimination from those Slow Tissues. This is especially warranted if you're doing multiple deco dives per day for a week or more -and I would also recommend taking a day-off/break after three consecutive days of multiple deep deco dives per day. . .

-
Hello Kev,

I guess this is the sticking point. It is an article of faith for you that allowing fast tissues to supersaturate early in a profile that places less deep stops in your ascent is harmful, and there is probably nothing I can do to change your mind on that. However, I must point out that you only believe that because someone has told you it is so. It is an attractive theoretical assumption that many people believe(d) in the absence of any confirmatory data. The point is, that there is now data that challenge the idea. As UWSojourner's heat maps have illustrated the NEDU deep stops profile did reduce fast tissue supersaturation compared to the shallow stops profile, but this did not result in better outcomes. If tight control of fast tissue supersaturation early in the ascent is as important as you believe, why did the profile with the best control of fast tissue supersaturation early in the ascent produce the highest DCS rate?

Anyway bud, if you do what you say you are going to do and significantly pad your shallow oxygen decompression it may not matter too much what you do earlier. Just don't have a seizure please!

I hope you have a fabulous trip. I may have mentioned I am going back with Pete Mesley in November.

Simon

21 consecutive dive days completed here at Truk, including 10 straight days of two deco dives per day with an average 3hr SIT. Except for the North Pass site of the Oite Destroyer at 57m average depth, all deep morning dives were mostly on the wrecks of the Fourth Fleet Anchorage (San Francisco Maru, Aikoku Maru etc) with ave depths of 45m to 51m with 45min to 60min Bottom Times, and total run times of two-and-half to over three hours. All but two deep dives were on Air bottom mix, the other two using 20/20 "Tropical Economy Trimix" (for reel-line penetration of Aikoku Maru's engine room at 60m max), with 50% and 100% O2 for deco; and Nitrox30 for the repetitive dives in the afternoon with O2 deco only- all on Open Circuit. No prompt or delayed acute DCS symptoms/signs post-dive this time compared to last year Oct-Nov, with only a few upper arm/shoulder "niggles" felt overnight once. (Air & water temperatures 27 deg C, wind chill Winter conditions with NE winds 8 to 12 knots, 1m to 2m surface water chop with scattered rainshowers inside the atoll/lagoon).

The disadvantage of tactically compensating for the deep stop slow tissue loading with elective extra O2 deco time of around 10 to 20 minutes maximum was as both you & I expected: an uncomfortably high CNS OxTox figure result of 300 to over 500 max as tracked by the Petrel dive computer on 30/85 GF. By the start of this last week, I discarded the Ratio Deco Profile (along with Nitrox50 intermediate deco S-curve profiles emphasizing the high ppO2/"Oxygen Window" at 21m & 18m, and only slowing the ascent rate from the bottom at 10m/min to 3m-6m/min, at where that first required Ratio Deco/One Minute Deep Stop would have been), and instead followed the Petrel computer at GF's 30/85 with further conservative resetting on-the-fly of the Surfacing GF to 70 or 60, in order to extend the O2 deco profile (I really like and found this feature of the Shearwater Petrel Dive Computer most useful along with the @+5min/"predicted deco time remaining to surface staying at current depth for 5 more minutes" function). The CNS loading in this instance never went beyond 250 max.

Anecdotal Impression: I did not notice or feel any difference qualitatively post-dive using either Ratio Deco w/ Deep Stops, or Buhlmann GF's 30/85 as calculated by the Petrel Computer -both with using high N2 fractional bottom mixes of Air, 20/20 Trimix, or Nitrox30 & extended O2 profiles. The disadvantage of using elective extended O2 profiles to conservatively compensate & eliminate slow tissue loading is noted above with excessive CNS/Oxygen Toxicity rating factor, especially with deco profile implementation of the Ratio Deco Algorithm with Deep Stops.

 

[NAM001]

Hi rivers. Hey expaain something to me. You blew my mind with the statement about min deco being for 32% ir 30/30. Are you saying that the 2 gasses are the same? If not then i s my understanding about deco getting the N2 out wrong cause 32% has 68% N2 and 30/30 has 40% N2. How are teh 2 gasses similar enough to work with the same table? Lookin to be edumacated.

The GUE min deco table is for 32% and 30/30. From what I understand is that on Rec 1, air is included because nitrox is not available everywhere, etc. But whether that is it's own set of tables or just a handy formula, I don't know