Deep Stops Increases DCS

[KevinNM]

However, about 60% of the cases for heliox alone were type 2, whereas about 5% of the cases for the switch to air were type 2.

Ahhhh, so what were the other 35%???

I suspect it's two sets that both independently add up to 100, not one set that adds to 100.

 

[Michael Guerrero]

Yeah, I have that study and the charts. It's not the one I referenced, but it talks about air dives and is the one that had results where the Pyle stop was the best (from a small sample size), though the authors explicitly say the results for the Pyle stop were statistically non-significant. In no instance was a deep stop profile better. Seems to be in line with the rest of the man-tested studies.

 

[Slamfire]

Why in gods name would anyone switch off helium to an EAN 40 mix? Of course they had bigger bubbles, they started on gassing nitrogen. Counter diffusion anyone? F-that.

I switch off 18/45 and 15/55 to 50% nitrox all the time.

When I can't get O2 boosted to 3000 psi and need the volume, I'll settle for 80% EAN for last deco mix. When I use 80%EAN I prefer to bump the usual 50% EAN deco gas to 40% EAN. My last two gas switches are then at 100ft and 30ft. Never had any issues when I use these gases coming off from helium.

 

[Dr. Lecter]

When I can't get O2 boosted to 3000 psi and need the volume, I'll settle for 80% EAN for last deco mix. When I use 80%EAN I prefer to bump the usual 50% EAN deco gas to 40% EAN. My last two gas switches are then at 100ft and 30ft. Never had any issues when I use these gases coming off from helium.

Suffice to say that the 0.5 ATA limit seems to be seriously over conservative, at least for most dives. If I havegas switches below 100m, I would be much more concerned about it, but for shallower stops the issue of IBCD just doesn't seem to be borne out for 50-60% HE blends. Maybe if you were being really nutty like diving HeliOx around 100-150m and jumping to air at 220' or something...I dunno.

 

[Kevrumbo]

Critical question: What were the statistical results of those divers with Doppler/VGE bubble formation counts also exhibiting acute DCS Signs/Symptoms?

. . .Not sure I understand the question, but every study I've seen has reported markedly higher bubble scores with both deep stops and helium vs. those with shallower stops and some form of Nitrox. They have also reported higher incidence of type 2 DCS with those same deep stop/helium-only profiles.

Mike, there is no statistical correlation with the incidence of DCS and low-grade Venous Gas Emboli (VGE) bubble scores; even Spencer Grade IV bubbles correlate only approximately to a 45% risk of clinical DCS (Rogers RE et al, Doppler ultrasound monitoring of gas phase formation following decompression and repetitive dives).

________
This article link below nicely sums up the current Deep Stops controversy as it stands:

http://dspace.rubicon-foundation.or...dle/123456789/9617/DHM_V37N3_3.pdf?sequence=1

 

[tomfcrist]

I switch off 18/45 and 15/55 to 50% nitrox all the time.

Yeah, second order rule..cool..do your thing, but switching to nitrogen at 100 ft? It's easy to keep the inspired fraction relative and avoid an ICD slam. We aren't talking H2O2 here, just switch onto another trimix.

Figure 3 from this paper (1) compared type 1 and type 2 DCS using either heliox or switching to air during decompression. The rate for DCS on heliox was 34/999 (3.4%) and for the switch to air 25/715 (3.4%). However, about 60% of the cases for heliox alone were type 2, whereas about 5% of the cases for the switch to air were type 2.

Another interesting observation of this paper was that bubbles have the potential to enhance washout because they carry much more gas than what is dissolved in an equivalent volume of blood. I would assume that this enhancement would hold as long as the bubbles did not substantially occlude blood flow.

--------------

1: Recreational technical diving part 2: decompression from deep technical dives, David J Doolette and Simon J Mitchell, Diving and Hyperbaric Medicine Volume 43 No. 2 June 2013, which references the following three studies:

30 Survanshi SS, Parker EC, Gummin DD, Flynn ET, Toner CB, Temple DJ, et al. Human decompression trial with 1.3 ATA oxygen in helium. Technical Report. Bethesda (MD): Naval Medical Research Institute; 1998 Jun. Report No.: 98-09.

31 Gerth WA, Johnson TM. Development and validation of 1.3 ATA PO2-in-He decompression tables for the MK 16 MOD 1 UBA. Technical Report. Panama City (FL): Navy Experimental Diving Unit; 2002 Aug. Report No.: 02-10.

32 Tikuisis P, Nishi RY. Role of oxygen in a bubble model for predicting decompression illness. Report. North York (ON, CAN): Defence and Civil Institute of Environmental Medicine; 1994 Jan. Report No.: 94-04.

Everyone loves to reference doolette and Mitchell...but once again they choose to do their experiment with an experimental profile. 3.4% DCS rate??? I recall some of y'all giving kevrumbo **** for getting bent 5 times and not changing his parameters...it would be helpfull if these guys did experiments of this nature using profiles that actual divers use.

3.4% is unacceptable.

 

[Slamfire]

Yeah, second order rule..cool..do your thing, but switching to nitrogen at 100 ft? It's easy to keep the inspired fraction relative and avoid an ICD slam. We aren't talking [-]H2O2[/-] He O₂ here, just switch onto another trimix.

I'm assuming you meant heliox and not hydrogen peroxide as you wrote originally. It's pretty much like Dr Lecter said, for a gas switch that shallow (100ft) IBCD shouldn't not be much of an issue, particularly when any other deco mix before this has had a low amount of helium (eg. something like 25/25 or 20/20) -- you've been slowly weaning out of high fractions of helium. I've never had any issues whatsoever. I wouldn't necessarily want to jump directly from a 300+ft mix down to either 40% nor even 50% EAN.

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*Edit* Found an example in my log where I jumped from bottom mix to 40% EAN. I planned the dive for 250ft, but ended up finding what I was looking for at 200ft. Gases are 14/49, 40%, 79%. See attached pic:

 

[Michael Guerrero]

Mike, there is no statistical correlation with the incidence of DCS and low-grade Venous Gas Emboli (VGE) bubble scores; even Spencer Grade IV bubbles correlate only approximately to a 45% risk of clinical DCS (Rogers RE et al, Doppler ultrasound monitoring of gas phase formation following decompression and repetitive dives).

________
This article link below nicely sums up the current Deep Stops controversy as it stands:

http://dspace.rubicon-foundation.or...dle/123456789/9617/DHM_V37N3_3.pdf?sequence=1

I think what you meant to say was there is a weak correlation, and I know. But it's the best indicator of DCS, aside from the several military studies (which we have, and which I cited) that have ACTUAL DCS as their end-state, that we have.

I didn't read the article you linked, but I feel capable of summing up the current "state of the art" without doing so. In several man-tested studies of immersed divers, which had actual instances of DCS as their objective, deep stops have been repeatedly contraindicated because they have resulted in higher incidence of 1) DCS, 2) type 2 (neurological) DCS, and 3) high bubble grades post-dive, which are a weak indicator of DCS.

Also, I thought it might be useful to point out that the impetus for the NEDU study back in 2005 was because the principal researchers of the study (Wayne Gerth and David Doolette), who were completely sold on the theories of bubble models, were trying to convince the U.S. Navy to adopt a bubble model as opposed to its existing model(s). The Navy said "show me". And as they attempted to, by constructing an experiment to demonstrate the efficacy of deep stops vs. shallow stops, while controlling other variables, they were confronted with the data which contraindicated for deep stops.

If you listen to Wayne's presentation at the DAN 2008 Deep Stops conference, he describes this event as "losing my religion", like that famous R.E.M. song, because he really did believe in the bubble model theory.

 

[tomfcrist]

Im assuming you meant heliox and not hydrogen peroxide as you wrote originally. It's pretty much like Dr Lecter said, for a gas switch that shallow (100ft) IBCD shouldn't not be much of an issue, particularly when any other deco mix before this has had a low amount of helium (eg. something like 25/25 or 20/20) -- you've been slowly weaning out of high fractions of helium. I've never had any issues whatsoever. I wouldn't necessarily want to jump directly from a 300+ft mix down to either 40% nor even 50% EAN.

------------------------------
*Edit* Found an example in my log where I jumped from bottom mix to 40% EAN. I planned the dive for 250ft, but ended up finding what I was looking for at 200ft. Gases are 14/49, 40%, 79%. See attached pic:

View attachment 199586

Yes, H2O2 is what this idiotic smartphone decided to auto correct with.

As far as the "gradual weening process" the study referenced doesn't do that. It either goes from 100m trimix to 50% or 100m trimix to air. Not the brightest idea.

I think what you meant to say was there is a weak correlation, and I know. But it's the best indicator of DCS, aside from the several military studies (which we have, and which I cited) that have ACTUAL DCS as their end-state, that we have.

I didn't read the article you linked, but I feel capable of summing up the current "state of the art" without doing so. In several man-tested studies of immersed divers, which had actual instances of DCS as their objective, deep stops have been repeatedly contraindicated because they have resulted in higher incidence of 1) DCS, 2) type 2 (neurological) DCS, and 3) high bubble grades post-dive, which are a weak indicator of DCS.

What you are failing to understand is that these studies you refer to were DESIGNED to bend divers...if there was 0 incidence of DCS then the study would be worthless. But when you deliberately change protocol to induce DCS, or at least make it more likely, you invalidate the findings.
The only thing I have found worthwhile in these studies is that if you dive thier bull**** deco profile, you will get bent 3.4% of the time.

 

[Kevrumbo]

I think what you meant to say was there is a weak correlation, and I know. But it's the best indicator of DCS, aside from the several military studies (which we have, and which I cited) that have ACTUAL DCS as their end-state, that we have.

I didn't read the article you linked, but I feel capable of summing up the current "state of the art" without doing so. In several man-tested studies of immersed divers, which had actual instances of DCS as their objective, deep stops have been repeatedly contraindicated because they have resulted in higher incidence of 1) DCS, 2) type 2 (neurological) DCS, and 3) high bubble grades post-dive, which are a weak indicator of DCS.

Also, I thought it might be useful to point out that the impetus for the NEDU study back in 2005 was because the principal researchers of the study (Wayne Gerth and David Doolette), who were completely sold on the theories of bubble models, were trying to convince the U.S. Navy to adopt a bubble model as opposed to its existing model(s). The Navy said "show me". And as they attempted to, by constructing an experiment to demonstrate the efficacy of deep stops vs. shallow stops, while controlling other variables, they were confronted with the data which contraindicated for deep stops.

If you listen to Wayne's presentation at the DAN 2008 Deep Stops conference, he describes this event as "losing my religion", like that famous R.E.M. song, because he really did believe in the bubble model theory.

No Mike . . .read the article link below. It definitively explains the current controversy with Deep Stops objectively better than your conjecture & speculative rhetoric above. . .

http://dspace.rubicon-foundation.or...dle/123456789/9617/DHM_V37N3_3.pdf?sequence=1