In-Water Recompression, Revisited

[Dr Simon Mitchell]

Hello Akimbo,

TT5 IWR... interesting question. This comes to mind:

After a serious decompression dive (which I wouldn't do without a chamber within an hour). Edit: Omitted decompression perhaps. What is serious decompression? More than half an hour feels about right.

Severe/undeniable Type 1 symptoms or any hint of Type 2 etc

Given the hilarious body bag reference I'm not entirely sure how serious you are about this, or the degree to which you are conflating the typical tech diving world with the commercial diving environment that you obviously inhabit. On a subject like this we should probably not discuss them together because there is little practical point in doing so, and it may create confusion about what is acceptable in the tech diving world.

So, in relation to tech diving there is nothing that would justify taking an immersed diver to 2.8ATA breathing 100% oxygen. I don't care how serious the DCS, how provocative the dive, or about any other rationalisation someone might come up with. And for the record, as someone who has inhabited your world and still provides related advice, I would not recommend it for well-equipped commercial divers either (and as you point out, most of them have chambers anyway). The marginal benefit of going beyond ~9 - 10m is dubious (see below), and the danger (see my earlier post above) is just too great (more than 50% of people are likely to develop symptoms of oxygen toxicity).

Advocacy for an immersed Table 5 appears predicated on an assumption that compression to 2.8 ATA will almost certainly improve clinical outcome. In fact, the advantage in efficacy of going beyond 10m is likely to be relatively small. David Doolette and I wrote a review on IWR for the UHMS Precourse on field management of DCS held in Florida 6 weeks ago, This is a short relevant extract:

Since the introduction of the U.S. Navy Treatment Tables 5 and 6,21 treatment tables which begin oxygen breathing at 60 fsw (18 msw) have become the standard of care, and there has been essentially no experimentation with shallower initial HBO treatment of DCS at shallower depths of for shorter durations. However, the development of these minimal pressure oxygen breathing tables included testing both 33 fsw and 60 fsw treatment depths and relatively short durations of HBO. The “provisional” protocol for the treatment of DCS was to compress divers breathing oxygen to 33 fsw, and if complete relief of symptoms occurred within 10 minutes at 33 fsw, oxygen breathing was continued at this depth for 30 minutes after relief of symptoms and during 1 fsw/min decompression to the surface. If relief was not complete within 10 minutes at 33 fsw, divers were compressed to 60 fsw. If complete relief of symptoms occurred within 10 minutes at 60 fsw, oxygen breathing was continued at this depth for 30 minutes and during 1 fsw/min decompression to the surface. Goodman and Workman tabulate 31 shallow recompression treatments that generally followed these rules:21 27 at 33 fsw, three at 30 fsw and one at 20 fsw. Seven treatments had longer time at maximum depth than specified above. Excluding one 26-hour treatment, the total treatment times ranged from 35 to 180 minutes (mean 70 minutes). DCI signs and symptoms treated at 33 fsw or shallower (number of treatments) included pain (26), special senses (6), rash (5), sensory (3), chokes (3), syncope (3), motor weakness / paralysis (3), loss of consciousness (1), and nausea and vomiting (1). Being largely treatments for experimental dives, the delay to recompression was relatively short, with a median of 37 minutes (range 0–270 minutes). It is perhaps pertinent that many of the inciting dives were non-trivial, including trimix bounce decompression dives to 200–400 fsw and no-decompression drop-out from shallow 12-hour subsaturation and repetitive air decompression dives to a maximum of 255 fsw. Twenty five of 31 shallow treatments resulted in complete relief. Two treatments resulted in substantial relief; in one case the residuals are reported to have resolved spontaneously over three days. Four treatments were followed by recurrence of symptoms; in three cases complete relief was reported following a second treatment.

So, outcomes, were fairy good with compression to only 33 fsw, especially when it is considered that the manifestations had to resolve within 10 minutes or the treatment would be escalated.

Hope you find this interesting.

Simon M

Reference:
Goodman MW, Workman RD. Minimal-recompression, oxygen-breathing approach to treatment of decompression sickness in divers and aviators. Research Report. Washington DC: Navy Experimental Diving Unit; 1965 Nov. 40 p. Report No.: NEDU TR 5-65.

 

[Akimbo]

Given the hilarious body bag reference I'm not entirely sure how serious you are about this,...

I would say serious as a heart attack... so to speak.

I would not drop directly to 60' before trying to evaluate symptoms at 25-33'. I would only consider progressing to a TT5 IWR if I believed I would die or be severely injured anyway.

You basically have to resign yourself to dying
with your fins on and hope you get lucky.​

... or the degree to which you are conflating the typical tech diving world with the commercial diving environment that you obviously inhabit.

The main difference between the majority of commercial diving today and some rebreather dives done on expeditions is they are have been illegal for commercial diving in many areas of the world for decades... for very good reason. All diving below 50m in the North Sea effectively is saturation. Commercial divers always had chambers onboard, even during the wild-west era in the 1970s. Nobody would consider IWR if they had a chamber onboard. I have never seen any data that indicates being paid or not affects DCS risk.

I have never suggested IWR at 60' unless shallower didn't work... I don't know how the quote above in red and the body bag reference could be viewed as ambiguous. However, thinking that treating a serious DCS hit at 25' from a 300-500' expedition dive will always be effective is naive.

... However, the development of these minimal pressure oxygen breathing tables included testing both 33 fsw and 60 fsw treatment depths and relatively short durations of HBO. The “provisional” protocol for the treatment of DCS was to compress divers breathing oxygen to 33 fsw, and if complete relief of symptoms occurred within 10 minutes at 33 fsw, oxygen breathing was continued at this depth for 30 minutes after relief of symptoms and during 1 fsw/min decompression to the surface...

OK, but how does that relate to serious symptoms after a rebreather dive to 200-500'? I doubt very seriously that an any diver that got bent after an experimental HeO2 dive at EDU and lost bladder control was ever dropped to 30' on O2 to see if it worked.

I agree that recreational divers, which most tech divers are since they are diving for fun, should be discouraged from IWR and very heavily discouraged from TT5 IWR. The problem isn't IWR, regardless of depth. The problem is diving great distances from a chamber. The problem is even greater when you are making very high risk decompression dives with no back-up options for DCS.

 

[Kay Dee]

The problem is diving great distances from a chamber. The problem is even greater when you are making very high risk decompression dives with no back-up options for DCS.

Well, as the battle hardened Moshe Dayan once said " Times change and I change with them" and in this instance my mind changed re going home with my bat and ball and hence have put that on hold for just one moment.

So I'd respectfully just like to rejoin the fray for just one moment to comment on the above, not get re-involved in any way with the other 'discussion' on IWR protocols which I no longer want any part of, nor will input on again re same on this thread.

So forgive me for re-intruding but........... re the above Akimbo, with all due respect it seems you do little if any true expeditionary diving. Nothing wrong with that,but then please don't criticize those explorers who choose to explore in obscure locations with a chamber not even remotely available (or the appropriate IWR gear available / on hand, for whatever reason that may be). We all have free will, or still do at the moment in some places of the world, and if the only way to do the exploration one wants to do is far far from the nearest chamber, then thats ones own choice. No? But of course, in that situation, don't come crying if you get bent and cant get treated. An explorer has to analyse the risk, and either except it or not.

Anyway, no offense meant Akimbo, but as Simon said, commercial and technical diving are two very different things, literally apples to oranges so to speak as far as 'surface support' goes (although most technical divers would sell their soul to have what what commercially trained divers take for granted as 'support'). But not having that support is not going to stop some of them (us) from exploring in remote regions just 'cause they don't have that support.

You say you choose to only dive when a chamber is max an hour away, others choose not to operate under that constraint. Its their choice.

Simple as that, and nothing wrong with that IMO, as long as one accepts the risks involved.

Best fishes and safe diving to you!

 

[Dr Simon Mitchell]

Hello Akimbo.

The main difference between the majority of commercial diving today and some rebreather dives done on expeditions is they are have been illegal for commercial diving in many areas of the world for decades... for very good reason. All diving below 50m in the North Sea effectively is saturation. Commercial divers always had chambers onboard, even during the wild-west era in the 1970s. Nobody would consider IWR if they had a chamber onboard. I have never seen any data that indicates being paid or not affects DCS risk.

I accept all that. Every technical dive I do would be illegal in NZ if I was being paid in some way for the dive. I think Kay Dee has done a good job of articulating the tech diving philosophy. It is the essence of the discipline that we must all be informed risk acceptors. If tech divers were not prepared to accept more risk than commercial divers then there would be no tech diving. None of this really has anything to do with what IWR protocol is acceptable.

I have never suggested IWR at 60' unless shallower didn't work.

Fair enough, but what you do appear to be suggesting is taking a compromised diver (perhaps severely compromised) who appears not to respond at 30' to a depth where they are a long way from the surface, the diver(s) accompanying them may accumulate a decompression obligation, and there is an extremely high chance they are going to suffer an oxygen toxic seizure; all based on an assumption that this risk is offset by an expectation of outcome benefit.

Cases that don't respond at 30' will not automatically respond at 60'. Moreover, cases that don't appear to respond at 30' initially will not automatically have a bad outcome. I can say this with confidence because we have seen divers with what appears to be very severe DCS have a complete recovery with surface oxygen and no recompression at all. Put simply, if you go to 60' you would be accepting a high risk of death for a poorly defined (and probably small) chance of reducing disability.

However, thinking that treating a serious DCS hit at 25' from a 300-500' expedition dive will always be effective is naive.

I can promise you that when it comes to treating DCS naivety is not something that neither DDM nor I suffer from. We know perfectly well it will not always be effective. We also know, from nuanced knowledge that we have acquired in treating 100s of divers, that escalating an IWR oxygen treatment from 30' to 60' is not worth the risk under any circumstances.

OK, but how does that relate to serious symptoms after a rebreather dive to 200-500'? I doubt very seriously that an any diver that got bent after an experimental HeO2 dive at EDU and lost bladder control was ever dropped to 30' on O2 to see if it worked.

Read the quote from our pending paper again.

Being largely treatments for experimental dives, the delay to recompression was relatively short, with a median of 37 minutes (range 0–270 minutes). It is perhaps pertinent that many of the inciting dives were non-trivial, including trimix bounce decompression dives to 200–400 fsw and no-decompression drop-out from shallow 12-hour subsaturation and repetitive air decompression dives to a maximum of 255 fsw.

I agree that recreational divers, which most tech divers are since they are diving for fun, should be discouraged from IWR and very heavily discouraged from TT5 IWR.

The modified guidelines which will be published do not discourage tech divers from IWR provided they have appropriate training and follow a sensible selection and treatment protocol. They will certainly discourage the use of a TT5.

The problem isn't IWR, regardless of depth. The problem is diving great distances from a chamber. The problem is even greater when you are making very high risk decompression dives with no back-up options for DCS.

I doubt that many tech divers have no back up options (depending on how you define those). But this is back to the philosophical discussion that Kay Dee dealt with nicely.

Simon M

 

[Akimbo]

... But not having that suport is not going to stop some of them (us) from exploring in remote regions just 'cause they don't have that support.

You say you coose to only dive when a chamber is max an hour away, others choose not to operate under that constraint. Its their choice.

Simple as that, and nothing wrong with that IMO, as long as one accepts the risks involved...

I never meant to imply that "wrong" was the issue. The issue is divers are doing it... individual risk decision are just that. Since people do it and will get bent the question becomes what to do about it?

I am pleased that the diving community has evolved past the NEVER DO IT hysteria that prevailed just a few years ago, but there is still a long way to go. The Navy Manual is the most vetted guideline we have for chamber treatment and they follow the logical guideline of drop to 60' on O2, which is pretty safe in a chamber given a qualified inside tender, and evaluate symptoms. Tables 6a and the super-rare Table 4 (no O2) are available that take you to 165' when symptoms persist. Table 8 is even more rarely used takes you to 225' but is available, mostly for omitted decompression from deeper dives. The ultimate treatment option is to just go to a saturation decompression schedule... if you have the facilities and endurance to pull it off.

I'll use the term expedition diver, but it is really anyone diving great distances from a chamber that wants to plan for the worst yet stay within their means. I think of the recently accepted IWR protocols a lot like Table 5 and 6 for chambers... they will work most of the time and are the go-to first option. However unlike some, I am not willing to just give up when it doesn't work.

Just because I try not to get deeper into decompression than about half a hour unless there is a chamber nearby doesn't mean that I won't get bent. Entrapment and omitted decompression are always lurking and I know that people I dive with will do whatever it takes to help save my sorry butt unless I die on them first.

So, here I am at about 30' on a FFM sucking Oxygen. That beats sitting on deck sucking O2 but is a lot more dangerous, especially if I had stoke instead, or maybe in addition to, DCS. Either way it is my best guess that I'm bent. 10-15 minutes goes by and I believe it isn't improving and maybe getting worse. Now what?

I might just stay there if it was my third day doing 4 dives/day to less than 130'. I would be thinking really hard about going deeper, if my leg went limp after a 220' jump. It basically becomes a personal decision. I've spent enough time in FFMs to believe I would stand a decent chance of recovering from a convulsion (with an air bailout and tender on air).

... Read the quote from our pending paper again...

Yep, I did. It is a very small sample for deeper exposures but encouraging. You must consider at least a dozen cases that I know of where symptoms didn't resolve at 60' on O2 or 165' on air from HeO2 bounce dives and those divers are permanently disabled or dead. Yes, hundreds fully recovered, but that isn't much consolation when you are the unfortunate one going home in a bag.

There are lots of incident reports where combat swimmers had to hit or exceed 60' on O2 rebreathers and didn't convulse, and far more that aren't reported. If I were personally serious about expedition diving with limited means my first priority would be to work on survivability of convulsions and bias my IWR strategy to DCS treatments with a vast body of evidence that works the great percentage of the time... like 60' on O2.

 

[cerich]

Ya'all are talking like oxygen is the only viable treatment for dcs...oxygen is just a better gas in some circumstances. Pressure is a treatment by and itself. My gut is telling me that getting some depth, even on air then on getting shallow start pushing the PPO2 ...just my gut here..based on a bit of experience.

Iwr really is a window of possible mitagation depending on the symptons, a truly screwed up diver is truly screwed anyhow sans a chamber on site.
My 2psi. I may be off base and gotten lucky in the past

Hello Akimbo,



Given the hilarious body bag reference I'm not entirely sure how serious you are about this, or the degree to which you are conflating the typical tech diving world with the commercial diving environment that you obviously inhabit. On a subject like this we should probably not discuss them together because there is little practical point in doing so, and it may create confusion about what is acceptable in the tech diving world.

So, in relation to tech diving there is nothing that would justify taking an immersed diver to 2.8ATA breathing 100% oxygen. I don't care how serious the DCS, how provocative the dive, or about any other rationalisation someone might come up with. And for the record, as someone who has inhabited your world and still provides related advice, I would not recommend it for well-equipped commercial divers either (and as you point out, most of them have chambers anyway). The marginal benefit of going beyond ~9 - 10m is dubious (see below), and the danger (see my earlier post above) is just too great (more than 50% of people are likely to develop symptoms of oxygen toxicity).

Advocacy for an immersed Table 5 appears predicated on an assumption that compression to 2.8 ATA will almost certainly improve clinical outcome. In fact, the advantage in efficacy of going beyond 10m is likely to be relatively small. David Doolette and I wrote a review on IWR for the UHMS Precourse on field management of DCS held in Florida 6 weeks ago, This is a short relevant extract:

Since the introduction of the U.S. Navy Treatment Tables 5 and 6,21 treatment tables which begin oxygen breathing at 60 fsw (18 msw) have become the standard of care, and there has been essentially no experimentation with shallower initial HBO treatment of DCS at shallower depths of for shorter durations. However, the development of these minimal pressure oxygen breathing tables included testing both 33 fsw and 60 fsw treatment depths and relatively short durations of HBO. The “provisional” protocol for the treatment of DCS was to compress divers breathing oxygen to 33 fsw, and if complete relief of symptoms occurred within 10 minutes at 33 fsw, oxygen breathing was continued at this depth for 30 minutes after relief of symptoms and during 1 fsw/min decompression to the surface. If relief was not complete within 10 minutes at 33 fsw, divers were compressed to 60 fsw. If complete relief of symptoms occurred within 10 minutes at 60 fsw, oxygen breathing was continued at this depth for 30 minutes and during 1 fsw/min decompression to the surface. Goodman and Workman tabulate 31 shallow recompression treatments that generally followed these rules:21 27 at 33 fsw, three at 30 fsw and one at 20 fsw. Seven treatments had longer time at maximum depth than specified above. Excluding one 26-hour treatment, the total treatment times ranged from 35 to 180 minutes (mean 70 minutes). DCI signs and symptoms treated at 33 fsw or shallower (number of treatments) included pain (26), special senses (6), rash (5), sensory (3), chokes (3), syncope (3), motor weakness / paralysis (3), loss of consciousness (1), and nausea and vomiting (1). Being largely treatments for experimental dives, the delay to recompression was relatively short, with a median of 37 minutes (range 0–270 minutes). It is perhaps pertinent that many of the inciting dives were non-trivial, including trimix bounce decompression dives to 200–400 fsw and no-decompression drop-out from shallow 12-hour subsaturation and repetitive air decompression dives to a maximum of 255 fsw. Twenty five of 31 shallow treatments resulted in complete relief. Two treatments resulted in substantial relief; in one case the residuals are reported to have resolved spontaneously over three days. Four treatments were followed by recurrence of symptoms; in three cases complete relief was reported following a second treatment.

So, outcomes, were fairy good with compression to only 33 fsw, especially when it is considered that the manifestations had to resolve within 10 minutes or the treatment would be escalated.

Hope you find this interesting.

Simon M

Reference:
Goodman MW, Workman RD. Minimal-recompression, oxygen-breathing approach to treatment of decompression sickness in divers and aviators. Research Report. Washington DC: Navy Experimental Diving Unit; 1965 Nov. 40 p. Report No.: NEDU TR 5-65.

 

[Dr Simon Mitchell]

Hello again Akimbo,

So, here I am at about 30' on a FFM sucking Oxygen. That beats sitting on deck sucking O2 but is a lot more dangerous, especially if I had stoke instead, or maybe in addition to, DCS. Either way it is my best guess that I'm bent. 10-15 minutes goes by and I believe it isn't improving and maybe getting worse. Now what?

Stay where you are. That is the safest option.

I might just stay there if it was my third day doing 4 dives/day to less than 130'. I would be thinking really hard about going deeper, if my leg went limp after a 220' jump. It basically becomes a personal decision.

I agree. Every action is personal decision. You can do whatever you like. But we are having a conversation on a public website about different perspectives on a safety-critical issue that might influence other divers' "personal decisions". Discussions of this nature are exactly what these sites are for of course. But this one (on the medical forum) has been running long enough for it to become clear that you appear to be endorsing diving medical practice that is considered overtly dangerous by two of the medical moderators; one a representative of the USA's premier diving medicine unit, and the other an extremely experienced diving physician who is currently leading a panel of international diving medicine experts reviewing this exact issue. As a commercial diver that should give you food for thought.

I've spent enough time in FFMs to believe I would stand a decent chance of recovering from a convulsion (with an air bailout and tender on air).

This may well be true, but it is not sufficiently generalizable. You are conflating your personal world with the wider technical diving world, again.

Yep, I did. It is a very small sample for deeper exposures but encouraging. You must consider least a dozen cases that I know of where symptoms didn't resolve at 60' on O2 or 165' on air from HeO2 bounce dives and those divers are permanently disabled or dead.

You are kind of making my point for me. 60' does not always work. And there is certainly not enough evidence of an incremental benefit for 60' if 30' is not working for me to endorse escalating an IWR oxygen exposure to 60' with the associated high risk of an oxygen toxic seizure.

There are lots of incident reports where combat swimmers had to hit or exceed 60' on O2 rebreathers and didn't convulse, and far more that aren't reported.

This anecdote is entirely compatible with the data I cited in an earlier post. Not everyone has a seizure. But as demonstrated by the hard data I cited there are plenty who do.

If I were personally serious about expedition diving with limited means my first priority would be to work on survivability of convulsions and bias my IWR strategy to DCS treatments with a vast body of evidence that works the great percentage of the time... like 60' on O2.

Actually, that "vast body of evidence" you refer to is just experience at one treatment pressure. There are no studies that establish 2.8ATA of oxygen as the optimal dose. We do it in a chamber where seizures are almost invariably benign, but in water - no way. In addition, that "vast body of evidence" comes almost exclusively from use of a Table 6, often with extensions, for the more serious cases that you are most concerned about. If you are going to cite "the vast body of evidence that works the great percentage of the time" in support of your dangerous suggestion to conduct IWR at 2.8ATA, then are you going to conduct a Table 6?, with extensions? If not, how do you know that the choice you are advocating will make sufficient difference to outcome to justify the risk?

You are over-estimating the likely benefit of 60' vs 30' in water, and completely underestimating the risks for members of the general technical diving community who might attempt it.

Simon M

 

[Akimbo]

Ya'all are talking like oxygen is the only viable treatment for dcs...oxygen is just a better gas in some circumstances.

Agreed, but O2 is the only gas where any idiot diver can be sure that every tissue in the body is not taking on more diluent, which can make matters worse later even when full relief of symptoms is achieved at depth. Perhaps more importantly, higher ppO2s removes diluent from the blood stream much faster, which is likely to restore blood flow faster.

As explained to me by Navy Diving docs during long night watches over decompressing sat teams, "it is complicated". Simple physics says that the greatest advantage of bubble compression occurs at shallower depths (no news to you) so returning to the max depth of the dive is rarely justified for treatment. Doppler was pretty new then but the simple minded description for sailors was to think of a log jam in the blood stream. Removing half the logs, or reducing the log volume by compressing to 33', will often restore flow. Reducing to a third (or 2.8 at 60') is even better, but not as effective as the first 33'.

Really high ppO2 actually removes the diluent gas "logs" from the river and pure O2 makes sure that no logs are being added. Yes it also drives the diluent gas into solution, which is where the log jam analogy falls apart, but that doesn’t negate the problem of getting it out without re-forming log jams on ascent.

That is why treatment tables to 60' have made Table 6a, 4, and 8 rarely used. The only major fly in the IWR ointment is convulsion... besides misdiagnosing DCS for a heart attack or stroke.

 

[Dr Simon Mitchell]

Pressure is a treatment by and itself. My gut is telling me that getting some depth, even on air then on getting shallow start pushing the PPO2 ...just my gut here..based on a bit of experience.

Hello cerich,

IWR on air was considered in our review. I have already broken the publishing rules by pasting a segment of it earlier, and I can`t reproduce any more. Suffice to say there is limited evidence to suggest that air is not as effective as oxygen for IWR and Akimbo has provided some mechanistic discussion above. There are stories of it having appeared to work, but also some disasters too.

Simon M

 

[Akimbo]

Actually, that "vast body of evidence" you refer to is just experience at one treatment pressure. There are no studies that establish 2.8ATA of oxygen as the optimal dose.

No debate, but it is the only significant body of evidence we have. Like I wrote earlier, the Navy settled on 60' instead of 66' because of low precision of depth gauges on fleet chambers rather than physiology thresholds for OxTox. Data was slow to develop in the last 60 years because even the Navy didn't bend divers intentionally to test tables. Early mixed gas table development and the fleet gave them the secondary opportunity to test and verify treatment tables. Unfortunately the ability to accumulate a significant body of evidence for 25-30' efficacy will take a very long time.

You are over-estimating the likely benefit of 60' vs 30' in water, and completely underestimating the risks for members of the general technical diving community who might attempt it.

Not really, I am asking the question "what to do when it doesn't work", just like the treatment decision matrix does with Table 5 in a chamber.

You are over-estimating the likely benefit of 60' vs 30' in water, and completely underestimating the risks for members of the general technical diving community who might attempt it.

Perhaps, but we do know that increasing the ppO2 by almost 5x (pure O2 on deck) is not as effective as about 8.3-9x or we wouldn't be talking about the new IWR protocols at all... which were nearly universally condemned a short time ago. I don't think that 13.3x at 60' will go away. We can wait generations to compile enough data to answer that question or we can simultaneously investigate in-water convulsion management, especially since convulsions are still a problem at 25'. Yes, that is an engineer's approach, but it must be important or FFMs would not be part of the IWR kit at all.