In-Water Recompression, Revisited

[Akimbo]

I'm not sure how you'd simulate that

The working theory was you don't want to blow chucks in the mask or hat since you only have one regulator and you are in deep trouble if you aspirate even a small bit with stomach acid. It is actually pretty easy in the Kirby-Morgan Band Masks because the seals are super wide and soft. You usually have a little warning so you keep your hands poised on the mask, look down, lift the mask off your mouth, blow bits, and pull the mask on with the freeflow running. It's not hard to simulate if you think about it... just exhale as fast as you can.

You really need to keep thinking "block your airway until you mask is on" since the reflex is to immediately inhale after projectile vomiting. Substitute purge button for free-flow valve on a recreational FFM. You need to experiment though. The band masks are forgiving enough that you don't need to loosen the spider, but you might need to on an AGA style mask... especially if you are cinched down enough to keep in on during convulsions. You also want to simulate a convulsion in the water so you can see what it takes to keep the FFM on.

You also need to practice removing and replacing the mask in case you didn't manage to anticipate; yet somehow was able to gracefully recover. We used a handful of course sawdust to simulate. Start by standing in a 4' deep pool before progressing to the deep end.

I've seen lots of convulsions,...

I know we discussed this before but I can't remember the details. Were they all experienced divers or were some HBOT patients? I wonder if there is some kind of acclimation component that explains our different experiences? I tended to assume it was the vigilance of the team. We probably got tunnel vision and twitching more than any of the other VENTDIC symptoms... except we mostly ignored the "I" (for irritability). Most were cranky when they got off the chopper.

You or someone else mentioned that O2 runs are no longer used to qualify military and commercial divers like it was in my day. Can you fill in the blanks?

 

[Dr Simon Mitchell]

Nope, definitely what I would do and the evolution of how I would deal with worsening situations.

Fair enough. So long as we are crystal clear that, for very good reason, technical divers should not be conducting IWR at 2.8 ATA on oxygen.

How are you addressing convulsion management beyond just saying use an FFM? From personal experience, I submit that recreational FFM training is not nearly enough for IWR.

The vast majority of technical divers will not have had even recreational FFM training, and they should not be using a FFM for the first time with no training in the context of an emergency procedure in a compromised state. Those who have an FFM and training should use an FFM. Others should use a properly designed mouthpiece retaining device like the Drager gag strap.

The biggest risk isn't convulsion; it is barfing in the mask and not knowing how to deal with it.etc

Once again, we are straying into territory where what works / may be appropriate in the commercial diving environment is being confused with what is pragmatic and safe in the recreational environment.

If a recreational technical diver undergoing IWR is vomiting they should not be in the water. There is too high a risk of aspiration and drowning, and as you point out the vomiting may be due to oxygen toxicity and the next event may be a convulsion. Vomiting prior to entering the water is a contraindication to IWR. Vomiting in the water is an indication for terminating the procedure, surfacing, remaining on surface oxygen and evacuating.

Similarly, no attempt should be made to manage a convulsion in the water. If a convulsion occurs, the diver should be brought to the surface.

The diver has to made acutely aware of all OxTox symptoms because their in-water tender can't see many of them like they could in a chamber. They also need a Jon-line so they can float effortlessly and MUST be trained to breathe very deeply and slowly to manage CO2, which is worse in a FFM and is believed to exacerbate OxTox.

Agreed.

someone else mentioned that O2 runs are no longer used to qualify military and commercial divers like it was in my day. Can you fill in the blanks?

Oxygen tolerance tests used to be a part of military diver selection processes, until they figured out that the test had no validity; in no small part because the principle risk factor (which you mention above) that most likely characterises an individual's risk is carbon dioxide retention, and carbon dioxide retention could not be factored into the old oxygen tolerance tests. When this was realised, attention shifted to testing individual diver's ventilation response to rising CO2 but this has also been abandoned pretty much everywhere (to my knowledge). Divers are not stupid and caught on to what the test was about. They would hyperventilate intentionally right from the start just to pass the test. In addition it is very difficult to replicate all the real-world contributory factors to CO2 retention (dense gas, immersion, resistance of UBA, exercise) in a single test protocol. When we finally get an accurate end tidal CO2 monitor in rebreathers, and data logging throughout dives, I suspect there will be renewed interest in this.

Simon M

 

[Dr Simon Mitchell]

My point regards air was actually along the lines of what Akimbo talked about regards mechanics..

I wonder if taking advantage of a deep drop on air followed by the more shallow high PPO2 I as per the study may have some benefits ..in consideration of the mechanical stuff that Akimbo mused about.

This has certainly been a part of some protocols such as the "Hawaiian method" that Richard Pyle has used. [1] There is a theoretical advantage in compressing bubbles further, and perhaps encourage obstructing bubbles in the vascular tree to redistribute into the venous system.

However, if tissue bubbles are the problem, then they will just re-expand when the diver returns to shallower depths to use oxygen, and in the meantime the diver will have absorbed more inert gas. Moreover, the use of a deep air spike adds complexity to the procedure. Complexity is something we want to minimise in the context of a high stress emergency situation. To your point below, if the diver becomes more compromised in the early phase of IWR and we have taken them to 100', then we are much further from the surface, and facing a long rapid ascent if things become unmanageable quickly. For these reasons our contemporary recommendations will be to follow a simple 100% oxygen protocol at a maximum depth of 30' such as the Australian or French methods. [2,3] In this setting if something goes wrong at any time the diver has absorbed no inert gas, you are close to the surface, and a rapid ascent is much less likely to be harmful.

There are times when IWR even when planned out and prepared for won't be an option. The "patient" is simply going to be too afflicted. (A very recent Doria death springs to mind, from reports I have heard iwr or even a chamber on site would likely have not made much of a outcome difference)

Absolutely. And the patient's condition may change rapidly (in either direction) early in the course of IWR, which is why IWR plans need to be compatible with a rapid exit strategy and why deep air spikes have significant risks. I think there is a perception among divers that "if we can just recompress then everything will start to get better". This is sometimes true, but there are times when it is not. I have seen even rapidly instituted Table 6 or Comex 30 protocols (the latter a 4ATA treatment) fail to control rapidly evolving symptoms, and all experienced diving physicians will have seen divers deteriorate despite recompression.

1. Mitchell SJ, Pyle R, Moon RE. Therapy for decompression illness. In: Vann RD, Mitchell SJ, Denoble PJ, Anthony TG (eds). Technical Diving. Proceedings of the Divers Alert Network 2008 January 18-19 Conference. Durham NC, Divers Alert Network, 178-203, (ISBN 978 1 930536 53 1), 2009

2. Edmonds C. Pearls from the deep. A study of Australian pearl diving 1988-1991. SPUMS J 1996;26 Suppl:26-30.

3. Blatteau JE, Pontier JM, Buzzacott P, Lambrechts K, Nguyen VM, Cavenel P et al. Prevention and treatment of decompression sickness using training and in-water recompression among fisherman divers in Vietnam. Inj Prev 2016;22:25-32.

 

[Akimbo]

... Drager gag strap <snip> Similarly, no attempt should be made to manage a convulsion in the water. If a convulsion occurs, the diver should be brought to the surface...

I don't understand, why are you using a gag strap? My experiments indicated it was useful when the diver is marginally conscious but not totally blacked out. Also, how do you manage the airway before surfacing when they are convulsing?

If a recreational technical diver undergoing IWR is vomiting they should not be in the water.

I totally agree, but my comments related to OxTox symptoms that develop during treatment rather than before leaving the deck. People who are compromised, stressed, and spend long periods moving in a swell often get sea sick even after they have their sea legs (so to speak).

The vast majority of technical divers will not have had even recreational FFM training...

I'm confused. What is involved in your prep beyond someone on deck with an IWR table, a timer, and some O2 stage bottles?

 

[Dr Simon Mitchell]

I don't understand, why are you using a gag strap? My experiments indicated it was useful when the diver is marginally conscious but not totally blacked out. Also, how do you manage the airway before surfacing when they are convulsing?

The gag strap is used to retain the mouthpiece and protect the airway in the event of loss of consciousness. The efficacy of the gag strap for this purpose can be inferred from a series of 54 loss of consciousness events published by the French Navy. [1] Of these 54 cases there were only 3 drownings, so the gag strap seems effective. I am not aware of any published experiments that discriminate a difference in gag strap efficacy between semi- and fully unconscious states. If you published your work anywhere, please provide a reference.

In a convulsion, if the mouthpiece is retained, the rescuer waits until the convulsion has ceased and then immediately brings the victim to the surface. If the mouthpiece is not retained, the rescuer brings the victim to the surface during the convulsion per the UHMS recommendations. [2]

I totally agree, but my comments related to OxTox symptoms that develop during treatment rather than before leaving the deck. People who are compromised, stressed, and spend long periods moving in a swell often get sea sick even after they have their sea legs (so to speak).

If oxygen toxicity symptoms of any sort develop during IWR then the treatment should be abandoned immediately.

I'm confused. What is involved in your prep beyond someone on deck with an IWR table, a timer, and some O2 stage bottles?

Off the top of my head:

Preferably specific training in IWR eg per the IANTD course.
Everyone involved (surface person, victim, diver accompanying victim) trained to minimum of decompression procedures using oxygen
FFM (if trained) or Drager gag strap
Stage, bars, platform with tether of some sort
Victim consents, and has no contraindications to IWR
Sufficient oxygen and means of delivery
Thermal considerations (tick)
Environmental considerations (tick)
Australian or French or USN protocol.
Contact diving medical authority to discuss diver disposition during or immediately after IWR

Simon M

1. Gemmp E, Louge P, Blatteau J-E, Hugon M. Descriptive epidemiology of 153 diving injuries with rebreathers among French military divers from 1979 to 2009. Mil Med 2011;176;446-452.

2. Mitchell SJ, Bennett MH, Bird N, Doolette DJ, Hobbs GW, Kay E, Moon RE, Neuman TS, Vann RD, Walker R, Wyatt HA. Recommendations for rescue of a submerged unconscious compressed gas diver. Undersea Hyperbaric Med 2012;39:1099-1108.

 

[northernone]

As a chamber operator living far from a chamber I am heartedly enjoying this dialogue. Thank you all for putting this discussion into a forum.

Warm regards,
Cameron

 

[Akimbo]

If you published your work anywhere, please provide a reference.

Nope, private report under contract. I doubt I even have a copy. The French Navy data is consistent with our findings since total loss of consciousness in combat swimmers is rare, typically slow hypoxia or and/or hypercarbia. We were looking at sudden anoxia and electrocution inside hyperbaric welding habitats charged with inert gas.

The electrocution simulation, which would be violent like a convulsion, was not effective keeping the mouthpiece in place. It may be better in the water but I doubt it. We stopped testing after subjects (including me) were allowed to fall asleep with a gag-strap and nose clip. The seal was lost to the point that the demand regulators (supply and exhaust) didn’t activate. We rearranged some umbilical systems which negated the short-term usefulness of a mouthpiece.

Side Bar: probaby not something tech divers will see but interesting
Anoxic (0.02 ppO2 or less) blackout is interesting if you haven't had the opportunity to experience or witness it. Just about every system shuts down instantly... like before you complete a inhalation. It happened to me during system pre-dive checks when the lines weren't completely purged of deep-mix. Fortunately I followed protocol by not strapping the BIBS mask on. I woke up some unknown period of time later, lying on the deck plate, a knot in the back of my head, drool running down my cheek, and no idea how I got there. I couldn’t have been out that long because I wasn't cyanotic.

A yard worker was climbing into a top-mount bell and fell back to the transfer lock deck plates. His head barely got past the hatch seal. A slow helium leak filled the bell. We started installing O2 analyzers that could be seen from the transfer lock because of that. There are several cases of yard workers that blacked out and one who died under similar circumstances.

 

[Dr Simon Mitchell]

The French Navy data is consistent with our findings since total loss of consciousness in combat swimmers is rare, typically slow hypoxia or and/or hypercarbia.

Actually, as far as I can tell about half of the LoC events in the French study were due to seizures. I can send you the paper if you want. I don't agree that the French results are confluent with yours because you are saying that the retaining device did not work well, and their data infers that it did - at least well enough for the buddy to rescue the diver to the surface without incident in the vast majority of cases. The presence of a buddy and immediate rescue to the surface if a seizure occurs are key aspects of the practice of IWR by recreational divers.

Parenthetically, this discussion speaks to the importance of minimizing the risk of seizures as far as practicable in the first place; hence the maximum depth of 30'. There is still a risk, but it is far smaller than at 60'.

The electrocution simulation, which would be violent like a convulsion, was not effective keeping the mouthpiece in place.

With all due respect, in the absence of a formal report of the methodology it is hard to assess the relevance of your observation to the use of properly designed mouthpiece retaining devices by divers in IWR. For example, I am not sure exactly how you would confidently achieve high fidelity simulation of the airway-relevant aspects of electrocution in a human, and even if you could, how confident you could be that this produces events similar to those of an oxygen seizure. You do not specify what mouthpiece retaining device you used.

Simon M

 

[Duke Dive Medicine]

My point regards air was actually along the lines of what Akimbo talked about regards mechanics..
First, I think it's important to consider when IWR is being considered. For some expeditions it's "part of the plan" and they will have stuff life a ffm and gas planned and available. That may fall inside their risk acceptable. Others, if budget allows may go flexdec. Most seem to go with a prayer however and a irrational faith that between DAN and the local whoever will come thru.
There are times when IWR even when planned out and prepared for won't be an option. The "patient" is simply going to be too afflicted. (A very recent Doria death springs to mind, from reports I have heard iwr or even a chamber on site would likely have not made much of a outcome difference)
I wonder if taking advantage of a deep drop on air followed by the more shallow high PPO2 I as per the study may have some benefits ..in consideration of the mechanical stuff that Akimbo mused about.

Hi cerich,

If IWR is a consideration on a dive series or expedition, it should always be pre-planned. It should never be an afterthought. I concur (and it's been sprinkled throughout the thread) that there are times when a diver will be so severely afflicted that IWR is not an option.

Re the deep air spike, it's been explained previously why that is inadvisable. To reiterate, the diver is farther from the surface, likely colder, possibly hypercapnic, and will probably be taking up inert gas rather than eliminating it, which will ultimately contribute to bubble growth and further harm. IWR is not equivalent to hyperbaric chamber treatment, and so the same theories do not apply. The idea of going deeper comes from, among other things, the Navy protocol for hyperbaric chamber treatment of severe DCS symptoms that don't resolve at 60 feet. This is extremely rare to begin with, but also, if performed, takes place in the controlled environment of a hyperbaric chamber.

Best regards,
DDM

 

[Duke Dive Medicine]

The working theory was you don't want to blow chucks in the mask or hat since you only have one regulator and you are in deep trouble if you aspirate even a small bit with stomach acid. It is actually pretty easy in the Kirby-Morgan Band Masks because the seals are super wide and soft. You usually have a little warning so you keep your hands poised on the mask, look down, lift the mask off your mouth, blow bits, and pull the mask on with the freeflow running. It's not hard to simulate if you think about it... just exhale as fast as you can.

You really need to keep thinking "block your airway until you mask is on" since the reflex is to immediately inhale after projectile vomiting. Substitute purge button for free-flow valve on a recreational FFM. You need to experiment though. The band masks are forgiving enough that you don't need to loosen the spider, but you might need to on an AGA style mask... especially if you are cinched down enough to keep in on during convulsions. You also want to simulate a convulsion in the water so you can see what it takes to keep the FFM on.

You also need to practice removing and replacing the mask in case you didn't manage to anticipate; yet somehow was able to gracefully recover. We used a handful of course sawdust to simulate. Start by standing in a 4' deep pool before progressing to the deep end.



I know we discussed this before but I can't remember the details. Were they all experienced divers or were some HBOT patients? I wonder if there is some kind of acclimation component that explains our different experiences? I tended to assume it was the vigilance of the team. We probably got tunnel vision and twitching more than any of the other VENTDIC symptoms... except we mostly ignored the "I" (for irritability). Most were cranky when they got off the chopper.

You or someone else mentioned that O2 runs are no longer used to qualify military and commercial divers like it was in my day. Can you fill in the blanks?

Thanks, I know the theory, just haven't seen it done. In the Navy the only masks we were taught ditch-and-don procedures for were the Jack Browne (early on) and AGA after it came into the fleet. At the College of Oceaneering we taught the commercial students to ditch-and-don Superlites, KMB-18s and Miller hats. That goes way beyond the scope of IWR for tech diving expeditions and gets more into commercial/military work.

All the O2 hits I've seen have been in the chamber. I've never seen one in the water column. Re the O2 runs, the Navy eliminated that requirement some years ago with the rationale that individual vulnerability to O2 toxicity is highly variable.

Best regards,
DDM