DCS hit during final stop? Has it ever happened?

[dmaziuk]

DAN, Ross H, and the subsurface people (and I guess Suunto, Garmin and Shearwater) all have collections of dive data but without outcomes.

I'm pretty sure the subsurface cloud people are serious about not "having" it: merely hosting it.

 

[dirkhh]

I'm pretty sure the subsurface cloud people are serious about not "having" it: merely hosting it.

Well those people are me, myself, and I.
And you are correct, I don't access the data, there is zero analysis, aggregation, or anything else done.
The data belong to the individual users and aren't accessed or used in any way shape or form, other than making them available to that user.

 

[MultiDeco]

Another "thought experiment"!

Given that the vast majority of divers now use some form of dive computer, and given most DC's both log the dive and are able to push that info up to a internet connected PC, don't we already have a way of carrying out the worlds biggest deco study, effectively, almost for free?

At each surfacing event, the computer would pop up some "rating" quesitions, allowing the user to fill in their subjective thoughts on the deco performance and symptoms of DCS, and all that gets fed back to some server somewhere where the mother of all analysis algorythms tries to make sense of it all?

From 3m pool dives, to 300m world records, all the data, together? That would make the everyone a contributor to deco theory

This has been done once already. The DAN PDE program ran for 20 years, collecting data up to 2017. It took data from divers and dive computer profile logs, and demanded extensive post dive survey data on all aspects. This included 4 popular tech computers at the time.

DAN has data on deco models and stop depth choices and the success rates of each, but very little info has emerged from this study of interest for tech divers.

Divers who used our dive computer programs, contributed 6,970 reports to DAN PDE program. Many dive reports were serious deco dives, and they include dives with both VPM-B and a mix of ZHL + GF settings. Only two of those reports contained issues. database

 

[Duke Dive Medicine]

Agreed! This is the biggest issue with DeComp Science, that the varriables are, er, too varriable!

What set me off on this line of questioning was if there was an empirical evidence (rather than theoretical or model based) for the appearance of DCS below say 10m.

This i found interesting because the gas compression is an inverse exponential against depth, but gas consumption is broadly linear with depth.

For example:

at 5m, where ambient pressure is 1.5 bar(abs), gas volume is 66% of Surface Volume, and OC consumption is 150% of Surface Consumption

at 10m, where ambient pressure is 2 bar (abs) so gas volume is 50% of SV, and OC consumption is 200% of SC

at 20m, where ambient pressure is 3 bar (abs) so gas volume is 33% of SV, and OC consumption is 300% of SC


Assuming no surface hung/dropped air supply is available, then obviously the maximum amount of deco time on any given remaining gas is going to be longer the shallower you are.

At our 5m point above we are using 50% more air than on the boat, but our bubbles are (nominally) 44% smaller
At our 10m point, we are using 100% more air, and our bubbles are 50% smaller
At our 20m point, we are using 200% more air, and our bubbles are 66% smaller


So in a theoretical emergency situation, what is the best depth to stop at and use up ALL your remaining gas? The answer is as shallow as possible whilst juuust avoiding any symptoms of DCS !! Hence my initial question

At the risk of returning to the original question: yes, it's possible to suffer from decompression sickness while still in the water column, but it's rare and is an indicator of significant decompression stress. Ascending while bent just to maximize gas supply duration is probably not a good idea, since it would likely make symptoms worse.

Some organized tech agencies (e.g. WKPP) have protocols for managing in-water DCS, as do military and commercial diving organizations. The U.S. Navy's is in the U.S. Navy Diving Manual, revision 7, available for download on the Navy Supervisor of Salvage website. For discussion purposes only, the U. S. Navy's process for addressing in-water DCS for an electronically-controlled CCR diver is reproduced from Chapter 15 below.

"Decompression Sickness in the Water. Decompression sickness may develop in the water during EC-UBA diving. The symptoms of decompression sickness may be joint pain or may be more serious manifestations such as numbness, loss of muscular function, or vertigo.

Managing decompression sickness in the water will be difficult in the best of circumstances. Only general guidance can be presented here. Management decisions must be made on site, taking into account all known factors. The advice of a Undersea Medical Officer should be sought whenever possible.

Diver Remaining in Water. If prior to surfacing the diver signals that he has decompression sickness but feels that he can remain in the water:

1. Dispatch the standby diver to assist. Continue to decompress the other divers according to the original schedule.
   
   
2. Have the diver descend to the depth of relief of symptoms in 10-fsw increments, but no deeper than two increments (i.e., 20 fsw).
   
   
3. Compute a new decompression profile by multiplying all stops by 1.5. If recompression went deeper than the depth of the first stop on the original decompression schedule, use a stop time equal to 1.5 times the first stop in the original decompression schedule for the one or two stops deeper than the original first stop.
   
   
4. Ascend on the new profile.
   
   
5. Lengthen stops as needed to control symptoms.
   
   
6. Upon surfacing, transport the diver to the nearest appropriate chamber. If he is asymptomatic, treat on Treatment Table 5. If he is symptomatic, treat in accordance with the guidance given in Chapter 17.

Diver Leaving the Water. If the diver indicates that he has decompression sickness and feels he cannot safely remain in the water:

1. Surface the diver at a moderate rate (not to exceed 30 fsw/min).
   
   
2. Recompress the diver immediately at the closest available chamber and treat in accordance with the guidance given in Chapter 17."

Clearly, gas supply could become an issue with a protocol like this, especially in open-circuit apparatus. Other questions to think about:

Diagnosis. How certain is the diver that he/she has DCS? Vertigo can happen on ascent if one middle ear equalizes before the other. Partial facial paralysis can happen under the same circumstances. That old football injury could rear its head under pressure. The diver could be suffering from a medical event not related to decompression.

Depth. The deeper the hit, the more serious the event is, the more gas supply is a factor as you pointed out, and the less opportunity there is to maximize the inspired partial pressure of O2. For shallow hits where it's possible to breathe a hyperoxic mix, it would be reasonable for divers to use a gas that maximizes the inspired pO2, remaining mindful of safe limits and considering that they could be at higher risk of seizure if they have CNS symptoms.

Ambient conditions. Is it choppy? Cold? Dark? Would it be safer for the diver to decompress normally and then breathe O2 on the surface until he or she can get to a chamber?

Diver condition. How serious is the hit? Can he or she safely commit to an in-water protocol? Is there a buddy who can deploy to help the diver?

IWR. Is the team trained, experienced and equipped for IWR? If so, it may be reasonable to segue directly into it while the diver is still in the water.

(Obvious guy says) there are a lot of moving parts to this. If you're anticipating diving in conditions where this could be a possibility, it would be worth mitigating the risks as much as possible and getting the training and experience to deal with the circumstance should it arise.

Best regards,
DDM

 

[MaxTorque]

Thanks for that detailed reply! Interesting stuff, i guess there probably aren't many cases where IWR has actually done? (unless along way from any chamber where there may not be any other option)


I guess perhaps a short question that covers most of the points being made is:

If you are concerned you may be showing signs of DCS in-water, does it make more sense to do a longer stop at a shallower depth if you have a limiting gas supply?

For example, at a 10M stop you think you feel some DCS symptoms, by rising to 5m you could increase by 50% your potential in-water decompression time

 

[MaxTorque]

This has been done once already. The DAN PDE program ran for 20 years, collecting data up to 2017. It took data from divers and dive computer profile logs, and demanded extensive post dive survey data on all aspects. This included 4 popular tech computers at the time.

I wonder if this data has more value as time goes on as the ability to comuputational sift through it to find statistically meaningful patterns increases as AI gets better and better?

I guess the problem is that ultimately to find the limit, someone has to get bent. Back in 1920's that was almost certainly a lot easier to organise and justify than in 2021

 

[mc42]

What I've gathered from various IWR resources (and mentioned by DDM) is to descend to the depth where symptoms subside, which makes sense to me for helping reduce the pressure gradient and the bubbles. My personal priority would be getting the inert gas under control by descending, rather than ascending and extending the deco time, as the longer the DCS symptoms persist, the more damage is potentially being done.

Tempering my decision would be factors like thermal protection (being cold will slow off gassing anyway, so at some point you may as well surface), solo vs buddy diving, underwater and surface conditions, gas supply, availability of help on the boat or shore, and location of nearest chamber (the IWR might not help, so you're prolonging getting to a chamber and beginning proper treatment). As a tech diver, there's a good chance I'll have higher O2 (50% or 100%) with me, or a buddy, or nearby on the boat, so I'd consider staying down for a reasonable amount of time, as long as I felt OK and/or have a buddy check over me. But every situation is going to be dynamic.

 

[Duke Dive Medicine]

Thanks for that detailed reply! Interesting stuff, i guess there probably aren't many cases where IWR has actually done? (unless along way from any chamber where there may not be any other option)


I guess perhaps a short question that covers most of the points being made is:

If you are concerned you may be showing signs of DCS in-water, does it make more sense to do a longer stop at a shallower depth if you have a limiting gas supply?

For example, at a 10M stop you think you feel some DCS symptoms, by rising to 5m you could increase by 50% your potential in-water decompression time

You're most welcome! It would actually be interesting to find out how much IWR is being done. I think it happens more frequently than a lot of the medical community realizes. I've had a survey-based study on the back burner for a while.

Re your question, if a diver realizes that he/she has DCS at 10m, it would not be at all prudent to ascend to 5m right away just to be able to breathe for longer. Doing so could cause the symptoms to worsen significantly. On the other hand, if the diver is just shy of 6m when he/she first notices DCS symptoms and ascending to 6m would allow him/her to safely switch from 50/50 N2O2 to 100% O2, then an argument *could* be made for ascending slightly to make the switch. That's a soft call though.

Best regards,
DDM

 

[GJC]

I wonder if these guys have any data on the number of in water re compression that are actually done.

In-Water Recompression Provider

 

[kekenned]

Data point: I have gotten bent while in-water.

I was taking GUE Tech 1 and we were on our second experience dive. After we finished our final deco stop at 20' and started a 3 ft/min ascent, I felt this strong and bizarre pain in my chest and belly. This was only my second tech dive ever and so I was a bit overly goal-focused and also a bit confused. I thought, "Is it a suit squeeze? Can't be, I'm ascending..." The pain was a major task-load and all I could do was manage my 3 ft/min ascent and stay focused on my buddy; it didn't occur to me to consider signaling my buddy that I wanted to go back to 20' and hang out a bit longer. When we got to the surface, I felt okay for a bit while we were floating and waiting for the boat pick-up, but mentioned the weird pain to my instructor.

Then, very quickly, I was not okay. I couldn't figure out where my hands were in space. Also, they felt like they were made of static, or 4th of July sparklers -- like the most intense tingling you have ever felt. I indicated to my team that I needed help doffing my gear. I focused on keeping my face out of the water (and someone thankfully stuck a reg in my mouth) and managed to hold onto the side of the boat while my team removed my gear and pulled me in. I got on O2, DAN was called, and I was rushed to the chamber. At this point I couldn't really walk or see clearly due to lost proprioception and the world spinning around me like I was a piece of lint in a washing machine. It was diagnosed as an inner-ear hit and I did 5 days of chamber rides at the hospital, and another week or two of steroids until I could turn my head without blurring/dizziness. After a month, it was like nothing had ever happened.

Soon after the hit, I was diagnosed with a PFO which I've since had repaired. So far I've only been doing recreational dives, but my post-dive experience feels completely different now -- no more extreme exhaustion after every dive. Also, my visual migraines are totally gone as well. I'm looking forward to doing a little mini-Tech 1 refresher and finishing my last required class experience dive sometime this fall.