DCS hit during final stop? Has it ever happened?

[kekenned]

@Duke Dive Medicine it was interesting to read your criteria for whether or not to stay below when bent in-water. I honestly can't say what would have been better for me. I had plenty of 50% left to do extra deco, but no O2 stage.

Also, I felt in control when I was underwater, but once I got to the surface I was not in a position to manage my dive gear any longer. Perhaps if I'd stayed under, I would have been much less bent when I surfaced. Alternately, perhaps I would have deteriorated and then been in a position where I was underwater and unable to manage myself and my equipment. When I surfaced, I very quickly got to the point where, for example, I couldn't find my waist belt or my face. When I tried to take my mask off and managed to get my hand on it, I then confusedly thought my hand on my own mask was actually my instructor's hand... Not exactly optimal.

Is it difficult to predict whether in-water DCS will get significantly worse if you extend deco? Or are symptoms likely to remain fairly stable if you, say, go back down to 20' from 17' where symptoms started and just hang out for a while?

 

[ginti]

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.

What kind of visual migraines did you have? Aura? Aura (symptom) - Wikipedia

 

[Duke Dive Medicine]

@Duke Dive Medicine it was interesting to read your criteria for whether or not to stay below when bent in-water. I honestly can't say what would have been better for me. I had plenty of 50% left to do extra deco, but no O2 stage.

Also, I felt in control when I was underwater, but once I got to the surface I was not in a position to manage my dive gear any longer. Perhaps if I'd stayed under, I would have been much less bent when I surfaced. Alternately, perhaps I would have deteriorated and then been in a position where I was underwater and unable to manage myself and my equipment. When I surfaced, I very quickly got to the point where, for example, I couldn't find my waist belt or my face. When I tried to take my mask off and managed to get my hand on it, I then confusedly thought my hand on my own mask was actually my instructor's hand... Not exactly optimal.

Is it difficult to predict whether in-water DCS will get significantly worse if you extend deco? Or are symptoms likely to remain fairly stable if you, say, go back down to 20' from 17' where symptoms started and just hang out for a while?

@kekenned I can't take credit for those criteria, I just copied and pasted them from the Navy Diving Manual.

It's difficult to predict the course of DCS since the cases are so individual and there are a lot of things about it that have yet to be understood. Re the choice to surface, there's some physics involved. Abdominal and chest pain in DCS are considered serious symptoms. If they happen while still on decompression, it's pretty ominous and indicates that you already had a significant bubble load before you even surfaced, which means that something could have gone awry with your decompression process. Surfacing immediately (assuming you were at 20 fsw) would have increased the bubble volume by 60%, which is probably what led to the severe neurological symptoms that you experienced.

You already know this as a tech diver, but for general readership: again assuming you were at 20 feet (1.6 atmospheres absolute), the inspired partial pressure of nitrogen in 50/50 would be 0.8 ata, which is just slightly higher than that in ambient air on the surface. The partial pressure of oxygen would also be 0.8 ata, which is almost four times that in surface air. It would not be the same as breathing 80% O2 on the surface (roughly the amount you'd get from a non-rebreather O2 mask) since the inspired partial pressure of nitrogen in that instance would be roughly 0.2 ata. Still, considering that you were breathing a hyperoxic mix, it would have been reasonable to either remain at the depth you were at or descend slightly to see if the symptoms resolved, then stay down for as long as you could, as long as your symptoms remained stable or were improving. If you found that your symptoms were worsening, you may have been better off surfacing and calling for help immediately.

I'm curious to know how large your PFO was and whether you shunted at rest. Did they do an echo after the procedure to see if you were still shunting? Also out of curiosity, what deco algorithm were you using, did you change the gradient factors (if the algorithm used them) from the default setting, and if so, what did you change them to?

Best regards,
DDM

 

[MaxTorque]

Wow, it's good to hear some real world a stories and also good that those involved managed to come out of those situations ok!

It's going to be hugely situation dependant but it sounds like if you feel some early symptoms in-water, then gas supply and back-up team allowing, staying in the water is a sensible option, at least in the short term? I guess i wouldn't want to be alone in the water at this point, and having a hang line or fixed deco point is going to make a huge difference to the risks involved in extending your shallow deco plan!

 

[Wibble]

Wow, it's good to hear some real world a stories and also good that those involved managed to come out of those situations ok!

It's going to be hugely situation dependant but it sounds like if you feel some early symptoms in-water, then gas supply and back-up team allowing, staying in the water is a sensible option, at least in the short term? I guess i wouldn't want to be alone in the water at this point, and having a hang line or fixed deco point is going to make a huge difference to the risks involved in extending your shallow deco plan!

Use a Surface Marker Buoy on a spool or reel. It bounces around in front of you as your reference and acts as the boat's reference.

You can put up a second SMB on the same line -- e.g. small yellow one -- to alert the boat to you having problems (subject to you agreeing that protocol with the boat!).

 

[MaxTorque]

It makes sense for an open water dive to use to use the SMB to guage the sea conditions too i guess! Things can change quickly, and just because it was a mill pond when you stepped in an hour or so ago doesn't mean it is now......

 

[boulderjohn]

I think it happens more frequently than a lot of the medical community realizes

I think so, too. I imagine the vast majority of successful cases do not get reported.

It all depends, too, on how liberal you are with the definition. If you go to the Wikipedia page on this topic, you will see a nice list of the different formal protocols that can be used. Scroll to the bottom of the page and you will find this paragraph:

Although in-water recompression is widely regarded as risky, and to be avoided, there is increasing evidence that technical divers who surface and demonstrate mild DCS symptoms may often get back into the water and breathe pure oxygen at a depth 20 feet/6 meters for a period of time to seek to alleviate the symptoms. This trend is noted in paragraph 3.6.5 of DAN's 2008 accident report.[18] The report also notes that whilst the reported incidents showed very little success, "[w]e must recognize that these calls were mostly because the attempted IWR failed. In case the IWR were successful, [the] diver would not have called to report the event. Thus we do not know how often IWR may have been used successfully."
​

I have seen that done first hand, with great success. In such a case, if it were not successful, the diver would have headed off to a chamber, and we would know about it. As that quote from DAN indicates, you really only find out about an IWR case when it doesn't work, and so the success rate is poor. Even if it doesn't work, you can't really be sure it didn't work. If someone shows up at a chamber and gets treatment for mild DCS after IWR, how are we to know how serious the case might have been had there been no IWR?

 

[boulderjohn]

It's going to be hugely situation dependant but it sounds like if you feel some early symptoms in-water, then gas supply and back-up team allowing, staying in the water is a sensible option, at least in the short term?

If you have a computer that graphs tissue loading as you ascend, I suggest that at the end of some dive, you watch that graph as you head for the surface. The difference in those last few feet is astounding.

In the cases I mentioned seeing, the divers felt fine during their final deco stop, and then felt a problem in the last few feet or just as they surfaced. They then descended immediately to the depth of their stop with a buddy and breathed the oxygen they were already breathing until it was about gone, then went to the surface and felt fine. (They did not do any more diving after that.)

 

[kekenned]

@kekenned I'm curious to know how large your PFO was and whether you shunted at rest. Did they do an echo after the procedure to see if you were still shunting? Also out of curiosity, what deco algorithm were you using, did you change the gradient factors (if the algorithm used them) from the default setting, and if so, what did you change them to?

I think the major risk factor I left out earlier is that it was my second tech dive of the day, and the 5th day of a six-day class. The day before, we'd done three 100' ascents. Other possible risk factors: water temperature, being a bit overweight, dehydration. I've got an autoimmune disease and a bunch of steel in my ankle from a compound fracture, and I've always wondered if either of those contribute to DCS risk.

We used Deco Planner to plan the dives, set for Buhlmann with a gradient factor of 20/85. (I did go back after the fact and re-run the numbers with a gradient factor of 30/70 instead, and honestly it didn't make much of a difference.)

The dives were in freshwater, from a boat. The water was 46 F at depth and 70 F at 20'.

First dive: planned to 130' for 20 minutes of bottom time, using 21/35 and 50%. Gas switch at 70', 10 ft/min to 20', and 8 minutes of deco at 20', followed by 3 ft/min to the surface.

90 minute surface interval: I had an aura (large fuzzy blotches migrating across my visual field). We discussed it. It was not uncommon for me to get an aura, either diving or sitting around at home, so we decided to do the second dive. I didn't realize at the time that visual migraines were a DCS risk factor. (I'd asked the doctor who did my initial diving physical about my auras and diving, and he said not to worry about it.)

Second dive: planned to 140' for 20 minutes of bottom time, using 21/35 and 50%. We dipped down to 152' for a minute or two, and I also ended our bottom time several minutes early because I was feeling really tired. Gas switch at 70', 10 ft/min to 20', and 18 minutes of deco at 20', followed by 3 ft/min to the surface. My DCS symptoms started at 17', where I developed that sudden and bizarre-feeling chest and belly pain. At the surface, I had skin bends on my arms and the wild inner-ear DCS symptoms as described in my earlier post.

My instructor had his computer set for 20/85 (not gauge mode) for insurance, and it told him that we completed about 10 minutes of extra deco beyond what was required on the second dive.

As far as my PFO: the thing was a bear to find. I worked with Dr. James Holm in Hyperbarics at Virginia Mason, along with Dr. Gordon Kritzer as my interventional cardiologist. We did a TTE, didn't see bubbles at rest, and couldn't see what was going on during provocation because my lungs kept getting in the way. So we did a TEE, where they found a small resting PFO. My understanding was we were assuming it was passing quite a lot of bubbles when provoked but were just having trouble visualizing it. ("If it walks like a duck, and quacks like a duck...")

We did a TTE bubble study after closure twice with provocation and did not see a shunt -- I'd gotten a bit better at controlling my lung position during the TTE at this point.

Since closure, I've noticed some significant differences. I used to be unreasonably exhausted after every dive. I chalked it up to being a chronically ill person (I have celiac disease that is not fully resolved by a gluten free diet, and some other autoimmunity stuff). However, since my PFO closure I just... don't get tired like that after dives. Feel free to correct me if I'm wrong, but I can only assume I was basically constantly subclinically bent for my first 150 or so dives. Also, I used to get visual migraines on a fairly regular basis, and I haven't had a single one since the procedure in February.

 

[Wibble]

Since closure, I've noticed some significant differences. I used to be unreasonably exhausted after every dive. I chalked it up to being a chronically ill person (I have celiac disease that is not fully resolved by a gluten free diet, and some other autoimmunity stuff). However, since my PFO closure I just... don't get tired like that after dives. Feel free to correct me if I'm wrong, but I can only assume I was basically constantly subclinically bent for my first 150 or so dives. Also, I used to get visual migraines on a fairly regular basis, and I haven't had a single one since the procedure in February.

Just curious if the PFO closure's positively affected you out of the water? For example do you feel as if you've more stamina, less fatigue, etc. when you're just walking around?