Question Deserved DCS hit even with deco cleared due to high exertion during the dive?

[Cragene]

Hello everyone,
This is my first thread on Scubaboard (had been a lurker for a long time now), and I wanted to discuss a potential case of DCS during a relatively shallow technical dive.
I am a 31-year-old beginner technical diver, with a total of about 200 dives since my certification; and I dive very often in lakes (about 2-3 times per week); during the dive I'll be describing here I had my first "real" experience of a potential DCS after the dive, even if I didn't do any major mistakes (no repetitive dives, no fast ascents, no deco ceiling violations, and so on).

The dive​

A couple of days ago I did a lake dive, using air as bottom gas and EAN50+Oxygen to accelerate deco, with a profile like this one:

• 10 minutes total for the slow descent to about 42 meters (140 feet)
• 20 minutes spent at 42 meters (140 ft)
• 10 minutes to ascent to 21 meters (68 ft); let's say that this is another 10 minutes spent at 30 meters
• switched to EAN50, then spent another 15 minutes at 18 meters (60 ft)
• 10 minutes of slow ascent to 6 meters (20 ft)
• switched to Oxygen, 12 minutes spent at 6 then 5 meters once the ceiling of 6 meters cleared
• short 2-minute extra stop on back gas (air) and slow ascent to surface (2 minutes to reach surface from 5 meters)

For a total dive time of 80 minutes, more or less.
Deco planned using GF 50/80; with the surfacing GF in the pilot compartment being about 68%.
My surface interval before the dive was exactly 92 hours (almost 4 days).

Now, for me, this is a moderately "deep" dive, but I also did several other dives deeper but with less total bottom time (like, 20 minutes at 55 meters (180 ft) or 25 minutes at 50 meters (165 ft)), and always used the same GF settings and surfaced with 70% or less of GF; without issues or strange symptoms.

Symptoms after the dive​

This time, after the dive I was ok, did a quick lunch, and went back home; during the ride home (about 2-3hours after the dive) I started to feel "strange", but at the beginning I blamed the sun (I ate outside during lunch and it was a very sunny day here), and the fact that I hadn't drank a lot of water.

Then, at home (now about 4 hours or less from the dive), I unloaded the doubles and deco tanks from my car and the other equipment, and after a bit started to feel unwell: a bit of dizziness, a general sense of nausea that lasted a couple of minutes, accelerated heart rate.
I then noticed also that I had swollen arms near the wrists (and the wristwatch I had on the left wrist was "compressing" the edema) but I had no itching, no bruises or rashes on the skin (not on the arms, body, back, or torso).

Got tested by a hyperbaric doctor​

I contacted the DAN emergency hotline, and they suggested to go get checked at my local hospital. Thankfully I live about 2km from a large hospital with a hyperbaric chamber available, so I immediately went to get checked and breathed Oxygen during the 10-minute drive.

Note: I also pointed out that I was already tested last year for a potential PFO (transcranial bubble test with just 1 bubble at rest and 3 bubbles after the Valsava maneuver, indicating a potential very small PFO). I got the results checked by a hyperbaric doctor who gave me the green light for technical dives (with no more than a single technical dive per day just for precaution, but this is what I would've already considered anyway)

They tested me with many different kinds of exams, and everything came back clean: ABGA, torso x-rays, standard blood tests, and neurological tests; in addition, I also got checked directly by a hyperbaric doctor to whom I also shared my dive profile.
In the meantime, the swelling in the arms regressed, and the blood pressure and heartbeat went back to normal.

In the end, they diagnosed me with a potential very mild DCS, exacerbated by dehydration (and they prescribed me a series of IV drips to help with hydration).
I avoided a chamber ride, and they suggested I take complete rest for at least 24/48 hours and no altitude change in the following days.

What was different on this dive and why do I think it might be a "deserved" DCS hit?​

After being discharged from the hospital in the late evening, I went back home to rest and started to feel much better, I slept well and the day after took full rest. Today (2 days after the dive) I feel even better.

What I did wrong in my opinion during the dive:

• I swam very fast during the dive, both on the bottom and on the way back (was a wall dive, I turned the dive after about 40 minutes to go back to the shore)
• I spent too much time during the ascent, and I spent about 20 minutes in the 20-15 meters range instead of going up to 6 meters (20 ft).
• Probably I didn't drink enough water both before and after the dive (especially after the dive)
• Even if it's winter here, the day was hot on the surface and I was exposed directly to sunlight for over an hour just after the dive during lunch (this may have worsened the dehydration)
• I didn't account for an extra "safety stop" after the deco obligations cleared, since the temperature of the water was cold (7°C - 44.5 °F), my high exertion during the dive and the long bottom time that probably started saturating also slower compartments.

And, the exertion after the dive (climbing stairs with doubles on, loading/unloading diving gear, etc.) might also have caused my very small PFO to cause a shunt, but it's impossible to know for sure.

Now, my questions:
(And first of all, thanks in advance for reading this long wall of text)

To sum up, what do you think of everything?
Have you ever had a case like this one?
Might it be a mild DCS or the subclinical symptoms I had (without visible skin bends or neurological issues) might indicate that it wasn't a real DCS but more a sum of several things I did wrong during/after the dive?
Should I be worried and change my type of diving, or be even more careful/conservative from now on?

 

[wetb4igetinthewater]

You didn't mention your age, another risk factor. While my brother's name is Simon, our last name isn't Mitchell, and I'm no expert on dive medicine, but my understanding is that hydration is an important factor.

I'd be curious as to the results of you repeat the dive with the same dive profile, repeating what you feel you did wrong, minus the hydration part and exerting yourself after the dive.

I personally am very conservative with diving, as my technical diving involves a rebreather of which I am not proficient (I will hire an instructor for the breather I have for extensive training before I resume diving).

I am no doctor, and being conservative myself (I have a 4 year old that I need to walk down the aisle one day), I would just increase conservatism and ensure I'm well hydrated and don't exert myself after a dive.

Most of my future technical diving will be in Greece so hydration/heat are important factors to address.

 

[Cragene]

You didn't mention your age, another risk factor. While my brother's name is Simon, our last name isn't Mitchell, and I'm no expert on dive medicine, but my understanding is that hydration is an important factor.

You're right, I'll edit the first post, I'm 31 years old; in good shape, and physically fit.

I'd be curious as to the results of you repeat the dive with the same dive profile, repeating what you feel you did wrong, minus the hydration part and exerting yourself after the dive.

I already did the same dive, in the same location, about a month ago.
What was different is that the dive was slightly deeper (about 50 meters - 165 ft), with a more square profile (20 minutes on the bottom, then ascending to 20 meters, then 12 meters, and then 6 meters on the way back).
The total dive time was very similar, about 75 minutes, and I surfaced with a comparable GF (66%).
In that dive I swam faster than usual (since it's a long wall), but I was for sure more hydrated and rested than this time.

 

[OTF]

Good writeup. Sounds like a number of small factors added up. Dehydration is a major contributor, well recognized as a root cause in many DCS cases.

Being cold at depth then very warm (and exerting yourself) on the surface post-dive would have contributed as well. Both things can increase the rate of bubble formation. This is why there is consistent advice to avoid things like hot showers and strenuous activity after diving.

As for working hard on the dive itself, I've certainly heard discussion of this increasing DCS risk, but I'm not sure about the mechanism (separate from CO2 issues), maybe some of the dive docs and research people could comment.

It sounds like you handled this whole thing very well - recognizing the issue without denial right away, breathing O2, having an emergency plan and knowing the hospital, getting there quickly, and sharing this post so others can learn from your experience. Well done.

 

[Capt Jim Wyatt]

I am confident that there aren't many on this forum who can provide a diagnosis or a prognosis for you.

• Did the hyperbaric physician you saw complete a fellowship in hyperbaric medicine?
• Did you use a dive computer ? If so what kind?
• Did you follow prescribed ascent rates?
• Have you considered having the PFO repaired?
• How old are you?
• Why did you have to swim "fast" on the dives?
• Are you certain the gas mixes? Did you personally analyze the mixtures?

 

[lowwall]

I suspect dehydration was the major factor here. Exercise at depth is going to increase the rate of perfusion of nitrogen into the tissues, but the models were all built on an assumption that divers would be performing work at depth so it should not have taken you beyond theoretical limits.

I'm curious why you switched to air for the final "safety stop" and ascent?

 

[Vicko]

Did you go over some mountain passes on your drive home?

 

[Cragene]

I am confident that there aren't many on this forum who can provide a diagnosis or a prognosis for you.

I know, in fact I'm writing this more for potential advice or if someone has ever experienced a similar thing.

Regarding you questions:

• Did the hyperbaric physician you saw complete a fellowship in hyperbaric medicine?

I think/hope so, the hyperbaric facility here in Milan is well recognized and one of the best of the country.

• Did you use a dive computer ? If so what kind?

Yes, a classic Shearwater Perdix

• Did you follow prescribed ascent rates?

Yes, never more than 10 meters per minute, actually was way less without spikes or ascents above the ceiling.

• Have you considered having the PFO repaired?

It's so small that actually cannot be operated right away, and the other hyperbaric doctor who saw the bubble test results advised against the operation, unless a major DCS incident occurs.

• How old are you?

31 years old

• Why did you have to swim "fast" on the dives?

I'm sincere: stupidity. I wanted to see as much as possible of the wall, instead of splitting the dive in two or more different dives.
This time I was the one guiding the dive, the other time (with a different buddy) I was following at its same pace.

• Are you certain the gas mixes? Did you personally analyze the mixtures?

I didn't analyze the back gas (air) but the fill was from a dive shop I already went to several times.
I personally analyzed the EAN50 mix; didn't analyze the last oxygen fill since it was a direct transfill from a 50 liter tank (transfill done by the dive shop).

I suspect dehydration was the major factor here. Exercise at depth is going to increase the rate of perfusion of nitrogen into the tissues, but the models were all built on an assumption that divers would be performing work at depth so it should not have taken you beyond theoretical limits.

I'm curious why you switched to air for the final "safety stop" and ascent?

I'm used to standard air breaks after 15-20 minutes of oxygen, and if I complete the oxygen stops I then switch to air to add an extra stop and the final ascent.
Don't know if this is a standard practice or not.

Did you go over some mountain passes on your drive home?

No, the opposite: the lake was at 250m (820 ft), my home is at a lower elevation of 130m (426 ft).

 

[ChrisMBC]

A few idle thoughts, based on my complete layperson's understanding of the scientific literature on DCS:

- Working at depth: There is a fairly well-proven link between elevated heart rate/respiration at depth and incidence of DCS. I believe that the mechanism is increased circulation causing a higher rate of on-gassing.

- Working at depth - thermal factor: There is also a well-proven link between being warm on the bottom phase of a dive, and on-gassing (same mechanism as exercise - increased circulation, especially in your extremities). All the studies that I've seen look at the effects of water temperature/thermal protection, but if you're in a drysuit and swimming hard, it stands to reason that you'll be warmer than if you're floating on deco. This well-known experiment suggests that doing a Warm [bottom section] --> Cold [during deco] dive, even doing 3x the required amount of deco(!!!), resulted in DCS in 22% of cases!

So, if your heart rate was higher and you were warmer during the bottom stage of your dive, you will have on-gassed more (than expected), raising your risk of DCS.

- Effect of different dive profiles: Although hard data on the probability of DCS isolated to just dive profile is difficult to come by (given the relatively low incidence of DCS, inconsistency in reporting, number of variables other than dive profile...), this paper suggests that most dive models are 'more conservative' for short/deep dives, and 'less conservative' for long/shallow dives. My layperson's understanding of this is (within reason):

Given two dive profiles conducted with identical gradient factors, a shorter/deeper dive will have a lower probability of DCS than a longer/shallower dive.

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

All that aside, your post (which I thought laid out the variables/conditions of the dive very well), illustrates to me that the terminology of 'Deserved' and 'Undeserved' DCS hits is bad. Most dives that we do have some probability of DCS (call it 0.1%), which we all accept. Doing dives with more aggressive profiles (or bad thermal profiles, or with exercise, etc, etc) will raise that probability of DCS - let's say to 5%, on a fairly aggressive dive. At what point do we call that hit 'Deserved' or 'Undeserved'? Much better terminology would be 'low-probability' and 'higher-probability', which would more accurately reflect the nature of DCS.

 

[lowwall]

I'm used to standard air breaks after 15-20 minutes of oxygen, and if I complete the oxygen stops I then switch to air to add an extra stop and the final ascent.
Don't know if this is a standard practice or not.

I'm not qualified to comment on standard practices here. But in terms of lessening decompression stress, finishing the dive and even doing any surface swim on a higher O2 mix would be beneficial. If you want to avoid the irritation of 100%, then perhaps switch to your 50% instead.

Let's see what the tech divers have to say.