11 y/o Surfaces with Convulsions

[tech_diver]

I'm not a doctor or a hyperbaric physiologist but I've been a diver for a while. When I read the story, my first impression was an expansion injury with neurological involvement (CAGE).

I would think medical exams could spot this but not sure what diagnostics would be used.

 

[DandyDon]

I don't understand. Wouldn't reducing the PPCO by ascending be a little less terrible?

Nope, PPCO does not reduce quickly on ascent. But I think you corrected yourself in the rest of that post.

Come to think of it, reducing the PPO2 by ascending would have a significant negative effect on someone already compromised by CO poisoning.

 

[DandyDon]

Yep, corrected, thanks.

 

[Akimbo]

Nope, PPCO does not reduce quickly on ascent.

All partial pressures change in direct proportion to changes in ambient pressure. CO uptake is faster with higher PPCOs than lower, whether it is caused by elevated pressure or a higher percentage on the surface. The practical impact on divers may be perceived as reducing PPCO being the problem, but the actual problem is a lower PPO2 when already compromised by CO. It is a fine point but an important distinction.

 

[Biotech Diver]

Has no one else seen Carbon Monoxide as a possibility? The tank would have to have a high ratio to hurt someone at 15-20 feet, but it's possible. Ascending is when PPCO poisoning kicks in the worst, convulsions are a common symptom, having only one tainted tank of a lot certainly does happen, and most divers & Ops don't bother testing. Plus, there probably will not be a controlled tank after the injury so no report.

I don’t know why you always suspect carbon monoxide poisoning. Possibility? Yeah. Probable? Very unlikely. Everyone else diving probably had their tanks filled at the same place and time with no issues and undoubtedly many other people got their tanks filled at the same place presumably with no issues either. You are assuming extreme negligence on the part of the shop that filled the tanks. Do you have reason to believe that? It’s almost slanderous to suggest that with no basis in facts?

 

[DandyDon]

I don’t know why you always suspect carbon monoxide poisoning.

I don't, but it's possible in this event, and it was not ruled out by controlled testing.

Probable? Very unlikely.

No, not at all unlikely, since shops and divers don't test.

Everyone else diving probably had their tanks filled at the same place and time with no issues and undoubtedly many other people got their tanks filled at the same place presumably with no issues either.

That's The Big Lie with tank CO risks. When a tainted tank is found, it's often the only one from the batch.

You are assuming extreme negligence on the part of the shop that filled the tanks.

Nope, just observing a possibility that's continuously ignored.

As long as divers ignore the risks and fail to understand like you, the risk will persist.

 

[tursiops]

I don’t know why you always suspect carbon monoxide poisoning.

Because that's his hot-button.

 

[DandyDon]

Because that's his hot-button.

I don't, but it's possible in this event, and it was not ruled out by controlled testing.

I did wait for four pages, but no one else brought it up.

 

[GJC]

This might be misleading. Blacking out from hyperventilation is not the same as shallow water blackout. Extreme hyperventilation can cause the Carbon Dioxide (CO2) in your lungs and blood stream to fall too low to stimulate breathing, which causes the body to shut down.

Shallow water blackout occurs when freedivers consume enough oxygen that the PPO2 in their lungs and blood stream at depth falls near hypoxic limits. They black out from hypoxia on ascent when the pressure drops and the PPO2 becomes too low to support consciousness.

That wouldn't be possible for a Scuba diver, even in 20' of water, because their tissues are hyper-saturated with Oxygen from their time at depth. It would require holding their breath on the bottom long enough to deplete the O2 in their system, which would cause very high CO2 levels. That is very hard to do voluntarily. An OOA diver might black out for CO2 poisoning, but that can't sneak up on you. In addition, holding their breath on ascent would embolize them.

It is not uncommon for freedivers that push their limits too far to black out just after reaching the surface and taking their first breath. Their tissues are depleted enough that their first lung full doesn't get into their blood stream before the body triggers the blackout, which is basically shutting down everything except blood flow to the brain. The problem is freedivers will fall face-down and drown if their buddy isn't there to help.

Freediving courses train you to dive in teams so their buddy stays on the surface while the other dives. The buddy follows the diver and is there when they break surface. The diver is supposed to signal the buddy for about 10 seconds, through hand signals or speech, until the risk of blackout on the surface passes. Of course the buddy is there in case the diver blacks out before leaving the surface. Buddies in competitive apnea diving will dive down to meet their diver at around 30'/10M and follow them up. Deep freedivng buddy pairs may also do that but it might not be practical in low visibility.

This is extremely rare with inexperienced and otherwise untrained freedivers because their tolerance to CO2 isn't developed enough to deplete their Oxygen that low under normal conditions. CO2 buildup is what causes the desperate urge to breath, not low Oxygen. Freedivers can develop a tolerance to CO2 over time and through conditioning. That was especially interesting to me because the amount of time past the point where you start to feel desperate to breathe is MUCH longer that you would imagine before you actually black out.

The lesson for Scuba divers is don't panic, which is really hard to do with CO2 buildup, but can easily be the difference between killing yourself and having a great sea story to tell your grandchildren.

I did poorly describe the sequence of shallow water blackout. Rising CO2 level in our body is the primary respiratory driver that makes you want to take a breath. Hyperventilation lowers your CO2. You can lower your CO2 level low enough so that your body doesn't think it needs to take a breath even though oxygen levels in your body get low enough to cause you to pass out.

This can occur with swimmers trying to swim as long as they can underwater on 1 breath. I have witnessed shallow water blackouts in a pool that was only 5 feet deep after swimmers hyperventilated to blow off CO2 to decrease their respiratory drive and tried to swim underwater longer or just stay underwater longer than another swimmer.

Without additional information about this case, I still suspect that this 11 year old became hypoxic enough to cause unconsciousness and a seizure. The fact that he recovered quickly and fully pretty much rules out a lot of other things that can cause unconsciousness and a seizure.

 

[Angelo Farina]

Still, I suspect a lung over-expansion. This is by far the most common and risky severe accident occurring to new divers in shallow water.
As I trained my sons since very early age, they were taught to always exhale when ascending: they started doing this in the pool from less than one meter depth around 2.5 years, and when they first did dive in the sea, 2 years later, this was almost a reflex for them. They did always expire automatically while ascending, as this is what they had trained for years in the pool.
Despite this long preliminary training, I and my wife were quite concerned of this risk, as you cannot predict as a young baby can react in case of panic or danger. Our decision was to favour the risk of drowning than the risk of a lung over expansion. This resulted in not giving a BCD to them, and to keep them slightly over-weighted.
Furthermore, as we are old-style instructors, which did spend the first 5 years of our teaching activity using the ARO (a pure-oxygen CC rebreather) as the basic scuba system for training students, we did teach our children to always breath underwater with the inspiratory pause (as it is mandatorily done with the ARO).
Most "modern" instructors instead teach to "breath continuously" and to "never hold your breath" while scuba diving. This is actually a bad practice for preventing lung over-expansion during a panic ascent.
In fact, students are not trained to interrupt the breath-holding while ascending, They usually breath continuously until something bad happens, such as loosing the reg from their mouth, or loosing the mask. At that point they speed for the surface, not breathing anymore and not exhaling...
When instead a student is taught to ALWAYS hold the breath after every inspiration, and to ALWAYS exhale when ascending (even by a few centimeters), interrupting the apnea, in case of a panic ascent they will automatically exhale.
And I have proof of this with our sons, we "tested" them several times, by abruptly removing their mask and/or reg, and watching how they did react.
The first times they did surface quickly, of course, but always exhaling...
After a while they did learn the joke, and started searching for the mask and reg without surfacing anymore. This way we had proof of their proper training for avoiding the risk of lung over expansion, so we started going deeper and deeper.
At 10 years old they were diving routinely at 18-20 meters. At 12 years they were both certified Advanced Open Water, diving down to 30m.