Oxygen poisoning seizure > how to react ?

[rjack321]

10/70 hypoxic. I'm not happy to breathe that on the surface for any length of time and even take precautions not to inhale it through the ADV until I'm on my way down.

I'm not changing the way I dive to suit whatever diluent I happen to have. It caters for what I COULD have.

Does it matter where the BOV is plugged into? If it's offboard, it's still the same/similar gas unless you add the clusterf*ck of gas blocks and switching.

The gag strap is more to stop you inspiring water and drowning rather than worrying about wtf you're breathing.

As I said, the mask strap goes under my hood.

None of this is a perfect solution but what I do works for me and the gag strap adds a massive level of comfort to my everyday diving regardless of the miniscule possibility that it would prevent me from drowning.

Ummm because for the run of the mill 60m / 35min dive you can dive your 10/70 dil or whatever you like and bail 18/45? (or get switched to)

I don't see how any of this scenario is different if you have a BOV in your mouth, aside from adding even more complexity for your potential rescuer(s). Unless I'm missing something?

EDIT: I almost always dive alone, so this is all a bit academic really

For the vast majority of CCR dives without support divers (so say those in the ~75m range) your rescuers can put you onto a breathable gas.

Doing 100m+ 10/70 dives solo, no buddies, no support... welp good luck with that in the long term. Te gag strap is just window dressing here.

 

[doctormike]

1. You tox at depth
2. the DSV is held in nicely by the gag strap
3. they dil flush you as they keep you in position and stabilize you
4. you come round and are semi conscious, as @nickbutcher points out, it could be quite some time before you are lucid.

So now what?

The loop isnt really breathable in the long term and they are in no position to remedy that. If they try to switch, you are quite likely to aspirate. If they don't switch you, your loop could very well go hypoxic on ascent and present your rescuers with another issue.

Right. Can't cover every eventuality. The ADV maneuver is more for rescue from a non-breathable loop than postictal.

But I'm not sure I understand your point. Are you saying that you don't think that the DSV/strap combo is advisable?

 

[rjack321]

Right. Can't cover every eventuality. The ADV maneuver is more for rescue from a non-breathable loop than postictal.

But I'm not sure I understand your point. Are you saying that you don't think that the DSV/strap combo is advisable?

I'm saying the DSV/gag strap combo is better than DSV/standard mouthpiece.

But less than ideal, particularly in mixed teams. You can dismiss BOVs all day long, but the reality is that BOVs are really the only way for a buddy to put you onto a breathable gas (for more than a dil flush moment). If the loop goes non-breathable to the point of you toxing and you're dil flushed - on nearly pure dil it's now quite likely to not be a breathable loop on ascent (unless the solenoid is stuck open, voting logic is trying to add O2 or on mCCR someone is adding O2). You need to be off that loop. Yet your mental state is going to be questionable. The solution is breathable offboard OC gas - via a BOV.

 

[doctormike]

I'm saying the DSV/gag strap combo is better than DSV/standard mouthpiece.

Thanks! Gonna order one, just have to figure out which one. Was just on the phone with Mike from Silent Divng about the AP one. He wasn't sure if it would fit the JJ, but they have a return policy so I might try it. Any thoughts about that vs. the Drager vs. the Narked@90?

But less than ideal, particularly in mixed teams. You can dismiss BOVs all day long, but the reality is that BOVs are really the only way for a buddy to put you onto a breathable gas (for more than a dil flush moment). If the loop goes non-breathable to the point of you toxing and you're dil flushed - on nearly pure dil it's now quite likely to not be a breathable loop on ascent (unless the solenoid is stuck open, voting logic is trying to add O2 or on mCCR someone is adding O2). You need to be off that loop. Yet your mental state is going to be questionable. The solution is breathable offboard OC gas - via a BOV.

I'm not dismissing BOVs at all, I definitely see the advantage. But there are some tradeoffs, so it's not like DSVs are completely foolish choices. If someone thoughtful like Jan has designed the JJ without one, that means something, especially given the thought that goes into every other aspect of the design. I don't think that it's just to cut costs.

And I totally agree - getting back to the OP - that there are circumstances where a quick squirt of dil isn't going to fix things. So the choices come down to how likely each of those failure modes are for the diver in question.

 

[BlueTrin]

I would have assumed that a computer like a Shearwater would not lock you but continue to off gas faster (according to the model).

So when you go back to your stop, it would just continue to apply the tissue on/off gassing as it would have never stopped but I do not know for sure.

I am gonna ask them.

@Etmutt here’s the reply from Shearwater:

What happen is that deco info will remain on the screen until it actually clears based on ambient pressure (at the surface). Because off gassing is calculated based on ambient pressure, the displayed deco time may reduce faster then it would if they were at the correct stop depth

In an emergency such as this, descending and following the displayed decompression information may not be enough to avoid decompression sickness due to already formed bubbles. Always make sure you follow your training with regards to what should be done in the event of a missed decompression stop.

 

[Etmutt]

Thanks !

 

[Doc Harry]

Hello Harry,

This is not quite true. The other mitigation (which I personally use) that is much less complicated and expensive than a FFM is a mouthpiece retainer device. The Drager gag strap is the best designed one in my opinion. Unlike many things in diving medicine there is actually some evidence for their efficacy. I have uploaded a paper by the French Navy group reporting rebreather accidents among which there were 54 loss of consciousness events with only 3 drownings. I would have expected many more drownings in 54 divers who lost consciousness underwater, but I believe all of them were wearing a gag strap, and most had buddies close by. To be objective, most of these probably occurred in shallow rebreather operations typical of operational attack swimming training, but the point still remains that they had high survivability after losing consciousness with the use of mouthpiece retainers and prompt rescue, which could easily apply in many technical diving situations if we chose to make it so.

Simon M

The study you provided is flawed in regards to question being asked, i.e., the survival of a seizure underwater. The study you provided included all forms of loss of consciousness, not just seizures, which means you're comparing apples to oranges. Furthermore, the study you quoted did not break down the survival rate for the hyperoxia/seizure group, which means that study is irrelevant to this discussion. Furthermore, the study size is so small that their guess is as good as mine.

 

[rjack321]

The study you provided is flawed in regards to question being asked, i.e., the survival of a seizure underwater. The study you provided included all forms of loss of consciousness, not just seizures, which means you're comparing apples to oranges. Furthermore, the study you quoted did not break down the survival rate for the hyperoxia/seizure group, which means that study is irrelevant to this discussion. Furthermore, the study size is so small that their guess is as good as mine.

Please tell us about all these "other forms of loss of consciousness" that you think are happening amongst these 54 divers on oxygen rebreathers.

 

[Doc Harry]

Please tell us about all these "other forms of loss of consciousness" that you think are happening amongst these 54 divers on oxygen rebreathers.

Did you even read the article that you posted?
LOL

 

[rjack321]

Did you even read the article that you posted?
LOL

I've read it multiple times. It's also about as good of a retrospective study on LOC, seizures, and drowning risk as you are ever going to get. Do you even dive a rebreather?