CNS toxicity symptom occurrence...or not

[Doppler]

Context: morning dive on a ledge running from 170' to 205' on EAN23, with 50% and 100% for deco. First dive of that day, but had conducted one shorter dive the previous afternoon to 175' on air with 100% for deco. ...

Forget what thermal protection you were wearing, and your aunt's maiden name, I would be more interested to hear more about that previous dive and what you calculated as your 24-hour or daily CNS limit for these two dives. Thank you.

 

[DevonDiver]

Why don't you tell me more about how otherwise unexplained tingling sensations in the face and/or extremities is "extremely atypical for O2tox"?

Knowing the 'T' from the acronym VENTID is something you can learn online. Understanding how that 'T' manifests...and how the symptom would likely feel to the victim is something that you probably couldn't bluff and blag from a Google search...

Quite aware of the max 1.66 pO2 at the bottom, yes.

If your incident had ended in injury, I'm quite sure the consensus would identify this particular decision as the trigger for an accident chain. An utterly avoidably trigger.

I'll say this again... if you had limited to a more prudent and supported pO2, then the potential for OxTox wouldn't have leapt so readily into your mind. That, in turn, wouldn't have lead to a flawed diagnosis that left you seriously considering omitting necessary decompression.

Not at all. Chose to address it differently than you would have -- by limiting O2 exposure during the previous day's dives, limiting time spent above 1.4 on the bottom, total bottom time, and exertion level during the bottom portion of the dive -- which is quite different from ignoring the pO2.

Given that you're the one posting in 'near misses', perhaps you should consider 'addressing it your way'. "Your way" seems to provide a certain tangible feedback that it is incorrect...

Maybe "your way" would change if you remedied your lack of effective knowledge and training?

 

[tracydr]

I wondered about your bailout tables and I'm glad you brought that up. Re how much to lower the pO2: with the caveat that this has not been studied extensively with immersed individuals and this shouldn't be taken as gospel, the vasoconstrictive effect begins at an inspired pO2 of about 0.6 ATA. There's no hard-and-fast with this, though, and I would not stake my life on it.

I always thought O2 was a vasodilator. You're saying that at 0.6 ATM it becomes a vasoconstrictor?

 

[Dr. Lecter]

I'll say this again... if you had limited to a more prudent and supported pO2, then the potential for OxTox wouldn't have leapt so readily into your mind. That, in turn, wouldn't have lead to a flawed diagnosis that left you seriously considering omitting necessary decompression.

It's interesting you refer to it as "necessary" decompression when I've confirmed for you that I had and considered bailing to a contingency profile -- according to which it was not necessary. Do you not teach your students about how and why to generate such bailout plans, and when they might go to them?

Forget what thermal protection you were wearing, and your aunt's maiden name, I would be more interested to hear more about that previous dive and what you calculated as your 24-hour or daily CNS limit for these two dives. Thank you.

Less about thermal protection and more about the fact there was no hood covering my face. I'll consult my planned tables and logs when I get home and post the numbers, but I remember the prior day's dive running up 85% CNS for that dive. I can't say for certain without looking at my logs, but it's possible the gap between ending the prior day's dive and starting the dive during which this occurred was more than 24 hours.

 

[Duke Dive Medicine]

I always thought O2 was a vasodilator. You're saying that at 0.6 ATM it becomes a vasoconstrictor?

O2 itself isn't a vasoconstrictor. The reactive oxygen species that are produced during hyperoxia bind with endogenous nitric oxide. Since NO is a vasodilator, the decrease in NO has a net vasoconstrictive effect.

 

[DevonDiver]

It's interesting you refer to it as "necessary" decompression when I've confirmed for you that I had and considered bailing to a contingency profile -- according to which it was not necessary.

You state you run "a very conservative profile", but I see nothing to support that. I see short-cuts and computer-reliance (and, if I interpret correctly, some settings that are far from 'very conservative').

Do you not teach your students about how and why to generate such bailout plans, and when they might go to them?

My students "first thought" wouldn't be O2Tox, because they don't dive beyond the strict limits imposed by every agency out there. So no, they wouldn't be bailing out, or missing deco, because of a minor marine life sting.

You pick your algorithm and settings (deco conservatism and pO2) based on your own physiology. That takes into account how you 'feel' after dives (fatigue..seems familiar to you?) and whether there are DCI/OxTox pre-disposing factors evident in your planned dive.

With my students, I encourage discussion and assessment of their post-dive physiological sensations. This is used to shape their optimal algorithm settings.

Cutting a uber-swift bailout is a trade-off... inherent risk of shorter deco versus other potential emergency factors. It isn't cut-and-dried 'safe' as you've deluded yourself to believe. It isn't something you switch to at the slightest provocation (such as a potty-panic over OxTox because you subconsiously recognize the idiocy of your gas/depth selection and pO2 encountered).

I don't accept "extreme fatigue" as an acceptable post-dive experience. I tend to feel very fresh and energized after a technical dive.

 

[Dr. Lecter]

Doppler, with regards to CNS: the prior day's dive ran up 17% (172' max depth, but following a steep bottom contour and less than 10 minutes on O2), and concluded 24 hours and 6 minutes before the start of the dive when this happened. It was the dive in question that ran up 85% CNS.

 

[rsingler]

Dr. Lecter,
I'll commend you for bringing up a tough issue in a very honest fashion.
Thanks again for having the courage to bring up an incident where there are lots of factors to debate.
Good on you! You've got more support than you might think.

 

[DevonDiver]

A (constructive) critical attitude is a key component in honest accident analysis.

Debate on technical dive issues is best limited to the T-2-T forum, but one must have the credentials to get membership there. Technical mindset might appear a bit arrogant to those not familiar with that level of diving. There's not much that'll explain that - but you'll understand when/if you get to that level.

A critical attitude also tends to be a good component in technical diving instruction. Trust me, the last thing you need (rather than want) is some chump that'll give you high-fives as you flounder and flop through a weak skill-set en-route to a piece of plastic that opens you to conduct dives that can hurt you easily.

 

[Doppler]

Doppler, with regards to CNS: the prior day's dive ran up 17% (172' max depth, but following a steep bottom contour and less than 10 minutes on O2), and concluded 24 hours and 6 minutes before the start of the dive when this happened. It was the dive in question that ran up 85% CNS.

Thanks.

Only 17 percent on the previous day... surprised, however, if that's the case, my GUESS would be that your incident was unlikely to have been related to central nervous system oxygen toxicity.

Had your 24-hour CNS loading from the previous day's diving been higher... and the beginning of your second immersion a little earlier in the day... I would suspect something different.

Dive safe.