Mailing List Archive Mailing List Archive
--- Jim Cobb <cobber@ci*.co*> wrote:
> Some practicable information from what I've picked up over the
> years...
>
> While bubble formation has it's hazards in deco diving, it's
> generally
> manageable outside of clusterfucks. What does concern me is
> the
> unpredictability of oxygen toxicity. As anyone who works in a
> hospital can
> tell you, oxygen will fuck up your lungs. They are very
> careful about how
> long they put patients on 100% because O2 can be toxic and
> will cause
> permanent tissue damage.
Jim - thanks for your continually interesting posts.
I'm a critical care RN and work in a large urban ICU and we
never put patients on 100% O2 except in code (resuscitation)
events. You always strive for the least possible FiO2 (inspired
oxygen) that will keep SaO2 (oxyhemoglobin saturation) at 92% or
better. In the ER setting, 100% O2 is much more common, but
only because it won't last longer than the 1-2 hours that it
takes to get your diagnosis figured out a little better and get
you on the right O2.
One aspect of oxygen I have not heard about (regarding deco and
pO2 levels) is that our respiratory drive is two pronged in
nature. Our first impulse to inspire air is triggered by a
dropping pH (or increasing acidity) of our cerebrospinal fluid.
When we don't breathe enough O2, the ph drops and we get a
trigger to breathe. It happens very quickly. Barring that
stimulus, our backup respiratory drive trigger is actually the
hypoxic drive, or our low O2 emergency situation. The chronic
smoker/emphysema ("chronic lunger") patient will have long since
altered his/her body chemistry into a chronic acidic state where
their brain doesn't care anymore what the spinal fluid pH is
(I'm exaggerating only a little). And in this patient the risk
is giving them too much O2 or you will satisfy their hypoxic
drive (a bad thing in this instance) and bingo, their
respiratory drive slows to a crawl. They get a faraway look in
their eyes as CO2 builds up, and then it's the beginning of the
end. Thus patients come into the ER pale and gasping and we put
them on a measley 2 liters a minute so as not to shut them down.
Usually this patient will get paralyzed and intubated, and
placed on a ventilator.
Why did I say all that? I wonder if continually high inspired
O2 percentages by physically fatigued/stressed divers cannot
reproduce this chemical situation, basically shutting down the
hypoxic respiratory drive causing a (probably not unpleasant)
buildup of CO2 and unconsciousness. I wonder if a lot of the
"we found him hanging at his deco stop unconcscious" type
stories don't show this exact scenario, as opposed to the more
generally assumed seizure activity from an oxygen
toxicity/neurological syndrome. I am certainly not advocating
80/20 as a "safer, lower O2" deco gas because the vast majority
of divers are young and healthy and the object of deco is to
offgas toxic nitrogen first and foremost, not necessarily to get
out of the water as quickly as possible.
I am not a decompression diver yet...I'm here to STFD and STFU
and listen to experts, but I thought that the above might be
something to consider.
Cheers
Ryan McNabb
=====
__________________________________________________
Do You Yahoo!?
Yahoo! Mail - Free email you can access from anywhere!
http://mail.yahoo.com/
--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]