Surface oxygen and CNS O2 toxicity

[Troutmaster]

First and formost, Thank You Duke Diving Med. I hope that if I ever get bent, I am diving in your parking lot and get treated in your chamber.

I think too many divers confuse "whole body/pulminary" O2 toxicity and CNS O2 toxicity. While this is covered (at least in TDI training) alot of divers confuse the two. This might be a interesting topic to be discussed by you folks who know a heck of alot more about it than I do.

The biggest problem is denial. "There is no way I am bent" attitude messes up alot of divers, including those of us who know better. Surface O2 is not going to hurt you so "hit the bottle" if you have any symptoms or doubts. O2 is cheap. The long term effects of getting bent suck.

 

[TSandM]

---

---

A ScubaBoard Staff Message...

Please keep this excellent discussion of DCS symptoms and treatment on track. There is no need to involve personalities!

---

 

[Duke Dive Medicine]

Thanks to everyone for your kind feedback. Perhaps the discussion got a bit technical for this particular forum. I had no way of knowing which way the thread would go.
That said, I'd like to put my two cents in about asking questions. DDM is very new to this forum and we don't have anything to do with moderation or governance, but I think we should all recognize the wide variety of training, experience, and ability of the folks on a discussion board like this. Also, we're typing on computers so it's often easy to misinterpret the writings of others and take a conversation to a level that it would never get to were we speaking face to face. For our part, we are happy to answer questions of any type, either publicly or privately, as quickly as the writer can get to them. I have the advantage of being able to tap some tremendous resources here. This is a terrific site for interaction and education, and many thanks go to the creators, moderators, and participants.
Sincerely,
Eric Hexdall, RN, CHRN
Duke Dive Medicine

 

[lowviz]

...............Both divers refused surface oxygen aboard their dive boats. They were happy to get O2 once they came to us.
...................

There are some morals here for all divers: if you think you may be bent, don't go diving again, especially in that river called Denial. Use as much surface O2 as somebody is willing to give you. Above all, seek treatment immediately, don't wait.

Duke Dive Medicine,

Is there any situation on a boat that contraindicates O2? Seems to me that refusing O2 on the boat is always the worst thing you can do to yourself. Maybe there is an absolute in diving, this could be it...

Regards,
lowviz

 

[Duke Dive Medicine]

Greetings Lowviz,
If we're talking strictly about diving-related injuries, then I can't think of a contraindication to O2 that would apply. Not every illness on a dive boat is diving-related though, and O2 may not necessarily be the first priority in all situations. O2 might be contraindicated in a COPD patient whose breathing drive has shifted. That person wouldn't likely be found on a dive boat, but you never know. This is why O2 should always be administered by a trained provider and used as an adjunct to other appropriate treatments.
Regards,
Duke Dive Medicine

 

[techintime]

DDM,
From your description of the dive profiles, it looks like there were no deep stops. Just multiple long deep dives and then direct ascents to 15-20 feet for decompression. I saw no mention of a known violation of either tables or the computer-derived deco obligation, i.e. no recognized deco obligation. With the exception of the potentially rapid ascent, these start to look like "undeserved hits" albeit agressive profiles.
Two questions:
1. Do you think deep stops would prevented these incidents? O.ne deep-stop rule of thumb is to make your first stop at half your maximum depth. Most computers do not drive you to make a deep stop
2. Were either of the divers evaluated for a PFO?

 

[Duke Dive Medicine]

Good morning tech,
There's a gray area between what we'd call "undeserved hits" and DCS symptoms that aren't entirely unexpected with the provocative dive profiles these two divers had. Regarding your questions:
1. The only study that looked at DCS incidence and deep deco stops was done at the NEDU by Gerth, et al in 2007, linked here. Rubicon Research Repository: Item 123456789/5069 It was terminated early due to the relatively high rate of DCS found in the deep stop group. Studies looking at intravascular bubble formation have had mixed results. So, there doesn't appear to be any evidence that a deep stop would have helped these divers, and it's really impossible to look at that retrospectively anyway because there are too many individual factors.
2. We didn't evaluate either diver for PFO. There's no solid "go/no-go" criteria for whether to check for PFO or not, but we typically do it when the diver's symptoms seem out of proportion to the dive profile or if something else about the symptom presentation arouses our suspicion. For example, we had a diver about a year ago with two dives to about 98 feet for around 30 minutes(unknown surface interval, the history was a bit sketchy). He presented with serious spinal cord and brain symptoms and also elevated cardiac and liver enzymes, which was very suspicous for a large bubble shower. He was evaluated for PFO and found to have one. Another diver we saw had ascended normally but ignored her computer's admonition to perform a decompression stop, surfaced asymptomatic, and was sent back down to complete her decompression by the divemaster on the boat. She went back down right away, completed her decompression per her computer, and fell unconscious immediately after climbing the ladder. She didn't have any of the classic "AGE" history, i.e. rapid, panic, or uncontrolled ascent, and so her symptom presentation was suspicous for PFO. She was evaluated and found to have one.
PFO tends to get a lot of attention, but it's really not clear what the relationship between PFO and risk of DCS is. Some 30% of the population has one, so by extension, 30% of divers have one, but we don't see anywhere near a 30% incidence of DCS. Of course dive profile would have an influence, but the exact relationships remain under investigation. Also, PFO is only one of many different areas of the body where blood and/or bubbles may be shunted. One area that's receiving attention right now is the pulmonary vasculature. Thanks for your questions and your interest!
Regards,
Duke Dive Medicine