Relatively low ppo2 oxtox incidents

[lamont]

I've seen it asked before if anyone has oxtox'd at less than 2.0 or 1.8 ppo2 and found a couple accounts yesterday, from http://www.iucrr.org/aa_misc.htm:

Pompano Beach, Florida USA

93OCT-A diver experienced what appeared to be the first onslaught of a CNS oxygen toxicity hit during an air dive to 228 fsw/70 msw on the RV Johnson, was able to make a rapid ascent to about 105 fsw/32 msw and survived. The diver and two others descended towards the wreck in order to set the anchor. Missing the wreck, and being deeper than they had planned, the divers began a hard swim at about 228 fsw/70 msw (PO2 = 1.66 atm) for about five minutes out of what was planned to be a 10 minute bottom time. He reached the mast at 190 fsw and tied off the anchor.

As he was working he got a severe pain in his molar, his lip began twitching and his jaw started chattering. Feeling a convulsion coming on, he held his regulator in his mouth, tried to signal to his partners and hit his BCD inflator just as he began to lose his vision and experience a mild convulsion. They symptoms began to clear during the rapid ascent and he was able to regain control about 115-120 fsw/35-37 msw and stopped himself at about 105 feet/32 meters. The diver was then able to pull himself together. He completed his scheduled decompression and included a 20 fsw/6 msw oxygen "hedge" stop on EAN 80 (80% O2, balance N2). He surfaced without incident. An extenuating factor may have been the prescription decongestant, Entex LA. The drug had been used by the diver at recommended doses during the preceding week of diving. He had previously bought a regulator retaining by "forgot" to bring it that day. According to the Divers Alert network (DAN) there is no data to link the drug to the incident.

Sydney, Australia

93AUG-A wreck diver lost consciousness during a 15 minute deep air dive to 78 msw/254 fsw on the paddle tug, Koputai, and drowned. The diver lost consciousness while returning to the anchor line after a 15 minute planned bottom time to make his ascent. Though his three partners attempted to ascend with the diver in tow, they were unable to maintain a regulator in his mouth and he subsequently drowned. The team preceded to lift the unconsciousness diver to 15 msw/50 fsw and released him to surface. Surface support personnel initiated EAR and radioed for emergency assistance/evacuation. The diver did not regain consciousness and was pronounced dead a short time later. Though the Coroner’s report has not been released, CNS toxicity (working PO2 = 1.85 atm) compounded by possible CO2 build-up and narcosis-characteristic of deep air dives-is suspected as the primary causal factor. The incident raised government concerns about local deep diving practices. Though mix training has just gotten started in Australia, most deep dives are still conducted on air.

-Submitted by Richard Taylor, Sydney, Australia.+

[BigJetDriver]

Studies done some time ago in which divers were put in pressure pots and exposed to high ppO2's until they convulsed, showed that the susceptability varies from individual to individual, and within each individual from day to day.

In other words, your mileage may vary...by a lot!

[MrConclusion]

I remember reading an article in one of the big British magazines (Diver?) about oxygen toxicity at low PPO2.

The things I remember are, that some divers have convulsed even within the 1.4 - 1.6 range, but there have been vanishingly few incidents at PPO2 1.3 or below.

There was also a correlation between likelyhood of O2-tox and low nitrogen content in the breathing gas. Apparently, there is evidence and growing belief that nitrogen acts as a CNS depressant, giving some protection. This was offered as an explaination as to why so many divers "get away with" high PPO2 on deep air dives. In other words, you may be more at risk with high-Helium trimix or heliox.

PLEASE REMEMBER this is from memory, and don't do anything stupid on my say-so.

[CameronMartz]

I was contacted by a diver who began to experience CNS ox tox symptoms at very shallow depths/low PO2. After much reflection, he realized they began when he started to drink a popular supplement that contained high amounts of ephedrine. He reported that his symptoms dissappeared once he stopped drinking the supplement.

Of course, this is just one diver, but this is only one of the reasons I caution divers of the potential for unpredictable effects of nutriceuticals at depth. While ephedra is now at least limited in its use in supplements, other CNS exciters have taken their place.

Cameron

[pipedope]

I have seen references to O2 tox incidents when CO2 levels were high.

In several cases the diver was fine at a certain PPO2 until they started working harder, then with rising CO2 they toxed.

Just something else to consider.

[String]

Originally Posted by CameronMartz

I was contacted by a diver who began to experience CNS ox tox symptoms at very shallow depths/low PO2. After much reflection, he realized they began when he started to drink a popular supplement that contained high amounts of ephedrine. He reported that his symptoms dissappeared once he stopped drinking the supplement.

That may fit in with the possibly link some mention between some decongestants (ie in this case pseudo-ephedrine containing methods) and an increased susceptability to O2 tox. Cant drag out any concrete studies with this though after trawling google and i cant access medline/nih from here.

[Spectre]

Originally Posted by CameronMartz

Of course, this is just one diver, but this is only one of the reasons I caution divers of the potential for unpredictable effects of nutriceuticals at depth. While ephedra is now at least limited in its use in supplements, other CNS exciters have taken their place.

Cameron

There was an accident in Little River a few years ago [you can find it in the iucrr reports] which looked a lot like an o2 tox, with fairly low PpO2. The buddy is convinced it had to do with antihistimines and sudafed. I seem to recall the sudafed was an older generation that had something along the lines of ephedrin in it... And the reason I get on a soapbox whenever someone wants to take something because they are stuffy before a dive.

[CameronMartz]

Originally Posted by Spectre

I seem to recall the sudafed was an older generation that had something along the lines of ephedrin in it...

The name "Sudafed" actually comes from "pseudo-ephedrine," which is the man-made version of nature's ephedrine the original Sudafed contained. It's kinda weird that there is a non-pseudoephedrine Sudafed now, but there is. (BTW, pseudoephedrine was contained in most OTC decongestants, not just Sudafed, but is being phased out because of cardiovascular risks associated with its use.)

Unfortunately, as String pointed out, there have not been any direct studies on this. Peter Bennett did some work suggesting that CNS exciters increased CNS ox tox susceptibility, and ephedra/ephedrine/psuedoephedrine is a CNS exciter. Bitter orange, ephedrine's replacement in "natural" weight loss supplements, is another.

Cameron

[Bruciebabe]

Many rebreather users now run at 1.2 PPO2 because of the CNS hits at 1.4.
It has been explained to me as like putting your finger in a candle flame. Leave it there and it will burn quickly, move it in and out and you can keep going all day. So it is with high PPO2. You need the occasional break to a lower PPO2 so as not to overstep your tolerance to O2. Maybe one day rebreathers will do this automatically.