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View Full Version : Oxygen Toxicity: What's the Real Story?



Vercingetorix
08-27-2007, 14:23
We all earn in Nitrox class that pure oxygen past 20 feet is lethal. We also learn that toxicity can occur at any depth. We know the signs. We know the dangers.

During a recent dive, I spoke with a hyperbaric chamber technician. He's worked in the field for over six years. He mentioned that during that time, he or other techs have taken over 10,000 patients down to 60 feet in the chamber on pure oxygen. During that time, he's read or seen only two cases of oxygen toxicity.

So...what's the real story? Does being under water increase the probability of toxicity?

mwhities
08-27-2007, 14:26
PPO2 build up? How long were they "down"? They lay there with out moving... no exercise.

You can go to (don't try per my suggestion) 400 + feet on AIR... just depends on how long you are there.

Michael

chinacat46
08-27-2007, 15:18
Lets also realize that oxygen toxocity may cause a convulsion. A convulsion is very rarely fatal above water. Underwater though you would probably loose your regulator and drown.

dmdoss
08-27-2007, 17:07
PPO2 build up? How long were they "down"? They lay there with out moving... no exercise.

You can go to (don't try per my suggestion) 400 + feet on AIR... just depends on how long you are there.

Michael


The air record is over 400ft.

Vercingetorix
08-27-2007, 17:38
Lets also realize that oxygen toxocity may cause a convulsion. A convulsion is very rarely fatal above water. Underwater though you would probably loose your regulator and drown.I repeat: only two convuslsions in thousands of treatments of PURE oxygen taken at 60 feet or more.

chinacat46
08-27-2007, 18:21
So would you like to be one of those at 60 feet underwater???

Centerius
08-27-2007, 18:21
Here (http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35) is a good article that talks about oxygen toxicity. I suggest reading it all the way through, since it has valuable information throughout the entire article.

b1gcountry
08-28-2007, 12:55
In a recompression chamber, they are breathing off of O2 masks, which only provide around 80-90% O2 due to leakage and improper sealing (the ambient gas is air). A lot of places also put you on air breaks every 15 minutes or so. You are also working more hanging out underwater than laying in a chamber, so it isn't a 1-1 comparison. I would still expect it to be higher incidence rate tho.
Tom

Harshal
08-28-2007, 13:05
Have any of you been in the chamber? I have never been in and hope would never have to be in one, but I have heard when they put you in chamber with pure oxygen, your minor cuts and bruises heal lot faster.

Any experience on that…… ?

Vercingetorix
08-28-2007, 13:06
So would you like to be one of those at 60 feet underwater???The patient is not REALLY underwater. The chamber is pressurized to the equivalent of 60 feet.

chinacat46
08-28-2007, 13:48
Duh and I thought chambers were underwater.Thnx for explaning that to me. But you still didn't answer my question.

Vercingetorix
08-28-2007, 21:30
Duh and I thought chambers were underwater.Thnx for explaning that to me. But you still didn't answer my question.That comment is rude and adds nothing to the discussion.

chinacat46
08-29-2007, 07:22
I take from your comment then that you wouldn't want to be underwater at 60feet breathing pure oxygen. Good choice.

Charlotte Smith
08-29-2007, 08:02
If thats the case...wouldn't it be nice to own one so everytime you got cuts or bruises you could heal yourself up fast and go back at it! I am one of those people that everything seems to happen to so I would be glad to heal much quicker. (aren't they terribly expensive?) I only know of a few in Arkansas.

Vercingetorix
08-29-2007, 10:32
I take from your comment then that you wouldn't want to be underwater at 60feet breathing pure oxygen. Good choice.Infer what you like. I implied nothing.


If thats the case...wouldn't it be nice to own one so everytime you got cuts or bruises you could heal yourself up fast and go back at it! The hyperbaric technician said that the chamber is often used for cancer treatments because it floods the cancerous area with oxygen.

chinacat46
08-29-2007, 10:39
Well I'd rather infer that you made the right choice. If however you wish to change that you are welcome to. Just don't dive with me if you do.

fire diver
08-29-2007, 10:54
The reason that the dive agencies have instituted the 1.4 / 1.6 PPO2 is one of safety. They looked at the empirical evidence of diver convulsions and decided that a max of 1.6 was safe for almost everyone. Since then, they have downgraded that again to say that 1.4 is max, and 1.6 should be max for deco / contingency.

Of course, there are a few who will still tox below 1.4 levels, and other who could go over 2.0 safely. Every person is different. The published max are designed towards the most easily toxed.

FD

TxHockeyGuy
08-29-2007, 11:06
Children, children, enough bickering already.

If you want to read up about oxygen toxicity and the history behind the recommendations I suggest reading http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35 from DAN. It's a little lengthy but gives a lot of information.

Edit: Oh and for a real world example. Back in the day the navy had my father down to 90 ft in a chamber for 30 minutes on pure o2. The test was designed to discover who was susceptible to oxygen toxicity and who was not. He had no problems, others did. It depends on the person, and your susceptibility is not the same day to day. So just because you can make it to 60 ft safely on 100% o2 today, doesn't mean you will be able to tomorrow.

Edit2: Didn't realize Centerius had already posted that link, sorry about that.

chinacat46
08-29-2007, 11:21
No worries, Rick and I have exchanged some PM's and we are both on the same page now. I just don't want people to take chances underwater because of what may happens in a chamber.

cummings66
08-29-2007, 17:58
I think anybody diving with Nitrox would know better than to try that. At least I'd hope they had the common sense to not try it.

tedwhiteva
08-29-2007, 20:19
Here (http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35) is a good article that talks about oxygen toxicity. I suggest reading it all the way through, since it has valuable information throughout the entire article.
Thanks Centerius for the link - good article. :smiley20:For those who didn't bother reading it, here's a couple of interesting quotes:

Compared to dry exposures, immersion decreases oxygen tolerance a great deal, decreasing exposure times up to a factor of four or five.
Exercise decreases oxygen tolerance a lot, compared to rest

That does sound like maybe tolerance in a chamber isn't the same as a dive.

TxHockeyGuy
08-29-2007, 20:49
Here (http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35) is a good article that talks about oxygen toxicity. I suggest reading it all the way through, since it has valuable information throughout the entire article.
Thanks Centerius for the link - good article. :smiley20:For those who didn't bother reading it, here's a couple of interesting quotes:

Compared to dry exposures, immersion decreases oxygen tolerance a great deal, decreasing exposure times up to a factor of four or five.
Exercise decreases oxygen tolerance a lot, compared to rest

That does sound like maybe tolerance in a chamber isn't the same as a dive.

My apologies to Centerius. I didn't notice he previously posted the article I did. Didn't mean to steal your thunder man.

Flatliner
08-29-2007, 20:58
Have any of you been in the chamber? I have never been in and hope would never have to be in one, but I have heard when they put you in chamber with pure oxygen, your minor cuts and bruises heal lot faster.

Any experience on that…… ?

They do use chambers to increase healing of wounds.

markndeana
08-29-2007, 21:09
Interesting article. thank you.

BSea
08-29-2007, 21:22
Oh and for a real world example. Back in the day the navy had my father down to 90 ft in a chamber for 30 minutes on pure o2. The test was designed to discover who was susceptible to oxygen toxicity and who was not. He had no problems, others did. It depends on the person, and your susceptibility is not the same day to day. So just because you can make it to 60 ft safely on 100% o2 today, doesn't mean you will be able to tomorrow.
You're right about how they navy test divers. I think I read where SEALS typically use 2.0 as the PO2 on their dives. Granted they are in much better shape & have been tested for their O2 tolerance.

So it probably isn't death if you breath pure O2 a little below 20 ft. But why risk it? Besides, what's the percentage of divers using pure O2? Even the really teckie diver I know rarely use more than 50/50. I know 1 that uses nearly pure O2 for safety stops & off gassing, but he's a little out there anyway.

torrey
08-29-2007, 22:36
Rick, occasionally the club will have a hyperbaric chamber rep come give a discussion at one of the monthly meetings. The primary focus is on treatment of open wounds. You might talk to Henry about bringing them in again for a meeting.

JahJahwarrior
08-30-2007, 17:51
[quote=TxHockeyGuy;39405] Besides, what's the percentage of divers using pure O2? Even the really teckie diver I know rarely use more than 50/50. I know 1 that uses nearly pure O2 for safety stops & off gassing, but he's a little out there anyway.

Down here, there are LOTS of cave divers. If you go to some rec shops, or if you are diving at the popular OW spots, you don't see very many stages filled with pure o2, but if you go to the shops that cater to technical/cave diving, it would be very odd to NOT see atleast one or two bottles leaning against the wall waiting to be picked up alabed "MOD 20." And when divers pull up and haul out the doubles, I'd bet money on their being a stage of pure o2 for offgassing/deco in the back of the truck too. But, most shops in town sell air and nitrox. That shop (and a few others I also know of) sells air, nitrox (banked at 32 and 36, I think, never bought nitrox), helium, o2 and argon. They can whip up any mixture of gas you would care to dive, and they do it cheaper than any shop in town.

So while in Arkansas many divers might not be using 100% o2, down here in Florida alot of technical divers use it very routinely. (but not rec divers. There are an awful lot of rec divers around too)

wgt
09-28-2007, 07:52
Oxygen Toxicity:

Under pressure, gases become more soluble in liquid. Pure oxygen breathed under pressure thus loads the liquid part of the blood, which only transports about 1% of your oxygen when breathing air at normal pressure. At three atmospheres of pressure in a hyperbaric chamber (breathing pure oxygen), the blood can carry an added 6 ml of oxygen for every 100 ml of blood. That is enough oxygen to keep you alive, even if you have lost all of your red blood cells. This means that high-pressure oxygen is great for some disease conditions characterized by inadequate delivery of oxygen (e.g., carbon monoxide poisining).

All of that added oxygen becomes dangerous, however, if too much of it is converted by the body into free radicals, highly reactive species that cause cellular dysfunction and injury. Over the course of many hours, the lungs may progressively fail. This can occur with pressures of oxygen of 0.5 atmospheres (e.g., breathing 50% oxygen for 24 hours). On the other hand, at the higher pressures (e.g., usually 3 or more atmospheres of pressure breathing pure oxygen in a hyperbaric chamber), the free radicals affect the brain in any of a variety of ways. The onset tends to be fast, providing little warning before a full-blown convulstion occurs. If one is lucky, a skilled technician may notice some warning signs (e.g., change in mood, pale skin, facial twitching) and remove the source of oxygen before the convulsive episode occurs.

In the hyperbaric chamber in clinically controlled conditions, seizures occur in roughly 1 of every 30,000 exposures to hyperbaric oxygen at absolute pressures of 2 atmospheres. The rate increases with added pressure. Conventionally, toxic reactions to oxygen are controlled by intermittent breathing of air and limited treatment durations. Patients are kept as calm as possible to reduce metabolism-dependent production of free radicals and carbon dioxide, and drugs can also be useful.

In the aquatic environment, physical activity, poor control of risk factors, accumulations of carbon dioxide, and perhaps some utterly unknown physiological mechanisms conspire to render persons more vulnerable to the toxic effects of oxygen. The point raised in a previous post is valid: Seizures themselves occurring in the hyperbaric chamber are a problem, but they are not inherently dangerous; seizures underwater are likely to be lethal. Those who survive such events may have interesting tales to tell (e.g., Jacques Cousteau).

In contrast to the perils of oxygen at depth underwater, one may find divers breathing oxygen at high concentration during deco stops. These stops would obviously need to be done in shallow water to avoid toxicity. However, under a bit of pressure, pure oxygen can significantly accelerate the shedding of nitrogen, thus reducing the chances of decompression illness.


Wounds:

When most of us cut or otherwise injure ourselves, the body undergoes a predictable series of changes that culminate in the healing of the wound within an expected period of time (that's why the cast stays on the broken leg for about 6 weeks). An important trigger of the healing is local hypoxia created by damage occuring to the local blood vessels. In an otherwise healthy person, new blood vessels grow into the wounded area to supply nutirents and rebuilding materials.

In some persons, however, healing does not occur as expected. Many factors can contribute (e.g., infection, malnutrition). Among the important predictors of failed healing is persistent hypoxia stemming from diseased blood vessels (as seen commonly in diabetics). When the disease is affecting primarily the small blood vessels, often in the feet, healing will probably fail. If the hypoxia can be reverse through the breathing of oxygen in the hyperbaric chamber, then the superoxygenation actually promotes the ingrowth of new blood vessels, and healing may be supported in a wound area that would not recover on its own.

The foregoing raises the question: Would hyperbaric oxygen accelerate the healing of minor wounds? This may indeed be the case. However, the savings in time in the healing of a minor wound that is going to heal on its own do not outweigh clinical risks and certain expense (it costs a lot of money to crawl into a chamber).


Cancer:

Hyperbaric oxygen is not used in the treatment of the tumors themselves, as suggested in a previous post. Its typical use relates to damage associated with radiation therapy for cancer. Radiation not only kills cancer cells, but it also kills or injures native cells like those forming blood vessels. Injured blood vessels may contribute to an inherently hypoxic environment that expresses non-healing wounds. Thus, hyperbaric oxygen is useful in the treatment of the condition known as radiation necrosis injury. In addition, it may actually play a preventive role in radiation necrosis injury. Before irradiating a cancerous jaw, teeth are removed surgically (they are going to fall out anyway from the radiation-induced damage). Before undergoing the procedure, a course of hyperbaric oxygen reduces ultimate structural damage associated with the course of therapy.

charlesml3
09-28-2007, 08:07
OK, I'm going to try to go back to what I thought was the real spirit of the question. These discussions on 100% O2 are academic at best. NONE of us are going to head down with a cylinder of 100% O2 because we all tested our tanks before we loaded them on the boat. Right? Given that:

Yes, you could potentially hit OxTox breathing Scuba mixes. Usually 32 or 36%. That said, it's pretty tough to do. When you're using Nitrox your dive computer is tracking oxygen exposure. That's not the same as nitrogen load. Nitrogen builds up in your bloodstream. Oxygen does not. The oxygen exposure bar on your computer is calculating how much O2 you've been exposed to over the past 24 hours.

I dive Nitrox whenever I can get it and as hard as I've tried, I cannot reach the "caution" zone of oxygen exposure before I hit my NDL. It's always Nitrogen load that's in control of the dive.

-Charles

wgt
09-28-2007, 08:39
Charles:

You are correct that the oxygen exposure feature of dive computers (geared at protecting the lungs) is a bit silly, perhaps decorative at best. Given the pressures and limited fractions of oxygen that we tend to breathe during realtively short exposures, the lungs are utterly unlikely to suffer from the breathing of nitrox during recreational dives.

On the other hand, full awareness of partial pressure of oxygen in relation to acutely toxic effects on the brain, the topic of the original question, is important. However, just as a good diver does not need a dive computer to reduce the chances of incurring decompression sickness, a good diver does not need a computer to tell him/her when the limit for the partial pressure of oxygen has been approached. Good training, good sense, and good experience can be brought along on every dive. To the contrary, computers can fail.

charlesml3
09-28-2007, 11:57
To the contrary, computers can fail.

Well yea, but most any thing _can_ fail. Your reg, your BC, etc. We all manage those risks by properly maintaining our gear and carry redundant systems for the most critical ones. I do not believe my computer is any more likely to fail than anything else. It's seen me through hundreds of dives and I consider it one of my most important pieces of gear.

If it were to fail during a dive I'd just head up. I'll know about how much gas I have left and I can tell when I'm 15' from the surface. I really can't imagine myself going back to diving tables. The computer lets me dive any kind of sawtooth profile I want. It tracks my Nitrogen load and O2 exposure automatically and in more detail than I could ever do by hand.

Anyway, I do agree with you. The best thing about the Nitrox class is the information on PP02, exposure and all the physiological issues. I'm one of those that really believes Nitrox is magic gas. Before I switched over, I was constantly hitting my NDL with plenty of gas in the tank.

-Charles

tbuckalew
09-28-2007, 12:14
Have any of you been in the chamber? I have never been in and hope would never have to be in one, but I have heard when they put you in chamber with pure oxygen, your minor cuts and bruises heal lot faster.

Any experience on that…… ?

I had the luck of taking a chamber "dive" in Munich, Germany back in 89 or 90 when I was taking my Avanced (now called Master) course.

The only dive rescue group in central Europe/southern Germany, Austria, was in one of the Munich fire stations. They had some nice gear, rescue boats, vehicles, and were a bunch of fun. They also had a chamber with operator on site and on call 24x7x365.

Our instructor was able to work out a visit in which we were to see and learn about the chamber. Afterward, they offered to give us a ride.

We were first searched of all metal and items creating friction and static due to the oxygen in the chamber (this included clicking pens, watches, belts, pretty much most of what we had with us). Those wearing jeams with metal on them were given shorts to change into.

I can't remember the equivelant depth of the "dive" - but I was told by them to log it, and I did. I'll have to pull that book out (still have that one) and see what it was - it wasn't that deep, somewhere between 60 and 80 feet I believe. It was an interesting experience, some loud noises, and they watched us extremely carefully and had the medic come out, just in case. The reason, we were told, was that some people are extremely susceptible to oxygen toxicity and they wanted to be sure we had immediate medical attention if one of us had a problem.

So, my ride wasn't for an injury, we did go below 20' on O2, they were very careful about possible injury because we were going "deeper than 4 meters", and they did explain that things in the chamber were different as we were not in the water.