Nitrogen Narcosis and Nitrox

[boulderjohn]

The book also states that the active ingredient in decongestants may act as o2 exciters but it does not state what this ingredient is. I asume its psudoephidrine. Is this correct or are there other drugs too?

The contention is that using Sudafed increases the risk of CNS Oxygen toxicity. DAN did a study of this, and it is available on their web site. It is a very interesting study in its wording--especially if you are familiar with the normal wording of such studies.

http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=51

It is interesting because it spends a lot of time telling you how studies work and what constitutes valid evidence. It then tells you that there is almost no valid evidence. All real evidence related to Sudafed (or Afrin) is anecdotal. A few divers were taking Sudafed or Afrin and died under unusual circumstances. In some cases, they showed signs of panic, which can be a symptom of CNS O2 toxicity. It is not clear that they actually had CNS O2 toxicity, and if they did, it is not clear that taking Sudafed had anything to do with it. In most cases, the DAN study discounts a connection. In addition, most of the cases were on air, not Nitrox. If pseudoephidrine were involved, it is more likely to have been a reaction of the individual diver to the drug itself--some people react to drugs differently from others.

The report then says that if that was all there was to go on, then they would say there is no indication of a cause for concern--you must be able to show some kind of causative link between the Sudafed and the symptoms. In a search of the literature, they found a 44-year old study (before the existence of Sudafed) that indicated that an ingredient similar to pseudoephidrine seemed to increase the risk of O2 toxicity in rats.

By focusing on the lack of real evidence in preparing you for their conclusion, DAN tells you clearly that their conclusion is based on the skimpiest evidence that they could possibly use. Their conclusion is that pseudoephidrine is probably safe, but it might be a good idea to avoid chronic use, and that it might be a good idea to avoid pseudoephidrine if you are going to exceed PO2 of 1.4 ata--which you should not do anyway.

Here it is verbatim:

What's the bottom line? In normal, healthy divers breathing air, occasional use of pseudoephedrine at the recommended dose is probably safe. This presumes that the drug has been taken during periods when no diving has occurred and that no undesirable reactions have occurred. However, one should avoid chronic (daily) use when diving, and it seems reasonable to avoid the drug entirely if diving while using oxygen-nitrogen mixes where the PO2 during a dive might exceed 1.4 ata, the current recommended "safe" open-circuit scuba limit.​

 

[havnmonkey]

not quite

diving nitrox on air tables gives you a greater safety margin as to decompression
issues, since you are essentially diving "shallower" by diving with Nitrox (as compared
to air, which you are planning your dive with).

but there's enough nitrogen in nitrox to really give you a good buzz, equivalent to air, at any depth

But wouldn't diving Nirox on Air tables expose you to less N2? So less chance of DCS (theoretically and dependent on diver/conditions/activity) and also less extent of Nitrogen Narcosis because of the lower level of N2... Right?:huh:

 

[MikeFerrara]

But wouldn't diving Nirox on Air tables expose you to less N2? So less chance of DCS (theoretically and dependent on diver/conditions/activity) and also less extent of Nitrogen Narcosis because of the lower level of N2... Right?:huh:

Less total yess but not a lower partial pressure. The important factor in narcosis is the partial pressure of the narcotic gas. It's not dependant on tissue gas loads as DCS is. The things that reduce the risk of DCS don't necssarily reduce the risk of narcosis. You can dive a very narcotic gas very deep and as long as your decompression is adequate you may not get DCS even though you were very narced. Reducing your time at depth (with that same narcotic gas) may reduce the risk of DCS but you'll still be very narced.

On the other hand you can get yourself all bent up using a less narcotic gas like helium and not get narced. The mechanisms are completely different (even if I didn't do a great job of explaining it).

 

[Packhorse]

But wouldn't diving Nirox on Air tables expose you to less N2? So less chance of DCS (theoretically and dependent on diver/conditions/activity) and also less extent of Nitrogen Narcosis because of the lower level of N2... Right?:huh:

If you dive a 32% nitrox mix compared to air you are using 50% more oxygen but only 16% less nitrogen. So based on this alone you may asume you only have a 16% less chance of nitrogen narcosis. And then add into that the 50% increase chance of O2 narcosis.
Does this sound right or have I got it all wrong?

 

[wedivebc]

If you dive a 32% nitrox mix compared to air you are using 50% more oxygen but only 16% less nitrogen. So based on this alone you may asume you only have a 16% less chance of nitrogen narcosis. And then add into that the 50% increase chance of O2 narcosis.
Does this sound right or have I got it all wrong?

No one is really sure what effect if any oxygen has on narcosis so it generally accepted that any effect will be somewhere between little and none. The effects are not cumulative and since O2 becomes toxic at a partial pressure well below that where it is likely to cause any narcosis effect it is very hard to judge. That means for practical purposes nitrox changes nartcosis either very little or not at all depending on which "experts" you believe. The true experts say they don't know for sure.

 

[havnmonkey]

word...

 

[Albion]

If you dive a 32% nitrox mix compared to air you are using 50% more oxygen but only 16% less nitrogen. So based on this alone you may asume you only have a 16% less chance of nitrogen narcosis. And then add into that the 50% increase chance of O2 narcosis.
Does this sound right or have I got it all wrong?

Any nitrox mix is narcotic to some degree, you just dont realise how much until you tried Trimix (ok i sound a bit smug here). I hav efound that ultimately it is your stress level which determines how narced you are, or when you (or your buddies) realise how narced you are.

 

[Rick Murchison]

Oxygen has about twice the lipid solubility as nitrogen, so, by that gauge, should be about twice as narcotic.
However, oxygen is both used in metabolism and scavenged by hemoglobin, so tissue levels are far below what you would expect were it an inert gas just getting transported like Nitrogen. Measurements in rats' brains show oxygen levels to be about a sixth +/- what you would expect if it were inert... so... twice the lipid solubility and a sixth the expected concentration... shall we say, oh, a third as narcotic as nitrogen?
Maybe, maybe not.
As WediveBC mentioned, narcotic partial pressures of pure oxygen are well above toxic partial pressures, so studies are sort of impractical, and oxygen's effect can only be guesstimated in concert with other gasses.
My take? I like the SSI wording: "It is best not to assume any reduced narcosis from Nitrox."
And I calculate my narcotic depth on trimix giving full narcotic value to the partial pressure of oxygen - that is, END in ATA = PPO2 + PPN2. That sort of assumes the small narcotic value of Helium is accomodated by the somewhat lower theoretical (based on the 2 X 1/6 outlined above) narcotic value of oxygen, eh?
Rick

 

[Web Monkey]

Question is does diving nitrox or trimix lower the effect of narcosis?
In the SSi nitrox book it says" You should not count on experiencing less narcosis or impairment". But if this is the case how do deep (50m+) divers deal with it?
What are your personal experiences? Is it a measurable effect that you caculate like EAD or PPN ?
The book also states that the active ingredient in decongestants may act as o2 exciters but it does not state what this ingredient is. I asume its psudoephidrine. Is this correct or are there other drugs too?

I've never been to 50m, but I've been to 40m on Nitrox 28 a number of times.

Once was in Tobermory. I just enjoyed the wreck, understood I was pretty well narced, and tried to not win any Darwin awards.

It's hard to do a lot of thinking when you're that fried, so I just worked on the basics (breathe, go slow, and keep checking my depth and tank pressure).

Probably the hardest part was remembering what my gauges said. I'd read the gauge, put it away, then not rememeber what it said, so I'd go check it again.

OTOH, compulsively checking my depth and pressure s probably a lot safer than forgetting them completely.

Also, the effect seems to depend a lot on the conditions. 40m in warm, bright blue Carribean water seems completely different than 40m in freezing cold darkness.

I wouldn't expect a whole lot of difference between air (21% O2) and Nitrox (28% O2), in terms of how narced you feel.

Terry

 

[Rick Murchison]

I am one who recommends extreme caution when it comes to over-the-counter oral cold remedies and decongestants. If you read their side effects you'll find a litany of nerve related unpleasantries. In my case, a single Sudafed/Actifed/Teldrin/etc can cause an irregular heartbeat for several days. Not painful but very disturbing and makes me very suspicious of those drugs' safety w/r/t elevated PPO2 use.
Rick