Oxygen Toxicity Discussion

[Dirty-Dog]

The sad truth about the medical field is that "probably" is about as definitive as it gets!

Hey! Sometimes it's "most likely" or even "almost surely" or "my best guess is...".

 

[Tigerman]

Hey! Sometimes it's "most likely" or even "almost surely" or "my best guess is...".

Well, atleast cyanide is pretty definitive

 

[Abdullah]

Doppler has a good article on CNS toxicity limits here

 

[DeepSeaDan]

My recollection from Nitrox training and review of DAN research is that there have been isolated cases of convulsions and/ or blackouts at ppO2 as low as 1.4, with higher frequency (though still low probability) of toxic effects at ppO2 of 1.6. My recollection is that the recommended maximum ppO2 level for Nitrox diving is 1.2. So, if diving Nitrox 32, maximum safe depth is about 90 feet. For Nitrox 36, maximum depth is about 70 feet. Using the same standard of max ppO2 of 1.2, maximum depth on air is about 160 feet. ppO2 of 1.8 would be considered VERY risky - anything more than a minute or two at that depth and there is a 50% or higher chance of adverse reaction from Oxygen toxicity. And you have to count the time that divers spent going from 160 feet (where ppO2 is 1.2) down to 250, and the time ascending back up to 160. I didn't learn about Oxygen toxicity until I took the Nitrox class. I wonder how many of these deep-diving morons never took the Nitrox class and were completely unaware of that particular risk? Is Oxygen toxicity risk covered now in the OW or AOW classes?

Back in the day ( 1979 ), in order to continue on in my commercial diving program, we had to pass an "O2 Tolerance Test" - the same test given to U.S. Navy Diver candidates. The test was to breathe 100% O2 @ 60' in a recompression chamber, for a total of 30 minutes. I'll always remember my test; at 29 minutes, one of my potential classmates started convulsing. If I recall correctly, out of 151 guys enrolled in the program, he was the only one who failed the test.

Years on into my career I heard that the test had been eliminated by most commercial diving training institutions. Perhaps a more recent graduate could confirm this.

Regards,
DSD

 

[uncfnp]

Looking at the limited research and anecdotal information available, there really is no compelling evidence against sudafed. The DAN article could find no documentation of association between sudafed and oxygen toxicity and there is only one limited known study in rats with a drug similar to sudafed that "seemed to enhance oxygen toxicity." Most of the arguments against sudafed are theoretical and based of the mechanism of action for this class of medications in that they may "enhance susceptibility to oxygen convulsions."

Given the number of divers that use sudafed to dive, including myself, it seems improbable that there would be a high correlation and not more anecdotal or physical evidence. As a precaution, it would be reasonable to avoid sudafed for deep dives or dives that push the ppo2 limit. An alternative if a decongestant is necessary for recrecational dives would be a nasal spray such as Afrin that would have less systemic effect then the oral counterpart. But nasal decongestant use should be limited to 3 to 4 days to avoid the rebound effect possible with nasal decongestants.

To me, a greater theoretical concern with sudefed would be the CVS side effects of oral decongestants rather then the CNS. Given the rare oxtox vs cardiovascular diving events and the, in my experience, greater occurrence of cv side effects with sudafed, I wonder if there is a correlation there. Has this been studied?

 

[DandyDon]

Just a note here: Y'all are using the brand name Sudafed in discussion, but that name is applied to several OTC meds.

I think the actual med intended to be discussed is Pseudoephedrine which can affect some people more than others, but is still the best decongestant I can find.

 

[tracydr]

Afrin has a pretty strong systemic effect. Anesthesiologist use it, or a very similar product, to bring the blood pressure up, especially on laboring pregnant women.

 

[boulderjohn]

Back in the day ( 1979 ), in order to continue on in my commercial diving program, we had to pass an "O2 Tolerance Test" - the same test given to U.S. Navy Diver candidates. The test was to breathe 100% O2 @ 60' in a recompression chamber. I'll always remember my test; at 29 minutes, one of my potential classmates started convulsing. If I recall correctly, out of 151 guys enrolled in the program, he was the only one who failed the test.

Years on into my career I heard that the test had been eliminated by most commercial diving training institutions. Perhaps a more recent graduate could confirm this.

Regards,
DSD

This information has been discussed in several threads in recent months. I will try to summarize the key ideas as I understood them.

1. The ability to withstand an OW toxicity hit in a chamber is for some as yet not understood reason very different from withstanding it under water. In a chamber you can go to much greater pressure without toxing than you can in the water. That makes the test pretty worthless.

2. An O2 toxicity hit is unpredictable. You might tox on Wednesday at a depth at which you were perfectly fine on Tuesday. That makes the test pretty worthless.

I believe it has been generally discontinued, although different commercial diving training operations might still use it.

 

[uncfnp]

Afrin has a pretty strong systemic effect. Anesthesiologist use it, or a very similar product, to bring the blood pressure up, especially on laboring pregnant women.

i admit I don't have a statistical comparison of systemic side effect profiles between Sudafed (pseudoephedrine) and Afrin (oxymetazoline) but my understanding is that Afrin has less of a cardiovascular impact and as such is a safer alternative for short term use in people with hypertension or the elderly. How this would translate to oxygen toxicity, no idea...

 

[DeepSeaDan]

This information has been discussed in several threads in recent months. I will try to summarize the key ideas as I understood them.

1. The ability to withstand an OW toxicity hit in a chamber is for some as yet not understood reason very different from withstanding it under water. In a chamber you can go to much greater pressure without toxing than you can in the water. That makes the test pretty worthless.

2. An O2 toxicity hit is unpredictable. You might tox on Wednesday at a depth at which you were perfectly fine on Tuesday. That makes the test pretty worthless.

I believe it has been generally discontinued, although different commercial diving training operations might still use it.

A chamber is a comparatively warm, comfortable place, and we were at rest, so it stands to reason that a body might withstand a higher PO2 for a longer period of time in a chamber. I treated a few divers in saturation who became symptomatic of bends during the ascent profile; they both experienced pulmonary irritation due to the higher PO2 of the treatment gases, which adversely affected their scheduled treatment.

O2 is a wonder drug for most divers, most of the time, but it isn't perfect by any stretch.

Regards,
DSD