Nitrox's O2 toxicity VS O2 in hospitals

[JonOh]

Thanks for finding that article. It was very informative. And it is very interesting that we still don't know why a wet exposure increases the risk of CNS tox.

 

[boulderjohn]

Thanks for finding that article. It was very informative. And it is very interesting that we still don't know why a wet exposure increases the risk of CNS tox.

The amount we still don't know about scuba in general is really astounding. The more I learn about it, the more I realize how little we really know.

 

[JonOh]

If you don't have time to read the Navy Manual, maybe read this: Scuba Dive Medical Articles ? Decompression, Heart Safety ? DAN | Divers Alert Network. It was in one of the links that JohnN attached.

It is a dumbed down version with lots of info. Gives you the why, what and how of O2 exposure

 

[KD8NPB]

ppN2 is 1.0 at 8.77 ft. You are correct that you would have an infinite dive time with a ppN2 of 1.0, but no specifically because it is 1.0 atm.

In the case of nitrogen, you are ongassing as long as the level in your tissues is less than the level you are breathing, so at 8.77 feet, you will definitely be on-gassing nitrogen initially as your tissues will start out with a ppN2 of of 0.79.

---------- Post added March 7th, 2013 at 02:15 PM ----------



I have never seen anything suggesting that O2 toxicity is different in the water. However, if you have a seizure in the water, you die. If you have a seizure in the chamber, you live.

Whoops, I had a math error there while calculating ppN2. Divided the wrong way!

So who wants to discuss the oxygen window?

 

[Seefourdc]

100% oxygen for an extended period of time is damaging in any environment. Also for the purposes of respiration there is a negligable difference between 60% O2 and 100% O2 due to Hgb binding characteristics, but sometimes that negligable difference is the difference in keeping a patient alive in the medical setting.

 

[rakpix]

What everyone else said is true, but to take it a little further....

It is my understanding that for reasons that no one understands, O2 toxicity happens in water differently than on land. When a person is on O2 under pressure in a recompression chamber, they apparently have to go much "deeper" to have the same effect that would happen on scuba.

You are correct in that the physiology of a dry dive and a wet dive are quite different. Inpatient hyperbaric oxygen therapy (HBOT) is routinely administered as high as 3.0 ATA. This is most safely provided at a multilock multiplace facility, where staff are better equipped to prevent seizures and can intervene in case of a seizure. At facilities that provide air break(s), we see fewer seizures. However, at facilities that provide air break(s): when a seizure occurs, it tends to occur during an air break. The consequences of a seizure in a dry environment pose a lower risk than those in a wet environment. In addition, the likelihood of experiencing CNS symptoms at a given ppO2 is less in a dry environment than a wet environment. This may be related to the documented effect of immersion on intercranial pressure (ICP) in primates. It has also been connected to the effect of negative-pressure breathing.

http://www.ncbi.nlm.nih.gov/pubmed/1567318

 

[TONY CHANEY]

There are a few differences here. Most often you are not breathing 100% O2 in a hospital. You may have a mask on but your likely mixing regular air with a little 100% O2. That's why if your suffering from a DCS hit you want that O2 delivery system cranked up to 15 lpm.

In one aspeck you are right...mask but for intubated patients some are receiving 100% O2. I do it all the time.

 

[Hatul]

It's been pointed out before, but it's the ppO2, not the FIO2 that your body cares about, and in the hospital we don't exceed a ppO2 of over 1 atm, and it's the hyperbaric ppO2s that cause the ox tox seizures.

 

[eweingarden]

The only way a patient in the hospital can get 100% oxygen is if they have an endotracheal tube in the trachea, and on a mechanical ventilator. It is only in extreme circumstances that a patient would be kept on 100% O2; that being if it were difficult to oxygenate the patient. There is a different form of oxygen toxicity in ventilated patients. Long term ventilation with 100% O2 would damage the lungs and lead to further difficulty in getting O2 into the body. If a patient's oxygen saturation could not be kept at an acceptable level, 100% O2 might be used for the shortest time possible, while other measures were taken to improve the oxygenation status.

 

[eponym]

Good discussion, thanks everyone.

So what about the same pp of 02 but in a chamber VS water. Will the effects of O2 toxicity be the same? There was a previous poster that said water might have a bigger effect on how the body gets 02 toxicity and it might actually be worse.

3‑9.2.2.1 Factors Affecting the Risk of CNS Oxygen Toxicity. A number of factors are known to influence the risk of CNS oxygen toxicity:
Immersion in Water. Immersion in water greatly increases the risk of CNS toxicity. The precise mechanism for the big increase in risk over comparable dry chamber exposures is unknown, but may involve a greater tendency for diver CO2 retention during immersion. Exposure limits must be much more conservative for immersed divers than for dry divers.

CO2 retention in divers is a fascinating subject. I recommend pages 134-135 of Jolie Bookspan's Diving Physiology in Plain English as an introduction to the concept.

One of my deco diving courses included a discussion of the vasodilation effects of CO2. This was cited as one factor that can increase the possibility of CNS toxicity at a given ppO2. And a darned good reason to work as little as possible at depth.

Another concept was that since we were supposed to be relaxed and not working while hovering at our deco stops, we could breathe higher pressures of oxygen than are suggested as limits for nitrox divers. This might not be current best practice, I don't know, but I remember breathing a deal more than 1.6 atmospheres of oxygen on stops.