hyperoxia and drain bamage

[do it easy]

i read on the internet that lack of oxygen can cause brain damage in 4-6 minutes, but what about when the diver is hyperoxic before he stops breathing. how much longer will the extra oxygen prevent permanant/serious brain damage.

let's say for the sake of the discussion, that the diver is breathing 100% O2 at 20 feet before he stops breathing. does the standard 4-6 minutes apply?

 

[TSandM]

Oxygenating with 100% O2 buys more time. This is standard practice, for example, in the operating room, where patients are pre-oxygenated with 100% before placing the endotracheal tube, in case there are difficulties getting it in. But one must remember that, while the patient has more time to consume oxygen, carbon dioxide is still being produced and not being carried away. Higher CO2 levels lead to acidosis, which is dangerous in and of itself.

If someone breathing 100% O2 at 20 feet stops breathing, they will have more time before irreversible brain damage sets in. But breathing O2 in order to breath hold longer or anything like that would be quite dangerous and inadvisable.

 

[do it easy]

If someone breathing 100% O2 at 20 feet stops breathing, they will have more time before irreversible brain damage sets in. But breathing O2 in order to breath hold longer or anything like that would be quite dangerous and inadvisable.

thanks, do you have any rough idea about how much time before brain damage and/or acidosis gets dangerous?

also, i assume that O2 and apnea is a bad idea because of the CO2 blackout danger?

 

[Dr Deco]

Hello easy:

There is no question that extra oxygen will help if you stop breathing underwater. The question is, for how long? The problem with the brain, in this case, is that it is very active metabolic system. It uses about one fifth of the energy in the body, even while asleep. Thus, the oxygen that you have in your breathing gas will not add many minutes to the time before injury.

The only successful method for warm-blooded creatures is to reduce the metabolic rate by cooling . [Hibernation would work but cannot yet be done. :snore: ]

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology is September 10 – 11, 2005 :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[TSandM]

You don't buy a great deal more time, and this is why: Most of the oxygen in the blood is carried on hemoglobin molecules, not dissolved in the liquid part of the blood. In a person with normal lungs breathing 21% O2, hemoglobin will be almost totally saturated -- in other words, it's already carrying as much oxygen as it can hold. Raising the inspired O2 level does not load the hemoglobin much more, if at all. Raising the inspired O2 DOES dissolve more oxygen in the liquid portion of the blood, but this is a very minor portion of the total blood oxygen content. As a result, total blood oxygen increases very little, and time to brain damage increases only slightly. The main value of breathing 100% is that you can be pretty sure the hemoglobin is entirely saturated at that inspired oxygen level.