RE: Hyperbaric oxygen for brain injury

[Guest guest]

Oxygen, when administered at pressures typically used in hyperbaric oxygen

(HBO) therapy, can cause cerebral vasoconstriction through inactivation of

nitric oxide. It was once believed that other free radical species, such as

superoxide dismutase, were involved but this has pretty much been disproven.

This pertains to oxygen at HBO pressures and not oxygen at 1 atmosphere.

Interestingly, the research does not show any benefit to using HBO for

stroke and head injuries. Likewise, the prevailing science does not show any

benefit of HBO therapy for carbon monoxide poisoning.

This argument involves basic science studies that are inconclusive and might

confuse a novice list reader. I would encourage EMS providers to learn more

about nitric oxide as it is becoming increasingly important in emergency

medicine.

BEB

From: Paramedicine [mailto:Paramedicine ] On

Behalf Of krin135@...

Sent: Sunday, March 11, 2007 11:34 PM

To: Paramedicine

Subject: Re: Hyperbaric oxygen for brain injury

In a message dated 3/11/2007 11:02:34 PM Central Daylight Time,

lnmolino@... <mailto:lnmolino%40aol.com> writes:

In a message dated 3/11/2007 10:23:30 P.M. Central Daylight Time,

_wegandy1938@wegandy_ (mailto:wegandy1938@...

<mailto:wegandy1938%40aol.com> ) writes:

And at what partial pressure does oxygen become toxic to humans?

I admit I had to look up the exact numbers but I recall from my Open Water

Diver days that 100% O2 is toxic to the CNS at 2 atmospheres (AKA 33 feet of

depth) and that this is a rapid onset of under one hour for CNS toxicity.

And

further that at greater then 300 feet compressed breathing air (21% O2

nominal) becomes toxic.

good start...this is part of the reason (the others being expense and the

detail that Heliox mixes suck heat out of your body) that various Trimix

(Oxygen, Nitrogen, Helium) gases are used for deep/saturation work during

commercial, historic and serious recreational dives.

ck

S. Krin, DO FAAFP

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[Guest guest]

I've been a DMT for about ten years now. In that time I have studied

the positive side of Hyperbaric Oxygen on multiple problems ranging

from dive injuries using Heliox to necrotizing fasciitis. One a bit

more common are Carbon Monoxide injuries. As we all know, the problem

with CO poisoning is that the CO overpowers the hemoglobin and takes

the space that is normaly filled by Oxygen. The affinity between

carbon monoxide and hemoglobin is 240 times stronger than the affinity

between hemoglobin and oxygen.

When a patient is put into a hyperbaric chamber (preferably

multiplaced so that there is an inside tender to treat other problems)

they are hooded and fed 100% oxygen.

Some voodoo medicine here: If a patient is compressed to 60 ft

(roughly 2.81 atmospheres absolute) and placed on 100% oxygen they

will receive a surface equivalent value of 281% oxygen.

Now think of CO poisoning in simple terms. If you have 20 seats on a

bus (you being the bus, seats being hemoglobin). Those seats are

usualy filled at a one for one ration of butts to seats (oxygen

molecules to hemoglobin). When you introduce carbon monoxide onto the

bus, it steals the seats (CO binding to hemoglobin) and takes up the

spots the oxygen would normaly take. ...but it doesnt take them

all....there are still some seats left open. When we put patients in

a hyperbaric environment as discussed above the oxygen molecules are

compressed, thus able to put more butts in one seat. On the surface

CO is 240 times stronger, at depth O2 is given the same (if not more)

binding capability.

As to the first question regarding Oxygen Toxicity. The max depth in

a chamber at which one would breath 100% O2 is 60ft (2.81 ATA). The

max amount of time at depth on such O2 would be 60 minutes (60/60).

During that time, the patient must be at rest and have a minimum of a

five minute air break (breathing normal chamber air (71/29) in the

middle of the dive.

This would not be conducted at depth by a diver under strenuous

conditions. The diver would experience oxygen toxicity. The effects

would be what is know as the " chokes " (little spasms). These effects

would be remedied simply by moving to a shallower depth.

O2 toxicity varies on two factors: time and amount. It gets a bit

more tricky because that figure changes with pressure (surface O2 vs.

compressed),but that falls into the ammount category.

Ref:

www.uhms.org

http://www.hyperchamber.com/carbon_monoxide_poisoning/index.htm

.....hope this helped/made sense.

Ed

--

Edwin Lard

The Castillero Group

Protective Security Consulting

Near East/Latin America

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