On pumped fuel gases: Point well taken, you're correct that it used to
be at least partly carbon monoxide. I think that industrial fuel gases
were even purer CO at one time. I have a vague memory that it was
produced by passing flue gases through heated iron pipes to convert CO2
to CO--is that correct?

On helium solubility: Thanks for the note, I wasn't aware of Trimix.
Similarly, I didn't know helium had a drug effect. Xenon must have the
most of all the noble gases; it has good anesthetic effect at about 70
Torr and is currently being proposed for actual surgical anesthesia. It
has the interesting problem of not being patentable, and therefore not
worth any company's money to get through FDA approval, so it may never
appear on the drug market. Of other small, nonpolar molecules, the one
I'm sorry I missed (it was gone before I started my practice) is
cyclopropane. It's similarly very blood insoluble and therefore
fast-acting (more on that if anyone's interested). It has the problem
of being not just inflammable like ether, but explosive. Spark
suppression used to be a big deal in operating room design.

Another interesting suicide-by-oxygen-dilution problem is automobile
exhaust. Catalytic converters work well enough that running a car
engine in a closed garage frequently produces anoxic brain damage (CO2
poisoning) rather than death (CO same). Perhaps that happens to some of
the suicides who are unaware that fuel gas got swapped for methane.

Things were quiet in the operating room today, and I had an hour to chat
with the anesthesiology residents. I told them about this Usenet
discussion and asked them to distinguish CO2 poisoning from that by CO.
They didn't do very well.

David

Don W wrote:
Hi David,

David Kazdan wrote:

Helium is almost exactly the dilutional asphyxiant that nitrogen
is. It's used in deep-diving artificial atmospheres for two reasons:
Nitrogen is a weak anesthetic gas, producing intoxication at several
atmospheres pressure--(nitrogen narcosis"), and it's soluble enough in
blood and other water-based body fluids to fizz out when the pressure
is released suddenly (the bends, caisson worker's disease). "Helium
has neither of these properties."


snip

David


David Kazdan, MD, PhD
Anesthesiologist
Pilot

I hesitate to enter this discussion since you are obviously well
qualified, however, that is often how learning occurs and I still
have a lot to learn.

I agree with all of your excellent post with one minor exception.
Helium _is_ absorbed into the bloodstream under high enough partial
pressure and does release bubbles when the pressure is released
too quickly. Heliox (Helium + O2) and Trimix (Helium + N + O2) are
common gasses used in the technical diving community, and they both
require decompression stops on the way back to the surface. Technical
divers use these mixes for dives from 130' (~5 atmospheres) to as much
as 1000' (~31 atmospheres). The O2 content of the mixes is reduced to
avoid oxygen toxicity effects at high PPO2. I also would point out
that helium at high PP--although not narcotic like Nitrogen--does
produce some strange physiological effects including a "buzz" similar
to having had a lot of caffein.

Don Woodbridge P.E.
Engineer
Technical Diver
Pilot