X-Message-Number: 2645
Date: 14 Mar 94 18:26:16 EST
From: Mike Darwin <>
Subject: SCI.CRYONICS Regarding BPI Tech Brief #5

Tim Freeman wrote to ask about the use of antifoam A.  Essentially his
question was: "Is the Antifoam-A eluted from the surfaces it is put on,
and does it then get perfused into the patient, and is this harmful?"

Good questions.

Antifoam-A has a long history in cardiovascular perfusion.  It was used in
the very first bubble oxygenators to convert the air/blood or oxygen/blood
foam (through which gas exchange occurred) back into a liquid before it is
perfused through the patient.  I am no expert on Antifoam-A but my
understanding is that it is not very soluable.  Indeed, if it were it
would quickly dissolve off of the defoaming column in the oxygenators and
cardiotomy reservoirs and cease to be effective.   Having said that I
would also say that it is a little soluable and no doubt small amounts of
it do dissolve in the perfusate or blood.  And no, this is not harmful,
at least not in any "gross" sense.  (Yes, there probably are statistical
effects such as 1 in every 200,000 people so exposed will develop a
silly-oma in 400 years -- the usual).

Also, it is worth pointing out that Antifoam-A is effective in very tiny
amounts.  To coat the VBL I simply moisten a laparatomy sponge (gauze
pad) with a dilute solution of Antifoam-A and wipe down the lid before
wrapping/sterilizing it.

Lucky thing all the work with Antifoam-A was done 30 years ago.  Now, with
FDA regulation of medical devices, it would be prohibitive to have
introduced such a product into medicine.  The course of cardiovascular
surgergy would have been radically altered with progress in open heart
surgergy being delayed for decades -- or longer.  Many, many lives would
have been forshortened as a consequence.  

And yes, it would be my guess (completely unsupported) that some idiot
somewhere could find some biological effect of Antifoam-A during toxicity
testing that would make the FDA stop its introduction.  And the pity is it
would all seem PERFECTLY REASONABLE since no bureaucrat and damn few MDs
would ever have believed that cardiovascular surgery would have been
possible or as commonplace as it has become 30 years ago when it was in
its infancy.  The flapping of a butterfly's wings can start a hurricane if
they are placed just right and just when...

One of the first bubble oxygenators was the Travenol VFI bubble
oxygenator.  It consisted of two sheets of vinyl plastic welded together
to form a blood path with a defoaming column consisting of big wads of
stainless steel wire sponges coated with Antifoam-A (the kind of thing
they used to make to scour kitchen sinks with).  The priming volume was
650cc! Ahhh those were the days...  You can just imagine how the blood
liked being frothed into foam and then being run over wire sink
scratchers.  Compared to today's hollow fiber membrane's there is no
comparison.  Still, it worked surprisingly well.

More to the point, cryoprotective agents may dissolve Antifoam-A, although
I have seen no evidence of this with glycerol.  One of my first
experiments was conducted with a few drops od dish detergent added to the
recirculating reservoir to create foam for my test runs.  The soap was
great at making microbubbles, but it killed the Antifoam-A!  It took me
an embarrassingly long time to figure out that that was why my defoaming
wasn't working.

Several people wrote to explain how I can include graphics with my
articles in the future.  I will work with my computer maven(s) on this end
to implement their advice.  It really was a shame not to be able to post
the graphics with Tech Brief #5 because they were very nice and really
supported the text.

Our thanks to all who have written and shown interest in the Tech Briefs.

Mike Darwin

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