X-Message-Number: 2884
Date: 12 Jul 94 23:33:46 EDT
From: Mike Darwin <>
Subject: CRYONICS Carotid Perfusion

Robert writes that the (I paraphrase here) "carotids do not provide adequate
flow in most patients and that is why Alcor cannulates the aorta..."

Actually the reverse is true.  In most people the carotids provide plenty of
flow, in fact you could probably perfuse a person's entire brain adequately
through *one* carotid -- this is because the two carotids and two vertebrals

join a circular structure (almost exactly like a European Traffic Circle) called
(appropriately enough) the Circle of Willis.  The purpose of the circle of
Willis is to protect the brain against *any* interruptions in flow even for a
brief period of time.  The reasons for this are twofold: 1) there is loss of

consciousness and the EEG becomes isoelectric after as little as 5-10 seconds of
no-flow (this is not conducive to survival) and 2) the brain is extremely
intolerant of ischemia and is incapable of spontaneous recovery from ischemic
episodes longer than 4-6 minutes under normal medical circumstances.

In a healthy, nonatherosclerotic human either carotid *should* do the job.  In
patients who have had slow progression of atherosclerotic disease it is not
uncommon to find that they are functioning on only their vertebrals or even
(rarely) on 1 vertebral!  Such patients are usually having problems like
transient ischemia attacks (TIAs) or are blind because of hyporperfusion of
their occiptal cortex!

In babies undergoing ECMO for respiratory problems, until recently, it was
common practice to just tie off one of their carotids after the procedure was
over! (Now they find out that a few such kids aren't quite as sharp as they
should be and guess what -- it's the  ligated (affected) hemisphere that is,
statistically, smaller).

Now, back to cryonics.  Another problem with perfusing through the carotids is
that some of your flow will "escape" through the Circle of Willis and down the
vertebrals (and thus down the drain).  This is annoying (and costly) when doing
closed circuit perfusion.  However, it is not normally a limitation when doing
open circuit perfusion.  As long as you keep your perfusion pressure at 40-60
mmHg you will perfuse the brain (as well of course, as loose some flow
retrograde down the vertebrals and to the drain).

So, where does this leave us as to why we perfuse through the chest rather than
the carotids here are most of the reasons:

1) It provides four possible paths to the brain thus protecting against
situations where due to atherosclerosis, post mortem clotting, or trauma one or
more of the vessels feeding the brain may be cut off from flow.

2) It conserves perfusate and allows for close-circuit perfusion.

3) It virtually guarantees that if the patient has a patent vessel to the brain
you will access it.  Sometimes you open the internal carotids only to find them
completely choked with plaque or so narrowed you cannot practically place a
cannula.  Another occurrence in the extremely elderly (atherosclerotic) or the

diabetic with advanced atherosclerosis is to have the carotid snap in two like a
piece of chalk when you try to elevate it for cannulation (I've seen the same
thing with the femorals).


4) A delicate, compromised, but still patent carotid may still deliver some flow
*if* no one has tried to cannulate it and failed, or broken it in half.  It is
thus safer to make your mistakes further away from your point of last recourse
(i.e., in the chest) and you are also likely to find the aorta easier to
cannulate.  Even in the chest there can be problems.  Dora Kent's aorta was so
calcified that we literally could not get an occluding clamp to close on it --
it was like a piece of cast iron pipe!

Now, back to your situation in Australia.  In most people you can use the
carotids and I would recommend using both (i.e., cannulating both).   Talk to
your mortician, but I think he will confirm that it is only in a minority of
cases that you encounter such severe atherosclerosis as I've described.

If everything goes *lucky* for you, you may get your patient to Alcor in a
timely fashion.  However, if it is a weekend or any of a number of myriad other
emergencies and delays occur you may find that not possible.  Since you are

prepared to go 3/4th of the way down the road, you might as prepare for the last
1/4 of the way.  The odds (in my opinion anyway) are just not good enough,
otherwise.

If you need blood pumps, circuits, oxygenators and so on I sell them at very
reasonable rates.

Mike Darwin

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