X-Message-Number: 33375
From: 
Date: Mon, 28 Feb 2011 01:56:27 EST
Subject: Melody Maxim's Distorted Reality 10

Content-Language: en

 
Mathew Sullivan: This isn't necessarily an argument against  filtering 

venous return, but to the extent that a clot may have gotten past the  arterial
pump, the clot filter prevents it from getting into the patient. I'm  not 
aware of any cases where the clot filter clogged and had to be swapped out.  
Aside from any potential concern of the arterial filter getting clogged, are  
there any other reasons to take into consideration? Could you provide more  
information on the filtering of the venous return? The reason why I ask is  
because I learned at Mechanisms that the cardiotomy reservoir has become 
the  scourge of perfusionists because it is a major source of micro bubbles, 
so I'm  curious to know if it is an internal filter or separate from it, and 
to what  extent it might introduce micro bubbles. At a minimum, I recommend 
that the  waste dump line be split off prior to reaching the filter to help 
ensure that  the filter does not become clogged during washout, similar to 
the way you  currently have it setup on the training pack.  
Mike Darwin ***Clotting should not be a problem in any cryopatient  who is 
a candidate for closed-circuit perfusion (recirculation). I have  

occasionally seen cast clots of the femoral artery or vein in patients who were
cutdown within 45 minutes of arrest and who were also promptly heparinized,  
medicated, and given closed-chest CPS and cooling. These clots appear to be  
antemortem due to profound shock and accompanying peripheral hypostasis. 

Despite  this ominous finding, Ive never seen macro clotting beyond this. In 
cases 
where  such a clot is found it is simply extracted with clot forceps; in 
all cases  these have been well formed, dark, retracted clots.  
If visible clotting (as opposed to cold agglutination) is observed  during 
blood washout, then the patient is not a candidate for recirculation  
barring the presence of a skilled perfusionist.   
Mathew is right on target about air bubbles and debris from  cardiotomy 
reservoirs and hard-shell venous reservoirs and there are additional  
considerations which are unique to cryonics cases:  
1) The higher (beyond safety constraints) that you run the  perfusate level 
in a reservoir the more microbubbles you will typically form.  This is 
especially true in hardshell reservoirs because they have a large column  of 
poorly stirred fluid with a debubbler column of open cell urethane foam  

covered with nylon tricot. The big column of poorly stirred fluid is the first
problem because it is cold. Because it is both cold, and far below ambient  
temperature, it will out-gas, or fizz. Unlike solids, gas solubility in water 
is  directly related to temperature: the colder the perfusate is, the more 
dissolved  gas it will hold. Any uninsulated standing reservoir of cold fluid 
will warm up  and will generate microbubbles. Soft drinks go flat very fast 
at ambient  temperature for this reason.  
2) An added problem is that the urethane and nylon tricot serve as  
fantastic nucleating sites for bubbles. Thus, they actually favor microbubble  

formation. You can see the same effect in soft drinks if you note that most of
the bubbles form on the interior of the glass and on the ice cubes; the 
latter  being far colder than the glass.  
3) Compared to plasma the MW of the colloid used in current washout  

solutions is astronomical (250,000 to (preferably) 500,000 KD versus 40,000 KD
for plasma proteins, principally albumin). In the near future I expect MHP-2 
to  be replaced with a solution containing polyglycerol, polyvinyl alcohol, 
and  possibly polyethylene glycol (the latter in MWs as high as 100,000 KD). 
These  molecules inhibit cellular edema in hypothermia and ischemia (cold 
and warm) but  are also profoundly effective at both facilitating the creation 
of, and  stabilizing foam.  
The air-liquid interface of the large surface area, open cell  urethane 
foam column, will facilitate the generation of bubbles as the liquid  level 
rises and falls dynamically. In blood, antifoam-A is used to inhibit this  

effect, and indeed, the large surface area of the urethane foam is designed to
serve as a matrix for the Antifoam-A and maximize the surface area of blood 
foam  exposed to Antifoam A. However, perfusate is not blood and the 

kinetics of air  bubble movement and the ability of Antifoam-A to uniformly 
reverse 
foaming are  untested at best, and in doubt at worst. Even with blood under 
clinical  conditions near normothermia, the presence of the de-foaming 
column is not  completely effective and we all know that cardiotomy and hard 
shell reservoirs  are a source of microbubbles during conventional bypass.  
Beyond these unusual problems, there is currently an inviolable  rule in 
CPB which has been in effect since I started using extraporeal equipment  in 
the mid-1970s; more surface area equals more debris. Prebypass filters were  
invented to deal with the ever-present load of plastic debris that comes out 
of  even the most carefully washed extracorporeal circuit. I have seen  
oxygenators/tubing/filters being cleaned at Gish prior to sterilization and 
even  washing with hundresof liters of ultrapure water leaves a lot of debris. 
While  not a major issue in cryonics (given the other horrors) I dont like 
the idea of  adding yet more debris.  
Finally, there is yet another problem unique to cryonics which  really 

demands discussion on its own. Cryonics started out relying heavily on  expired
products. Those of us in the vanguard of this use were very concerned  about 
this: actually, terrified would be a better adjective.  


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