AW: [HSF] Deairing the heart

[Rwmfglycar at aol.com]

In a message dated 3/2/2007 8:13:27 A.M. Eastern Standard Time,  
anianyanwu at hotmail.com writes:

But Hal  I would question the relevance of subtle neurological changes that 
require a  battery of sophisticated tests to demonstrate. A lot of these 
changes IMHO are  integral to having artificial extracorporeal circulation and 
indeed MRI  studies show changes in many patients with no neurological 
complications. Air  and embolism are an integral part of CBP and in most cases are likely 
of no or  of minimal consequence. Obviously though we must exclude gross air 
bubbles and  our deairing approach, including CO2 and TEE is very similar to 
yours. 
.  
However, I think to a great degree air is an invention of TEE and most of  
what we see on TEE or strive to achieve with TEE is of little relevance above  
that which can be determined clinically as in Novick's practice or in the  
practice of the 1980s. Like you I vent the root up to 15 mins after coming of  
bypass and I suspect in most patients this will be sufficient to deal with any  
rogue bubbles that failed deairing - regardless of the presence of  TEE.

I am not sure there is any direct evidence that the incidence of  
neurological complication or neuropsychometric deficit has changed with the  advent of 
TEE or that the incidence is different in centers that routinely use  TEE and 
centers that don't. Those surgeons in life courses who don't seem to  deair 
properly may not necessarily be harming their patients. In my previous  center 
(Harefield with Yacoub) we generally ignored the snowstorms seen on TEE  and 
apparently (I know I know) to no consequence



Dear Ani,
When I had residents who expressed views like yours I would ask them if  they 
knew of any serious consequence of massive air embolism. They said yes. I  
then asked how much air it took to produce the appearance of air seen on  
echocardiography. They would not know but said it must be less than one would  see 
in a case of massive air embolism. I agreed but then asked if they thought  
that 1 cc of air would be much less than massive air embolism.They were sure of  
that. I would then ask them if they would let me inject 1cc of air up one of  
their carotids.  They would not. I then told them that until they had  proven 
conclusively that a certain quantity of air correlated with a certain  density 
of bubbles in the cardiac chambers did NOT produce any cerebral  
consequences, it was unethical not to clear the air seen on  echocardiography from the 
cardiac chambers before coming of  bypass. 
Studies were done on dogs of the consequences of injecting 1 cc increments  
of air into their carotids. Clinical consequences were evident with very  small 
amounts of air. I had an inverted U tube between the ascending aorta  and the 
caval cannulae for 20 years. The large bubbles that would collect  while the 
echo appearance of air dissipated were impressive.
You  are in fact doing various maneuvers to get rid of air but at the  same 
time state  "Air and embolism are an integral part of CBP and in most  cases 
are likely of no or of minimal consequence" . If you really believe that  why 
bother to deair? You also invoke your time with Magdi:  "In my previous  center 
(Harefield with Yacoub) we generally ignored the snowstorms seen on TEE  and 
apparently (I know I know) to no consequence". If you are aware that this is  
rubbish evidence don't present it. I have seen the snowstorms at Harefield and 
I  got the impression that you were too busy to have time to evaluate subtle  
changes in your patients' cerebral function, in the postop period.
Cerebral dysfunction after extracorporeal circulation does occur and has  
many possible causes.  Air is one obvious cause that we can detect and do  
something about. The evaluation of cerebral function remains a weak branch of  
medicine.The fact that, because of that weakness, we cannot state  that air removal 
is not important but do know that it may be  important obligates us to do 
something about it. 
Bob 
 
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