AW: [HSF] Deairing the heart

Fri Mar 2 23:56:58 EST 2007

Thank you for your insightful reply Dr Frater - both yourself and Hal have summed up the contradictions in my views - certainly I would rather all air out than in if I was having surgery and additionally I myself do use CO2 and TEE and aim to get rid of as much air. So I certainly do believe air is harmful. 

However for the point of view of academic discussion I try to separate my personal views from the logic and evidence (which is what should guide our specialty as a whole, rather than anecdote). So my personal approach to deairing does not mean I am getting it right and does not detract from the thesis that we do not have evidence to justify our practice and maybe we are overdoing things. 

So then I would not suggest that outcomes are certainly (or even likely) better because one uses these adjuncts, compared to someone who does not. TEE is very sensitive for air. Indeed our anesthesiologists often find micro-air bubbles in the descending aorta - sometimes even before we have gone on CPB or even touched the patient. No one really knows what is the obligatory amount of circulating air inherent in any CPB procedure and what quantity must be extracted to prevent pathological embolization. A lot of what we do is not founded on evidence - air removal is one of them. There are as many different de-airing rituals as there are surgeons - if it was as crucial as we all believe their would certainly be a more uniform approach. Unfortunately we will likely never know because no patient (certainly not me) will be willing to try this experiment.

Ani
  ----- Original Message ----- 
  From: Rwmfglycar at aol.com<mailto:Rwmfglycar at aol.com> 
  To: OpenHeart-L at lists.hsforum.com<mailto:OpenHeart-L at lists.hsforum.com> 
  Sent: Friday, March 02, 2007 11:18 PM
  Subject: Re: AW: [HSF] Deairing the heart

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