X-Message-Number: 16260
Date: Sat, 12 May 2001 00:39:42 EDT
Subject: (no subject)



By Mike Darwin


 If it so bad, why use CPR on cryopatients? The answer to that question is 
both a simple one and a good one: Because both clinical practice and relevant 
animal research demonstrated that in the setting of cryopatient transport the 
results are clearly better when CPR is used than when it isn't. The criteria 
for determining what constitutes "better results" also need to be discussed 
at this point, especially when we are talking about cryonics procedures where 
the patient doesn't get up and walk away, or not, as the case may be.

While conventional CPS isn't very good and doesn't circulate blood for very 
long it does move some blood. Typically significant flow to the brain ceases 
after about 15 minutes of closed chest CPS. However, during that time there 
is a window of opportunity to deliver anticoagulant and other drugs to 
prevent undesirable postmortem change. Unarguably just preventing postmortem 
blood clotting is justification enough for using CPS because clotting 
interferes with blood washout and most importantly prevents adequate 
distribution of cryoprotectant. Patients given CPS who are also administered 
heparin or other anticoagulant rapidly after cardiac arrest do not experience 
extensive system wide clotting seen in patients simply administered 
anticoagulant post cardiac arrest or patients who are packed in ice with no 
other intervention.

Several other positive effects of prompt CPS in cryopatients are also worth 
noting. Chief amongst these is that there is less edema, more rapid cooling 
during the critical initial minutes following legal death, and on average, 
the blood concentrations of enzymes released by various body cells when they 
are damaged or ruptured is significantly lower (p<0.05) {Darwin unpublished 
case studies}. Animal studies bear out these positive clinical findings.

Closed chest CPS is better than nothing at all. But extensive animal research 
and a few clinical cryopatient cases demonstrate unequivocally that there is 
a lot of room for improvement. Because CPS is so poor at supplying adequate 
blood flow, and because the window of opportunity for delivery of 
anticoagulants and other protective drugs to the brain at the tissue level is 
so short, there is a lot of unnecessary added injury. 

Many small vessels become filled with a thick sludge of blood cells (mostly 
red blood cells) and plasma proteins and the tissues supplied by these 
vessels are sequestered from delivery of cryoprotectant agent(s) (CPA) until 
the concentration of CPA has risen to dangerously high levels for tissues 
which have no CPA in them. Clotting also occurs in many of the small and 
medium caliber arterioles and venules because anticoagulant did not reach 
these small vessels and this also interferes with CPA perfusion. And finally, 
tissues deprived of blood supply adequate to meet their metabolic needs are 
by definition ischemic and are thus experiencing a multitude of deleterious 
biochemical changes and other injuries. 

Ideally we want to be able to restore circulation adequate to meet the 
patient's needs and to prevent all these undesirable post arrest changes. It 
should be noted than in a few patients both in the medical setting and in the 
setting of cryoTransport conventional closed chest CPS works well enough to 
sustain life and even consciousness for many minutes. The reasons for these 
exceptions are complex and cannot be detailed here. The important point is 
that they are just that, exceptions.


As was noted above, a lot of effort has gone into improving CPR for 
resuscitation of people in the arena of emergency and critical care medicine 
and yet there has been no change in the way CPR is performed in the United 
States. Many different approaches have been tried such as simultaneous 
compression ventilation-CPR (SV-CPR), high impulse CPR (HI-CPR), abdominal 
counterpulsation CPR (where the abdomen is compressed during the pause 
between each chest compression, to name a few. Some of these techniques 
failed because while they improved brain blood flow they resulted in 
decreased blood flow to the heart preventing defibrillation and thus 
resuscitation of the patient. 

Injury to the lungs and the liver were also major problems with techniques 
such SCV-CPR and abdominal counterpulsation CPR. Perhaps most importantly, 
almost all of these techniques required a machine and that meant much added 
cost and delay until the time the treatment could be applied since most 
patients who need CPR don't experience cardiac arrest next to a resuscitation 
machine. And, if they did, a defibrillator would be the first resuscitation 
machine used, not a CPR device; if you can get one of these devices to the 
patient quickly you can just as easily get the other. 

For cryopatients the situation is different. A defibrillator would not be 
appropriate. Indeed, if a cryopatient were successfully defibrillated the 
patient would be legally alive since the clinical criteria for pronouncing 
death would no longer be present; cessation of spontaneous breathing and 
heartbeat. Furthermore, it is the brain we are most interested in protecting 
in these patients and it is not of great concern if the heart or some other 
organ does not receive adequate blood flow to allow the patient to recover 
spontaneous heartbeat and breathing. Finally, in many cases we know the 
patient is going to experience cardiac arrest well in advance and thus we 
have the opportunity to have a specialized resuscitation machine ready and 
waiting. Thus, these kind of interventions need careful examination before 
they are ruled out as being of little or no value. In Part III of this series 
we will be doing just that.


Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=16260