X-Message-Number: 16260 From: Date: Sat, 12 May 2001 00:39:42 EDT Subject: (no subject) KRYOS NEWS #5 MAKING CPR WORK BETTER LONGER, PART II By Mike Darwin WHY USE IT IN CRYONICS? 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0.05) {Darwin unpublished case studies}.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. WHAT'S TO BE DONE? 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. END OF PART II Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=16260