426 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



In animals which were cooled by refrigerated air and ice immersion, Gollan was 

 not able to reach as low a temperature and the percentage of long-term survivals 

 was markedly decreased. 



Some of the problems involved in cooling and rewarming can be emphasized by- 

 citing a personal experience. Using the surface application of ice, we lowered the 

 temperature of a newborn infant with a transposition of the great vessels to the 

 surprisingly low level of 11 degrees centigrade. The heart did not fibrillate but 

 went into standstill. At the end of the procedure, an effort was made to warm the 

 baby : hot w-ater bottles were placed around the infant and warm saline was used 

 on the heart and the chest ; cardiac massage was instituted to restore some degree of 

 circulation. The temperature was raised to 26° C. degrees at the end of an hour and 

 a half. At around 20° C, heart action returned, though the ventricular contractions 

 were not sufficient to maintain an adequate pressure. At 26° C, heart action ap- 

 peared to be improving but then became progressively worse. Cardiac massage was 

 carried out for a two-hour period during this rewarming. Massage was necessary, 

 for the only way in which warmth could be spread throughout the body was by 

 producing a circulation. On the other hand, the only method of olitaining an ade- 

 quate circulation was to have an adequate heart beat which in turn was dependent 

 upon sufficient rewarming. It was our feeling that perhaps the chief cause of the 

 death of this child was prolonged cardiac massage. At the start of cardiac massage, 

 the appearance of the myocardium was excellent ; but, as massage continued, small 

 petechial hemorrhages appeared and the myocardium gradually became increasingly 

 edematous. Had we had a vein-to-artery warming system at hand, it seems probable 

 that we could have warmed with more speed, maintained coronary circulation with- 

 out massage and, thus, avoided the trauma to the myocardium. If the desired aim 

 is to lower body temperature to where cardiac standstill appears and where the 

 circulation can be cut off for a prolonged period of time, it appears to us that we 

 cannot rely on external methods of warming l)ut must be able to maintain a circula- 

 tion artificially until such a time as the heart is able to resume normal function. 

 It may be that the temperature of 26° to 28° C. that has been termed ideal by many 

 authors is not ideal. It is possible that a much lower temperature would offer more 

 safety, besides permitting a longer period of circulatory arrest without damage to 

 the heart and brain. If external methods of warming are used, the risk of going to 

 such low temperatures is certainly great ; for to rewarm, one must have a circulation 

 and to have a circulation, one must rewarm. The use of a venous-arterial cooling 

 and warming system may eliminate this problem and permit much lower tempera- 

 tures to be reached with less danger and better results. 



During the past few years a great deal of interest, time and effort have gone into 

 development of an adequate artificial oxygenator and pump, one that can maintain 

 life while the inflow and outflow tracts of the heart are closed. The difficulties of 

 such a machine are tremendous: it must be efficient, safe, capable of handling large 

 volumes of blood and not productive of damage to various components of blood. 

 Many of the difficulties involved in the production of an adequate pump and 

 oxygenator can l)e answered satisfactorily by the addition of hyi)othermia. At low- 

 temperatures, life can be sustained with a much smaller systemic blood flow. Conse- 

 quently, a pump-oxygenator used with hypothermia would be required to handle a 



