EXPERIMENTAL AND CLINICAL OBSERVATIONS ON THE USE 



OF HYPOTHERMIA TO PREVENT ISCHEMIC DAMAGE TO 



THE CENTRAL NERVOUS SYSTEM * 



ROBERT G. PONTIUS and MICHAEL E. De BAKEY 



The tissues of the central nervous system are particularly vulnerable to ischemic 

 damage from even brief periods of circulatory arrest. This constitutes a serious 

 hazard in the performance of certain cardiovascular procedures such as resection 

 of aortic aneurysm, in which it may be necessary to interrupt aortic circulation 

 for periods up to one hour.* Since it has been well established that hypothermia 

 reduces total body metabolism and oxygen requirements of tissues, it is reasonable 

 to assume that the central nervous system is similarly affected and that this might 

 provide a useful measure in minimizing the ischemic dangers associated with these 

 operative procedures."' ^ Accordingly, studies have been directed toward deter- 

 mining the protective value of hypothermia against such ischemic damage to the 

 central nervous system during periods of temporary aortic occlusion. 



Experiments along these lines have been done by a number of investigators as 

 well as by us.^' '~^- Thus, in a control group of 50 dogs occlusion of the aorta just 

 distal to the left subclavian artery for a period of one hour was associated with 

 an immediate mortality of 32 per cent and a paraplegia rate in the surviving ani- 

 mals of 65 per cent. The same procedure in a comparable group of 47 hypothermic 

 dogs (body temperature was reduced to between 75 and 80° F.) was associated 

 with an immediate mortality of 25 per cent and with a paraplegia rate of zero in 

 the surviving animals (fig. 1). On the basis of these experiments as well as similar 

 observations reported by other workers, the conclusion has been drawn that hypo- 

 thermia has a protective influence against ischemic damage to the spinal cord fol- 

 lowing high aortic occlusion. 



While the exact mechanism of protection afforded by hypothermia is not entirely 

 clear, gross and histologic studies of the damaged spinal cord provide some clues 

 to the problem. Gross examination of the spinal cords of the paraplegic animals 

 showed bilateral symmetrical malacia of the grey matter of the lumbar, sacral, and 

 coccygeal segments. Serial sections showed the lesions to begin consistently between 

 Ti2 and L2 and continue distally. On microscopic examination pronounced changes 

 were present in the grey matter, but the white matter was spared. As the specimens 

 were obtained 12 days after injury evidence of repair by microglial phagocytes or 

 gitter cells with foamy cytoplasm and proliferation of new capillaries through the 

 destroyed area was present (figs. 2, 3, and 4). These changes are quite similar to 

 those observed in the brain following anoxemic damage to this organ. They do not 

 suggest thrombosis or infarction as the vessel lumens were patent. The animals pro- 

 tected by hypothermia failed to show these changes. 



Experiments along similar lines directed toward determining the protective 

 effects of hypothermia against ischemic damage to the brain proved much more 



* Supported in part by grants from the Houston Heart Association and the Cora and Webb 

 Mading Fund for Surgical Research. 



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