BRAIN COOLING—JKNSEN, PARKINS Axn VARS 275 



I'.arly twpKtr.'itory c'X]K'rinicnts rcxcali'd that maximal incidciux' ol" pai'aplcgia, 

 shock, and death occurred wlien a l)all(ion catheter occlusion was jjositioned at the 

 level t)f the mid descending thoracic aorta, i.e., hetvveen the 8th and 10th inter- 

 vertehral space, l^ighty per cent of these dogs survived ,W minutes of occlusion; 

 50 per cent of which hecame paraplegic. l'"orty per cent survived 1 hour of occlu- 

 sion, with all jiaralyzed in the hind quarters. Following 2 hours of occlusion, death 

 occurred in all animals hetween 2 and 6 hours after release of the ohstruction. 



Surface cooling to a rectal temperature of 30° C. was found highly effective in 

 protecting the spinal cord from anoxial damage during a 1-hour period of occlu- 

 sion. None of these hypothermic animals were paralyzed. There was no increase, 

 however, in survival rates compared to that of the controls. 



A similar result was obtained by generalized hypothermia induced by blood 

 refrigeration reducing the rectal temperature to 30° C. When the temperature was 

 reduced to still lower levels (2-1— 27° ) l)y blood refrigeration, the first indication of 

 protection against the hemoconcentration, hypotension, shock, and death was ob- 

 tained. Seven of 11 dogs survived 1 hour of occlusion without paraplegia. 



If liver ischemia were the primary factor limiting the time of tolerance to occlu- 

 sion, liver arterialization by a carotid-portal shunt should be effective. By immer- 

 sion of the shunt in ice water, the temperature of the liver w^as differentially 

 reduced from the body mass to levels below those obtained with generalized hypo- 

 thermia (liver 20° — rectal 30° C). Liver arterialization alone did not ameliorate 

 the shock-like state which followed a 1-hour period of occlusion ; only two of nine 

 survived. A moderate protection against shock was indicated in the hypothermic 

 animals with five of eight surviving 72 hours with complete recovery. None of the 

 hypothermic survivors was paraplegic. 



In view of the negative result with liver arterialization, and noting the correla- 

 tion of intestinal infarction, bloody diarrhea, and profuse sloughing of the mucosa 

 with mortality, our attention was focused upon the intestine. Differential cooling of 

 the intestine was accomplished by rapid filling of the abdominal cavity with iced 

 saline. In initial experiments, saline was recirculafed through a coil immersed in an 

 ice water bath. This was done to maintain the temperature of the duodenum at 

 10-15° or 20°, while the liver temperature was about 25°, and organs central to 

 occlusion about 30°. 



The first four animals were occluded simultaneously with administration of the 

 iced saline. After 1 hour of occlusion all survived 72 hours. Hemoconcentration 

 and hypotension were minimal ; bloody diarrhea and mucosal sloughing were not 

 observed in these animals. Their recovery was prompt, without paraplegia, and 

 with a wide margin of safety. 



We proceeded, therefore, to a 2-hour interval of occlusion in 10 animals. Six 

 animals were occluded at the beginning of cooling, five of which survived, one 

 being paraplegic. In four animals the cooling was delayed until 15 minutes after 

 the occlusion. All four survived ; 2, however, were paralyzed in the hind quarters. 



To simplify this method of direct visceral cooling, the iced saline (65 cc./kg.) 

 was injected interperitoneally within two to three minutes. This cooling was supple- 

 mented by placing an ice pack on the lower abdomen. Five of 5 animals occluded 

 for 1 hour simultaneously with cooling, survived; 2 being paraplegic. Five of 5 

 survived a 2-hour period of occlusion. Three of these, however, were paraplegic. 



Ten dogs were precooled to a rectal temperature of about 25° C. by this method 



