HEAIORRHAGIC SHOCK—OVERTON and De BAKEY 387 



at the end of the eight hours, and at termination liad r('<[uircd only moderate re- 

 placement of hlood for maintenance of compensation. These ol)servations are per- 

 haps the most significant of this study, since they most closely ])arallel the control 

 animals in the amount and rapidity of the hlood lost, and would indicate a varia- 

 tion in the animals" resistance to "irreversibility" rather than a \ariation in the 

 experiment. 



That cooling might l)e beneficial in shock was suggested much earlier than cur- 

 rent interest would indicate, for it has been noted by several (observers that animals 

 subjected to burn, epinephrine drip, t(nu-ni(|uet release, and hemorrhagic shock 

 demonstrated much greater resistance when the enviroinnental temperature of the 

 laboratory was low.^- ■'• ^-- "'*• *-• ''''• -■'• '' In his studies on the nervous system in 

 shock. Remington-''-' found that it was necessary to bleed the animals significantly 

 more during the winter months. Allen,' in studies on tourni(|uet release shock, 

 applied refrigeration to the constricted limb with an increase in survival of both 

 animals and limbs, Init he noted he had also inadvertently secured general body 

 hypothermia. In comparing the effects of heat and cold in the prevention and treat- 

 ment of shock, Blalock^- found a significant increased tolerance to duration of 

 shock when the animals were cooled but no increase in survival. Cooling was applied 

 after shock was in progress, however, and the degree of hypothermia secured 

 (average 25° C.) without supportive measures for respiration perhaps influenced 

 the mortality adversely. These and other studies coupled with our results perhaps 

 do not fully support the theory advanced that hypothermia has a protective action 

 in hemorrhagic shock but do suggest the need for further inquiry into the problem. 



The mechanism involved in the beneficial effects of hypothermia is not identified 

 in this experiment, but may be due to one of several factors : first, it seems likely 

 that the lowered metabolism and reduced requirements of the tissues for oxygen 

 prevent irreparable damage to the vital centers responsil)le for maintenance of 

 compensation. This is an appealing concept in that it carries prevention of peripheral 

 stagnant anoxia further than one is able to do liy correction of hypovolemia. Recent 

 studies have demonstrated the ability of cooling to protect a variety of organs from 

 the acute anoxia of temporary interruption of circulation.--' ^*' ^^ It has been sug- 

 gested, since tissue repair continues during hypothermia, that the temporary main- 

 tenance of the animal allows capillary beds damaged by anoxia to improve enough 

 to prevent irreversibility.^- In this regard selective cooling of viscera might add 

 information as to the organ most responsible for maintaining compensation. 



The second explanation for the beneficial efifects of hypothermia is also con- 

 jectural but is based on possible alteration of effective blood flow to various body 

 compartments during shock. Selective vasoconstriction, vasodilation or both to 

 organs vital to compensation may be accomplished by cc^oling.^- ^-' ^^' ''^ Aside from 

 the known local and reflex vasomotor responses to heat and cold,*- ^*^' °^ it has been 

 demonstrated that the temperature of the blood entering and leaving different viscera 

 varies. ^"^ Rodbard"- and D'Amato-^ and others'"'' have suggested that whole blood 

 sequestrated in various vascular channels would account for the unexplained reduc- 

 tion of plasma volume that occurs in hyjiothermia. The close correlation of the 

 amount and rapidity of l)lood lost among the controls and among the hypothermia 

 animals in our experiment would tend to discount involvement of any shunting 

 mechanism. 



