iiFi i:c:t of hypothermia on tolerancb to 



HEMORRHAGIC SHOCK* 



E. W. FRIEDMAN,! D. DAVIDOFF and J. FINE 

 With the technical assistance of Dorothy Kaufman 



During peripheral vascular collapse the disparity between the tissue requirements 

 for blood and the amount available results in rapid impairment of many vital func- 

 tions. Since hypothermia reduces this imbalance by reducing the tissue requirements, 

 its value as a means for the preservation of tissue function during peripheral vas- 

 cular collapse deserves exploration. A beneficent effect upon hemorrhagic and 

 tourniquet shock by lowering the environmental or body temperature has been 

 observed. Thus, Warren^ noted a lower mortality rate in tourniquet shock at a 

 room temperature of 16° C. as compared to a room temperature of 28° C, and 

 Delorme- and Adams-Ray^ state that the hypothermia protects the dog from 

 otherwise lethal severe hemorrhagic shock. The studies described below deal with 

 the effect of hypothermia on hemorrhagic shock in the dog with particular refer- 

 ence to the cardiovascular dynamics and survival rate. 



PRELIMINARY STUDIES WITH VENO-VENOUS COOLING 



Various methods of cooling were considered in order to find the one that would 

 best satisfy the requirements of our standard hemorrhagic shock experiment.* Since 

 the development of a state refractory to transfusion is a function of time, we 

 sought the method which would produce the desired reduction in body temperature 

 as rapidly as possible. Veno-venous cooling^ has the disadvantage that an extra- 

 corporeal circuit imposes upon the circulation. But the promise of very rapid cool- 

 ing (1° every 4 minutes) with a minimum of shivering and a low incidence of 

 ventricular fibrillation led us to try it. 



The cooling equipment consisted of a rotary pump which sucked blood froin the 

 superior vena cava and drove it back into a femoral vein after circulation through 

 a coil immersed in an ice bath. All tubing except for a rubber segment in the pump 

 was polyvinyl plastic, 15 feet in length, connected to plastic cannulus inserted into 

 the superior vena cava via the jugular vein, and into the femoral vein. The femoral 

 artery was cannulated for sampling, pressure readings, and bleeding. The trachea 

 was cannulated for measurements of respiratory finiction and oxygen consumption. 

 Mixed venous blood for measurement of cardiac output (Fick method) was ob- 

 tained from the caval cannula advanced into the right auricle. Because of the de- 

 sirability of avoiding barbiturates and anesthetics in the animal to be put into 

 shock, the foregoing procedures were performed under local anesthesia. 



All dogs were given 2mg./kg. of morphine one to two hours before the experi- 

 ment. After 2 mg./kg. of heparin was injected intravenously, the extracorporeal 



* Supported by a contract with the Research and Development Division, Office of the Surgeon 

 General, U.S. Army; and by a grant from the U.S. Public Health Service. 

 t Fellow of the American Heart Association. 



369 



