18 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



elusion of the general circulation potassium appeared to accumulate in the tissue 

 spaces. Upon resumption of flow, potassium levels increased rapidly in the serum and 

 the concentration after occlusion was greater than he fore occlusion. These authors 

 were successful in converting ventricular filirillation in hypothermic dogs to a normal 

 beat by the injection of potassium chloride followed by calcium chloride. 



Osborn^^ also reported a decrease in serum potassium in hypothermia and 

 Brewer^^ found that the depression of body temperature following decerebration 

 was associated with a depression in the plasma potassium level. He observed fur- 

 ther that increases in body temperature l)rought al)Out by dinitrophenol resulted in 

 increased plasma potassium levels. If the dinitrophenol was given to the decerebrated 

 preparation no decrease in body temperature or plasma potassium occurred. Fur- 

 thermore, the stimulus of low environmental temperature, producing an increase 

 in general body metabolism, increased the plasma potassium in both normal and 

 decerebrated animals. Brewer concluded that there was a rather good positive cor- 

 relation between metabolic activity and the plasma potassium level. 



It appears that several factors must be taken into account when considering plasma 

 or serum potassium levels in hypothermia. The observation that the release of car- 

 bohydrate from the liver is associated with simultaneous release of potassium, ''^ 

 together with the finding that the liver glycogen is rapidly utilized during hypo- 

 thermia and that blood glucose increases during the early phases of hypothermia 

 and remains elevated in previously fed rats,^- indicates the necessity of delineating 

 the nutritional status of the animal at the time the experiments are performed. In 

 rats which were starved previous to the induction of hypothermia the blood glucose 

 was maintained or fell during the course of cooling.^- The rate at which animals 

 are cooled may also play a role since slowly-cooled, fed rats exhibit the same blood 

 glucose picture as rapidly cooled, starved animals.^- The presence or absence of 

 shivering as a sign of muscular activity and the severity of the shivering response 

 must also be considered, since it has been demonstrated that increased muscular 

 activity is associated with loss of potassium from the muscles and increased blood 

 levels.*''' ^° The finding of Swan ct fl/.*° that hyperventilation alone results in de- 

 creased potassium, together with their observed decrease in potassium levels in hy- 

 perventilated, hypothermic dogs, suggests that the ventilation of the experimental 

 animals must be considered. ]\Iackay's" findings were suggestive of a correlation 

 between hypercapnia and potassium but McMillan ct al.^'- were unable to demonstrate 

 any correlation between these variables during hypothermia. At present the relation- 

 ship between COo content and serum potassium is not clear. 



Calcium. Elliot and Crismon*" found a statistically significant increase in rat 

 serum calcium levels upon reduction of the temperature to 25° C. This was asso- 

 ciated with an increased potassium level but the Ca/K ratio was reduced from 

 1.46 to 1.08. Bigelow et al.*'^ reported an increased serum calcium in 3 out of 4 

 experiments on dogs. McMillan ct al^'- also observed an increased serum concentra- 

 tion of calcium in both spontaneously respiring and artificially respired dogs. They 

 determined free and bound calcium and, with the exception of the bound calcium 

 in artificially respired animals, observed progressive increases down to rectal tem- 

 peratures of 19° C. Since they also observed little change in potassium, the Ca/K 

 ratio increased, in contrast to tlic findings (»f ■'".lliot and Oismon.'' On the other 



