40 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



oxygenated, and refrigerated in a small pump-oxygenator, a degree of over-oxygena- 

 tion can be achieved in which the arterio-venous difference in oxygen and carbon 

 dioxide content almost disappears (fig. 4). At the lowest temperature of 3° C, 

 measured in the right heart, we were then dealing with animals practically devoid 

 of venous blood. The oxygen consumption of such dogs in respiratory and cardiac 

 arrest can be calculated from the arterio-venous oxygen difference in the inlet and 

 outflow of the pump-oxygenator. The oxygen consumption below 10° C. (fig. 5) 

 was exactly where one would expect it to I)e. namely on a line between the known 

 value at 16° C. and 0° C. Thus, at 5° C. the oxygen consumption of a dog is ^/^o of 

 normal. Since the blood flow of about 45 cc./kg./min. exceeded by far the neces- 

 sary flow of about 7 to 10 cc./kg./min. to cover the needs of such animals, the total 

 amount of oxygen supplied (closed circles) would have been sufHcient to keep dogs 

 at about 30° C. in oxygen balance. The content of physically dissolved oxygen in 

 plasma rose from 0.3 volume per cent at normal body temperature to about 4.0 vol- 

 ume per cent at 5° C. and therefore even the amount of dissolved oxygen supplied 

 (open circles) exceeded the oxygen consumption at 5° C. 



To test this point we washed out all red cells and substituted Ringer's solution 

 and plasma for blood until the dog's hematocrit was lowered to 0.5 per cent. Before 

 rewarming the circulating fluid the red cells were returned to the circulation and 

 these animals, just like the ones who had the benefit of hemoglobin, survived and 

 did not show any sequelae of this trying procedure. 



VOLUME 

 PER CENT 



30 



34 



38 



2 6 10 14 18 22 26 

 HEART TEMPERATURE, 'C 



Fig. 4. — Arterio-venous difference in O., and CO., content duriny hypotlierniia by l)lood cooling. 



