EFFECT OF LOW BODY TEMPERATURES 

 ON RESPIRATORY GAS EXCHANGE 

 IN THE ANESTHETIZED DOG 



Arthur B. Otis, Deportment of Physiology, University of 

 Florida, College of Medicine, Gainesville, Florida 



D, 



'l'ring the past few years a considerable amount of information has 

 accumulated regarding the effect on various jihysiological processes of 

 lowering the body temperature of the anesthetized dog. JNIuch of the work 

 involved has been carried out or given impetus by surgeons interested pri- 

 marily in the application of hypothermia to clinical surgery. In this they 

 have met with considerable success, and at the same time they have con- 

 tributed information and revealed problems of interest to the general 

 physiologist. 



The author's experience in this particular field is limited to some experi- 

 ments done during the past year in collaboration with members of the 

 Department of Surgery at the Johns Hopkins University, Dr. James Jude 

 in particular. The purpose here is not to present the results of this work 

 in detail, but rather to summarize in a general way what is known about 

 the effect of lowering the body temperature on physiological processes in- 

 volved in respiratory gas exchanges, and to mention in passing some prob- 

 lems of general physiological interest which remain largely unsolved. 



Cooling of the anesthetized dog may be accomplished by immersion in ice 

 water, by wrapping the body in a special blanket through which a coolant 

 is pumped or by leading the circulation from a large artery through a 

 cooling coil and returning it to a vein. The rate of cooling depends, of 

 course, on many factors but is usually of the order of 10°C per hour. 



METABOLISM 



When a dog, anesthetized deeply enough to prevent shivering, is pro- 

 gressively cooled from a body temperature of 36° to 38° his oxygen con- 

 sumption diminishes by about 5% of its initial value for each degree drop 

 in body temperature (1, 2). Thus at a body temperature of 25°, oxygen 

 consumption is only about 30% of normal and at temperatures below 

 20° C it is so small as to be difficult to measure with any precision by or- 

 dinary methods. If the anesthesia is not deep enough to prevent shivering, 

 then during the initial phases of cooling the oxygen consumption may in- 

 crease by as much as five fold, until a body temperature of about 32°C 



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