412 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



fibrillate for various periods of time. These dogs were found to survive 60 minutes 

 of ventricular fibrillation with complete recovery. After 75 and 90 minutes of 

 fibrillation, survivors were found to have only a mild, persistent hindquarter weak- 

 ness. Resuscitation in these animals was not a problem, but as the periods of 

 ventricular fibrillation were lengthened to three, four, and five hours, resuscitation 

 became increasingly difficult. 



Resuscitation was accomplished by removing the animal from the ice water bath, 

 placing the animal on a warm water mattress, opening the chest and irrigating of 

 the pleural spaces with sterile saline at 45° C. With each 1° C. rise in rectal tem- 

 perature a single defibrillation shock of 200 volts was administered to the heart for 

 a period of 0.13 second. This routine was continued until defibrillation occurred 

 and the animal had established its own adequate circulation. This warm saline irri- 

 gation, which we considered an extremely important factor in converting the fibril- 

 lating heart, was continued about the heart until a rectal temperature of 28° C. 

 was reached. 



Dr. Szvan: I agree with Dr. Longmire that it is difficult to evaluate clinically what 

 happens when one is dealing with a very sick patient and the patient dies. To try 

 to implicate any part of the procedure is almost impossible. I hope that many others 

 as well will think about and attempt to evaluate this problem. 



I would like to thank Dr. McMillan for his comment, because in our laboratory, 

 at least, we have found that the time of the year has a profound effect upon our 

 experimental results. We in Denver have hot summers and fairly cold winters. 

 We do not have the advantages of having an air-conditioned, temperature-con- 

 trolled animal room, and our dogs are subjected in the wintertime to cold nights. 



I believe this concept of pre-conditioning is of considerable importance in experi- 

 mental hypothermia, and that it is one of the major causes why there is a great 

 variety of results obtained in different parts of the country in studying this problem. 



