210 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



renal damage was severe. Glomerular filtration rate and renal blood flow in tlie 

 occluded kidney were then reduced to aliout 10 per cent of the contralateral kidney. 

 In fact, there was no renal damage on the contralateral side, again indicating that 

 a low pressure in the aorta for two hours was adequate to protect the kidney from 

 damage due to inadecjuate circulation. 



When h}pothermia was employed during renal ischemia, it appeared that 

 moderate protection was given to the kidney. Observations made three days after 

 the renal artery and aortic occlusion indicated that the renal function was de- 

 pressed overall only to about f of the control level as compared to 10 per cent 

 of the control under normothermic conditions. These observations indicate that 

 under states of severe ischemia, hypothermia gives some protection against severe 

 renal damage. 



OBSERVATIONS IN MAN 



Methods. Observations on renal function were made in four patients in whom 

 hypothermia was employed for resectional therapy of aortic aneurysms. The tem- 

 perature was reduced to 88° to 91° F. The primary purpose of the hypothermia 

 was to prevent ischemic spinal cord damage during cross clamping of the descend- 

 ing thoracic aorta. Observations on renal function were made before and after 

 induction of anesthesia. Total body cooling was then induced and observations on 

 renal function were repeated. During the surgical procedure renal function was 

 measured at approximately the mid-period of aortic occlusion and immediately 

 after release of the occluding clamps. Renal function was again determined after 

 rewarming and, in two cases, one week following operation. Inulin clearance was 

 used to measure glomerular filtration rate (GFR) and low concentrations (2 to 

 4 mg. per cent) of para-aminohippurate to measure renal plasma flow (RPF) 

 employing methods and techniques previously described. (2). Values listed in the 

 tables and figures are averages of two or three 10-minute collecting periods. 



RESULTS AND DISCUSSION 



Due to the inherent difficulty in making these observations on patients during 

 hypothermia and surgery, a relatively small number of patients were studied. 

 However, as detailed information was obtained, the data are presented as case 

 reports demonstrating pertinent points. 



Case 1. — A 66-year-old Negro male had a thoraco-abdominal aneurysm involving 

 the celiac axis, the superior mesenteric and both renal arteries. The (rectal) tem- 

 perature was reduced to 90° F. employing refrigeration blankets. The aneurysm 

 was resected and replaced with a lyophilized homograft extending from the lower 

 thoracic aorta to the abdominal aorta distal to the renal arteries. The period of 

 aortic and bilateral renal artery occlusion was one hour and forty niiinites. 



Figure 12 graphically demonstrates the effects of these procedures on renal func- 

 tion. The control values showed a slightly depressed renrd l)l()od flow and glo- 

 merular filtration rate. I'entothal anesthesia did not produce any striking changes. 

 As in the experiments with dogs, there was some depression in both renal ])lti(Kl 

 flow and glomerular filtration rate associated with an increase in urine \i>hnne. 



