222 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



the advisability of employing hypothermia to lower the blood pressure and cardiac 

 output, slow the heart rate, and reduce the oxygen requirement particularly of nerve 

 tissue distal of the point of aortic occlusion. What was at the outset a problem of 

 interruption of the hepatic circulation is for practical purposes a study of the 

 ischemic response of the animal to occlusion of the descending thoracic aorta. 



Method and Results. Three groups of experiments were performed on adult 

 mongrel dogs of either sex. anesthetized with sodium pentobarbital, and subjected 

 to the following technique of hepatic circulatory obstruction. Through a transverse 

 thoracoabdominal incision the chest and peritoneal cavities were entered between 

 the 10th and 11th ribs on the right. The diaphragm was incised to the level of the 

 vena cava. Twill tapes were placed around the vena cava above the diaphragm and 

 below the liver. The hepatic artery and portal vein were occluded with a noncrush- 

 ing clamp after the aorta had been clamped at the level of the 10th intercostal space. 

 Next, the caval tourniquet l)elow the liver was secured, and finally the supra- 

 diaphragmatic cava was occluded. Theoretically this technique totally separated the 

 liver from its circulation. All animals received penicillin postoperatively. 



Dogs in Groups II and 111 underwent partial right hepatic lobectomy. Because 

 the dog liver conforms more closely to a lobular pattern than does the human, a 

 large divot was purposely sliced from the right lobe to create a raw surface of 

 generous proportions which included numerous holes in the vena cava. No effort 

 was made to ligate individually at the hilus those members of the portal triad affer- 

 ent to the right lobe. The amount of bleeding varied, but the presence of con- 

 siderable quantities of bright red blood encountered in all resections led to the 

 inescapal)le conclusion that the collateral circulation of the dog liver is extensive 

 and endures even after supradiaphragmatic occlusion of the aorta. In this respect 

 the dog liver resists attempts to render it totally ischemic almost as vigorously as 

 does the dog brain. Cardiac stasis is probably the only method of insuring absolute 

 cerebral circulatory arrest! After suture ligation of all vessels and l)ile ducts on the 

 cut surface of the liver and repair of the vena cava, the occlusion was released in 

 reverse order to that of application. Bleeding sites obscured by the occlusion were 

 then evident and dealt with accordingly. I^nally the raw area was covered with 

 Gelfoam and the incision closed without drainage. 



Group I. Four dogs were submitted to hepatic circulatory occlusion for one 

 hour at normal temperature. No liver resection was performed. Table I lists the 

 results. Shortly before demise two animals developed massive melena. The two 

 survivors were free of neurological deficit. 



Group II. Six dogs underwent hepatic resection of the right lobe during 40 

 minutes of occlusion at normal temperature. Results are reviewed in table II. 

 Three of the four survivors had transient hind limb weakness. The two deaths 



TABLE I 



Occlusion of Hepatic Circulation at Normal Tkmi'erature 



No Duration 



dogs occlusion Kc-m.-uks 



4 60 minutes 2 died, death preceded by niekna 



2 survived 



