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Acute ligation of the portal vein Johnstone, Frederick Robert Carlyle

Abstract

A review of the literature on ligation of the portal vein has been presented. A brief survey of the literature on the ligation of the hepatic veins and the hepatic artery has been included. The review reveals that while there is no disagreement that the result of sudden acute ligation of the portal vein in dogs is inevitably death, there is disagreement as to the cause of death. The main theories are (i) that exsanguination into the splanchnic vascular bed occurs, (ii) that the loss of blood is insufficient to cause death, and that other factors must be implicated, the "toxic" theory. The species difference in the effects of ligation appears to lie in the degree of porto-systemic venous anastomoses. The experiments described in this thesis were performed with the dog as the experimental animal. A measurement of the decrease in circulating blood volume following ligation of the portal vein, using the "labelled" red cell method, was made. It was considered that valid consecutive estimations of blood volume could be made using the "labelled" red cell method. With 11 dogs, 30 minutes after portal vein ligation, the decrease amounted to 57.9% of the original blood volume. The measurement of the normal splanchnic vascular blood volume was made using 10 dogs. This amounted to 21.7% of the circulating blood volume, or 17.7 ml. per kilogram body weight. As the total vascular bed had been reduced by the exclusion of this splanchnic portion, the smaller circulating blood volume was required to serve a smaller vascular area, and it was considered that the true decrease in circulating blood volume was therefore 44.8%. It was considered that this amount of blood loss was not adequate to account for the inevitability of death, or the short period of survival (79.7 minutes) when compared to the effects of bleeding comparable quantities of blood, or bleeding to comparable levels of blood pressure. Haematocrit estimations were made on the systemic arterial blood and portal venous blood before and after ligation of the portal vein. There was a significant decrease in the systemic arterial haematocrit, and rise in the portal venous haematocrit. By the injection of latex into the portal vein of 3 dogs, the main porto-systemic venous anastomoses were found to occur in relation to the vagus nerves at the lower end of the oesophagus. Other porto-systemic venous anastomoses were of minor importance. It was not possible to influence the outcome of acute portal vein ligation by splenectomy, or by antibiotics under the conditions of the experiments.

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