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The portal vein is next identified in the hepatoduodenal ligament by the same careful dissection (Figure 7). It may be helpful during this dissection to place a tape or rubber tissue drain about the common bile duct in order to facilitate exposure of the portal vein (Figure 8). The portal vein should be exposed from the hilum of the liver to the superior surface of the pancreas, where the usual pancreatic tributaries should be located and protected. Once the three structures of the hepatoduodenal ligament have been identified clearly, the remaining adipose tissue containing enlarged venous and lymphatic channels may be divided in order to bring the portal vein in proximity with the vena cava (Figure 9). The area at which the portal vein crosses closest to the cava is ordinarily just proximal to the entrance of the renal veins.
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At this point, if a side-to-side shunt has been decided upon, two noncrushing clamps are applied to the portal vein so that it may be rotated to expose its inferior surface (Figure 10). This is necessary to prevent twisting or angulation of the portal vein as the anastomosis is accomplished. Two points must be borne in mind in preparing the anastomotic sites. The first is that the portal vein and the inferior vena cava are not parallel to each other; therefore openings in the longitudinal axis of each vein would result in twisting of the anastomotic site when the clamps are released. It is necessary to incise the portal vein obliquely to avoid any twisting (Figure 11). Second, a simple longitudinal window, either in the portal vein or in the vena cava, is not adequate for a satisfactory shunt because of the low pressures in the venous system. A simple slit opening will behave more like a valve and tend to close, resulting in a high incidence of shunt failure. The anastomosis should be between windows cut in the veins by excising a definite portion of their walls in an elliptical fashion (Figure 12). Usually it is not necessary to cross-clamp the vena cava completely. A curved, noncrushing clamp, placed to exclude a portion of the lumen, is satisfactory for this purpose (Figure 13). The anastomosis should be made so that it is at least ...