Effect of flushing pressure on rat small bowel transplants

Excessive flushing pressure in rat small bowel transplants may cause graft failure, but the optimal pressure for manual flushing has not been established. The goal of this study was to determine a safe yet effective pressure for intravascular graft flushing and to evaluate the consequences of higher pressures. The "usual" manual flush was found to be at a pressure of approximately 40 mm Hg. After harvest, grafts were flushed manually with heparinized normal saline solution while connected to a transducer. Two groups of 25-cm jejunal grafts (n = 5 each) were harvested from Lewis rats (200 g) on a pedicle of superior mesenteric artery and vein. Group 1 grafts underwent 3 successive flushes at 50, 100, 200 mm Hg, respectively. After each flush, full-thickness biopsies were obtained for light and transmission electron microscopy. Two grafts underwent syngeneic small bowel transplantation (SBTx), and biopsies were taken after reperfusion. Group 2 grafts were flushed at 50 mm Hg and biopsies were obtained. All grafts underwent SBTx and biopsies as in group 1. After flushing at 50 mm Hg. biopsies were essentially normal. When flushed at 100 mm Hg, there was pronounced epithelial separation with dilatation of the core of the villus. Flushing at 200 mm Hg resulted in complete separation of the villi, with occasional disruption in the crypts. All group 1 transplanted grafts were grossly nonviable immediately after reperfusion, while transplanted grafts in group 2 were grossly normal. The findings were consistent within each group and the difference between groups was statistically significant (0 vs. 100%). The results suggest that flushing pressures of 50 mm Hg in rat SBTx provide optimal evacuation of blood with minimal, reversible tissue injury. Higher pressures cause progressive histologic damage and may produce nonviable grafts. Flushing pressures in the rat model of SBTx should therefore be maintained at approximately 50 mm Hg.