Portal versus caval venous drainage of small bowel allografts: technical and metabolic consequences

The potential metabolic and technical consequences of systemic (portacaval anastomosis [PC-A]) as opposed to portal venous drainage (portaportal anastomosis [PP-A]) of orthotopic small bowel isografts was evaluated in a rat model. Rats with portacaval (PC) shunts were studied for comparison. During the study period of 6 months, rats with small bowel grafts (PP-A or PC-A) gained weight at rates equal to that of normal age-matched rats (+40% of the preoperative weight) whereas rats with PC shunts lost 20% of their weight. At autopsy 6 months after operation, rats with PC shunts had significant liver atrophy (2.0% of total body weight) in comparison with rats with orthotopic isografts. Moderate liver atrophy was detected in rats with grafts and PC-A in comparison with those with PP-A (2.6% versus 2.8% of total body weight, statistically not significant). Serum ammonia levels were significantly elevated for PC shunts (560 +/- 148 micrograms/dl) and PC-A (140 +/- 22 micrograms/dl) when compared with PP-A (83 +/- 10 micrograms/dl). In terms of technical difficulties, both PC-A and PP-A could be achieved with the same success rate. Systemic venous drainage for small bowel grafts is followed by metabolic alterations that are similar, although much less pronounced, to those seen after a PC shunt. Thus our findings do not offer compelling reasons to prefer PP-A over PC-A. However, with longer follow-up and the use of hepatotoxic immunosuppressive drugs, these minimal alterations may progress and induce metabolic sequelae of clinical significance. Under these circumstances it would be advisable to use the physiologic portal drainage rather than systemic venous drainage in small bowel transplantation.