Small-for-size graft injury in living donor adult liver transplantation

Since the first successful living donor adult liver transplantation (LDALT) was reported in 1993, many technical innovations have been reported (1). The number of adult patients undergoing LDLT has recently increased. According to a recent Japanese survey, the 5-year survival rate in adults after surgery is only 69.7%, which is significantly poorer than that in pediatric series. Small-for-size grafts remain a problem in LDALT. The major limitation of LDLT for adult recipients is the size of the graft. The most commonly used liver graft for adult patients has shifted from the left liver to the right, which alleviates the problem of size disproportion. Marcos et al. and many other surgeons concluded that right lobectomies for living donation can be performed safety with minimal risk to both donor and recipient although providing adequate liver mass for an average size adult patient. Lo et al. reported that LDALT using the extended right lobe living graft decreases the risk in the recipient, while increasing the risk in the donor (2). On the other hand, concerning the safety of the donor, Sugawara et al. reported that right lobectomy from living donors is a safe procedure with acceptable morbidity, but some care should be taken early after the operation for donors with small residual liver and aged donors (3). We also reported that postoperative liver functions including total bilirubin and ALT levels of the right lobe donors were significantly higher than those of left lobe donors (4). From these findings, we use left lobe with caudate lobe graft to minimize the risk of the donor. Recipient survival may depend not only on the size and quality of the graft but on the recipient status too. The mechanisms leading to injury of a small-for-size graft after liver transplantation are complex. Two main factors have been identified for small-for-size graft injury: small functional mass and small vascular bed. Small functional mass means high demand of metabolic function and synthetic function, which leads to hepatic failure. Small vascular bed and excessive portal flow and portal pressure and also congestion can produce graft injury. There were many reports about methods to prevent small-for-size graft injury. To avoid hepatic failure due to small functional mass high-flow continuous hemodiafiltration (CHDF) or slow plasma exchange (PE) or portal infusion were performed. To avoid graft injury due to excessive portal flow and portal pressure, splenic artery ligation or splenectomy or port-systemic shunting were performed. And also to avoid graft injury due to congestion, venoplasty and portal infusion were performed.
It has been suggested that excessive portal flow secondary to relative portal hypertension may be the cause and that portal decompression may improve graft survival. To minimize the small for size graft injury, several methods were used. Ku et al. reported an improved outcome of canine liver transplantation using a quarter-graft with the aid of a porthepatic vein shunt. The effect of a porthepatic vein shunt on portal vein decompression should be an important factor for preventing graft injury after circulation in an extremely small graft (5). To avoid outflow disturbance, we recommended a recipient venoplasty with a matching venoplasty of multiple graft hepatic veins to create a singlewide outflow orifice (6). We also reported the impact of splenectomy or splenic artery ligation on the outcome in LDALT using a left lobe graft (7). In a majority of the cases the portal pressure as well as the portal vein flow after a splenectomy decreased in comparison to that before the splenectomy. To decrease portal flow and portal pressure, Boillot et al. completely divided the superior mesenteric venous flow by a mesocaval shunt with downstream ligation of the superior mesenteric vein in order to avoid graft congestion and failure by overperfusion (8). Malago et al.
performed the same method as Boillot et al. However, by artificial shunting method, the portal blood flow is stolen to the vena cava, and there is a risk that the portal blood flow will decrease.
Different from these surgical methods, we performed intraportal infusion to improve small for graft injury. Recently, Shimazu et al. showed the feasibility of controlling rejection and other complications in adult-ABO incompatible liver transplantation under intraportal infusion therapy. They performed intraportal infusion therapy after transplantation with methylpredonisolone, prostaglandin E1, and gabexate mesilate (9). Our previous report also demonstrated that the regeneration rate of small graft was over 2.0, one week after transplantation (10). From this finding, we supported small grafts by intraportal infusion treatment in the first week after transplantation.
Small-for-size graft injury is constituted by many factors. And small-for-size graft injury might occur not only in small left lobe graft but large right lobe graft. In living donor adult transplantation, we have to recognize exact preoperative recipient risk factors, such as portal hypertension, graft size or graft anatomy, to be prepared to perform intraoperative procedures such as portcaval shunting, bypass graft venoplasty et al. and to follow a postoperative treatment plan including intraportal infusion, hyperbaric oxygenation, plasma exchange et al. in order to avoid small-for-size graft injury.

References
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7. Boillot, O., Delafosse, B., Mechet, I., Boucard, C., Pouyet, M. - Small-for-size partial liver graft in an adult recipient; a new transplant technique. Lancet, 2002, 359:368.
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