[Liver transplantation in low portal vein flow: separation of portal vein areas with divided portal-venous and arterialized caval-venous liver perfusion. 1. Clinical case report]

Portal vein arterialisation as a technical option in liver transplantation: impact on function, regeneration, and morphology of the liver following hemihepatectomy in pigs

BACKGROUND

Arterialisation of the portal vein has been propagated as a technical variant in liver transplantation. However, the consequences of this unphysiological vascular supply are insufficiently known.

METHODS

Twenty-seven healthy pigs were subjected to a left hemihepatectomy and divided into three groups. The first group received complete arterialisation of the portal vein (PVA). In the second group hepatic artery blood flow was also interrupted by dividing the artery (PVA/DHA). Nine animals served as controls (Group C).

RESULTS

Early mortality in the PVA/DHA group (6/9) was significantly increased in comparison with the PVA (2/9) and control (2/9) groups (P < 0.05). In the surviving animals, arterialisation (PVA and PVA/DHA) led to significantly faster hepatic regeneration in comparison with control animals, with comparable liver function and with liver size increasing to 278% and 293% vs 134% (P = 0.002) after 3 weeks, in liver ... weeks. This was accompanied by enhanced hepatic expression of the proliferation markers MIB-1 (22.4% and 16.7% vs 5.9%, P = 0.002) and PCNA (86% and 68% vs 66%, P = 0.002) one week postoperation. At the same time, the number of apoptotic hepatocytes increased from 1.6% to 2.5% and 2.3% (P = 0.002). No significant difference was found in the collagen content of the liver after 3 weeks.

CONCLUSIONS

Arterialisation of the portal vein promotes early and enhanced hepatic regeneration without impairing liver function. This technique may therefore be useful in split-graft liver transplantation, where this aspect would be of particular importance.

Effects of portal vein arterialization on liver regeneration after partial hepatectomy in the rat

Although portal venous supply is considered essential to preserve hepatic integrity, in this study, effects of portal arterialization on liver regeneration were evaluated in a rat model of partial hepatectomy (PH). Ninety-six Lewis rats were randomly assigned to four groups of 24 rats each: PH only (group 1), PH with either venous or arterialized portal supply (groups 2 and 3, respectively), and PH without portal supply (group 4). Liver regeneration rate (LRR), 5-bromo-2-deoxyuridine (BrdU) labeling index, and liver biological characteristics were assessed on days 1, 2, 3, and 7. Compared with group 1, all tested rats had a marked body weight loss after surgery, and only rats in group 4 showed no signs of recovery on day 7. With maintained portal inflow (groups 1, 2, and 3), LRRs increased steadily to day-7 values of 89.2% +/- 11.8%, 81.4% +/- 8%, and 77.4% +/- 9.4%, respectively (P = not significant), and 24-hour peak values of BrdU labeling index were 159 +/- 26, 157 +/- 42, and 149 +/- 48, respectively (P = not significant). Conversely, rats deprived of portal supply (group 4) showed profound inhibition of these two parameters (14 +/- 13; P <.01;32.1% +/- 7.7%; P <.001, respectively). These results indicate that proper portal blood supply is essential to initiate and maintain liver regeneration after PH. With an equivalent portal inflow rate of either venous or arterial source, the hepatic regeneration response can be sustained.

Cavoportal hemitransposition in liver transplantation

Over the last decade a large number of patients with portal vein thrombosis have undergone successful liver transplantation. In most of these patients, simple modifications in vascular reconstruction techniques are adequate. However, anastomosis of the donor portal vein may not be possible in the presence of extensive portal and superior mesenteric venous thrombosis and in the absence of any other large tributary of the portal venous system. Cavoportal hemitransposition has been described as a salvage technique under these circumstances. We report a 43-year-old patient who underwent such a procedure and remains well 1 year later. We review the literature and discuss the implications of cavoportal hemitransposition.

Arterialization of the portal vein in liver transplantation: a new microsurgical model in the rat

BACKGROUND

A preexisting thrombosis of the portal vein and the deep splanchnic bed can make it extremely difficult to reestablish the portal blood flow in orthotopic liver transplantation in man. Complete arterialization of the liver transplant, including the donor portal vein, might be a viable therapeutic option. A new rat transplantation model is described, in which the liver is completely arterialized.

METHODS

The outflow of the portal blood in the recipient was secured via a portocaval shunt. Hepatectomy was then performed and the liver transplant placed in orthotopic position. An interposed aortic segment was used for direct arterialization of the donor portal vein.

RESULTS

The laboratory parameters determined in the serum at the end of the observation period of 28 days revealed normal functioning of the transplant. The histological examinations showed largely normal cellular architecture, with no signs of necrosis, but incipient fibrosis.

CONCLUSIONS

Using this new surgical technique in the rat liver transplantation model, long-term morphological and functional changes in a completely arterialized liver graft, and the regenerative capability of liver tissue perfused in this way, can be investigated.

Caval inflow to the graft: a successful way to overcome diffuse portal system thrombosis in liver transplantation

Portal vein thrombosis was considered to be a major contraindication to liver transplantation before the introduction of vessel grafts from the recipient's area of confluence of the splenic and superior mesenteric veins, behind the neck of the pancreas, to the graft's portal vein. Refinement in surgical technique has given rise to a large number of possibilities to overcome portal vein thrombosis in OLT recipients, ranging from portal vein thrombectomy to several different venous graft jump reconstructions. All these reconstructions require the presence of a patent vein of the portal system. When neither splanchnic veins nor sufficiently large venous collaterals are available, liver transplantation has been considered impossible. Salvage solutions include arterialization of the portal vein with the associated risk of liver damage in the longterm, a combined liver and bowel transplantation has been proposed but not yet reported (and in any case the results of combined liver and bowel transplants are not as good as those of liver transplantation alone) and finally the use of blood inflow from the inferior vena cava as first reported by Tzakis and coworkers. Portal flow from the inferior vena cava may be performed as a last resort. Although the consequences of severe pretransplantation portal hypertension remain and should be treated before, during, and after transplantation, liver function is normal in the short and midterm. With this new procedure, diffuse portal vein thrombosis is no longer an absolute contraindication to liver transplantation. But this needs to be confirmed in light of further experience and longterm followup.

Delayed correction of portal hypertension after portal vein conduit arterialization in liver transplantation

A 55-year-old woman underwent orthotopic liver transplantation for autoimmune chronic active hepatitis. Extensive portal and superior mesenteric venous thrombosis precluded standard portal venous reconstruction and necessitated use of a venous conduit from the recipient splenic vein of the donor liver. Flow through this conduit was poor, however, and to prevent subsequent portal venous thrombosis and graft loss, the conduit was arterialized by end-to-side anastomosis with the recipient hepatic artery. This ensured graft survival but resulted in prehepatic portal hypertension, which required ligation of the arterioportal fistula for 4 months. The patient had a satisfactory outcome.

Liver transplantation: newer surgical approaches

The standard procedure for orthotopic liver transplantation remains transplantation of the whole organ together with resection of the vena cava and the use of venovenous bypass. In cases of severe mismatch of the donor and recipient vena cava, the piggyback technique, if necessary with vena cava plasty, is preferable. Furthermore, in all cases where venovenous bypass cannot be performed, the piggyback or other technique preserving the vena cava should be performed. In paediatric patients, reduced/size liver transplantation may be indicated because of the shortage of small livers. In the hands of experienced surgeons, the results of reduced-size liver transplantation in paediatric patients are similar to those of whole organ transplantation. Further innovative procedures to overcome the problem of organ shortage include split-liver and living related transplantation in children. Distinct advantages of living related transplantation can be seen in a well-functioning graft, lack of preservation injury, elective operation and optimal graft-size matching. The immunological advantage that has been claimed could not be demonstrated so far, and will need to be examined in the long-term follow-up. However, there remains a distinct disadvantage for living related transplantation with regard to the surgical technique. Preoperative portal venous thrombosis should be carefully assessed, but is not a contraindication to liver transplantation if the confluence of the superior mesenteric vein and splenic vein is patent. Arterial reconstruction at the confluence of two arteries (hepatic and gastroduodenal or splenic artery) seems to be preferable to an end-to-end anastomosis because of improved inflow into the graft and a reduced risk of arterial stenosis and thrombosis. Where the common hepatic arteries are small, with reduced or reversed flow, and in patients with coeliac trunk stenosis, we recommend a direct approach to the suprarenal or infrarenal aorta. Bile duct anastomosis may preferably be performed with a side-to-side technique, to reduce early and late biliary complications.

Evaluation of temporary portal vein arterialization: the minimum arterialized blood flow for maintaining liver viability

The effect of temporary portal vein arterialization (PVA) on hepatic energy metabolism was investigated by changes in the arterial blood ketone body ratio (KBR) and hepatic energy charge (EC) level in 17 dogs. The KBR decreased markedly after clamping the hepatic hilar vessels combining mesocaval shunt and remained at a low level throughout hepatic ischemia. After PVA, the KBR was rapidly restored and maintained at sufficient levels. EC at 60 min after arterialization also recovered to the preclamping level. By reducing the arterial shunt flow, the critical point of arterialized blood flow for maintaining the KBR at high levels was assessed to be about 10% of the total hepatic blood flow (THBF). These findings demonstrate that temporary PVA is an effective method for maintaining the functional capacity of the liver, and that the minimum arterialized blood flow needed to preserve liver viability is only about 10% of the total hepatic blood flow.