Partial hepatic grafting: porcine study on critical volume reduction

Small-For-Size Syndrome and Graft Inflow Modulation Techniques in Liver Transplantation

BACKGROUND

Partial liver transplantation has recently been proposed to alleviate organ shortages. However, transplantation of a small-for-size graft is associated with an increased risk of posttransplant hepatic dysfunction, commonly referred to as small-for-size syndrome (SFSS). This review describes the etiology, pathological features, clinical manifestations, and diagnostic criteria of SFSS. Moreover, we summarize strategies to improve graft function, focusing on graft inflow modulation techniques. Finally, unmet needs and future perspectives are discussed.

SUMMARY

In fact, posttransplant SFSS can be attributed to various factors such as preoperative status of the recipients, surgical techniques, donor age, and graft quality, except for graft size. With targeted improvement measures, satisfactory clinical outcomes can be achieved in recipients at increased risk of SFSS. Given the critical role of relative portal hyperperfusion in the pathogenesis of SFSS, various pharmacological and surgical treatments have been established to reduce or partially divert excessive portal inflow, and recipients will benefit from individualized therapeutic regimens after careful evaluation of benefits against potential risks. However, there remain unmet needs for further research into different aspects of SFSS to better understand the correlation between portal hemodynamics and patient outcomes.

KEY MESSAGES

Contemporary transplant surgeons should consider various donor and recipient factors and develop case-specific prevention and treatment strategies to improve graft and recipient survival rates.

Small-for-size syndrome in liver transplantation: Definition, pathophysiology and management

BACKGROUND

Since the first success in an adult patient, living donor liver transplantation (LDLT) has become an universally used procedure. Small-for-size syndrome (SFSS) is a well-known complication after partial LT, especially in cases of adult-to-adult LDLT. The definition of SFSS slightly varies among transplant physicians. The use of a partial liver graft has risks of SFSS development. Persistent portal vein (PV) hypertension and PV hyper-perfusion after LT were identified as the main factors. Hence, various approaches were explored to modulate PV flow and decrease PV pressure in order to alleviate this syndrome. Herein, the definition, clinical symptoms, pathophysiology, basic research, as well as preventive and treatment strategies for SFSS are reviewed based on an extensive review of the literature and on our own experiences.

DATA SOURCES

The articles were collected through PubMed using search terms "liver transplantation", "living donor liver transplantation", "living liver donation", "partial graft", "small-for-size graft", "small-for-size syndrome", "graft volume", "remnant liver", "standard liver volume", "graft to recipient body weight ratio", "sarcopenia", "porcine", "swine", and "rat". English publications published before March 31, 2020 were included in this review.

RESULTS

Many transplant surgeons performed PV flow modulation, including portocaval shunt, splenic artery ligation and splenectomy. With these techniques, patient outcome has been improved even when using a "small" graft. Other factors, such as preoperative recipients' nutritional and skeletal muscle status, graft congestion, and donor factors, were also identified as risk factors which all have been addressed using various strategies.

CONCLUSIONS

The surgical approach controlling PV flow and pressure could help to prevent SFSS especially in severely ill recipients. In the absence of efficacious medications to resolve SFSS, conservative treatments, including aggressive fluid balance correction for massive ascites, anti-microbiological therapy to prevent or control sepsis and intensive nutritional therapy, are all required if SFSS could not be prevented.

Significance of Portal Venous Velocity in Short-term Graft Function in Living Donor Liver Transplantation

BACKGROUND

Graft regeneration and functional recovery after reperfusion of transplanted graft are very important for successful living donor liver transplantation (LDLT). The aim of this study was to evaluate the significance of postoperative portal venous velocity (PVV) in short-term recovery of graft function in LDLT.

PATIENTS AND METHODS

From February 2007 through December 2015, we performed 17 primary LDLTs, which were included in the present study. The patients ranged in age from 12 to 65 years (mean: 50 years), and 11 were female patients. Postoperatively, Doppler ultrasonography was performed daily to measure PVV (cm/s), and liver function parameters were measured daily. The change in PVV (ΔPVV) was defined as follows: ΔPVV = PVV on postoperative day (POD) 1 - PVV on POD 7. Maximal value of serum aspartate aminotransferase (ASTmax) and maximal value of serum alanine transaminase (ALTmax) at 24 hours after graft reperfusion were used as parameters of reperfusion injury. Correlation analyses were performed as follows: (1) correlation of ΔPVV and PVV on POD 1 (PVV-POD 1) with the values such as ASTmax, ALTmax, other liver function parameters on POD 7 and graft regeneration rate; (2) correlation of ASTmax and ALTmax with other liver function parameters on POD 7.

RESULTS

ΔPVV significantly correlated with the values of serum total bilirubin (P < .01), prothrombin time (P < .01), and platelet count (P < .05), and PVV-POD 1 significantly correlated with the values of serum total bilirubin (P < .05) and prothrombin time (P < .05).

CONCLUSION

ΔPVV and PVV-POD 1 may be useful parameters of short-term functional recovery of the transplant liver in LDLT.

Adult left liver transplantation from split livers and living donors: a 14-year single-center experience

BACKGROUND

In an era of organ scarcity, the use of left liver grafts for adult recipients could increase the access to liver transplantation (LT). The aim of this study was to evaluate the results in a single-center series of adult left LT over a 14-yr period.

PATIENTS AND METHODS

Between March 1996 and March 2010, 30 adult patients underwent LT with a left liver obtained from 16 split cadaveric livers and 14 living donors (LD). Portal vein inflow modulation was performed in selected cases.

RESULTS

A total of 19 (63.3%) grafts had early dysfunction leading to graft failure in six cases (20%). One third of the grafts developed small-for-size syndrome (SFSS). One-yr patient and graft survival was 80% and 76.7%, respectively. Regarding two successive periods, one-yr patient and graft survival dramatically increased from 62.5% to 100% (p = 0.01) and 56.2% to 100% (p = 0.002), respectively. Multivariate analysis disclosed that completion of a portosystemic shunt and the occurrence of post-operative ascites were significantly associated with graft failure.

CONCLUSIONS

Our results support that improved surgical techniques and careful patient selection can lead to a safe use of left livers for transplantation in adult recipients. Inflow modulation could be performed in very selected cases.

Portal hyperperfusion: mechanism of injury and stimulus for regeneration in porcine small-for-size transplantation

Understanding the pathogenesis of small-for-size (SFS) syndrome is critical to expanding the applicability of partial liver transplantation. We aimed to characterize its acute presentation and association with alterations in hepatic hemodynamics, microstructure, and regeneration in a porcine model. Eighteen SFS liver transplants were performed. Donors underwent 70% hepatectomy. Partial grafts were implanted into larger recipients. Whole liver transplants were also performed (n = 6). Recipients were followed until death or for 5 days. Hemodynamics were measured, and tissue was sampled intraoperatively and at the study end. Serum was sampled regularly during follow-up. Seventeen SFS transplants and 6 whole liver transplants were included. SFS grafts represented 23.2% (19.3%-25.3%) of the recipients' standard liver volume. The survival rate was 29% and 100% in the SFS and whole liver groups, respectively. The portal venous flow, pressure gradient, and resistance were significantly higher in recipients of SFS grafts versus whole livers after portal and arterial reperfusion. Arterial flow as a percentage of the total liver blood flow was significantly lower after reperfusion in SFS grafts and remained so when measured again after 5 days. Markers of endothelial cell injury increased soon after reperfusion, and those of hepatocellular injury increased later; both predicted the appearance of either graft failure or histological recovery. Proliferative activity peaked earlier and higher among nonsurvivors in the SFS group. Surviving grafts demonstrated a slower but maintained rise in regenerative activity, although metabolic activity failed to improve. In SFS transplantation in the acute setting, portal hyperperfusion is a stimulus for regeneration but may simultaneously cause irreparable endothelial injury. This porcine model not only helps to elucidate the inciting factors in SFS pathogenesis but also offers a clinically relevant means to study its prevention.

Predicting liver failure following major hepatectomy

Pre-operative determination of the risk of liver dysfunction has come under criticism with regards to its usefulness in clinical practice. Opinion is split between centres which use such tests uniformly on all patients and those where clinical judgment alone is used. Published data would not suggest any difference in mortality, morbidity or liver failure rates between these groups. This review outlines and presents the evidence for pre-operative quantification of functional liver remnant volume.

Liver failure after major hepatic resection

INTRODUCTION

The consequence of excessive liver resection is the inexorable development of progressive liver failure characterised by the typical stigmata associated with this condition, including worsening coagulopathy, hyperbilirubinaemia and encephalopathy. The focus of this review will be to investigate factors contributing to hepatocyte loss and impaired regeneration.

METHODS

A literature search was undertaken of Pubmed and related search engines, examining for articles relating to hepatic failure following major hepatectomy.

RESULTS

In spite of improvements in adjuvant chemotherapy and increasing surgical confidence and expertise, the parameters determining how much liver can be resected have remained largely unchanged. A number of preoperative, intraoperative and post-operative factors all contribute to the likelihood of liver failure after surgery.

CONCLUSIONS

Given the magnitude of the surgery, mortality and morbidity rates are extremely good. Careful patient selection and preservation of an obligate volume of remnant liver is essential. Modifiable causes of hepatic failure include avoidance of sepsis, drainage of cholestasis with restoration of enteric bile salts and judicious use of portal triad inflow occlusion intra-operatively. Avoidance of post-operative sepsis is most likely to be achieved by patient selection, meticulous intra-operative technique and post-operative care. Modulation of portal vein pressures post-operatively may further help reduce the risk of liver failure.

Excessive portal flow causes graft failure in extremely small-for-size liver transplantation in pigs

AIM

To evaluate the effects of a portocaval shunt on the decrease of excessive portal flow for the prevention of sinusoidal microcirculatory injury in extremely small-for-size liver transplantation in pigs.

METHODS

The right lateral lobe of pigs, i.e. the 25% of the liver, was transplanted orthotopically. The pigs were divided into two groups: graft without portocaval shunt (n = 11) and graft with portocaval shunt (n = 11). Survival rate, portal flow, hepatic arterial flow, and histological findings were investigated.

RESULTS

In the group without portocaval shunt, all pigs except one died of liver dysfunction within 24 h after transplantation. In the group with portocaval shunt, eight pigs survived for more than 4 d. The portal flow volumes before and after transplantation in the group without portocaval shunt were 118.2+/-26.9 mL/min/100 g liver tissue and 270.5+/-72.9 mL/min/100 g liver tissue, respectively. On the other hand, in the group with portocaval shunt, those volumes were 124.2+/-27.8 mL/min/100 g liver tissue and 42.7+/-32.3 mL/min/100 g liver tissue, respectively (P<0.01). As for histological findings in the group without portocaval shunt, destruction of the sinusoidal lining and bleeding in the peri-portal areas were observed after reperfusion, but these findings were not recognized in the group with portocaval shunt.

CONCLUSION

These results suggest that excessive portal flow is attributed to post transplant liver dysfunction after extreme small-for-size liver transplantation caused by sinusoidal microcirculatory injury.

Liver failure following partial hepatectomy

While major liver resections have become increasingly safe due to better understanding of anatomy and refinement of operative techniques, liver failure following partial hepatectomy still occurs from time to time and remains incompletely understood. Observationally, certain high-risk circumstances exist, namely, massive resection with small liver remnants, preexisting liver disease, and advancing age, where liver failure is more likely to happen. Upon review of available clinical and experimental studies, an interplay of factors such as impaired regeneration, oxidative stress, preferential triggering of apoptotic pathways, decreased oxygen availability, heightened energy-dependent metabolic demands, and energy-consuming inflammatory stimuli work to produce failing hepatocellular functions.

Porcine partial liver transplantation: a novel model of the "small-for-size" liver graft

Increasing shortage of cadaveric grafts demands the utilization of living donor and split liver grafts. The purpose of this study was to 1) define the "small-for-size" graft in a pig liver transplant model 2) evaluate pathological changes associated with small-for-size liver transplantation. Pigs were divided into four groups based on the volume of transplanted liver: (a) control group (n=4), 100% liver volume (LV) (b) group I (n=8), 60% LV (c) group II (n=8), 30% LV (d) group III (n=15), 20% LV. Tacrolimus and methyl prednisone were administered as immunosuppression. Animals were followed for 5 days with daily serum biochemistry, liver biopsies on day 3 and 5 for light microscopy, and tissue levels of thymidine kinase (TK) and ornithine decarboxylase (ODC). Liver grafts were weighed pretransplant and at sacrifice. All the recipients of 100%, 60%, and 30% grafts survived. Transplantation of 20% grafts (group III) resulted in a 47% mortality rate. Group III animals showed significantly prolonged prothrombin times (p<0.05), elevated bilirubin levels (p<0.05), and ascites. The rate of regeneration, as indicated by TK activity and graft weight was inversely proportional to the size of the transplanted graft. The severity of the microvascular injury was inversely proportional to graft size and appeared to be the survival-limiting injury. Frank rupture of the sinusoidal lining, parenchymal hemorrhage, and portal vein injury were prominent in group III animals 1 hour following reperfusion. This study established a reproducible large animal model of partial liver grafting; it defined the small-for-size syndrome in this model and described the associated microvascular injury.

Living donor liver transplantation with special reference to ABO-incompatible grafts and small-for-size grafts

Living donor liver transplantation (LDLT) has developed on the basis of increased safety of conventional liver surgery and the need for expanding donor sources, especially in children. Indications for LDLT were soon extended to adult patients in Japan, where cadaveric donation was limited. The right liver is now routinely transplanted to adults to avoid small-for-size graft syndrome, even though the right liver graft has the disadvantages of less remaining donor liver and the question of donor safety. Assessing the suitable size or quality of the graft, as well as of the remnant donor liver, is one of the most important problems in adult LDLT. Although several tactics have been proposed to manage the small-for-size syndrome, their efficacy remains a question. We suggest that small-for-size syndrome is preventable by engaging in careful donor selection or using effective agents for hepatic microcirculatory disturbance control. Sometimes for LDLT only ABO-incompatible grafts are available from relatives, but they must be transplanted despite the expected poor outcome in adults and older children. To overcome the problems in this situation, we developed a novel protocol including intraportal infusion therapy with methylprednisolone, prostaglandin E1, and gabexate mesylate. Two adult patients undergoing ABO-incompatible LDLT have now survived 53 and 35 months after transplantation with good liver function. However, the other two patients suffered thrombotic microangiopathy postoperatively and died owing to cerebral hemorrhage or multiple organ failure, respectively. Further investigation is needed to improve the outcome of liver transplantation across the ABO blood group barrier.

Portal vein pressure is the key for successful liver transplantation of an extremely small graft in the pig model

In partial-liver transplantation, the use of small grafts sometimes results in graft failure, usually caused by portal hypertension after transplantation (Tx). Portal hypertension after Tx can be decreased with a porto-caval shunt (PCS). The purpose of this study is to clarify the effect of the PCS on extremely reduced-size liver Tx. In a pig model, the posterior segment of 25% of a whole liver was transplanted orthotopically. The pigs were divided two groups: group A, graft with PCS ( n=7), and group B, graft without PCS ( n=7). The PCS was made by means of side-to-side anastomosis of the portal vein and the inferior vena cava. We examined the portal vein pressure, survival rate, regeneration rate of the graft, Ki-67 as an index of cell proliferation, and histological findings, and carried out liver-function tests. In group A, five pigs survived for more than 4 days and the remaining two died of a perforated gastric ulcer on post-operative day (POD) 2. In group B, all pigs except one died of graft failure within 24 h. Portal vein pressure after reperfusion in group A and group B was of statistically significant difference ( P<0.05), 14.2+/-3.2 and 18.9+/-4.7 cmH(2)O, respectively. In group A, the regeneration rate of the graft was 94%, 4 days after Tx, and Ki-67 stained remarkably in the parenchymal hepatocytes. In TEM finding, structure of the sinusoid was also well maintained after Tx. From these results we can conclude that the key to success in liver Tx with extremely small grafts lies in the control of the portal vein pressure.

Small-for-size partial liver graft in an adult recipient; a new transplant technique

We report a new technique of adult liver transplantation using a small-for-size graft. In order to avoid graft congestion and failure by overperfusion, we completely diverted the superior mesenteric venous flow by a mesocaval shunt with downstream ligation of the superior mesenteric vein. The recipient recovered well, and the graft had normal histology and function at 5 months follow-up. Given the current scarcity of cadaveric donors, this technique may increase the numbers of adult recipients by using left lobes from cadaveric split liver grafts.

Effects of deletion variant of hepatocyte growth factor on reduced-size liver transplantation in rats

BACKGROUND

The deletion variant of hepatocyte growth factor (dHGF) exerts mitogenic and antifibrotic effects. The purpose of this study was to evaluate the effect of dHGF on rats that had undergone syngeneic or allogeneic reduced-size (60%) orthotopic liver transplantation (ROLT).

METHODS

Starting immediately after the syngeneic (Lewis to Lewis) and allogeneic (Lewis to Brown Norway) ROLT, 500 microg/kg dHGF was administered i.v. twice a day until the day the rats were killed. Its effect on hepatic graft weight, regeneration, and biochemical parameters was evaluated.

RESULTS

dHGF promoted restoration of the liver volume and liver regeneration as well as protein synthesis in the rats that underwent syngeneic ROLT. In the rats that underwent allogeneic ROLT, dHGF reduced the level of serum cytosolic enzymes related to acute cellular rejection, but a significant improvement in liver regeneration and protein synthesis was not seen. When tacrolimus was administered to prevent rejection of the allogeneic grafts, the beneficial effect of dHGF was apparent, and was as beneficial as in syngeneic ROLT.

CONCLUSIONS

Administering dHGF after liver transplantation augments the regeneration and functional recovery of partial liver grafts and reduces hepatocyte injury in acute cellular rejection.

[Orthotopic liver transplantation from a living adult donor to an adult using the right hepatic lobe]

STUDY AIM

In children, living donor liver transplantation has been shown to be efficient in treating end-stage liver diseases when the left lateral segment is harvested. In adults, more liver mass is needed to provide adequate hepatic function. The aim of this study is to report 2 successful cases of living donor liver transplantation using a right hepatic lobe from adult.

PATIENTS AND METHODS

In 2 sons, the right hepatic lobe was harvested without the middle hepatic vein for transplantation in their fathers who were suffering from end-stage liver cirrhosis. Hepatectomy was done without vascular inflow occlusion after dissection of vascular and biliary structures, itself strictly restricted to the right side. In recipients, the graft was implanted orthotopically with preservation of the native inferior vena cava and after temporary porto-caval shunt.

RESULTS

The duration of donors procedures was 7 h and 11 h 45 min; intra-operative transfusions comprised of 700 mL from cell-saver in the first case, and 1300 mL plus 1 autologous red blood cell unit in the second case. Graft weights were 770 g and 1100 g. None of the donors experienced liver failure and both were able to leave the hospital 9 days after the operation. In recipients, initial graft function was excellent in the first case and correct in the second case, despite the necessity to redo intra-operatively the hepatic vein anastomosis secondary to a twisting. Patients were discharged 20 and 40 days respectively following transplantation.

CONCLUSION

Adult living donor liver transplantation using a right hepatic lobe is efficient and safe. This option could contribute to reducing the mortality of patients on the waiting list.