Shear stress theory and small-for-size graft in adult living related liver transplantation

A portal pressure cut-off of 15 versus a cut-off of 20 for prevention of small-for-size syndrome in liver transplantation: A comparative study

AIM

Portal hypertension has recently been implicated in the pathogenesis of small-for-size syndrome (SFSS) in adult-to-adult living-donor liver transplantation (A-LDLT). The aim of our study is to compare the portal venous pressure (PVP) cut-off values of 15 mmHg and 20 mmHg in terms of prevention of SFSS in A-LDLT.

METHODS

Seventy-six patients underwent A-LDLT. A PVP <20 mmHg at the end of the operation was targeted using graft inflow modulation. Patients were divided into two groups: group A, final PVP <15 mmHg; and group B, final PVP 15-19 mmHg. Peak serum bilirubin and peak international normalized ratio in the first month after A-LDLT, as well as hepatic encephalopathy, SFSS, 90-day morbidity, and mortality were observed in both groups.

RESULTS

Final PVP was well controlled below 20 mmHg in all patients (group A, n = 39; group B, n = 37). Six patients suffered SFSS in group B (16.2%) compared to one patient (2.6%) in group A (P = 0.04). Nine patients died in group B (24.3%), four of whom died of SFSS, compared to three patients in group A (7.7%) (P = 0.047).

CONCLUSION

A PVP cut-off of 15 mmHg seems to be a more appropriate target level than a cut-off of 20 mmHg for prevention of postoperative SFSS in A-LDLT.

Challenges to liver transplantation and strategies to improve outcomes

Liver transplantation (LT) is a highly successful treatment for many patients with nonmalignant and malignant liver diseases. However, there is a worldwide shortage of available organs; many patients deteriorate or die while on waiting lists. We review the important clinical challenges to LT and the best use of the scarce organs. We focus on changes in indications for LT and discuss scoring systems to best match donors with recipients and optimize outcomes, particularly for the sickest patients. We also cover controversial guidelines for the use of LT in patients with hepatocellular carcinoma and cholangiocarcinoma. Strategies to increase the number of functional donor organs involve techniques to perfuse the organs before implantation. Partial LT (living donor and split liver transplantation) techniques might help to overcome organ shortages, and we discuss small-for-size syndrome. Many new developments could increase the success of this procedure, which is already one of the major achievements in medicine during the second part of the 20th century.

"Small-for-flow" syndrome: shifting the "size" paradigm

The "small-for-size" syndrome and "post-hepatectomy liver failure" refers to the development of liver failure (hyperbilirubinemia, coagulopathy, encephalopathy and refractory ascites) resulting from the reduction of liver mass beyond a certain threshold. This complication is associated with a high mortality and is a major concern in liver transplantation involving reduced liver grafts from deceased and living donors as well as in hepatic surgeries involving extended resections of liver mass. The limiting threshold for liver resection or transplantation is currently predicted based on the mass of the remnant liver (or donor graft) in relation to the body weight of the patient, with a ratio above 0.8 being considered safe. This approach, however, has proved inaccurate, because some patients develop the "small-for-size" syndrome despite complying with the "safe" threshold while other patients who surpass the threshold do not develop it. We hypothesize that the development of the "small-for-size" syndrome is not exclusively determined by the ratio of the mass of the liver remnant (or graft) to the body weight, but it is instead strictly determined by the hemodynamic parameters of the hepatic circulation. This hypothesis is based in recent clinical and experimental reports showing that relative portal hyperperfusion is a critical factor in the development of the "small-for-size" syndrome and that maneuvers that manipulate the hepatic vascular inflow are able to prevent the development of the syndrome despite liver-to-body weight ratios well below the "limiting" threshold. Measurements of hepatic blood flow and pressure, however, are not routinely performed in hepatic surgeries. Focusing on the "flow" rather than in the "size" may improve our understanding of the pathophysiology of the "small-for-size" syndrome and "post-hepatectomy liver failure" and it would have important implications for the clinical management of patients at risk. First, hepatic hemodynamic parameters would have to be measured in hepatic surgeries. Second, these parameters (in addition to liver mass) would be the principal basis for deciding the "safe" threshold of viable liver parenchyma. Third, the hepatic hemodynamic parameters are amenable to manipulation and, consequently, the "safe" threshold may also be manipulated. Shifting the paradigm from "small-for-size" to "small-for-flow" syndrome would thus represent a major step for optimizing the use of donor livers, for expanding the indications of hepatic surgery, and for increasing the safety of these procedures.

Method for spontaneous constriction and closure of portocaval shunt using a ligamentum teres hepatis in small-for-size graft liver transplantation

BACKGROUND

We have developed a new portocaval (PC) shunt creation technique for use in small-for-size (SFS) graft liver transplantations. PC shunts are already used to avoid SFS graft syndrome in cases of adult-to-adult living donor liver transplantation (LDLT), but the current method of creating these shunts is subject to two problems: reportal hypertension and liver dysfunction after premature ligation of the PC shunt; and graft atrophy and liver dysfunction because of the loss of portal venous flow late in the recovery period after LDLT.

METHODS

Our new technique avoids these two problems simultaneously by using the interposed obliterated ligamentum teres hepatis (LTH) to create the PC shunt, then obstructing the PC shunt after regeneration of the liver graft.

RESULTS

We have used this technique in four cases. In all cases, portal venous pressures after shunting were lower than those before shunting, and PC shunts with lower portal pressure were obstructed faster than that with higher portal pressure.

CONCLUSION

Our results suggest that the LTH can function as a shape memory graft to reduce portal venous flow after regeneration of the graft liver. Using the LTH to create a PC shunt might help to prevent both SFS graft syndrome early in the recovery period after LDLT and loss of portal venous flow late in the recovery period.

Portal pressure <15 mm Hg is a key for successful adult living donor liver transplantation utilizing smaller grafts than before

To prevent small-for-size syndrome in adult-to-adult living donor liver transplantation (A-LDLT), larger grafts (ie, right lobe grafts) have been selected in many transplant centers. However, some centers are investigating the benefits of portal pressure modulation. Five hundred sixty-six A-LDLT procedures using right or left lobe grafts were performed between 1998 and 2008. In 2006, we introduced intentional portal pressure control, and we changed the graft selection criteria to include a graft/recipient weight ratio >0.7% instead of the original value of >0.8%. All recipients were divided into period I (1998-2006, the era of unintentional portal pressure control; n = 432) and period II (2006-2008, the era of intentional portal pressure control; n = 134). The selection of small-for-size grafts increased from 7.8% to 23.9%, and the selection of left lobe grafts increased from 4.9% to 32.1%. Despite the increase in the number of smaller grafts in period II, 1-year patient survival was significantly improved (87.9% versus 76.2%). In 129 recipients in period II, portal pressure was monitored. Patients with a portal pressure <15 mm Hg demonstrated better 2-year survival (n = 86, 93.0%) than patients with a portal pressure >or=15 mm Hg (n = 43, 66.3%). The recovery from hyperbilirubinemia and coagulopathy after transplantation was significantly better in patients with a portal pressure <15 mm Hg. In conclusion, our strategy for A-LDLT has changed from larger graft-based A-LDLT to controlled portal pressure-based A-LDLT with smaller grafts. A portal pressure <15 mm Hg seems to be a key for successful A-LDLT.

Successful super-small-for-size graft liver transplantation by decompression of portal hypertension via splenectomy and construction of a mesocaval shunt: a case report

We performed a successful super-small-for-size graft liver transplantation by decompressing portal hypertension via splenectomy and a mesocaval shunt. A 46-year-old woman with Child-Pugh class C liver cirrhosis associated with Wilson's disease underwent a living donor liver transplantation (LDLT). The donor had an anomalous portal vein, hepatic vein, and bile duct, so we had to use the right lateral segment for the graft. Preoperative computed tomographic (CT) volumetry showed the volume of this area to be 433 mL; graft-to-recipient weight ratio (GRWR) was 0.72; and graft-to-standard liver volume (GV/SLV) was 39.0%. However, the real volume of the resected right lateral segment was 281 g; GRWR was 0.47; and GV/SLV was 25.3%--a super-small-for-size graft. After implantation, congestion of the small graft was severe due to excessive portal hypertension. Therefore, we tried decompressing the portal vein. First, we performed splenectomy which reduced the portal pressure which remained excessive. Second, a mesocaval shunt was constructed decreasing the portal pressure from 38 to 30 cm H2O. Additionally, we initiated continuous portal injection of prostaglandin E1. The postoperative course was not smooth, but the general status slowly recovered. Over 25 cm H2O of portal hypertension was observed until postoperative day 21 when it improved. At last, the recipient was discharged on postoperative day 156. Accurate preoperative CT volumetry is important to obtain sufficient graft volume. Our case may be one of the smallest-for-size grafts that was successfully transplanted. Management of excessive portal hypertension is important for LDLT, especially using a small-for-size graft. Splenectomy and construction of a mesocaval shunt may be useful strategies to decompress the portal vein.

Management of Major Portosystemic Shunting in Small-for-Size Adult Living-Related Donor Liver Transplantation with a Left-Sided Graft Liver

PURPOSE

We investigated the mechanisms of small-for-size graft syndrome by time-lag ligation, a novel approach to treating major portosystemic shunts in small-for-size adult living-related donor liver transplantation (LRDLT) using left-sided graft liver.

METHODS

Five patients with end-stage liver failure and major splenorenal shunting underwent LRDLT using left lobe grafts. The average graft volume to recipient body weight (GV/RBW) ratio was 0.68 +/- 0.14. Two patients underwent time-lag ligation of their splenorenal (SR) shunts on postoperative days (PODs) 8 and 14, respectively. The shunts of the other three patients were untreated.

RESULTS

The portal pressures in the first patient who underwent time-lag ligation rose above 300 mmH(2)O and remained there for 2 weeks. Thus, we ligated the SR shunt in the second patient on POD 14, resulting in an increase from 177 mmH(2)O to 258 mmH(2)O, but it decreased again thereafter. In the other three patients, the SR shunt was not ligated because portal blood flow volumes remained sufficient. Total bilirubin levels in the first time-lag ligation patient rose to 16 mg/dl, paralleling the rise in portal pressures. Although they increased after ligation in the second patient, they did not exceed 10 mg/dl.

CONCLUSIONS

We recommend time-lag ligation if portal venous blood flow decreases in the early post-transplant period, but not until at least 2 weeks after transplantation. If the portal venous blood flow does not decrease, early postoperative ligation is unnecessary. If there are no major portosystemic shunts, making a portosystemic shunt might decompress excessive portal hypertension. With donor safety priority in LRDLT, novel approaches must be developed to enable the use of smaller donor grafts. We describe a potential means of using left lobe grafts in adult LRDLT.

The 'small for size' liver syndrome

PURPOSE OF REVIEW

Small-for-size syndrome (SFSS) is a clinical syndrome described following liver transplantation (LT) and extended hepatectomy. New evidence has emerged documenting the importance of preoperative evaluation of functional liver mass, liver quality, influence of portal hypertension, and variations in surgical technique to improve outcome.

RECENT FINDINGS

SFSS is characterized by postoperative coagulopathy and liver dysfunction due to insufficient functional liver mass. Recent radiologic advances allow accurate preoperative estimation of total, graft, and remnant liver volume (RLV). In adult-to-adult living donor liver transplantation (LDLT), a graft-to-recipient body weight ratio > or = 0.8% or graft weight ratio > or = 30% are important to avoid SFSS. Minimal functional RLV following extended hepatectomy is > or = 25% in a normal liver, and > or = 40% with preoperative liver dysfunction. Preoperative portal vein or hepatic artery embolization to increase RLV and function after extended hepatectomy, and the increasing use of parenchymal-sparing segmental resections have improved outcome. In LT, the evolving use of split livers, LDLT and marginal grafts has resulted in increased recognition of SFSS. This has led to a renewed interest in defining the pathophysiology, and the development of new surgical techniques to reduce its incidence.

SUMMARY

Current radiologic imaging techniques can be used to evaluate liver volume and the risk of SFSS following LT and extended hepatectomy. Intraoperative techniques to predict postoperative dysfunction are emerging, and may be helpful in directing the use of pre-emptive surgical interventions. The future lies in the development of perioperative liver protection and support in predicted SFSS, and enhancement of healthy liver regeneration.