Pathophysiologic observations and histopathologic recognition of the portal hyperperfusion or small-for-size syndrome

Pediatric Donor to Adult Recipients in Donation After Cardiac Death Liver Transplantation: A Single-Center Experience

BACKGROUND

The impact of using liver allografts from donors who are younger than 14 years at the time of donation after cardiac death (DCD) liver transplantation in terms of early allograft dysfunction (EAD) and graft survival is undefined. To determine if adults undergoing DCD liver transplantation who receive a graft from a donor age younger than or equal to 13 years have similar outcomes to recipients of organs from older than 18-year-old donors.

METHODS

Records from adult patients undergoing DCD liver transplantation between March 2012 and December 2015 who received whole grafts from donors after cardiac death were reviewed. Patients with donors younger than or equal to 13 years (group 1) and older than 18 years (group 2) were compared for EAD rates, hepatic artery thrombosis (HAT), and graft survival.

RESULTS

Records of 60 DCD liver transplantation patients were analyzed. The 90-day and 1-year graft survival rate of both groups was 90% versus 96% (P = .427) and 80% versus 84% (P = .668), respectively. The EAD rates of groups 1 and 2 were 30% versus 34% (P = .806). The incidence of HAT was 20% in group 1 compared with 12% in group 2 (P = .610). Also, 0.7% < graft to recipient weight ratio (GRWR) <0.8% was also usable for pediatric donor to adult recipients.

CONCLUSIONS

Whole liver grafts from donors younger than or equal to 13 years can potentially be used in selected size-matched (GRWR >0.7%) DCD adult recipients.

Assessment and optimization of liver volume before major hepatic resection: Current guidelines and a narrative review

Post hepatectomy liver failure (PHLF) remains a significant cause of morbidity and mortality after major liver resection. Although the etiology of PHLF is multifactorial, an inadequate functional liver remnant (FLR) is felt to be the most important modifiable predictor of PHLF. Pre-operative evaluation of FLR function and volume is of paramount importance before proceeding with any major liver resection. Patients with inadequate or borderline FLR volume must be considered for volume optimization strategies such as portal vein embolization (PVE), two stage hepatectomy with portal vein ligation (PVL), Yttrium-90 radioembolization, and associating liver partition and portal vein ligation for staged hepatectomy (ALPPS). This paper provides an overview of assessing FLR volume and function, and discusses indications and outcomes of commonly used volume optimization strategies.

Small for size syndrome difficult dilemma: Lessons from 10 years single centre experience in living donor liver transplantation

AIM

To analyze the incidence, risk factors, prevention, treatment and outcome of small for size syndrome (SFSS) after living donor liver transplantation (LDLT).

METHODS

Through-out more than 10 years: During the period from April 2003 to the end of 2013, 174 adult-to-adults LDLT (A-ALDLT) had been performed at National Liver Institute, Menoufiya University, Shibin Elkoom, Egypt. We collected the data of those patients to do this cohort study that is a single-institution retrospective analysis of a prospectively collected database analyzing the incidence, risk factors, prevention, treatment and outcome of SFSS in a period started from the end of 2013 to the end of 2015. The median period of follow-up reached 40.50 m, range (0-144 m).

RESULTS

SFSS was diagnosed in 20 (11.5%) of our recipients. While extra-small graft [small for size graft (SFSG)], portal hypertension, steatosis and left lobe graft were significant predictors of SFSS in univariate analysis (P = 0.00, 0.04, 0.03, and 0.00 respectively); graft size was the only independent predictor of SFSS on multivariate analysis (P = 0.03). On the other hand, there was lower incidence of SFSS in patients with SFSG who underwent splenectomy [4/10 (40%) SFSS vs 3/7 (42.9%) no SFSS] but without statistical significance, However, there was none significant lower incidence of the syndrome in patients with right lobe (RL) graft when drainage of the right anterior and/or posterior liver sectors by middle hepatic vein, V5, V8, and/or right inferior vein was done [4/10 (28.6%) SFSS vs 52/152 (34.2%) no SFSS]. The 6-mo, 1-, 3-, 5-, 7- and 10-year survival in patients with SFSS were 30%, 30%, 25%, 25%, 25% and 25% respectively, while, the 6-mo, 1-, 3-, 5-, 7- and 10-year survival in patients without SFSS were 70.1%, 65.6%, 61.7%, 61%, 59.7%, and 59.7% respectively, with statistical significant difference (P = 0.00).

CONCLUSION

SFSG is the independent and main factor for occurrence of SFSS after A-ALDLT leading to poor outcome. However, the management of this catastrophe depends upon its prevention (i.e., selecting graft with proper size, splenectomy to decrease portal venous inflow, and improving hepatic vein outflow by reconstructing large draining veins of the graft).

Impact of Portal Hemodynamic Changes in Partial Liver Grafts on Short-Term Graft Regeneration in Living Donor Liver Transplantation

BACKGROUND

Regeneration of partial liver grafts is critical for successful living donor liver transplantation (LDLT), especially in adult recipients. The purpose of this study was to investigate the intraoperative hemodynamic changes in partial liver grafts and characterize their potential impact on post-transplant liver regeneration in LDLT.

METHODS

We examined the portal venous flow (PVF) and hepatic arterial flow (HAF) to partial liver grafts by means of ultrasonic transit time flowmeter of donors immediately before graft retrieval and of the corresponding recipients after vascular reconstruction in 48 LDLT cases. We evaluated post-transplant liver regeneration according to the changes in graft liver volume between the time of transplantation and the 7th post-transplant day.

RESULTS

There was a significant increase in PVF to the partial liver grafts in recipients (rPVF) compared with that in donors. In contrast, graft HAF in recipients significantly decreased compared with that in donors. The rPVF inversely correlated with graft weight (GW)-recipient body weight ratio (GRWR), whereas HAF volume showed no significant correlation. The rPVF/GW positively correlated with the rate of liver regeneration (GRR), which inversely correlated with GRWR. The rPVF/GW was significantly higher, and GRR tended to be larger in the small graft group than in the non-small graft group.

CONCLUSIONS

Intraoperative portal hemodynamic changes in partial liver grafts strongly affect their post-transplant regeneration. In particular, in small liver grafts, an immediate and remarkable increase in graft PVF may contribute to rapid liver regeneration after LDLT if the increased PVF remains within a safe range.

Graft inflow modulation in adult-to-adult living donor liver transplantation: A systematic review

INTRODUCTION

Small-for-size syndrome (SFSS) has an incidence between 0 and 43% in small-for-size graft (SFSG) adult living donor liver transplantation (LDLT). Portal hypertension following reperfusion and the hyperdynamic splanchnic state are reported as the major triggering factors of SFSS. Intra- and postoperative strategies to prevent or to reduce its onset are still under debate. We analyzed graft inflow modulation (GIM) during adult LDLT considering the indications, efficacy of the available techniques, changes in hemodynamics and outcomes.

MATERIALS AND METHODS

A systematic literature search was performed using PubMed, EMBASE, Scopus and the Cochrane Library Central. Treatment outcomes including in-hospital mortality and morbidity, re-transplantation rate, 1-, 3-, and 5-year patient overall survival and 1-, 3-, and 5-year graft survival rates, hepatic artery and portal vein flows and pressures before and after inflow modulation were analyzed.

RESULTS

From 563 articles, 12 studies dated between 2003 and 2014 fulfilled the selection criteria and were therefore included in the study. These comprised a total of 449 adult patients who underwent inflow modulation during adult-to-adult LDLT. Types of GIM described were splenic artery ligation, splenectomy, meso-caval shunt, spleno-renal shunt, portocaval shunt, and splenic artery embolization. Mortality and morbidity ranged between 0 and 33% and 17% and 70%, respectively. Re-transplantation rates ranged between 0% and 25%. GIM was associated with good survival for both graft and recipients, reaching an 84% actuarial rate at 5 years. Through the use of GIM, irrespective of the technique, a statistically significant reduction of PVF and PVP was obtained.

CONCLUSIONS

GIM is a safe and efficient technique to avoid or limit portal hyperperfusion, especially in cases of SFSG, decreasing overall morbidity and improving outcomes.

Preconditioning by portal vein embolization modulates hepatic hemodynamics and improves liver function in pigs with extended hepatectomy

BACKGROUND

Portal vein embolization is performed weeks before extended hepatic resections to increase the future liver remnant and prevent posthepatectomy liver failure. Portal vein embolization performed closer to the operation also could be protective, but worsening of portal hyper-perfusion is a major concern. We determined the hepatic hemodynamic effects of a portal vein embolization performed 24 hours prior to hepatic operation.

METHODS

An extended (90%) hepatectomy was performed in swine undergoing (portal vein embolization) or not undergoing (control) a portal vein embolization 24 hours earlier (n = 10/group). Blood tests, hepatic and systemic hemodynamics, hepatic function (plasma disappearance rate of indocyanine green), liver histology, and volumetry (computed tomographic scanning) were assessed before and after the hepatectomy. Hepatocyte proliferating cell nuclear antigen expression and hepatic gene expression also were evaluated.

RESULTS

Swine in the control and portal vein embolization groups maintained stable systemic hemodynamics and developed similar increases of portal blood flow (302 ± 72% vs 486 ± 92%, P = .13). Portal pressure drastically increased in Controls (from 9.4 ± 1.3 mm Hg to 20.9 ± 1.4 mm Hg, P < .001), while being markedly attenuated in the portal vein embolization group (from 11.4 ± 1.5 mm Hg to 16.1 ± 1.3 mm Hg, P = .061). The procedure also improved the preservation of the hepatic artery blood flow, liver function, and periportal edema. These effects occurred in the absence of hepatocyte proliferation or hepatic growth and were associated with the induction of the vasoprotective gene Klf2.

CONCLUSION

Portal vein embolization preconditioning represents a potential hepato-protective strategy for extended hepatic resections. Further preclinical studies should assess its medium-term effects, including survival. Our study also supports the relevance of hepatic hemodynamics as the main pathogenetic factor of post-hepatectomy liver failure.

Postoperative Liver Failure

Technical innovations in surgical techniques, anaesthesia, critical care and a spatial understanding of the intra-hepatic anatomy of the liver, have led to an increasing number of liver resections being performed all over the world. However, the number of complications directly attributed to the procedure and leading to inadequate or poor hepatic functional status in the postoperative period remains a matter of concern. There has always been a problem of arriving at a consensus in the definition of the term: postoperative liver failure (PLF). The burgeoning rate of living donor liver transplants, with lives of perfectly healthy donors involved, has mandated a consensual definition, uniform diagnosis and protocol for management of PLF. The absence of a uniform definition has led to poor comparison among various trials. PLF remains a dreaded complication in resection of the liver, with a reported incidence of up to 8 % [1], and mortality rates of up to 30–70 % have been quoted [2]. Several studies have quoted a lower incidence of PLF in eastern countries, but when it occurs the mortality is as high as in the West [3].

Establishing a Porcine Model of Small for Size Syndrome following Liver Resection

BACKGROUND

Small for size syndrome (SFSS) is responsible for a high proportion of mortalities and morbidities following extended liver resection.

AIM

The aim of this study was to establish a porcine model of SFSS.

METHODS

Twenty-four Landrace pigs underwent liver resection with a remnant liver volume of 50% (group A, n = 8), 25% (group B, n = 8), and 15% (group C, n = 8). After resection, the animals were followed up for 8 days and clinical, laboratory, and histopathological outcomes were evaluated.

RESULTS

The survival rate was significantly lower in group C compared with the other groups (p < 0.001). The international normalized ratio, bilirubin, aspartate transaminase, alanine transaminase, and alkaline phosphatase levels increased shortly after surgery in groups B and C, but no change was observed in group A (p < 0.05 for all analyses). The histopathological findings in group A were mainly mild mitoses, in group B severe mitoses and hepatocyte ballooning, moderate congestion, and hemorrhage, along with mild necrosis, and in group C extended tissue damage with severe necrosis, hemorrhage, and congestion.

CONCLUSIONS

Combination of clinical, laboratory, and histopathological evaluations is needed to confirm the diagnosis of SFSS. 75% liver resection in porcine model results in SFSS. 85% liver resection causes irreversible liver failure.

A Case Report of Severe Hepatic Artery Vasospasm Induced by Hepatic Arterial Buffer Response After Liver Transplantation

The management of severe hepatic artery vasospasm soon after liver transplantation (LT) is challenging because it can lead to hepatic artery thrombosis and subsequent graft failure. A 61-year-old man with hepatitis C cirrhosis and portal vein thrombosis received a deceased donor LT. On postoperative day 1, Doppler ultrasonography revealed a high-resistance waveform in the hepatic artery. Angiography showed severe vasospasm of the donor hepatic artery on postoperative day 3. Strong hepatic arterial buffer response (HABR) was considered for this etiology due to high portal vein velocity. Therefore, vasodilators, including nitroglycerin and prostaglandin E₁, were initiated. The waveform of the hepatic artery vasospasm gradually improved as portal vein velocity decreased by Doppler ultrasonography within 7 days after LT. In conclusion, hepatic arterial buffer response can induce hepatic artery vasospasm immediately after LT. This vasospasm type may be managed conservatively with a positive outcome.

The beneficial role of simultaneous splenectomy after extended hepatectomy: experimental study in pigs

BACKGROUND

The role of hepatic hemodynamic modulation in the development of "small-for-size" syndrome (SFSS) after extended hepatectomy (EH) or living-donor liver transplantation is still controversial. We have designed an experimental study to investigate the effect of hemodynamic parameters of the liver circulation on the development of SFSS after EH in a porcine model.

METHODS

Eighteen pigs were randomly divided into two groups: group A has received EH (75%-80%) without splenectomy, and group B with EH and simultaneous splenectomy was carried out. Portal hemodynamics, liver function tests, histologic findings, injury and survival rates were compared between groups A and B.

RESULTS

The 7-d survival rate in the splenectomy group was significantly improved compared with group A (88.9% versus 44.4%, P < 0.05). Portal vein pressure, portal vein flow, and liver function tests in the splenectomy group were significantly lower than in group A immediately after splenectomy and postoperatively until the day of sacrifice. Histologic findings in group A clearly illustrate severe inflammation, bridging necrosis, ischemic cholangitis, and severe congestion, while in group B there were less serious histologic changes.

CONCLUSIONS

Our experimental study indicates that perioperative portal modulation can successfully prevent the manifestation of SFSS after EH. Therefore, by focusing on "flow" rather than on "size," researchers may understand better the pathophysiology of this syndrome.

Split liver transplantation in adults

Split liver transplantation (SLT), while widely accepted in pediatrics, remains underutilized in adults. Advancements in surgical techniques and donor-recipient matching, however, have allowed expansion of SLT from utilization of the right trisegment graft to now include use of the hemiliver graft as well. Despite less favorable outcomes in the early experience, better outcomes have been reported by experienced centers and have further validated the feasibility of SLT. Importantly, more than two decades of experience have identified key requirements for successful SLT in adults. When these requirements are met, SLT can achieve outcomes equivalent to those achieved with other types of liver transplantation for adults. However, substantial challenges, such as surgical techniques, logistics, and ethics, persist as ongoing barriers to further expansion of this highly complex procedure. This review outlines the current state of SLT in adults, focusing on donor and recipient selection based on physiology, surgical techniques, surgical outcomes, and ethical issues.

Liver regeneration - mechanisms and models to clinical application

Liver regeneration has been studied for many decades and the mechanisms underlying regeneration of the normal liver following resection or moderate damage are well described. A large number of factors extrinsic (such as bile acids and circulating growth factors) and intrinsic to the liver interact to initiate and regulate liver regeneration. Less well understood, and more clinically relevant, are the factors at play when the abnormal liver is required to regenerate. Fatty liver disease, chronic scarring, prior chemotherapy and massive liver injury can all inhibit the normal programme of regeneration and can lead to liver failure. Understanding these mechanisms could enable the rational targeting of specific therapies to either reduce the factors inhibiting regeneration or directly stimulate liver regeneration. Although animal models of liver regeneration have been highly instructive, the clinical relevance of some models could be improved to bridge the gap between our in vivo model systems and the clinical situation. Likewise, modern imaging techniques such as spectroscopy will probably improve our understanding of whole-organ metabolism and how this predicts the liver's regenerative capacity. This Review describes briefly the mechanisms underpinning liver regeneration, the models used to study this process, and discusses areas in which failed or compromised liver regeneration is clinically relevant.

Small for Size and Flow (SFSF) syndrome: An alternative description for posthepatectomy liver failure

Small for Size Syndrome (SFSS) syndrome is a recognizable clinical syndrome occurring in the presence of a reduced mass of liver, which is insufficient to maintain normal liver function. A definition has yet to be fully clarified, but it is a common clinical syndrome following partial liver transplantation and extended hepatectomy, which is characterized by postoperative liver dysfunction with prolonged cholestasis and coagulopathy, portal hypertension, and ascites. So far, this syndrome has been discussed with focus on the remnant size of the liver after partial liver transplantation or extended hepatectomy. However, the current viewpoints believe that the excessive flow of portal vein for the volume of the liver parenchyma leads to over-pressure, sinusoidal endothelial damages and haemorrhage. The new hypothesis declares that in both extended hepatectomy and partial liver transplantation, progression of Small for Size Syndrome is not determined only by the "size" of the liver graft or remnant, but by the hemodynamic parameters of the hepatic circulation, especially portal vein flow. Therefore, we suggest the term "Small for Size and Flow (SFSF)" for this syndrome. We believe that it is important for liver surgeons to know the pathogenesis and manifestation of this syndrome to react early enough preventing non-reversible tissue damages.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

The outcomes of pediatric living donor liver transplantation using small-for-size grafts: experience of a single institute

PURPOSE

We aimed to evaluate patients who had undergone pediatric LDLT with small-for-size graft (SFSG) and identify risk factors of graft failure to establish a preoperative graft selection strategy.

METHODS

The data was collected retrospectively. SFSG was used in 14LDLTs (5.7%) of 245 LDLTs performed between May 2001 and March 2014. The mean patient age and body weight at LDLT were 12.6 ± 2.0 years and 40.5 ± 9.9 kg, respectively. The graft type was left lobe in six patients, left + caudate lobe in seven patients, and posterior segment in one patient.

RESULTS

The graft survival rates in SFSG and non-SFSG groups were 78.9 and 93.1%, respectively (p = 0.045). In the univariate analysis, bleeding volume during LDLT were an independent risk factors for graft failure (p = 0.011). Graft failure was caused by sepsis in all three patients and occurred at a median of 70 postoperative days 70 (range 14-88 days). Among them, two cases showed high preoperative PELD/MELD score (PELD; 19.4 and MELD; 22, respectively).

CONCLUSIONS

Pediatric LDLT using SFSG had poor outcome and prognosis, especially when it accompanies the surgical infectious complications with preoperative high PELD/MELD scores.

Liver regeneration after different degrees of portal vein ligation

BACKGROUND

Selective portal vein ligation (PVL) is followed by ipsilateral atrophy and contralateral hypertrophy of the liver lobes. Although the atrophy-hypertrophy complex induced by PVL is a well-documented phenomenon, the effect of different degrees of extended portal vein occlusion on liver regeneration is not known. The aim of this study was to assess the effects of different degrees of portal occlusion on portal pressure and liver regeneration.

MATERIALS AND METHODS

Male Wistar rats (n = 96; 220-250 g) were randomized into three groups and underwent 70%, 80%, or 90% portal vein ligation, respectively. The portal pressure was measured immediately and 24, 48, 72, 120, and 168 h after PVL (n = 6/group/time point). The hepatic lobes and the spleen were weighed, and liver regeneration ratio was calculated. Changes in liver histology and the mitotic activity were assessed on hematoxylin-eosin stained slides.

RESULTS

Higher degree of portal occlusion triggered a stronger regenerative response (regeneration ratio of PVL 70%168h = 2.23 ± 0.13, PVL 80%168h = 3.11 ± 0.37, PVL 90%168h = 4.68 ± 0.48) PVL led to an immediate increase in portal pressure, the value of which changed proportionally to the mass of liver tissue deprived of portal perfusion (PVL 70%acute = 17 ± 2 mm Hg, PVL 80%acute = 19 ± 1 mm Hg, PVL 90%acute = 26 ± 4 mm Hg). Findings in histology showed necro-apoptotic lesions in the atrophic liver lobes and increased mitotic cell count in the hypertrophic lobes. The mitotic cell count of PVL 90% peaked earlier and at a significantly higher value than of PVL 70% and PVL 80% (PVL 9024h%: 96.0 ± 3.5 PVL 70%48h: 64.0 ± 2.1, PVL 80%48h: 56.3 ± 4.0). The mitotic index after 24 h showed a strong correlation with the acute portal hypertension.

CONCLUSIONS

A higher degree of portal vein occlusion leads to a greater regenerative response, presumably triggered by the proportional increase in portal pressure, which supports the role of the so-called "blood-flow" theory of PVL-triggered liver regeneration.

Hepatic Arterial Buffer Response Maintains the Homeostasis of Graft Hemodynamics in Patient Receiving Living Donor Liver Transplantation

BACKGROUND

In living donor liver transplantation (LDLT), the hepatic hemodynamics plays important roles in graft regeneration, and the hepatic blood inflows are associated with graft size. However, the data of interplay between the hepatic arterial buffer response (HABR) and graft-to-recipient weight ratio (GRWR) in clinical LDLT are lacking.

AIMS

To identify the effect of the HABR on the hepatic hemodynamics and recovery of graft function and to evaluate the safe lower limit of the GRWR in carefully selected recipients.

METHODS

Portal venous and hepatic arterial blood flow was measured in recipients with ultrasonography, and the graft functional recovery, various complications, and survive states after LDLT were compared.

RESULTS

In total, 246 consecutive patients underwent LDLT with right lobe grafts. In total, 26 had a GRWR < 0.7 % (A), 29 had a GRWR between 0.7 and 0.8 % (B), and 181 had a GRWR > 0.8 % (C). For small-for-size syndrome, there was no significant difference (P = 0.176). Graft survival rates at 1, 3, and 5 year were not different (P = 0.710). The portal vein flow and portal vein flow per 100 g graft weight peaks were significantly higher in the A. Hepatic arterial velocity and hepatic arterial flow decreased in all the three groups on postoperative day 1; however, the hepatic arterial flow per 100 g graft weight was close to healthy controls.

CONCLUSIONS

HABR played important roles not only in the homeostasis of hepatic afferent blood supply but also in maintaining enough hepatic perfusion to the graft.

Modulation of splanchnic circulation: Role in perioperative management of liver transplant patients

Splanchnic circulation is the primary mechanism that regulates volumes of circulating blood and systemic blood pressure in patients with cirrhosis accompanied by portal hypertension. Recently, interest has been expressed in modulating splanchnic circulation in patients with liver cirrhosis, because this capability might produce beneficial effects in cirrhotic patients undergoing a liver transplant. Pharmacologic modulation of splanchnic circulation by use of vasoconstrictors might minimize venous congestion, replenish central blood flow, and thus optimize management of blood volume during a liver transplant operation. Moreover, splanchnic modulation minimizes any high portal blood flow that may occur following liver resection and the subsequent liver transplant. This effect is significant, because high portal flow impairs liver regeneration, and thus adversely affects the postoperative recovery of a transplant patient. An increase in portal blood flow can be minimized by either surgical methods (e.g., splenic artery ligation, splenectomy or portocaval shunting) or administration of splanchnic vasoconstrictor drugs such as Vasopressin or terlipressin. Finally, modulation of splanchnic circulation can help maintain perioperative renal function. Splanchnic vasoconstrictors such as terlipressin may help protect against acute kidney injury in patients undergoing liver transplantation by reducing portal pressure and the severity of a hyperdynamic state. These effects are especially important in patients who receive a too small for size graft. Terlipressin selectively stimulates V1 receptors, and thus causes arteriolar vasoconstriction in the splanchnic region, with a consequent shift of blood from splanchnic to systemic circulation. As a result, terlipressin enhances renal perfusion by increasing both effective blood volume and mean arterial pressure.

The Correlation of Hepatic and Systemic Hemodynamics During Liver Transplantation: Quantification of Hepatic Resistance as an Actual Value

The correlation between portal vein pressure (PVP) and flow (PVF) has not been established, and there is still lack of consensus about the optimal hemodynamics during liver transplantation (LT). We aimed to establish the correlation between systemic and hepatic hemodynamics during LT by applying the hepatokinetic power hypothesis, based on the law of energy conservation and hydrodynamics.A total of 103 adult liver transplant recipients were enrolled in this study from September 2012 to December 2014. Systemic and hepatic hemodynamics were assessed intraoperatively to calculate the hepatokinetic power status. Severe surgical complications (Clavien-Dindo grade ≥III) were recorded as the main outcome measure, and potential covariates were evaluated including recipient, donor, donor-recipient match, surgery-related factors, conventional hemodynamics, and the intraoperative hepatokinetic power profile.In multivariate analysis, hepatokinetic power gradient >4260 mL mmHg min100 g graft weight (P = 0.001), 2.2 < ratio of hepatokinetic power from the portal vein to the hepatic artery ≤8.7 (P = 0.012), and hepatic resistance of partial grafts ≤0.006 or >0.015 min mmHg mL (P = 0.012) were associated with a higher risk. None of the conventional hemodynamic parameters, such as PVP, PVF, and hepatic venous pressure gradient, entered into this regression model (c-statistic = 0.916) when competing with hepatokinetic power indexes.The hepatokinetic power hypothesis clarifies the correlation of systemic and hepatic hemodynamics in a simple, rational manner. The hepatic resistance, derived from the hepatokinetic power equation, can be quantified and has an effect on the incidence of severe surgical complications. This finding offers a new objective clinical approach to evaluate graft quality during transplantation.

Split liver transplantation: What’s unique?

The intraoperative management of split liver transplantation (SLT) has some unique features as compared to routine whole liver transplantations. Only the liver has this special ability to regenerate that confers benefits in survival and quality of life for two instead of one by splitting livers. Primary graft dysfunction may result from small for size syndrome. Graft weight to recipient body weight ratio is significant for both trisegmental and hemiliver grafts. Intraoperative surgical techniques aim to reduce portal hyperperfusion and decrease venous portal pressure. Ischemic preconditioning can be instituted to protect against ischemic reperfusion injury which impacts graft regeneration. Advancement of the technique of SLT is essential as use of split cadaveric grafts expands the donor pool and potentially has an excellent future.

Liver failure posthepatectomy and biliary fistula: multidisciplinar treatment

The main cause of morbimor-mortality after major liver surgery is the development of liver failure posthepatectomy(LFPH). Treatment must involve multiple options and will be aggressive from the beginning. We report a case of a patient with cholangiocarcinoma perihilar treated with surgery: right hepatectomy extended to sI + IVb with develop of LFPH and biliary fistula and being management successfully in a multidisciplinary way.

Risk factors for first-year hospital readmission after liver transplantation

OBJECTIVE

To investigate the frequency of and the risk factors for hospital readmission within the first year after liver transplantation (LT).

MATERIALS AND METHODS

Between January 1999 and August 2013, LTs were performed in 890 adult patients at our center. We collected medical data from the Chinese Liver Transplant Registry and performed a retrospective review of the medical records of these patients. We aimed to identify the factors that contribute toward readmission during the first year after LT. We also first investigated the relationship between the number and severity of post-transplant complications and the risk of readmission. The survival outcomes of patients with and without readmission were also studied.

RESULTS

A total of 165 rehospitalizations occurred in 142 patients (18.0%) within 1 year after discharge from their index admissions. The risk factors included hepatic malignancy as an indication for LT (P=0.01), previous abdominal surgery (P=0.03), the occurrence of any complications (P<0.001), biliary complications (P<0.001), vascular complications (P=0.005), rejection (P<0.001), pulmonary complications (P<0.001), infection (P<0.001), returning to the operating room (P<0.001), and other complications (P<0.001). First-year readmission rates increased as the number (P<0.01) and severity (P<0.01) of post-LT complications increased. Patients requiring readmission had decreased survival compared with those not requiring readmission during the first year of discharge after LT (P<0.001).

CONCLUSION

Our study identified the factors that place LT recipients at a high risk for readmission. This knowledge could help prevent and minimize rehospitalizations during the first year after LT.

Hepatic arterial vasodilation is independent of portal hypertension in early stages of cirrhosis

Introduction

The compensatory increase in hepatic arterial flow with a decrease in portal venous flow is known as the hepatic arterial buffer response. In cirrhosis with elevated portal pressure, the vascular resistance of the hepatic artery is decreased. Whether this lower resistance of the hepatic artery is a consequence of portal hypertension or not remains unknown.

Study Aim

The aim of the study was to investigate the hepatic arterial resistance and response to vasoconstriction in cirrhosis without portal hypertension (normal portal resistance).

Methods

Cirrhosis was induced by CCl₄-inhalation for 8 weeks (8W, normal portal resistance) and for 12–14 weeks (12W, elevated portal resistance). Bivascular liver perfusion was performed at 8W or 12W and dose response curves of methoxamine were obtained in the presence or absence of LNMMA (nitric oxide synthase blocker). Vascular resistances of the hepatic artery (HAR), portal vein (PVR) and sinusoids (SVR) were measured. Western Blot (WB) and Immunohistochemistry (IHC) were done to measure eNOS and HIF 1a expression.

Results

HAR in both groups of cirrhotic animals (8W and 12W) were lower compared to controls. Dose response curves to methoxamine revealed lower HAR in both cirrhotic models (8W and 12W) regardless the magnitude of portal resistance. LNMMA corrected the dose response curves in cirrhosis (8W and 12W) to control. WB and IHC show increased protein expression of eNOS and HIF1a in 8W and 12W.

Conclusion

Hepatic arterial resistance is decreased in cirrhosis independent of portal resistance. Vasodilation of the hepatic artery in cirrhosis seems to be influenced by hypoxia rather than increase in portal resistance. Nitric oxide is the main vasodilator.

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 size liver remnant following resection: prevention and management

In the latest decades an important change was registered in liver surgery, however the management of liver cirrhosis or small size hepatic remnant still remains a challenge. Currently post-hepatectomy liver failure (PLF) is the major cause of death after liver resection often associated with sepsis and ischemia-reperfusion injury (IRI). ''Small-for-size'' syndrome (SFSS) and PFL have similar mechanism presenting reduction of liver mass and portal hyper flow beyond a certain threshold. Few methods are described to prevent both syndromes, in the preoperative, perioperative and postoperative stages. Additionally to portal vein embolization (PVE), radiological examinations (mainly CT and/or MRI), and more recently 3D computed tomography are fundamental to quantify the liver volume (LV) at a preoperative stage. During surgery, in order to limit parenchymal damage and optimize regenerative capacity, some hepatoprotective measures may be employed, among them: intermittent portal clamping and hypothermic liver preservation. Regarding the treatment, since PLF is a quite complex disease, it is required a multi-disciplinary approach, where it management must be undertaken in conjunction with critical care, hepatology, microbiology and radiology services. The size of the liver cannot be considered the main variable in the development of liver dysfunction after extended hepatectomies. Additional characteristics should be taken into account, such as: the future liver remnant; the portal blood flow and pressure and the exploration of the potential effects of regeneration preconditioning are all promising strategies that could help to expand the indications and increase the safety of liver surgery.

Ultrasonographic evaluation of abdominal organs after cardiac surgery

BACKGROUND

Disturbances of the hepatosplanchnic region may occur after cardiac operations. Experimental studies have implicated impairment of splanchnic blood supply in major abdominal organ dysfunction after cardiopulmonary bypass (CPB). We investigated the impact of the cardiac operation and CPB on liver, kidney, and renal perfusion and function by means of ultrasonography and biochemical indices in a selected group of cardiac surgery patients.

MATERIALS AND METHODS

Seventy five patients scheduled for a major cardiac operation were prospectively included in the study. Criteria for selection were moderate or good left ventricular ejection fraction and absence of previous hepatic or renal impairment. Ultrasound examination of the hepatic and renal vasculature and examination of biochemical parameters were performed on the day preceding the operation (T0), on the first postoperative day (T1), and on the seventh postoperative day (T2).

RESULTS

Portal vein velocity and flow volume increased significantly, whereas hepatic artery velocity and flow volume decreased at T1 in comparison with T0. Hepatic vein indices remained unaffected throughout the observation period. Renal artery velocity and flow decreased, whereas renal pulsatility index and renal resistive index increased at T1 as compared with T0. Aspartate aminotransferase and alanine aminotransferase values were increased as compared with baseline values 24 h postoperatively. All parameters displayed a trend to approach preoperative levels at T2. Strong negative correlations between alanine aminotransferase values at T1 and hepatic artery velocity and flow volume at the same time point were also demonstrated (R = 0.638, P < 0.001 and r = 0.662, P < 0.001, respectively).

CONCLUSIONS

The increase in portal vein flow and velocity and the decrease in hepatic artery flow and velocity in the period after CPB might be attributed to the hypothermic bypass technique and the hepatic arterial buffer response, respectively. The decrease in renal blood flow and velocity and the parallel increase in Doppler renal pulsatility index and renal resistive index could be considered as markers of kidney hypoperfusion and intrarenal vasoconstriction. Maintaining a high index of suspicion for the early diagnosis of noncardiac complications in the period after CPB and institution of supportive care in case of compromised splanchnic perfusion are warranted.

Reduced hepatic arterial perfusion impairs the recovery from focal hepatic venous outflow obstruction in liver-resected rats

BACKGROUND

Extended partial hepatectomy (PH) in patients is leading to portal hyperperfusion but reduced hepatic arterial perfusion (HAP), and is invariably causing focal hepatic venous outflow obstruction (FHVOO). We observed in a rat model that PH in combination with right median hepatic vein ligation (RMHV-L) caused confluent parenchymal necrosis interspersed with viable portal tracts in the obstructed territory and large sinusoidal vascular canals in the border zone. Lack of HAP impaired the spontaneous course of recovery in terms of enlarged parenchymal necrosis, delayed regeneration, and the absence of draining vascular canals. We aimed to investigate whether pharmacological intervention modulates the imbalance between portal venous and hepatic arterial inflow, aggravates the liver damage, and delays the recovery process after FHVOO in liver-resected rats.

METHODS

Male Lewis rats were subjected to 70% PH and RMHV-L. Molsidomine or NG-nitro-L-arginine methyl ester (L-NAME) or saline were applied daily. Hepatic damage, microcirculation, regeneration, and vascular remodeling were evaluated at postoperative days 1, 2, and 7. Animals subjected to RMHV-L only were used as "no HAP" control.

RESULTS

Significant increase of portal venous inflow with a concomitant decrease in HAP was observed in all groups after PH. Molsidomine treatment did neither affect hepatic hemodynamics nor the spontaneous recovery. In contrast, L-NAME treatment further decreased HAP which impaired hepatic microcirculation, aggravated parenchymal damage, decelerated recovery, and impaired the formation of sinusoidal canals.

CONCLUSIONS

Reduction of HAP through inhibition of nitric oxide production worsened the recovery from FHVOO. Drugs increasing HAP need to be evaluated to reverse the hyperperfusion-induced impairment of the spontaneous course after FHVOO.

Hepatoprotective effect by pretreatment with olprinone in a swine partial hepatectomy model

Excessive portal flow to a small remnant liver or small-for-size graft is a primary factor of small-for-size syndrome. We demonstrated that olprinone (OLP), a phosphodiesterase III inhibitor, had a hepatoprotective effect in a rat extended hepatectomy model and a small-for-size liver transplantation model through a modification of the portal venous pressure (PVP). To identify the appropriate dose and duration of treatment for clinical applications, we conducted experiments with a swine partial hepatectomy model. Twenty microminipigs were divided into 4 groups that received the following treatments: (A) saline (control group), (B) OLP at 0.3 μg/kg/minute (preoperative and postoperative administration), (C) OLP at 0.1 μg/kg/minute (preoperative administration), and (D) OLP at 0.3 μg/kg/minute (preoperative administration). The pigs underwent 70% partial hepatectomy. Hemodynamic changes, including changes in PVP, were examined. Liver biopsy was performed 1 and 3 hours after hepatectomy. Blood samples were collected until postoperative day 7 (POD7). In comparison with group A, PVP elevations, periportal edema, and sinusoidal hemorrhaging were attenuated after left Glisson's ligation in groups C and D. Pretreatment with OLP in groups C and D preserved the microstructure of sinusoids and improved the prothrombin activity 1 and 3 hours after hepatectomy. These animals showed better recovery of the remnant liver volume and the plasma disappearance rate of indocyanine green on POD7. In contrast, group B showed exacerbation of liver damage. Measurements of the serum OLP concentration showed that 10 ng/mL OLP was appropriate for a hepatoprotective effect. In conclusion, pretreatment with OLP shows hepatoprotective effects in a swine partial hepatectomy model. OLP may have the potential to ameliorate patients' outcomes after hepatectomy or liver transplantation.

Small-for-size syndrome in living-donor liver transplantation using a left lobe graft

In living-donor liver transplantation with a left lobe graft, which can reduce the burden on the donor compared to right lobe graft, the main problem is small-for-size (SFS) syndrome. SFS syndrome is a multifactorial disease that includes aspects related to the graft size, graft quality, recipient factors and even technical issues. The main pathophysiology of SFS syndrome is the sinusoidal microcirculatory disturbance induced by shear stress, which is caused by excessive portal inflow into the smaller graft. The donor age, the presence of steatosis of the graft and a poor recipient status are all risk factors for SFS syndrome. To resolve SFS syndrome, portal inflow modulation, splenectomy, splenic artery modulation and outflow modulation have been developed. It is important to establish strict criteria for managing SFS syndrome. Using pharmacological interventions and/or therapeutic approaches that promote liver regeneration could increase the adequate outcomes in SFS liver transplantation. Left lobe liver transplantation could be adopted in Western countries to help resolve the organ shortage.

The safe minimally ischemic liver remnant for small-for-size syndrome in porcine hepatectomy

BACKGROUND

The minimal functional remnant liver mass or graft after an ischemic injury in hepatectomy or living donor liver transplantation (LDLT) is not clear. This study sought to determine the minimal remnant liver (MRL) size after 20 minutes hepatic inflow occlusion (HIO) and the maximal portal flow with which the liver remnant can sustain in a porcine model.

METHODS

Twenty pigs that underwent massive hepatectomy were randomly divided into 3 groups: 30% group, the remnant constituted about 30% of total liver volume (TLV); 35%+O group, the remnant constitute about 35% of TLV with 20 minutes HIO, and 30%+O group, the remnant constituted about 30% of TLV with 20 minutes of HIO. We evaluated survival rates, kinetic portal vein pressures (PVP), hemodynamics, hepatocyte metabolism, and injury.

RESULTS

The 14-day survival rate in the 30%+O group was significantly reduced compared with that of either the 30% group or the 35%+O group: l00% versus 28.6% versus 85.7% respectively (P = .009). The tissue, serum analyses, and PVP in the 30%+O group were significantly different compared with the measurements among the other groups (P < .05), revealing that the liver remnant in 30%+O group could not sustain more than 3 times baseline portal flow, whereas in 35%+O group it could sustain 2.8 times baseline portal flow.

CONCLUSIONS

Intraoperative ischemia can injure the sinusoidal endothelium, decreasing its ability to regulate portal hyperperfusion, causing less than 30% to 35% of TLV to show small-for-size syndrome or postoperative liver failure.

Graft-to-recipient weight ratio lower to 0.7% is safe without portal pressure modulation in right-lobe living donor liver transplantation with favorable conditions

BACKGROUND

The low graft-to-recipient weight ratio (GRWR) in adult-to-adult living donor liver transplantation (LDLT) is one of the major risk factors affecting graft survival. The goal of this study was to evaluate whether the lower limit of the GRWR can be safely reduced without portal pressure modulation in right-lobe LDLT.

METHODS

From 2005 to 2011, 317 consecutive patients from a single institute underwent LDLT with right-lobe grafts without portal pressure modulation. Of these, 23 had a GRWR of less than 0.7% (group A), 27 had a GRWR of ≥0.7%, <0.8% (group B), and 267 had a GRWR of more than and equal to 0.8% (group C). Medical records, including recipient, donor, operation factors, laboratory findings and complications were reviewed retrospectively.

RESULTS

The baseline demographics showed low model for end-stage liver disease score (mean 16.3+/-8.9) and high percentage of hepatocellular carcinoma (231 patients, 72.9%). Three groups by GRWR demonstrated similar characteristics except recipient body mass index and donor gender. For small-for-size syndrome, there were 3 (13.0%) in group A, 1 (3.7%) in group B, and 2 patients (0.7%) in group C (P<0.001). Hepatic artery thrombosis was more frequently observed in group A than in groups B and C (8.7% vs 3.7% vs 1.9%, P=0.047). However, among the three groups, graft survival rates at 1 year (100% vs 96.3% vs 93.6%) and 3 years (91.7% vs 73.2% vs 88.1%) were not different (P=0.539). In laboratory measurements, there was no group difference in total bilirubin and albumin. However, prothrombin time was longer in group A within postoperative 1 week and platelet count was lower in groups A and B within postoperative 1 month.

CONCLUSION

A GRWR lower to 0.7% is safe and does not need to modulate portal pressure in adult-to-adult LDLT using the right-lobe in favorable conditions including low model for end-stage liver disease score.

Early Graft Dysfunction in Living Donor Liver Transplantation and the Small for Size Syndrome

LDLT has arisen as a viable means to reduce waitlist mortality. However, its widespread embrace by the liver transplant community has been met with frustration centered on donor morbidity and small-for-size-syndrome. Focusing on the later entity, we describe the initial recognition of this early graft dysfunction, the theorized pathophysiology and solutions to remedy its emergence.

Liver function impairment in liver transplantation and after extended hepatectomy

Extended hepatectomy, or liver transplantation of reduced-size graft, can lead to a pattern of clinical manifestations, namely “post-hepatectomy liver failure” and “small-for-size syndrome” respectively, that can range from mild cholestasis to irreversible organ non-function and death of the patient. Many mechanisms are involved in their occurrence but in the recent past, high portal blood flow through a relatively small liver vascular bed has taken a central role. Therefore, several techniques of inflow modulation have been attempted in cases of portal hyperperfusion first in liver transplantation, such as portocaval shunt, mesocaval shunt, splenorenal shunt, splenectomy or ligation of the splenic artery. However, high portal flow is not the only factor responsible, and before major liver resections, preoperative assessment of the residual liver function is necessary. Techniques such as portal vein embolization or portal vein ligation can be adopted to increase the future liver volume, preventing post-hepatectomy liver failure. More recently, a new surgical procedure, that combines in situ splitting of the liver and portal vein ligation, has gradually come to light, inducing remarkable hypertrophy of the healthy liver in just a few days. Further studies are needed to confirm this hypothesis and overcome one of the biggest issues in the field of liver surgery.

Superoxide dismutase activity in portal vein endothelium after partial liver resection

PURPOSE

To investigate superoxide dismutase (SOD) activity in the portal vein endothelium and malondialdehyde acid (MDA) production in liver tissue of rats submitted to 70% hepatectomy.

METHODS

Twelve rats were distributed in two groups (hepatectomy and sham). Animals were sacrificed on post operative day 1 and portal vein, liver tissue and blood samples were collected. Portal vein SOD production was measured using lucigenin-amplified chemiluminescence assays. MDA measurement was used as an index of oxidative stress through the formation of TBARS (Thiobarbituric Acid Reactive Species).

RESULTS

There was no difference in post operative bilirubin, AST, ALT levels between groups. DHL level was higher in the hepatectomy group (p=0.01). MDA production in the remnant liver tissue and endothelial portal vein SOD activity were also significantly (p<0.05) elevated in the hepatectomy group when compared to control group. There was no correlation between MDA and SOD activity. SOD activity, on the other hand, showed a positive correlation with LDH level (p=0.038) and MDA levels showed a positive correlation with AST and ALT levels (p<0.001).

CONCLUSION

There is an increased production of malondialdehyde acid in liver tissue after partial hepatectomy and increased activity of superoxide dismutase in portal vein endothelium as well.

Losartan supports liver regrowth via distinct boost of portal vein pressure in rodents with 90 % portal branch ligation

OBJECTIVES

The study used a model of 90 % portal branch ligation (PBL) in rats to study the effect of losartan on portal vein pressure (PVP) and liver regeneration in rats after PBL.

METHODS

A total of 144 male Sprague-Dawley rats were arbitrarily designated into three treatment method groups: a sham operation group (Sham), a PBL treatment group (PBL), and a PBL plus losartan treatment group (PBL + L). Losartan (2 mg/day) was intragastrically gavaged 3 days before the PBL or sham operation to time points of study.

RESULTS

Both the PBL and PBL + L groups showed an intense surge in PVP after PBL treatment, peaking at 12 h postsurgery, then lessening progressively afterwards. PVP was substantially greater in these two groups compared with the Sham group at 6-72 h postsurgery (p < 0.01). Compared with the PBL group, the PBL + L group showed a noticeable reduction in PVP 6-48 h postsurgery (p < 0.05); the PBL group showed considerably raised levels of plasma ALT and AST 6-72 h postsurgery (p < 0.01). Compared to the PBL group, the PBL + L group showed drastically reduced plasma ALT and AST levels 12-72 h postsurgery (p < 0.05).

CONCLUSIONS

Losartan supports liver regeneration in 90 % of rats that underwent PBL. The mechanism may be related to losartan's ability to regulate PVP and increase serum hepatocyte growth factor levels.

Review of the surgical approach to prevent small-for-size syndrome in recipients after left lobe adult LDLT

Left lobe liver grafts increase the donor safety in adult-to-adult living-donor liver transplantation (ALDLT). However, the left lobe graft provides about 30-50 % of the required liver volume to adult recipients, which is insufficient to sustain their metabolic demands, which can lead to small-for-size syndrome (SFSS). Transient portal hypertension and microcirculatory hemodynamic derangement, apart from outflow obstruction, during the first week after reperfusion are the critical events associated with small-for-size graft transplantation. The incidence of SFSS in left lobe ALDLT can be decreased by increasing the left lobe graft volume by effective utilization of the caudate lobe with preserved vascular supply, by modulating the portal pressure with splenectomy or a porto-systemic shunt or by hepatic venous outflow reconstruction to prevent the development of venous congestion. In this review, we discuss the pathophysiology of SFSS and the various surgical strategies that can be performed to prevent SFSS in an effort to enhance the donor safety during living-donor liver transplantation.

Hypothermia predicts hepatic failure after extensive hepatectomy in mice

AIM

To investigate the effect of hypothermia on the function of the liver remnant (LR) after extended hepatectomy.

METHODS

We performed a 75% partial hepatectomy (PH) in male C57BL/6J mice. Body temperature was measured with a rectal probe. The study mice were prospectively grouped as hypothermic (HT) or normothermic (NT) if their body temperature was < 34 °C vs ≥ 34 °C, respectively. Blood and liver samples were obtained at 24 and 48 h after 75% PH. Various factors during and after 75% PH were compared at each time point and the most important factor for a good outcome after 75% PH was determined.

RESULTS

At 24 and 48 h after 75% PH, LR weight was decreased in HT mice compared with that in NT mice and the assay results in the HT mice were consistent with liver failure. NT mice had normal liver regeneration. Each intra- and post-operative factor which showed statistical significance in univariate analysis was evaluated by multivariate analysis. The most important factor for a good outcome after 75% PH was body temperature at both 24 and 48 h after surgery.

CONCLUSION

Hypothermia after an extensive hepatectomy predicts impending liver failure and may be a useful clinical marker for early detection of liver failure after extended hepatectomy.

Abnormal splenic artery diameter/hepatic artery diameter ratio in cirrhosis-induced portal hypertension

AIM: To determine an optimal cutoff value for abnormal splenic artery diameter/proper hepatic artery diameter (S/P) ratio in cirrhosis-induced portal hypertension.

METHODS: Patients with cirrhosis and portal hypertension (n = 770) and healthy volunteers (n = 31) underwent volumetric computed tomography three-dimensional vascular reconstruction to measure the internal diameters of the splenic artery and proper hepatic artery to calculate the S/P ratio. The cutoff value for abnormal S/P ratio was determined using receiver operating characteristic curve analysis, and the prevalence of abnormal S/P ratio and associations between abnormal S/P ratio and major complications of portal hypertension were studied using logistic regression.

RESULTS: The receiver operating characteristic analysis showed that the cutoff points for abnormal splenic artery internal diameter and S/P ratio were > 5.19 mm and > 1.40, respectively. The sensitivity, specificity, positive predictive value, and negative predictive value were 74.2%, 45.2%, 97.1%, and 6.6%, respectively. The prevalence of an abnormal S/P ratio in the patients with cirrhosis and portal hypertension was 83.4%. Patients with a higher S/P ratio had a lower risk of developing ascites [odds ratio (OR) = 0.708, 95%CI: 0.508-0.986, P = 0.041] and a higher risk of developing esophageal and gastric varices (OR = 1.483, 95%CI: 1.010-2.175, P = 0.044) and forming collateral circulation (OR = 1.518, 95%CI: 1.033-2.230, P = 0.034). After splenectomy, the portal venous pressure and maximum and mean portal venous flow velocities were reduced, while the flow rate and maximum and minimum flow velocities of the hepatic artery were increased (P < 0.05).

CONCLUSION: The prevalence of an abnormal S/P ratio is high in patients with cirrhosis and portal hypertension, and it can be used as an important marker of splanchnic hemodynamic disturbances.

"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.