Artificial circulation of the liver: machine perfusion as a preservation method in liver transplantation

Extended criteria brain-dead organ donors: Prevalence and impact on the utilisation of livers for transplantation in Brazil

BACKGROUND

Despite its association with higher postoperative morbidity and mortality, the use of extended criteria donor (ECD) livers for transplantation has increased globally due to the high demand for the procedure.

AIM

To investigate the prevalence of ECD in donation after brain death (DBD) and its impact on organ acceptance for transplantation.

METHODS

Retrospective analysis of DBD organ offers for liver transplantation between 2017 and 2020 in a high-volume transplant centre. The incidence of the Eurotransplant risk factors to define an ECD (ET-ECD) among DBD donors and the likelihood of organ acceptance over the years were analysed. The relationship between organ refusal for transplantation, the occurrence, and the number of ET-ECD was assessed by simple and multiple logistic regression adjustment.

RESULTS

A total of 1619 organ donors were evaluated. Of these, 78.31% (n = 1268) had at least one ET-ECD criterion. There was an increase in the acceptance of ECD DBD organs for transplantation (1 criterion: from 23.40% to 31.60%; 2 criteria: from 13.10% to 27.70%; 3 criteria: From 6.30% to 13.60%). For each addition of one ET-ECD variable, the estimated chance of organ refusal was 64.4% higher (OR 1.644, 95%CI 1.469-1.839, P < 0.001). Except for the donor serum sodium > 165 mmol/L (P = 0.310), all ET-ECD criteria increased the estimated chance of organ refusal for transplantation.

CONCLUSION

A high prevalence of ECD DBD was observed. Despite the increase in their utilisation, the presence and the number of extended donor criteria were associated with an increased likelihood of their refusal for transplantation.

Bionic Prostheses: The Emerging Alternative to Vascularised Composite Allotransplantation of the Limb

Twenty years have surpassed since the first vascularised composite allotransplantation (VCA) of the upper limb. This is an opportunity to reflect on the position of VCA as the gold standard in limb reconstruction. The paucity of recipients, tentative clinical outcomes, and insufficient scientific progress question whether VCA will remain a viable treatment option for the growing numbers of amputees. Bionic technology is advancing at a rapid pace. The prospect of widely available, affordable, safely applied prostheses with long-standing functional benefit is appealing. Progress in the field stems from the contributions made by engineering, electronic, computing and material science research groups. This review will address the ongoing reservations surrounding VCA whilst acknowledging the future impact of bionic technology as a realistic alternative for limb reconstruction.

[Modern concepts for the dynamic preservation of the liver and kidneys in the context of transplantation]

The increasing demand on donor grafts has forced experimental research on transplantation medicine to develop more efficient organ preservation strategies. Simple cold storage of grafts rarely offers optimal conditions for extended criteria donor organs. Hypothermic, oxygenated machine perfusion (HMP) is a classical method of dynamic organ preservation, which enables the provision of oxygen and nutrients to the tissue and provides a metabolic recovery of the graft prior to implantation. A more modern approach is normothermic machine perfusion (NMP), which instead simulates physiological conditions and enables an ex vivo evaluation and treatment of organ grafts. However, studies have found that a preceding period of cold storage significantly mitigates the functional advantage of NMP. A strategy to circumvent this phenomenon is controlled oxygenated rewarming (COR). The cold-stored graft is slowly and gradually rewarmed to subnormothermic or normothermic temperatures, providing a gentle adaption of energy metabolism and counteracting events of rewarming injury.

Organ Preservation into the 2020s: The Era of Dynamic Intervention

Organ preservation has been of major importance ever since transplantation developed into a global clinical activity. The relatively simple procedures were developed on a basic comprehension of low-temperature biology as related to organs outside the body. In the past decade, there has been a significant increase in knowledge of the sequelae of effects in preserved organs, and how dynamic intervention by perfusion can be used to mitigate injury and improve the quality of the donated organs. The present review focuses on (1) new information about the cell and molecular events impacting on ischemia/reperfusion injury during organ preservation, (2) strategies which use varied compositions and additives in organ preservation solutions to deal with these, (3) clear definitions of the developing protocols for dynamic organ perfusion preservation, (4) information on how the choice of perfusion solutions can impact on desired attributes of dynamic organ perfusion, and (5) summary and future horizons.

Oxaloacetate Protects Rat Liver From Experimental Warm Ischemia/Reperfusion Injury by Improving Cellular Energy Metabolism

Liver ischemia/reperfusion injury (IRI) is an important cause of liver damage especially early after liver transplantation, following liver resection, and in other clinical situations. Using rat experimental models, we identified oxaloacetate (OAA) as a key metabolite able to protect hepatocytes from hypoxia and IRI. In vitro screening of metabolic intermediates beneficial for hepatocyte survival under hypoxia was performed by measures of cell death and injury. In vivo, the effect of OAA was evaluated using the left portal vein ligation (LPVL) model of liver ischemia and a model of warm IRI. Liver injury was evaluated in vivo by serum transaminase levels, liver histology, and liver weight (edema). Levels and activity of caspase 3 were also measured. In vitro, the addition of OAA to hepatocytes kept in a hypoxic environment significantly improved cell viability (P < 0.01), decreased cell injury (P < 0.01), and improved energy metabolism (P < 0.01). Administration of OAA significantly reduced the extent of liver injury in the LPVL model with lower levels of alanine aminotransferase (ALT; P < 0.01), aspartate aminotransferase (AST; P < 0.01), and reduced liver necrosis (P < 0.05). When tested in a warm IRI model, OAA significantly decreased ALT (P < 0.001) and AST levels (P < 0.001), prevented liver edema (P < 0.001), significantly decreased caspase 3 expression (P < 0.01), as well as histological signs of cellular vesiculation and vacuolation (P < 0.05). This was associated with higher adenosine triphosphate (P < 0.05) and energy charge levels (P < 0.01). In conclusion, OAA can significantly improve survival of ischemic hepatocytes. The hepatoprotective effect of OAA was associated with increased levels of liver bioenergetics both in vitro and in vivo. These results suggest that it is possible to support mitochondrial activity despite the presence of ischemia and that OAA can effectively reduce ischemia-induced injury in the liver.

Partial Inhibition of HO-1 Attenuates HMP-Induced Hepatic Regeneration against Liver Injury in Rats

We found better liver graft regeneration with hypothermic machine perfusion (HMP) compared with static cold storage (SCS) for the first time in our pilot study, but the underlying mechanisms are unknown. Upregulated heme oxygenase- (HO-) 1 expression has been reported to play a pivotal role in promoting hepatocyte proliferation. Here, we evaluated the novel role of HO-1 in liver graft protection by HMP. Rats with a heterozygous knockout of HO-1 (HO-1^+/-) were generated and subjected to 3 h of SCS or HMP pre-half-size liver transplantation (HSLT) in vivo or 6 h of SCS or HMP in vitro; control rats were subjected to the same conditions (HO-1^+/+). We found that HSLT induced significant elevation of the HO-1 protein level in the regenerated liver and that HO-1 haplodeficiency resulted in decreased proliferation post-HSLT. Compared with SCS, HMP induced significant elevation of the HO-1 protein level along with better liver recovery, both of which were reduced by HO-1 haplodeficiency. HO-1 haplodeficiency-induced decreased proliferation was responsible for the attenuated regenerative ability of HMP. Mechanistically, HO-1 haploinsufficiency resulted in suppression of hepatocyte growth factor (HGF)/Akt activity. Our results suggest that inhibition of HO-1 mitigates HMP-induced liver recovery effects related to proliferation, in part, by downregulating the HGF-Akt axis.

Extended-criteria donors in liver transplantation Part II: reviewing the impact of extended-criteria donors on the complications and outcomes of liver transplantation

Extended-criteria donors (ECDs) have an impact on early allograft dysfunction (EAD), biliary complications, relapse of hepatitis C virus (HCV), and survivals. Early allograft dysfunction was frequently seen in grafts with moderate and severe steatosis. Donors after cardiac death (DCD) have been associated with higher rates of graft failure and biliary complications compared to donors after brain death. Extended warm ischemia, reperfusion injury and endothelial activation trigger a cascade, leading to microvascular thrombosis, resulting in biliary necrosis, cholangitis, and graft failure. The risk of HCV recurrence increased by donor age, and associated with using moderately and severely steatotic grafts. With the administration of protease inhibitors sustained virological response was achieved in majority of the patients. Donor risk index and EC donor scores (DS) are reported to be useful, to assess the outcome. The 1-year survival rates were 87% and 40% respectively, for donors with a DS of 0 and 3. Graft survival was excellent up to a DS of 2, however a DS >2 should be avoided in higher-risk recipients. The 1, 3 and 5-year survival of DCD recipients was comparable to optimal donors. However ECDs had minor survival means of 85%, 78.6%, and 72.3%. The graft survival of split liver transplantation (SLT) was comparable to that of whole liver orthotopic liver transplantation. SLT was not regarded as an ECD factor in the MELD era any more. Full-right-full-left split liver transplantation has a significant advantage to extend the high quality donor pool. Hypothermic oxygenated machine perfusion can be applied clinically in DCD liver grafts. Feasibility and safety were confirmed. Reperfusion injury was also rare in machine perfused DCD livers.

Normothermic liver preservation: a new paradigm?

Despite increasing donor numbers, waiting lists and pre-transplant mortality continue to grow in many countries. The number of donor organs suitable for liver transplantation is restricted by cold preservation and ischemia-reperfusion injury (IRI). Transplantation of marginal donor organs has led to renewed interest in new techniques which have the potential to improve the quality of preservation, assess the quality of the organ and allow repair of the donor organ prior to transplantation. If successful, such techniques would not only improve the outcome of currently transplanted marginal livers, but also increase the donor pool. Experimental evidence suggests that preservation under near physiological conditions of temperature and oxygenation abrogates IRI. Normothermic perfusion maintains the organ in a physiological state, avoiding the depletion of cellular energy and the accumulation of waste products, which occurs with static cold storage. It enables viability assessment prior to transplantation thereby reducing the risk of transplanting inherently marginal organs. Here we review the use of normothermic machine perfusion as a means of organ preservation.

Liver protection strategies in liver transplantation

BACKGROUND

Liver transplantation is the therapy of choice for patients with end-stage liver diseases. However, the gap between the low availability of organs and high demand is continuously increasing. Innovative strategies for organ protection are necessary to expand donor pool and to achieve better outcomes for liver transplantation. The present review analyzed and compared various strategies of liver protection.

DATA SOURCES

Databases such as PubMed, Embase and Ovid were searched for the literature related to donor liver protection strategies using following key words: "ischemia reperfusion injury", "graft preservation", "liver transplantation", "machine perfusion" and "conditioning". Of the 146 studies identified, only those with cutting edge strategies were analyzed.

RESULTS

A variety of therapeutic approaches were proposed to alleviate graft ischemia/reperfusion injury, which included static cold storage, machine perfusion (hypothermic, normothermic and subnormothermic), manual conditioning (pre, post and remote), and pharmacological conditioning. Evidences from animal experiments and clinical trials suggested that all these strategies could potentially protect liver graft; however, their clinical applications are limited partially due to their own disadvantages.

CONCLUSIONS

There are a plenty of methods suggested to decrease the degree of donor liver transplantation-related injury. However, none of these approaches is perfect in clinical practice. More translational researches (molecular and clinical studies) are needed to improve the techniques in liver graft protection.

Rewarming Machine Perfusion System for Liver Transplantation

The liver is one of the most essential organs, and transplantation is an established treatment for patients with end-stage disease who have lost their liver function. However, organ shortage is a critical problem in transplantation; thus, the development of an innovative preservation system to adopt critical grafts obtained from extended criteria donors or donation after cardiac death donors as viable organs for transplantation is necessary. We recently developed a novel rewarming machine perfusion preservation system for liver transplantation, and herein discuss this system, which allows the perfusion temperature to be controlled during the transition from hypothermic to subnormothermic conditions. This system has two functions: (1) the preservation and recovery of organ function and (2) screening the organ for viability. To achieve these functions, this system has three features: (1) temperature control of the preservation perfusate and liver graft, (2) dual-controlled perfusion of the portal vein and hepatic artery, and (3) real-time monitoring of the perfusion conditions, including the flow rate, perfusion pressure and temperature. This system was useful for liver preservation and for evaluating the graft viability and recovery of functions during machine perfusion before transplantation. This novel rewarming machine preservation system was tested in an experimental model using porcine liver grafts. We report that this system has certain advantages in liver preservation, and believe that this system will positively contribute to the expansion of the organ donor pool.

Assessing warm ischemic injury of pig livers at hypothermic machine perfusion

BACKGROUND

Livers originating from donation after circulatory death (DCD) donors are exposed to warm ischemia (WI) before liver transplantation (LTx). Currently, there are no objective tests to evaluate the damage sustained before LTx. This study aims to identify surrogate markers for liver injury that can be assessed during hypothermic machine perfusion (HMP) preservation. In addition, we want to use mathematical equation modeling combining these markers to improve our assessment of DCD livers for transplantation.

MATERIALS AND METHODS

Porcine livers were exposed to incremental periods of WI (0-120 min) and subsequently HMP preserved for 4 h. Biochemical and hemodynamic parameters were repeatedly measured in the perfusate during HMP. Subsequently, to mimic LTx, normothermic isolated-liver perfusion was applied for 2 h and the injury assessed using a morphological score.

RESULTS

With increasing WI periods, the perfusate became more acidotic, and levels of aspartate aminotransferase (AST), liver fatty acid binding protein, redox-active iron, and arterial vascular resistance increased. A damage index, combining AST and pH (damage index = 2 - 37 × β(AST) - 257 × β(pH)) based on multifactorial analysis of the changing pattern of these markers, had increased sensitivity and specificity to reflect WI and reperfusion injury.

CONCLUSIONS

This proof of concept study demonstrated the potential role for objective evaluation of DCD porcine livers during HMP and the advantage to use multifactorial analysis on the markers' changing pattern.

Resuscitation of ischemic donor livers with normothermic machine perfusion: a metabolic flux analysis of treatment in rats

Normothermic machine perfusion has previously been demonstrated to restore damaged warm ischemic livers to transplantable condition in animal models. However, the mechanisms of recovery are unclear, preventing rational optimization of perfusion systems and slowing clinical translation of machine perfusion. In this study, organ recovery time and major perfusate shortcomings were evaluated using a comprehensive metabolic analysis of organ function in perfusion prior to successful transplantation. Two groups, Fresh livers and livers subjected to 1 hr of warm ischemia (WI) received perfusion for a total preservation time of 6 hrs, followed by successful transplantation. 24 metabolic fluxes were directly measured and 38 stoichiometrically-related fluxes were estimated via a mass balance model of the major pathways of energy metabolism. This analysis revealed stable metabolism in Fresh livers throughout perfusion while identifying two distinct metabolic states in WI livers, separated at t = 2 hrs, coinciding with recovery of oxygen uptake rates to Fresh liver values. This finding strongly suggests successful organ resuscitation within 2 hrs of perfusion. Overall perfused livers regulated metabolism of perfusate substrates according to their metabolic needs, despite supraphysiological levels of some metabolites. This study establishes the first integrative metabolic basis for the dynamics of recovery during perfusion treatment of marginal livers. Our initial findings support enhanced oxygen delivery for both timely recovery and long-term sustenance. These results are expected to lead the optimization of the treatment protocols and perfusion media from a metabolic perspective, facilitating translation to clinical use.

New model of veno-venous bypass for management of anhepatic phase in experimental study on dogs

Blood is shunted from the inferior vena cava and portal vein to the superior vena caval system to prevent congestion in the lower parts of the body during the anhepatic phase (AP) of liver transplantation. It leads to overload in the superior vena caval system retarding cranial outflow due to a nonphysiological blood redistribution. To overcome this problem, we developed a new bypass in dogs: blood is shunted from the inferior (caudal) vena cava and portal vein to the suprahepatic inferior (caudal) vena cava. This model was compared with traditional one with or without a pump. Blood pressure and flow parameters were estimated during 3 hours of AP in four groups of four dogs each. The current study showed that a nontraditional scheme of venous bypass reduced circulatory complications during AP, especially in the cranial vena caval system, although a low rate of congestion remains in the caudal vena cava and portal vein systems. Whereas the same scheme using a pump effectively prevented congestion in all of the systems: cranial, caudal, and portal. We concluded that application of a nontraditional bypass scheme, providing venous blood return into suprahepatic part of caudal vena cava, can be considered to be a method of choice for experimental liver transplantation.

Experimental liver autotransplantation with novel scheme of veno-venous bypass as a model of liver denervation and delymphatization

The impact of denervation and delymphatization (DD) on liver tissue remains a topic of major interest in liver transplantation, as the organ or its part continues to function well. Various chemical and/or surgical interventions have been developed to achieve in situ liver denervation and delymphatization, but it is evident that DD can be achieved only through "ectomia", ie, complete isolation of the organ from adjacent and connected structures. This Study describes a liver DD model based on a technique of autotransplantation (replantation), maximally preventing ischemia in the transplanted (replanted) graft and dyscirculatory complications in the recipient. Experiments were performed on eight male mongrel dogs. Venous reservoir and roller pumps were used in a forced nontraditional bypass scheme. Autotransplantation was performed by step-by-step dissection of the suprahepatic, infrahepatic, and portal structures, leading to DD, with subsequent recovery of the blood vessel and bile duct. DD was achieved successfully with stable hemodynamic parameters during all surgery periods. All animals survived. This model of liver autotransplantation lead to DD of the organ. It was characterized by hemodynamic stability of the liver as well as of the whole body at every stage of the surgery, proffering liver DD for experimental studies.

Troubleshooting and improving the mouse and rat isolated perfused liver preparation

INTRODUCTION

Isolated perfused liver (IPL) model is not only widely performed in rats but is also used in mouse liver, although a detailed description of this procedure is absent. A comparison of the different techniques used on rats and mice will be discussed in this article association with a detailed description of the surgical and technical aspects needed to obtain and maintain the integrity of the livers during the organ isolation and perfusion.

METHODS

The surgical procedures, the IPL set-up, and the evaluation of hepatic function and damage will be described in relation to both rats and mice. In particular, the heparin dosage and administration, the portal vein cannulation avoiding portal leakage, the use of suprahepatic caval vein output, and the insertion of a cannula for bile collection will be reported. For the settings, the perfusion circuit, the perfusion solution, the temperature and the flow rate will be described, with particular regard to the balance between perfusion pressure and oxygen delivery. The monitoring of liver integrity by measuring oxygen concentration and calculating oxygen delivery rate and oxygen uptake rate, and recommendations for the collection of perfusate and bile samples will be considered. Accurate pH measurement with normalization, and the perfusion portal pressure assay by a calibrated water manometer will be also reported.

RESULTS AND DISCUSSION

This work analyzes the parameters crucial to performing a correct IPL both in rat and mouse, comparing our experience with the equivalent practice from other laboratories. An updated example of IPL applications in liver toxicology and pharmacology, physiology and pathophysiology, and liver graft preservation will be briefly presented, underlining how this technique provides essential information allowing a more accurate planning of the in vivo studies.

Donation after cardio-circulatory death liver transplantation

The renewed interest in donation after cardio-circulatory death (DCD) started in the 1990s following the limited success of the transplant community to expand the donation after brain-death (DBD) organ supply and following the request of potential DCD families. Since then, DCD organ procurement and transplantation activities have rapidly expanded, particularly for non-vital organs, like kidneys. In liver transplantation (LT), DCD donors are a valuable organ source that helps to decrease the mortality rate on the waiting lists and to increase the availability of organs for transplantation despite a higher risk of early graft dysfunction, more frequent vascular and ischemia-type biliary lesions, higher rates of re-listing and re-transplantation and lower graft survival, which are obviously due to the inevitable warm ischemia occurring during the declaration of death and organ retrieval process. Experimental strategies intervening in both donors and recipients at different phases of the transplantation process have focused on the attenuation of ischemia-reperfusion injury and already gained encouraging results, and some of them have found their way from pre-clinical success into clinical reality. The future of DCD-LT is promising. Concerted efforts should concentrate on the identification of suitable donors (probably Maastricht category III DCD donors), better donor and recipient matching (high risk donors to low risk recipients), use of advanced organ preservation techniques (oxygenated hypothermic machine perfusion, normothermic machine perfusion, venous systemic oxygen persufflation), and pharmacological modulation (probably a multi-factorial biologic modulation strategy) so that DCD liver allografts could be safely utilized and attain equivalent results as DBD-LT.

Flow Competition between Hepatic Arterial and Portal Venous flow during Hypothermic Machine Perfusion Preservation of Porcine Livers

Hypothermic machine perfusion (HMP) is regarded as a better preservation method for donor livers than cold storage. During HMP, livers are perfused through the inlet blood vessels, namely the hepatic artery (HA) and the portal vein (PV). In previous HMP feasibility studies of porcine and human livers, we observed that the PV flow decreased while the HA flow increased. This flow competition restored either spontaneously or by lowering the HA pressure (PHA). Since this phenomenon had never been observed before and because it affects the HMP stability, it is essential to gain more insight into the determinants of flow competition. To this end, we investigated the influence of the HMP boundary conditions on liver flows during controlled experiments. This paper presents the flow effects induced by increasing PHA and by obstructing the outlet blood vessel, which is the vena cava inferior (VCI).

Flow competition was evoked by increasing PHA to 55–70 mmHg, as well as by obstructing the VCI. Remarkably, a severe obstruction resulted in a repetitive and alternating tradeoff between the HA and PV flows. These phenomena could be related to intra-sinusoidal pressure alterations. Consequently, a higher PHA is most likely transmitted to the sinusoidal level. This increased sinusoidal pressure reduces the pressure drop between the PV and the sinusoids, leading to a decreased PV perfusion. Flow competition has not been encountered or evoked under physiological conditions and should be taken into account for the design of liver HMP protocols. Nevertheless, more research is necessary to determine the optimal parameters for stable HMP.

Protective effects of hypothermic ex vivo perfusion on ischemia/reperfusion injury and transplant outcomes

Hypothermic machine preservation (HMP) has been used in renal transplantation since the late 1960s with recent robust prospective, multicenter data showing lower rates of delayed graft function and improved graft survival. Although now clearly beneficial for renal transplantation, extrarenal machine perfusion has remained predominantly in preclinical investigations. Pancreatic HMP has drawn little clinical interest because HMP has been suggested to cause graft edema and congestion, which is associated with early venous thrombosis and graft failure. Early investigation showed no benefit of HMP in whole-organ pancreas transplant. One report did show that HMP increases islet cell yield after isolation. Preclinical work in liver HMP has been promising. Short- and long-term HMP has been shown to improve graft viability and reduce preservation injury, even in animal models of steatotic and donation after cardiac death. The first clinical study of liver HMP using a centrifugal dual perfusion technique showed excellent results with lower hepatocellular injury markers and no adverse perfusion-related outcomes. In addition, a dramatic attenuation of proinflammatory cytokine expression was observed. Further studies of liver HMP are planned with focus on developing a reproducible and standard protocol that will allow the widespread availability of this technology. Future research and clinical trials of novel organ preservation techniques, solutions, and interventions are likely to bring about developments that will allow further reduction of preservation-related ischemia/reperfusion injury and improved outcomes and allow safer utilization of the precious and limited resource of donor organs.

Subnormothermic machine perfusion at both 20°C and 30°C recovers ischemic rat livers for successful transplantation

BACKGROUND

Utilizing livers from donors after cardiac death could significantly expand the donor pool. We have previously shown that normothermic (37°C) extracorporeal liver perfusion significantly improves transplantation outcomes of ischemic rat livers. Here we investigate whether recovery of ischemic livers is possible using sub-normothermic machine perfusion at 20°C and 30°C.

METHODS

Livers from male Lewis rats were divided into five groups after 1 h of warm ischemia (WI): (1) WI only, (2) 5 h of static cold storage (SCS), or 5 h of MP at (3) 20°C, (4) 30°C, and (5) 37°C. Long-term graft performance was evaluated for 28 d post-transplantation. Acute graft performance was evaluated during a 2 h normothermic sanguineous reperfusion ex vivo. Fresh livers with 5 h of SCS were positive transplant controls while fresh livers were positive reperfusion controls.

RESULTS

Following machine perfusion (MP) (Groups 3, 4, and 5), ischemically damaged livers could be orthotopically transplanted into syngeneic recipients with 100% survival (N ≥ 4) after 4 wk. On the other hand, animals from WI only, or WI + SCS groups all died within 24 h of transplantation. Fresh livers preserved using SCS had the highest alanine aminotransferase (ALT), aspartate aminotransferase (AST), and the lowest bile production during reperfusion, while at 28 d post-transplantation, livers preserved at 20°C and 30°C had the highest total bilirubin values.

CONCLUSIONS

MP at both 20°C and 30°C eliminated temperature control in perfusion systems and recovered ischemically damaged rat livers. Postoperatively, low transaminases suggest a beneficial effect of sub-normothermic perfusion, while rising total bilirubin levels suggest inadequate prevention of ischemia- or hypothermia-induced biliary damage.

From vascular corrosion cast to electrical analog model for the study of human liver hemodynamics and perfusion

Hypothermic machine perfusion (HMP) is experiencing a revival in organ preservation due to the limitations of static cold storage and the need for better preservation of expanded criteria donor organs. For livers, perfusion protocols are still poorly defined, and damage of sinusoidal endothelial cells and heterogeneous perfusion are concerns. In this study, an electrical model of the human liver blood circulation is developed to enlighten internal pressure and flow distributions during HMP. Detailed vascular data on two human livers, obtained by combining vascular corrosion casting, micro-CT-imaging and image processing, were used to set up the electrical model. Anatomical data could be measured up to 5--6 vessel generations in each tree and showed exponential trend lines, used to predict data for higher generations. Simulated flow and pressure were in accordance with literature data. The model was able to simulate effects of pressure-driven HMP on liver hemodynamics and reproduced observations such as flow competition between the hepatic artery and portal vein. Our simulations further indicate that, from a pure biomechanical (shear stress) standpoint, HMP with low pressures should not result in organ damage, and that fluid viscosity has no effect on the shear stress experienced by the liver microcirculation in pressure-driven HMP.

Current state of hypothermic machine perfusion preservation of organs: The clinical perspective

This review focuses on the application of hypothermic perfusion technology as a topic of current interest with the potential to have a salutary impact on the mounting clinical challenges to improve the quantity and quality of donor organs and the outcome of transplantation. The ex vivo perfusion of donor organs on a machine prior to transplant, as opposed to static cold storage on ice, is not a new idea but is being re-visited because of the prospects of making available more and better organs for transplantation. The rationale for pursuing perfusion technology will be discussed in relation to emerging data on clinical outcomes and economic benefits for kidney transplantation. Reference will also be made to on-going research using other organs with special emphasis on the pancreas for both segmental pancreas and isolated islet transplantation. Anticipated and emerging benefits of hypothermic machine perfusion of organs are: (i) maintaining the patency of the vascular bed, (ii) providing nutrients and low demand oxygen to support reduced energy demands, (iii) removal of metabolic by-products and toxins, (iv) provision of access for administration of cytoprotective agents and/or immunomodulatory drugs, (v) increase of available assays for organ viability assessment and tissue matching, (vi) facilitation of a change from emergency to elective scheduled surgery with reduced costs and improved outcomes, (vii) improved clinical outcomes as demonstrated by reduced PNF and DGF parameters, (viii) improved stabilization or rescue of ECD kidneys or organs from NHBD that increase the size of the donor pool, (ix) significant economic benefit for the transplant centers and reduced health care costs, and (x) provision of a technology for ex vivo use of non-transplanted human organs for pharmaceutical development research.

Machine perfusion of the liver: past, present and future

PURPOSE OF REVIEW

This review considers the potential of machine perfusion to preserve livers for clinical transplantation, including steatotic or ischaemically damaged grafts and aims to go over the most significant achievements in liver machine perfusion over the last year. To reach acceptance in liver preservation, machine perfusion will need to improve outcomes compared with simple cold storage (SCS), provide objective measures of graft viability, and resuscitate less-than-ideal grafts before transplantation.

RECENT FINDINGS

Current machine perfusion protocols comprise both hypothermic (HMP) and normothermic (NMP) approaches. HMP increases energy stores compared to SCS, and NMP shows additional resuscitative potential. Dutkowski transplanted ischaemically damaged pig livers after HMP following SCS, which avoided graft failure observed after SCS alone. Guarrera performed 20 clinical transplants after 4-7 h HMP. Friend has performed porcine transplantations after NMP of 4-20 h and univocally demonstrated the significant resuscitative effects on ischaemically damaged grafts otherwise destined to fail. Whereas NMP promises resuscitative effects, it demands challenging, near-physiologic conditions. Subnormothermic perfusion is being tested as a promising medium in between.

SUMMARY

Despite recent substantial improvements, liver preservation by machine perfusion remains limited and in contrast to the global revival of kidney machine perfusion. However, liver machine perfusion may be close to returning to clinical practice if it has not already done so. History shows that superiority alone does not guarantee immediate clinical use. Further clear-cut benefits of machine perfusion such as viability assessment will have to be accompanied by usability and human factors, and innovative and improved perfusion solutions applied in novel perfusion protocols.

The influence of storage temperature during machine perfusion on preservation quality of marginal donor livers

BACKGROUND

Although non-heart-beating donors have the potential to increase the number of available organs, the livers are used very seldom because of the risk of primary non-function. There is evidence that machine perfusion is able to improve the preservation of marginal organs, and therefore we evaluated in our study the influence of the perfusate temperature during oxygenated machine perfusion on the graft quality.

METHODS

Livers from male Wistar rats were harvested after 60-min warm ischemia induced by cardiac arrest. The portal vein was cannulated and the liver flushed with Lifor (Lifeblood Medical, Inc.) organ preservation solution for oxygenated machine perfusion (MP) at 4, 12 or 21 degrees C. Other livers were flushed with HTK and stored at 4 degrees C by conventional cold storage (4 degrees C-CS). Furthermore two groups with either warm ischemic damage only or without any ischemic damage serve as control groups. After 6h of either machine perfusion or cold storage all livers were normothermic reperfused with Krebs-Henseleit buffer, and functional as well as structural data were analyzed.

RESULTS

Contrary to livers stored by static cold storage, machine perfused livers showed independently of the perfusate temperature a significantly decreased enzyme release of hepatic transaminases (ALT) during isolated reperfusion. Increasing the machine perfusion temperature to 21 degrees C resulted in a marked reduction of portal venous resistance and an increased bile production.

CONCLUSIONS

Oxygenated machine perfusion improves viability of livers after prolonged warm ischemic damage. Elevated perfusion temperature of 21 degrees C reconstitutes the hepatic functional capacity better than perfusion at 4 or 12 degrees C.

Hypothermic Liver Machine Perfusion With EKPS-1 Solution vs Aqix RS-I Solution: In Vivo Feasibility Study in a Pig Transplantation Model

OBJECTIVE

Hypothermic machine perfusion (HMP) is superior to simple cold storage for kidney preservation. We previous observed in a porcine liver transplantation model increased tumor necrosis factor-alpha (TNF-alpha) production eventually leading to poor recipient survival after HMP using standard kidney perfusion solution (KPS-1) compared with simple cold storage. We compared two solutions for HMP preservation of the liver: enriched KPS-1 (EKPS-1) and Aqix RS-I.

METHODS

Pig livers were obtained after cold flushing with histidine-tryptophan-ketoglutarate solution. Subsequently, the livers were subjected to dual-vessel perfusion with two preservation solutions: EKPS-1 (n = 6) and Aqix RS-I (n = 3). After HMP preservation and transplantation, graft and recipient survival, hepatocellular damage (aspartate aminotransferase concentration), TNF-alpha production, and endothelial cell damage (hyaluronic acid clearance) were recorded.

RESULTS

No primary graft nonfunction was observed. Recipient survival at postoperative day 3 was similar in both groups (33%). Aspartate aminotransferase concentration measured in serum samples after reperfusion was similar in both groups. After reperfusion, TNF-alpha concentration was higher and hyaluronic acid clearance was lower in the EKPS-1 group vs the Aqix RS-I group at 60, 120, and 180 minutes (all P < .05).

CONCLUSION

Hypothermic machine perfusion provided adequate longer term graft survival. After reperfusion, TNF-alpha production seems to be reduced, and endothelial cell dysfunction remains pronounced with Aqix RS-1 solution compared with EKPS-1 solution.