Normothermic kidney preservation. Curr Opin Organ Transplant. 2011;16:169-173. [PMID: 21415819 DOI: 10.1097/mot.0b013e3283446a5d]

Does Normothermic Machine Perfusion Still Provide an Advantage for Deceased Donor Kidney Transplantation? A Systematic Review and Preliminary Meta-Analysis

BACKGROUND

Patients with end-stage renal disease often face prolonged waiting times for kidney transplants. Historically, the use of marginal kidneys was limited due to suboptimal preservation methods. Normothermic machine perfusion (NMP) preserves physiological activity during the preservation process, potentially improving graft function and viability, expanding the use of marginal kidneys. While preliminary results are promising, NMP has not yet undergone sufficient clinical trials to determine whether it offers advantages over more widely used techniques. The aim of this systematic review is to assess several outcomes between kidneys that underwent NMP compared to traditional preservation methods after kidney transplant.

METHODS

A systematic review was conducted following PRISMA guidelines. Randomized controlled trials, case series, and studies comparing NMP with hypothermic machine perfusion (HMP) or static cold storage (SCS) were included. The primary outcome assessed was delayed graft function (DGF). Secondary outcomes included primary non-function (PNF), acute rejection, and 1-year graft survival.

RESULTS

Eight NMP studies met the inclusion criteria. Meta-analysis showed significant differences in DGF between NMP and control (HMP or SCS) groups (OR: 0.47 [0.22, 0.99], p < 0.05). There were no significant differences between NMP and controls for PNF, acute rejection, or 1-year graft survival.

CONCLUSIONS

These findings suggest that NMP yields similar adverse outcome rates compared to traditional methods. Notably, NMP could be associated with reduced rates of DGF. While NMP is a promising technique for renal allograft preservation, further randomized controlled trials are necessary to definitively establish its benefits over conventional preservation methods.

Real-time organ perfusion monitoring of human kidney transplants using ex vivo normothermic perfusion and reflectance spectroscopy

Transplantation is the standard treatment for end-stage kidney disease but carries with it a non-trivial risk of post-operative complication. There is a need for a continuous, real-time, not additionally invasive method of monitoring organ perfusion. We present an approach to allograft perfusion monitoring using a human kidney model using ex vivo normothermic perfusion (EVNP) and custom spectroscopic optical reflectance probes. Five discarded human kidneys underwent EVNP, spectroscopic measurement and were subjected to perfusion compromising events (rejection, thrombosis or haemorrhage). Oxygenated and deoxygenated haemoglobin spectra were fitted to the spectra acquired from the kidneys in order to estimate the oxygen saturation. Average oxygen saturations before the perfusion compromising events were estimated to be higher than after (or similar in the control cases). Changes in oxygen saturation estimated from measurements made continuously were synchronized well with changes in renal blood flow index measurements. This proof of concept study proves promising in identifying a technique for continuous monitoring of perfusion and oxygenation of a transplanted kidney in vivo with minimal additional invasiveness.

Outcomes of Kidney Perfusion Techniques in Transplantation from Deceased Donors: A Systematic Review and Meta-Analysis

The high demand for organs in kidney transplantation and the expansion of the donor pool have led to the widespread implementation of machine perfusion technologies. In this study, we aim to provide an up-to-date systematic review of the developments in this expanding field over the past 10 years, with the aim of answering the question: "which perfusion technique is the most promising technique in kidney transplantation?" A systematic review of the literature related to machine perfusion in kidney transplantation was performed. The primary outcome measure was delayed graft function (DGF), and secondary outcomes included rates of rejection, graft survival, and patient survival rates after 1 year. Based on the available data, a meta-analysis was performed. The results were compared with data from static cold storage, which is still the standard of care in many centers worldwide. A total of 56 studies conducted in humans were included, and 43 studies reported outcomes of hypothermic machine perfusion (HMP), with a DGF rate of 26.4%. A meta-analysis of 16 studies showed significantly lower DGF rates in the HMP group compared to those of static cold storage (SCS). Five studies reported outcomes of hypothermic machine perfusion + O₂, with an overall DGF rate of 29.7%. Two studies explored normothermic machine perfusion (NMP). These were pilot studies, designed to assess the feasibility of this perfusion approach in the clinical setting. Six studies reported outcomes of normothermic regional perfusion (NRP). The overall incidence of DGF was 71.5%, as it was primarily used in uncontrolled DCD (Maastricht category I-II). Three studies comparing NRP to in situ cold perfusion showed a significantly lower rate of DGF with NRP. The systematic review and meta-analysis provide evidence that dynamic preservation strategies can improve outcomes following kidney transplantation. More recent approaches such as normothermic machine perfusion and hypothermic machine perfusion + O₂ do show promising results but need further results from the clinical setting. This study shows that the implementation of perfusion strategies could play an important role in safely expanding the donor pool.

Artificial oxygen carriers in organ preservation: Dose dependency in a rat model of ex-vivo normothermic kidney perfusion

INTRODUCTION

Organ preservation through ex-vivo normothermic perfusion (EVNP) with albumin-derived perfluorocarbon-based artificial oxygen carriers (A-AOCs) consisting of albumin-derived perfluorodecalin-filled nanocapsules prior to transplantation would be a promising approach to avoid hypoxic tissue injury during organ storage.

METHODS

The kidneys of 16 rats underwent EVNP for 2 h with plasma-like solution (5% bovine serum albumin, Ringer-Saline, inulin) with or without A-AOCs in different volume fractions (0%, 2%, 4%, or 8%). Cell death was determined using TdT-mediated dUTP-biotin nick end labeling (TUNEL). Aspartate transaminase (AST) activity in both perfusate and urine as well as the glomerular filtration rate (GFR) were determined. The hypoxia inducible factors 1α and 2α (HIF-1α und -2α) were quantified in tissue homogenates.

RESULTS

GFR was substantially decreased in the presence of 0%, 2%, and 8% A-AOC but not of 4%. In accordance, hypoxia-mediated cell death, as indicated by both AST activity and TUNEL-positive cells, was significantly decreased in the 4% group compared to the control group. The stabilization of HIF-1α and 2α decreased with 4% and 8% but not with 2% A-AOCs.

CONCLUSION

The dosage of 4% A-AOCs in EVNP was most effective in maintaining the physiological renal function.

Uncontrolled non-heartbeating donors (types i-ii) with normothermic recirculation vs. heartbeating donors: evaluation of functional results and survival

OBJECTIVE

Non-heartbeating donors (NHBD) are an alternative to heartbeating donors (HBD). Our objective was to compare functional results and kidney survival from NHBDs and HBDs.

MATERIAL AND METHODS

A retrospective study comparing the results of 236 normothermically preserved kidneys from type i and ii type NHBDs with the results of 250 from HBDs that were transplanted in our center between 2005 and 2012. Homogeneity between groups was tested and we evaluated the presence of delayed graft function (DGF) associated with pretransplant variables of the donor and recipient.

RESULTS

Both groups show homogeneity in pretransplant characteristics in terms of: age, HLA incompatibilities, and recipient hemodialysis time. Average follow-up time was 33 months (range 0-87) for NHBDs and 38 months (range 0-90) for HBDs. 5.5% of NHBDs showed primary non-function (PNF) vs. 4% of HBDs (P=.42) and 80.9% of DGF vs. 46.8% of HBDs (P<.001). At the end of the follow-up, there were no statistically significant differences in the survival of grafts (92.8% for NHBD vs. 93.6% for HBD, P=.71) and recipients (99.1% NHBD vs. 98.6% HBD, P=.28).

CONCLUSIONS

Although the DGF percentage was greater for NHBDs, final creatinine as well as graft and recipient survival were similar for both groups. Therefore, in our experience, kidneys from NHBDs have similar results to those from HBDs and are an excellent source of organs for transplantation.

Short term ex vivo storage of kidneys cause progressive nuclear ploidy changes of renal tubular epitheliocytes

In renal transplantation, there has been considerable success, mainly in term of post-transplant graft function. However, upon closer scrutiny, it is known that severe dysfunction, including persistence of renal failure is seen after transplantation. The major condition that potentially cause significant lesion may be hypothesized to be related to the hypothermic approach to storage. To systematically examine these issues, we stored mammalian (sheep) kidneys in UWS at 4 °C for four different time points (0, 1, 3 and 6 hours). We obtained renal histological sections and examined tubular architecture as well as nuclear characteristics of tubular epitheliocytes. The results of our preliminary investigations suggest that there are temporal changes of tubular epitheliocytes, as well as genomic changes. These changes were also seen in tissues stored at room temperature. Our observations suggest the need for additional studies for redesigning of improvised storage solutions. Pilot studies using Celsior also revealed similar kind of nuclear changes, suggesting that storage conditions are contributory, including perfusion versus static conditions. The results may explain persistence of tubular injury several days after orthotopic transplantation, and may potentially be contributory to delayed graft function (DGF).

Hypothermic machine perfusion of kidneys retrieved from standard and high-risk donors

Hypothermic machine perfusion (HMP) of kidneys is a long-established alternative to static cold storage and has been suggested to be a better preservation method. Today, as our deceased donor profile continues to change towards higher-risk kidneys of lower quality, we are confronted with the limits of cold storage. Interest in HMP as a preservation technique is on the rise. Furthermore, HMP also creates a window of opportunity during which to assess the viability and quality of the graft before transplantation. The technology might also provide a platform during which the graft could be actively repaired, making it particularly attractive for higher-risk kidneys. We review the current evidence on HMP in kidney transplantation and provide an outlook for the use of the technology in the years to come.

Short-term result of renal transplantation using extracorporeal membrane oxygenation-supported brain-dead donors

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) is now widely used to maintain hemodynamic stability after traumatic events among medical centers. It remains unclear whether renal transplantation using ECMO-supported donors carries poorer outcomes.

METHODS

From February 2010 to March 2013, we performed 9 renal transplantations (6 females and 3 males) from 5 ECMO-supported donors. Demographic data and clinical outcomes were retrospectively analyzed through medical chart review.

RESULTS

The mean follow-up period was 15 ± 9 months (range: 8-37). Eight of the 9 grafts remained functioning within the follow-up period. One (11.1%) graft loss was noted after repeated acute rejection. Acute rejection occurred in 3/9 (33%) of cases. Delayed graft function was also observed in 3/9 (33%) of cases.

CONCLUSION

Renal transplantation using ECMO-supported brain-dead donors was not associated with an unacceptably high rate of graft loss in this short-term follow-up. It might be an alternative way to expand donor pools.

Preoperative assessment of the deceased-donor kidney: from macroscopic appearance to molecular biomarkers

Variation in deceased-donor kidney quality can significantly affect outcomes after kidney transplantation. Suboptimal organ selection for a given recipient can result in primary nonfunction, premature graft failure, or inappropriate discard of a suitable organ. Appraisal and appropriate selection of deceased-donor kidneys for use in transplantation is therefore critical. A number of predictive tools have been developed to assist the transplant team in evaluating the suitability of a deceased-donor kidney for transplantation to a given recipient. These include stratification of donors into "standard-" or "expanded-criteria" categories based on clinical parameters, pre-implantation biopsy scores, donor risk scores, machine perfusion characteristics, functional kidney weight, donor biomarkers and molecular diagnostic tools, ex vivo viability assessment using postmortem normothermic perfusion, and overall macroscopic appraisal by the surgical team. Consensus as to the role and predictive value of each of these tools is lacking and clinical practice regarding evaluation and selection of kidneys varies considerably.In this review, we seek to critically appraise the literature and evaluate the levels of evidence for tools used to assess deceased-donor kidneys. Although a plethora of appraisal tools exist, very few demonstrate desirable predictive power to be useful in clinical decision-making. Further research using large, well-designed prospective studies is urgently needed to advance this important field of transplantation science.

Hypothermic or normothermic abdominal regional perfusion in high-risk donors with extended warm ischemia times: impact on outcomes?

Donation after circulatory determination of death (DCD) has the potential to increase the applicability of transplantation as a treatment for end-stage organ disease; its use is limited, however, by the warm ischemic damage suffered by potential grafts. Abdominal regional perfusion (ARP) has been employed in this setting to not only curtail the deleterious effects of cardiac arrest by re-establishing oxygenated flow but also test and even improve the viability of the kidneys and liver prior to transplantation. In the present review article, we discuss experimental and clinical studies that have been published to date on the use of ARP in DCD, differentiating between its application under hypothermic and normothermic conditions. In addition to describing results that have been achieved thus far, we describe the major obstacles limiting the broader implementation of ARP in this context as well as potential means for improving the effectiveness of this modality in the future.

Endothelial cell preservation at hypothermic to normothermic conditions using clinical and experimental organ preservation solutions

INTRODUCTION

Endothelial barrier function is pivotal for the outcome of organ transplantation. Since hypothermic preservation (gold standard) is associated with cold-induced endothelial damage, endothelial barrier function may benefit from organ preservation at warmer temperatures. We therefore assessed endothelial barrier integrity and viability as function of preservation temperature and perfusion solution, and hypothesized that endothelial cell preservation at subnormothermic conditions using metabolism-supporting solutions constitute optimal preservation conditions.

METHODS

Human umbilical vein endothelial cells (HUVEC) were preserved at 4-37°C for up to 20 h using Ringer's lactate, histidine-tryptophan-ketoglutarate solution, University of Wisconsin (UW) solution, Polysol, or endothelial cell growth medium (ECGM). Following preservation, the monolayer integrity, metabolic capacity, and ATP content were determined as positive parameters of endothelial cell viability. As negative parameters, apoptosis, necrosis, and cell activation were assayed. A viability index was devised on the basis of these parameters.

RESULTS

HUVEC viability and barrier integrity was compromised at 4°C regardless of the preservation solution. At temperatures above 20°C, the cells' metabolic demands outweighed the preservation solutions' supporting capacity. Only UW maintained HUVEC viability up to 20°C. Despite high intracellular ATP content, none of the solutions were capable of sufficiently preserving HUVEC above 20°C except for ECGM.

CONCLUSION

Optimal HUVEC preservation is achieved with UW up to 20°C. Only ECGM maintains HUVEC viability at temperatures above 20°C.

Machine perfusion viability testing

PURPOSE OF REVIEW

Pretransplant assessment of kidney graft viability may help clinicians to decide whether to accept or discard a kidney for transplantation. With the increasing demand for donor kidneys and the increased use of marginal kidneys, the need of viability markers has increased to pursue superior transplant outcomes. Hypothermic machine perfusion (HMP) provides the theoretical opportunity to assess the viability of donor kidneys. We discuss the novel developments in viability testing during HMP and address the future prospects.

RECENT FINDINGS

HMP viability testing has focused on the analysis of machine perfusion parameters and perfusate biomarkers. Renal resistance and the biomarkers lactate dehydrogenase, aspartate transaminase, glutathione-S-transferase, N-acetyl-β-D-glucosaminidase, heart-type fatty acid binding protein, lipid peroxidation products, redox-active iron and IL-18 are correlated with transplant outcome in terms of development of delayed graft function or graft survival. However, they all lack adequate predictive value for transplant outcome. New techniques including contrast-enhanced ultrasound, three-dimensional ultrasound and magnetic resonance spectrometry are promising methods to test kidney viability during HMP, but their value has to be established. The introduction of normothermic machine perfusion offers other promising opportunities for viability testing.

SUMMARY

Machine perfusion characteristics and perfusate biomarkers have been extensively studied. They often correlate with the transplant outcome, but the present viability tests are not reliable predictors of transplant outcome. New developments in kidney graft viability assessment are necessary to have a chance of being clinically useful in the future.

Machine perfusion in organ transplantation: a tool for ex-vivo graft conditioning with mesenchymal stem cells?

PURPOSE OF REVIEW

Machine perfusion has emerged as a tool to evaluate pretransplant graft function more objectively during preservation. Machine perfusion also offers the possibility to recondition questionable organs and to 'immunomodulate' allografts ex vivo. This article aims to review the current knowledge on machine perfusion of the various solid thoracic and abdominal organs, and to discuss the new possibility of conditioning and treating grafts with mesenchymal stem cells (MSCs) during machine perfusion.

RECENT FINDINGS

Different methods of machine perfusion have been described varying among organs in temperature and composition of perfusate. Commercial devices have recently become available for machine perfusion of all organs, with the largest clinical experience acquired in kidney and lung transplantation. Clinical studies are ongoing for liver, heart, and pancreas. MSC therapy in organ transplantation is now emerging with clinical studies set up to investigate its potential to attenuate ischemia/reperfusion injury (innate immunity) and to downregulate the alloimmune response (adaptive immunity) and promote engraftment after transplantation. We hypothesize that delivery of MSCs directly into the machine perfusion circuit may provide a unique opportunity to treat and immunomodulate organs prior to transplantation. To our knowledge, no study on ex-vivo delivery of MSCs during machine perfusion has been reported.

SUMMARY

Machine perfusion of solid organs has regained much attention during the last decade. It provides a new promising tool that may allow pretransplant ex-vivo assessment, preservation, repair, and conditioning of grafts. Experimental research and clinical trials testing the administration of MSCs during machine perfusion are warranted to explore the potential benefit and mechanisms of this approach.

Kidney donation after cardiac death

There is continuing disparity between demand for and supply of kidneys for transplantation. This review describes the current state of kidney donation after cardiac death (DCD) and provides recommendations for a way forward. The conversion rate for potential DCD donors varies from 40%-80%. Compared to controlled DCD, uncontrolled DCD is more labour intensive, has a lower conversion rate and a higher discard rate. The super-rapid laparotomy technique involving direct aortic cannulation is preferred over in situ perfusion in controlled DCD donation and is associated with lower kidney discard rates, shorter warm ischaemia times and higher graft survival rates. DCD kidneys showed a 5.73-fold increase in the incidence of delayed graft function (DGF) and a higher primary non function rate compared to donation after brain death kidneys, but the long term graft function is equivalent between the two. The cold ischaemia time is a controllable factor that significantly influences the outcome of allografts, for example, limiting it to < 12 h markedly reduces DGF. DCD kidneys from donors < 50 function like standard criteria kidneys and should be viewed as such. As the majority of DCD kidneys are from controlled donation, incorporation of uncontrolled donation will expand the donor pool. Efforts to maximise the supply of kidneys from DCD include: implementing organ recovery from emergency department setting; improving family consent rate; utilising technological developments to optimise organs either prior to recovery from donors or during storage; improving organ allocation to ensure best utility; and improving viability testing to reduce primary non function.

Optimal flow and pressure management in machine perfusion systems for organ preservation

Intra-organ flow is the most critical parameter in machine-perfused organ preservation systems (MPS). Ultrasonic flow sensors (UFS) are commonly employed in MPS. However, UFS are sensitive to changes in fluid composition and temperature and require recalibration. Novel Coriolis-type mass flow sensors (CFS) may be more suitable for MPS because the measurement technique is not amenable to these factors. The effect of viscosity, colloids, temperature, pressure, and preservation solution on flow measurement accuracy of UFS and CFS was therefore investigated. A CFS-based MPS was built and validated for setpoint stability using porcine kidneys and the ability to reproduce different pressure and flow waveforms. The UFS exhibited a temperature- and preservation solution-dependent overestimation of flow rate compared to the CFS. The CFS deviated minimally from the actual flow rate and did not require recalibration. The CFS-based MPS conformed to the preprogrammed temperature, flow, pressure, and vascular resistance settings during 6-h kidney preservation. The system was also able to accurately reproduce different pressure and flow waveforms. Conclusively, CFS-based MPS are more suitable for organ preservation than UFS-based MPS. Our CFS-based MPS provides a versatile yet robust experimental platform for testing and validating different types of clinical and experimental MPS.

With respect to elderly patients: finding kidneys in the context of new allocation concepts

The elderly have benefited from increased access to renal transplantation in recent years. New allocation concepts would shift distribution of kidneys to younger recipients, making expanded criteria and living donor kidneys more relevant for seniors. Current issues impacting expanded criteria donor kidney availability and living donor transplant opportunities for the elderly are explored. It is hoped that the kidney donor profile index will improve risk assessment and utilization of marginal kidneys. The usefulness of procurement biopsy remains controversial. Dual kidney transplantation and machine perfusion appear to be effective mechanisms to increase organ availability. "Old-for-old" allocation systems, donation service area variation and regulatory and reimbursement issues highlight disparities and disincentives affecting expanded criteria donor organ utilization, and considerations for the way forward are discussed. Living donor transplantation, even with older donors, may provide the best option for elderly recipients, and careful expansion of the living donor pool appears appropriate. In light of new allocation concepts, it will be important to understand issues pertinent to seniors and develop effective strategies to maintain or improve their access to the benefits of transplantation.

Kidney transplantation from a donor following cardiac death supported with extracorporeal membrane oxygenation

To expand the donor pool, organ donation after cardiac death (DCD) has emerged. However, kidneys from DCD donors have a period of long warm ischemia between cardiac arrest and the harvesting of the organs. Recently, we used extracorporeal membrane oxygenation (ECMO) to minimize ischemic injury during 'no touch' periods in a Maastricht category II DCD donor and performed two successful kidney transplantations. The kidneys were procured from a 49-yr-old male donor. The warm ischemia time was 31 min, and the time of maintained circulation using ECMO was 7 hr 55 min. The cold ischemia time was 9 hr 15 min. The kidneys were transplanted into two recipients and functioned immediately after reperfusion. The grafts showed excellent function at one and three months post-transplantation; serum creatinine (SCr) levels were 1.0 mg/dL and 0.8 mg/dL and the estimated glomerular filtration rates (eGFR) were 63 mL/min/1.73 m(2) and 78 mL/min/1.73 m(2) in the first recipient, and SCr levels were 1.1 mg/dL and 1.0 mg/dL and eGFR were 56 mL/min/1.73 m(2) and 64 mL/min/1.73 m(2) in the second recipient. In conclusion, it is suggested that kidney transplantation from a category II DCD donor assisted by ECMO is a reasonable modality for expanding donor pool.