Machine Perfusion of Donation After Circulatory Death Liver and Lungs Before Combined Liver-lung Transplantation

Normothermic Machine Perfusion Systems: Where Do We Go From Here?

Normothermic machine perfusion (NMP) aims to preserve organs ex vivo by simulating physiological conditions such as body temperature. Recent advancements in NMP system design have prompted the development of clinically effective devices for liver, heart, lung, and kidney transplantation that preserve organs for several hours/up to 1 d. In preclinical studies, adjustments to circuit structure, perfusate composition, and automatic supervision have extended perfusion times up to 1 wk of preservation. Emerging NMP platforms for ex vivo preservation of the pancreas, intestine, uterus, ovary, and vascularized composite allografts represent exciting prospects. Thus, NMP may become a valuable tool in transplantation and provide significant advantages to biomedical research. This review recaps recent NMP research, including discussions of devices in clinical trials, innovative preclinical systems for extended preservation, and platforms developed for other organs. We will also discuss NMP strategies using a global approach while focusing on technical specifications and preservation times.

Geographic disparities in access to liver transplantation

Since the Final Rule regarding transplantation was published in 1999, organ distribution policies have been implemented to reduce geographic disparity. While a recent change in liver allocation, termed acuity circles, eliminated the donor service area as a unit of distribution to decrease the geographic disparity of waitlisted patients to liver transplantation, recently published results highlight the complexity of addressing geographic disparity. From geographic variation in donor supply, as well as liver disease burden and differing model for end-stage liver disease (MELD) scores of candidates and MELD scores necessary to receive liver transplantation, to the urban-rural disparity in specialty care access, and to neighborhood deprivation (community measure of socioeconomic status) in liver transplant access, addressing disparities of access will require a multipronged approach at the patient, transplant center, and national level. Herein, we review the current knowledge of these disparities-from variation in larger (regional) to smaller (census tract or zip code) levels to the common etiologies of liver disease, which are particularly affected by these geographic boundaries. The geographic disparity in liver transplant access must balance the limited organ supply with the growing demand. We must identify patient-level factors that contribute to their geographic disparity and incorporate these findings at the transplant center level to develop targeted interventions. We must simultaneously work at the national level to standardize and share patient data (including socioeconomic status and geographic social deprivation indices) to better understand the factors that contribute to the geographic disparity. The complex interplay between organ distribution policy, referral patterns, and variable waitlisting practices with the proportion of high MELD patients and differences in potential donor supply must all be considered to create a national policy strategy to address the inequities in the system.

Utilization of livers donated after circulatory death for transplantation - An international comparison

BACKGROUND & AIMS

Liver graft utilization rates are a hot topic due to the worldwide organ shortage and the increasing number of transplant candidates on waiting lists. Liver perfusion techniques have been introduced in several countries, and may help to increase the organ supply, as they potentially enable the assessment of livers before use.

METHODS

Liver offers were counted from donation after circulatory death (DCD) donors (Maastricht type III) arising during the past decade in eight countries, including Belgium, France, Italy, the Netherlands, Spain, Switzerland, the UK, and the US. Initial type-III DCD liver offers were correlated with accepted, recovered and implanted livers.

RESULTS

A total number of 34,269 DCD livers were offered, resulting in 9,780 liver transplants (28.5%). The discard rates were highest in the UK and US, ranging between 70 and 80%. In contrast, much lower DCD liver discard rates, e.g. between 30-40%, were found in Belgium, France, Italy, Spain and Switzerland. In addition, we observed large differences in the use of various machine perfusion techniques, as well as in graft and donor risk factors. For example, the median donor age and functional donor warm ischemia time were highest in Italy, e.g. >40 min, followed by Switzerland, France, and the Netherlands. Importantly, such varying risk profiles of accepted DCD livers between countries did not translate into large differences in 5-year graft survival rates, which ranged between 60-82% in this analysis.

CONCLUSIONS

Overall, DCD liver discard rates across the eight countries were high, although this primarily reflects the situation in the Netherlands, the UK and the US. Countries where in situ and ex situ machine perfusion strategies were used routinely had better DCD utilization rates without compromised outcomes.

IMPACT AND IMPLICATIONS

A significant number of Maastricht type III DCD livers are discarded across Europe and North America today. The overall utilization rate among eight Western countries is 28.5% but varies significantly between 18.9% and 74.2%. For example, the median DCD-III liver utilization in five countries, e.g. Belgium, France, Italy, Switzerland, and Spain is 65%, in contrast to 24% in the Netherlands, UK and US. Despite this, and despite different rules and strategies for organ acceptance and preservation, 1- and 5-year graft survival rates remain fairly similar among all participating countries. A highly varying experience with modern machine perfusion technology was observed. In situ and ex situ liver perfusion concepts, and application of assessment tools for type-III DCD livers before transplantation, may be a key explanation for the observed differences in DCD-III utilization.

The use of normothermic liver preservation in combined liver and lung transplantation: A single-center experience

Combined liver and lung transplantation (CLLT) is indicated in patients with both end-stage liver and lung disease. Ex-situ normothermic machine perfusion (NMP) has been previously used for extended normothermic lung preservation in CLLT. We aim to describe our single-center experience using ex-situ NMP for extended normothermic liver preservation in CLLT. Four CLLTs were performed from 2019 to 2020 with the lung transplanted first for all patients. Median ex-situ pump time for the liver was 413 min (IQR 400-424). Over a median follow-up of 15 months (IQR 14-19), all patients were alive and doing well. Normothermic extended liver preservation is a safe method to allow prolonged cold ischemia using normothermic perfusion of the liver during CLLT.

Ex situ machine preservation of donor livers for transplantation: HOPE for all?

Hypothermic oxygenated machine perfusion (HOPE) reduces ischaemia–reperfusion injury of donor livers and thereby improves outcomes after transplantation. End-ischaemic normothermic machine perfusion (NMP) enables assessment of hepatobiliary viability and selection of livers that would otherwise have been declined for transplantation. We advocate the combined use of (dual) HOPE and NMP for livers that are considered high risk, but may still be transplanted safely after ex situ resuscitation and assessment of hepatobiliary viability. Combined dual HOPE–NMP has the potential to substantially decrease the high rates of deceased donor liver discard.