A Modular Simulation Framework for Organ Allocation

BACKGROUND

We describe and validate a new simulation framework addressing important limitations of the Simulated Allocation Models (SAMs) long used to project population effects of transplant policy changes.

METHODS

We developed the Computational Open-source Model for Evaluating Transplantation (COMET), an agent-based model simulating interactions of individual donors and candidates over time to project population outcomes. COMET functionality is organized into interacting modules. Donors and candidates are synthetically generated using data-driven probability models which are adaptable to account for ongoing or hypothetical donor/candidate population trends and evolving disease management. To validate the first implementation of COMET, COMET-Lung, we attempted to reproduce lung transplant outcomes for U.S. adults from 2018-2019 and in the six months following adoption of the Composite Allocation Score (CAS) for lung transplant.

RESULTS

Simulated (median [Interquartile Range, IQR]) versus observed outcomes for 2018-2019 were: 0.162 [0.157, 0.167] versus 0.170 waitlist deaths per waitlist year; 1.25 [1.23, 1.28] versus 1.26 transplants per waitlist year; 0.115 [0.112, 0.118] versus 0.113 post-transplant deaths per patient year; 202 [102, 377] versus 165 nautical miles travel distance. The model accurately predicted the observed precipitous decrease in transplants received by type O lung candidates in the six months following CAS implementation.

CONCLUSIONS

COMET-Lung closely reproduced most observed outcomes. The use of synthetic populations in the COMET framework paves the way for examining possible transplant policy and clinical practice changes in populations reflecting realistic future states. Its flexible, modular nature can accelerate development of features to address specific research or policy questions across multiple organs.

A Population Health Approach to Transplant Access: Challenging the Status Quo

Transplant referral and evaluation are critical steps to waitlisting yet remain an elusive part of the transplant process. Despite calls for more data collection on pre-waitlisting steps, there are currently no national surveillance data to aid in understanding the causes and potential solutions for the extreme variation in access to transplantation. As population health scientists, epidemiologists, clinicians, and ethicists we submit that the transplant community has an obligation to better understand disparities in transplant access as a first necessary step to effectively mitigating these inequities. Our position is grounded in a population health approach, consistent with several new overarching national policy and quality initiatives. The purpose of this Perspective is to (1) provide an overview of how a population health approach should inform current multisystem policies impacting kidney transplantation and demonstrate how these efforts could be enhanced with national data collection on pre-waitlisting steps; (2) demonstrate the feasibility and concrete next steps for pre-waitlisting data collection; and (3) identify potential opportunities to use these data to implement effective population-level interventions, policies, and quality measures to improve equity in access to kidney transplantation.

A comparison between combined liver kidney transplants to liver transplants alone: A systematic review and meta-analysis

BACKGROUND

Since the introduction of the Model for End-stage Liver disease criteria in 2002, more combined liver kidney transplants are performed. Until 2017, no standard allocation policy for combined liver kidney transplant (CLKT) was available and each transplant center decided eligibility for CLKT or liver transplant alone (LTA) on a case-by-case basis. The aim of this systematic review was to compare the clinical outcomes of CLKT compared to LTA in patients with renal dysfunction.

METHODS

Databases were systematically searched for studies published between January 2010 and March 2021. Outcomes were expressed as risk ratios and pooled with a random-effects model. The primary outcome was patient survival.

RESULTS

Four studies were included. No differences were observed for mortality risk at 1 year (risk ratio (RR) 1.03 [confidence interval (CI) 0.97-1.09], 3 years (RR 1.06 [CI 0.99-1.13]) and 5 years (RR 1.08 [CI 0.98-1.19]). The risk of graft loss was similar in the first year (RR 1.10 [CI 0.93-1.30], while 3-year risk of graft loss was significantly lower in CLKT patients (RR 1.15 [CI 1.08-1.24]).

CONCLUSIONS

CLKT has similar short-term graft and patient survival as LTA in patients with renal dysfunction. More data is needed to decide from which KDIGO stage patients benefit the most from CLKT.

Attitudes, knowledge, and preferences of the Israeli public regarding the allocation of donor organs for transplantation

Background

There is a stark disparity between the number of patients awaiting deceased-donor organ transplants and the rate at which organs become available. Though organs for transplantation are assumed to be a community resource, and the organ supply depends on public willingness to donate, current allocation schemes do not explicitly incorporate public priorities and preferences. This paper seeks to provide insights regarding the Israeli public’s preferences regarding criteria for organ (specifically, kidney) allocation, and to determine whether these preferences are in line with current allocation policies.

Methods

A market research company administered a telephone survey to 604 adult participants representing the Jewish-Israeli public (age range: 18–95; 50% male). The questionnaire comprised 39 questions addressing participants’ knowledge, attitudes, and preferences regarding organ donation and criteria for organ allocation, including willingness to donate.

Results

The criteria that respondents marked as most important in prioritizing waitlist candidates were maximum medical benefit (51.3% of respondents) and waiting time (21%). Donor status (i.e., whether the candidate is registered as an organ donor) was ranked by 43% as the least significant criterion. Most participants expressed willingness to donate the organs of a deceased relative; notably, they indicated that they would be significantly more willing to donate if organ allocation policies took their preferences regarding allocation criteria into account. Unlike individuals in other countries (e.g., the UK, the US, and Australia) who responded to similar surveys, Israeli survey respondents did not assign high importance to the candidate’s age (24% ranked it as the least important factor). Interestingly, in some cases, participants’ declared preferences regarding the importance of various allocation criteria diverged from their actual choices in hypothetical organ allocation scenarios.

Conclusions

The findings of this survey indicate that Israel’s citizens are willing to take part in decisions about organ allocation. Respondents did not seem to have a strict definition or concept of what they deem to be just; yet, in general, their preferences are compatible with current policy. Importantly, participants noted that they would be more willing to donate organs if their preferences were integrated into the allocation policy. Accordingly, we propose that allocation systems must strive to respect community values and perceptions while maintaining continued clinical effectiveness.

Current allocation policy is favorable for patients with hepatocellular carcinoma waiting for liver transplantation

BACKGROUND

Patients with hepatocellular carcinoma (HCC) are a growing population of the transplantation waiting list (WL) for orthotopic liver transplantation (OLT). There is no consensus to prioritize these patients while on the WL.

AIMS

To assess whether patients with HCC were more prioritized than non-HCC patients based on their WL survival as primary outcome.

METHODS

Restrospective cohort study including patients listed for elective OLT from January 2013 to January 2016.

RESULTS

165 patients with cirrhosis were listed for OLT: 64 in the HCC group (38.78%) and 101 in the non-HCC group (61.22%). Outcomes (HCC vs. non-HCC) were: OLT in 75.51% vs. 64.37%; death or dropout due to worsening in 20.41% vs. 27.59%, and delisting because of improvement in 4.08% vs. 8.05%. HCC patients had a significantly higher WL survival rate (HR = 0.45; 95% CI: 0.21-0.96); lower MELD score at transplantation (21 [20-24] vs. 24 [20-30]; p = 0.021); higher delta-MELD - the difference between MELD at transplantation and MELD at listing time - (3 [2-6] vs. 0 [0-5]; p = 0.024) and longer waiting time until OLT (143 [70-233] vs. 67 [21-164] days; p = 0.008).

CONCLUSION

Despite having to wait longer, patients with HCC showed higher WL survival than non-HCC patients.

Current status and perspectives in split liver transplantation

Growing experience with the liver splitting technique and favorable results equivalent to those of whole liver transplant have led to wider application of split liver transplantation (SLT) for adult and pediatric recipients in the last decade. Conversely, SLT for two adult recipients remains a challenging surgical procedure and outcomes have yet to improve. Differences in organ shortages together with religious and ethical issues related to cadaveric organ donation have had an impact on the worldwide distribution of SLT. Despite technical refinements and a better understanding of the complex liver anatomy, SLT remains a technically and logistically demanding surgical procedure. This article reviews the surgical and clinical advances in this field of liver transplantation focusing on the role of SLT and the issues that may lead a further expansion of this complex surgical procedure.