Broader Geographic Sharing of Pediatric Donor Lungs Improves Pediatric Access to Transplant

Effects of broader geographic distribution of donor lungs on travel mode and estimated costs of organ procurement

On November 24, 2017, US lung transplant policy replaced donor service area with 250-nautical-mile radius as the first unit of allocation. Understanding this policy's economic impact is important, because the United States is poised to adopt the broadest feasible geographic organ distribution. All lung transplant recipients from January 1, 2015, to December 31, 2018, in the Scientific Registry of Transplant Recipients, were included. Recipients before and after November 24, 2017 were in the donor service area-first and 250-nautical-mile donor service area-free periods, respectively. Travel time was estimated using a Google application; mode was assigned as flying when driving time was longer than 60 min. Travel costs were estimated by mode and distance. Travel distance and time for organ procurement increased under the policy change. The estimated proportion of organs traveling by air increased from 61% to 76%. Estimated average costs increased by $14 051 if travel mode changed to flying, resulting in an average increase of $1264 for all transplants. Travel costs were highest for candidates <18 years and adults with high lung allocation scores. Broader geographic distribution increased estimated organ procurement costs for a small percentage of lung transplants. Further analysis should elucidate the broad economic impact of such policies.

Lung transplantation for pediatric pulmonary arterial hypertension-quo vadis?

In children with pulmonary arterial hypertension, lung transplantation illustrates a feasible treatment option once pharmacological therapy is exhausted. Timing of listing for lung transplantation in children remains difficult since hemodynamic deterioration often occurs abruptly and the time on the waiting list is usually hard to predict. Clear contraindications for lung transplantation are recent history of malignancies as well as irreversible end-organ failure. Generally, patients with pulmonary arterial hypertension in the absence of structural cardiac defects can safely undergo bilateral lung transplantation, combined heart-lung transplantation remains a procedure with a higher perioperative risk and should only be performed in selected cases with irreversible structural defects. Donor selection in recent years shows donors with extended criteria as well as lobar transplantation with good outcome, having the positive effect of broadening of the donor pool. Bridging to lung transplantation with veno-arterial ECMO treatment is feasible and has a good outcome in experienced transplant centers. Surgical considerations should include the risk of hemodynamic decompensation upon anesthesia induction and the need for extracorporeal support pre-, intra- and postoperative. Lung transplantation should be performed on veno-arterial ECMO support with either peripheral (>20 kg) or central cannulation (<20 kg). The surgical transplantation procedure includes the bronchial anastomosis as well as anastomoses of the pulmonary artery and the left atrium. Postoperative prolonged veno-arterial ECMO treatment for the immediate postoperative period allows for left ventricular remodeling given the new hemodynamic circumstances with lower pulmonary vascular resistance. Standard triple immunosuppression in most lung transplant programs currently includes steroids, mycophenolate mofetil and tacrolimus. Survival after pediatric lung transplantation for IPAH is comparable to pediatric lung transplants for other underlying diseases with a 1-year survival of approx. 80% and a 5-year survival of 64-65%. Therefore, evolving techniques in the field of lung transplantation led to overall improved survival prospects in children with end-stage pulmonary vascular disease.

Computational Eurotransplant kidney allocation simulations demonstrate the feasibility and benefit of T-cell epitope matching

The EuroTransplant Kidney Allocation System (ETKAS) aims at allocating organs to patients on the waiting list fairly whilst optimizing HLA match grades. ETKAS currently considers the number of HLA-A, -B, -DR mismatches. Evidently, epitope matching is biologically and clinically more relevant. We here executed ETKAS-based computer simulations to evaluate the impact of epitope matching on allocation and compared the strategies. A virtual population of 400,000 individuals was generated using the National Marrow Donor Program (NMDP) haplotype frequency dataset of 2011. Using this population, a waiting list of 10,400 patients was constructed and maintained during simulation, matching the 2015 Eurotransplant Annual Report characteristics. Unacceptable antigens were assigned randomly relative to their frequency using HLAMatchmaker. Over 22,600 kidneys were allocated in 10 years in triplicate using Markov Chain Monte Carlo simulations on 32-CPU-core cloud-computing instances. T-cell epitopes were calculated using the www.pirche.com portal. Waiting list effects were evaluated against ETKAS for five epitope matching scenarios. Baseline simulations of ETKAS slightly overestimated reported average HLA match grades. The best balanced scenario maintained prioritisation of HLA A-B-DR fully matched donors while replacing the HLA match grade by PIRCHE-II score and exchanging the HLA mismatch probability (MMP) by epitope MMP. This setup showed no considerable impact on kidney exchange rates and waiting time. PIRCHE-II scores improved, whereas the average HLA match grade diminishes slightly, yet leading to an improved estimated graft survival. We conclude that epitope-based matching in deceased donor kidney allocation is feasible while maintaining equal balances on the waiting list.

Kidney transplantation is the best treatment option for patients suffering permanent loss of kidney function. High degrees of histocompatibility between patients and organ donors improve long-term function of transplanted kidneys. In order to ensure fair access to transplantation whilst maximising utility of each donor kidney, organ allocation organizations established recipient waiting lists and well-balanced algorithms to allocate donors to patients. Changing the allocation algorithms requires careful consideration of side-effects to avoid disadvantages of certain groups of patients. In this study, we evaluated the feasibility of modifying the existing Eurotransplant Kidney Allocation System (ETKAS) to incorporate indirect T-cell epitope matching, a novel technique for assessing functional histocompatibility. Using Markov chain Monte Carlo simulations, we compared the modified allocation to the current algorithm and found an overall improvement of indirect T cell epitope compatibility. Simultaneously, we observed no negative impact on allocation fairness or waiting times. Our simulation framework may serve as a basis to evaluate further adjustments to ETKAS in the future. From our results, we conclude that epitope matching can be safely incorporated into ETKAS.

The Impact of Donor Asphyxiation or Drowning on Pediatric Lung Transplant Recipients

BACKGROUND

Donors with drowning or asphyxiation (DA) as a mechanism of death (MOD) are considered high risk in pediatric lung transplantation. We sought to evaluate whether recipients of DA donors had negatively impacted outcomes.

METHODS

Pediatric recipients recorded in the United Network for Organ Sharing registry between 2000 and 2019 were included. Primary stratification was donor MOD. Propensity matching with a 1:1 ratio was performed to balance the DA and non-DA MOD donor cohorts. Cox multivariable regression was used to determine the risk-adjusted impact of donor MOD. A subanalysis of the effect of lung allocation score was also evaluated.

RESULTS

A total of 1016 patients underwent bilateral lung transplantation during the study period, including 888 (85.6%) from non-DA donors and 128 (14.4%) from DA donors. Survival at 90 days, 1 year, and 2 years were similar in the matched and unmatched cohorts regardless of the donor MOD. Moreover, separate risk-adjusted analysis of drowning and asphyxiated donors was similar to other MOD donors at 30 days, 1 year, and 5 years. Similar survival findings persisted regardless of pretransplant lung allocation score. Although the rates of posttransplant stroke (1.0% versus 3.1%, P = 0.04) and the length of hospital stay (19 versus 22 d, P = 0.004) were elevated in the unmatched DA MOD recipients, these differences were mitigated after propensity matching.

CONCLUSIONS

This study evaluated the impact of DA MOD donors in pediatric lung transplant recipients and found similar rates of complications and survival in a propensity-matched cohort. These data collectively support the consideration of DA MOD donors for use in pediatric lung transplantation.

Validating thoracic simulated allocation model predictions for impact of broader geographic sharing of donor lungs on transplant waitlist outcomes

BACKGROUND

The thoracic simulated allocation model (TSAM) is used by the Scientific Registry of Transplant Recipients to predict the relative effect of organ allocation policy changes. A new lung allocation policy changing the first unit of allocation from donation service area to 250 nautical miles took effect on November 24, 2017. We studied TSAM's ability to correctly predict trends caused by changes in allocation policy.

METHODS

We compared the population characteristics from the TSAM cohort, 6,386 lung transplant candidates from 2009 to 2011, with the observed cohort of 7,601 candidates from the year before the policy change on November 24, 2017, and the year after. Simulations were run 10 times. Waitlist mortality and transplant rates were calculated and compared with observed mortality and transplant rates in the years before and after the policy change.

RESULTS

TSAM correctly predicted no change in overall waitlist mortality or transplant rates with the policy change. Observed waitlist mortality values were higher, as were transplant rates, because of increased organ donation and population change. TSAM predicted increased transplant rates for diagnosis group D (idiopathic pulmonary fibrosis), decreased rates for group A (chronic obstructive pulmonary disease), and increased rates for candidates with lung allocation score ≥50, but these changes did not occur in the waitlist and transplant populations after the policy change.

CONCLUSIONS

TSAM correctly predicted the relative trends caused by a change in allocation policy but smaller sub-group predictions were not seen.

Effect of broader geographic sharing of donor lungs on lung transplant waitlist outcomes

BACKGROUND

The United States lung allocation system prioritizes allocation based on medical urgency and benefit but does not address a federal mandate for broader geographic organ sharing. It is unknown whether broader geographic sharing of donor lungs would improve lung transplant waitlist outcomes.

METHODS

A discrete event microsimulation model simulated donor lung allocation according to different geographic lung-sharing policies, including the historic local donor service area (DSA)-based policy and hypothetical policies that prioritize candidates to donors within 500-mile or 1,000-mile geographic radii. Candidate waitlist mortality, number of transplants, and 1-year survival were compared across organ allocation policies. Waitlist mortality rates were further stratified by diagnosis, Lung Allocation Score (LAS) threshold, ABO blood type, and region.

RESULTS

Under broader geographic lung sharing, the proportion of chronic obstructive pulmonary disease transplant recipients decreased, whereas the proportion of pulmonary fibrosis recipients increased. Waitlist mortality decreased with broader geographic lung sharing with a 21.3% decrease in waitlist mortality with 500-mile lung sharing and a 31.8% decrease in waitlist mortality with 1,000-mile lung sharing. The decrease in waitlist deaths occured across all U.S. geographic regions and was greatest in candidates with pulmonary fibrosis and/or high medical urgency.

CONCLUSIONS

Broader geographic sharing of donor lungs could reduce waitlist mortality, particularly among pulmonary fibrosis and high-medical-urgency candidates.

State of the Art in Pediatric Lung Transplantation

Pediatric lung transplantation is a highly specialized therapy for end-stage pulmonary disease in children, and is performed in only a handful of transplant centers around the world. Advancement in the field has been made on many fronts in recent years, including in public policy and organ allocation strategies, donor selection and management, emerging technologies for donor lung rehabilitation and bridge-to-transplant support of listed candidates, and ongoing refinement of surgical techniques. Despite this progress, children continue to suffer discrepant waitlist mortality and longer waiting times than their adult counterparts, and face special challenges of donor availability and size matching. Here, we assess the current state of the art in pediatric lung transplantation, reviewing progress made to date and further opportunities to improve care for this unique group of patients.

High emergency organ allocation rule in lung transplantation: a simulation study

The scarcity of suitable organ donors leads to protracted waiting times and mortality in patients awaiting lung transplantation. This study aims to assess the short- and long-term effects of a high emergency organ allocation policy on the outcome of lung transplantation.

We developed a simulation model of lung transplantation waiting queues under two allocation strategies, based either on waiting time only or on additional criteria to prioritise the sickest patients. The model was informed by data from the United Network for Organ Sharing. We compared the impact of these strategies on waiting time, waiting list mortality and overall survival in various situations of organ scarcity.

The impact of a high emergency allocation strategy depends largely on the organ supply. When organ supply is sufficient (>95 organs per 100 patients), it may prevent a small number of early deaths (1 year survival: 93.7% against 92.4% for waiting time only) without significant impact on waiting times or long-term survival. When the organ/recipient ratio is lower, the benefits in early mortality are larger but are counterbalanced by a dramatic increase of the size of the waiting list. Consequently, we observed a progressive increase of mortality on the waiting list (although still lower than with waiting time only), a deterioration of patients’ condition at transplant and a decrease of post-transplant survival times.

High emergency organ allocation is an effective strategy to reduce mortality on the waiting list, but causes a disruption of the list equilibrium that may have detrimental long-term effects in situations of significant organ scarcity.

High emergency organ allocation is effective to reduce waiting list mortality when organ supply is sufficienthttp://ow.ly/KD1930fPs8I

Contemporary Issues in Lung Transplant Allocation Practices

PURPOSE OF REVIEW

To discuss the current state of donor lung allocation in the United States, and future opportunities to increase the efficiency of donor lung allocation.

RECENT FINDINGS

The current donor lung allocation system prioritizes clinical acuity by use of the Lung Allocation Score (LAS) which has reduced waitlist mortality since its implementation in 2005. Access to donor lungs can be further improved through policy changes using broader geographic sharing, and developing new technology such as ex vivo lung perfusion to recover marginal donor lungs.

SUMMARY

The number of lung transplants in the U.S. continues to increase annually. However, the demand for donor lungs continues to be outpaced by an ever growing waitlist. Efficient allocation can be achieved through improved allocation policies and new technology.

Improved waitlist and transplant outcomes for pediatric lung transplantation after implementation of the lung allocation score

BACKGROUND

Although the lung allocation score (LAS) has not been considered valid for lung allocation to children, several additional policy changes for pediatric lung allocation have been adopted since its implementation. We compared changes in waitlist and transplant outcomes for pediatric and adult lung transplant candidates since LAS implementation.

METHODS

The United Network for Organ Sharing database was reviewed for all lung transplant listings during the period 1995 to June 2014. Outcomes were analyzed based on date of listing (pre-LAS vs post-LAS) and candidate age at listing (adults >18 years, adolescents 12 to 17 years, children 0 to 11 years).

RESULTS

Of the 39,962 total listings, 2,096 (5%) were for pediatric candidates. Median waiting time decreased after LAS implementation for all age groups (adults: 379 vs 83 days; adolescents: 414 vs 104 days; children: 211 vs 109 days; p < 0.001). The proportion of candidates reaching transplant increased after LAS (adults: 52.6% vs 71.6%, p < 0.001; adolescents: 40.3% vs 61.6%, p < 0.001; children: 42.4% vs 50.9%, p = 0.014), whereas deaths on the waitlist decreased (adults: 28.0% vs 14.4%, p < 0.001; adolescents: 33.1% vs 20.9%, p < 0.001; children: 32.2% vs 25.0%; p = 0.025), despite more critically ill candidates in all groups. Median recipient survival increased after LAS for adults and children (adults: 5.1 vs 5.5 years, p < 0.001; children: 6.5 vs 7.6 years, p = 0.047), but not for adolescents (3.6 vs 4.3 years, p = 0.295).

CONCLUSIONS

Improvements in waiting time, mortality and post-transplant survival have occurred in children after LAS implementation. Continued refinement of urgency-based allocation to children and broader sharing of pediatric donor lungs may help to maximize these benefits.