The Past, Present, and Near Future of Lung Allocation in the United States

The first official donor lung allocation system in the United States was initiated by the United Network of Organ Sharing in 1990. The initial policy for lung allocation was simple with donor lungs allocated based on ABO match and the amount of time the candidates accrued on the waiting list. Donor offers were first given to candidates' donor service area. In March 2005, the implementation of the lung allocation score (LAS) was the major change in organ allocation. International adoption of the LAS-based allocation system can be seen worldwide.

The new allocation era and policy

Since the Department of Health and Human Services (DHHS) issued the Final Rule in 1998 as a guideline for organ transplantation and allocation policies, the lung allocation system has undergone two major changes. The first change came with the implementation of the lung allocation score (LAS) instead of waiting time as the primary determinant for donor lung allocation. The LAS model helped allocate donor lungs based on medical urgency and likelihood of post-transplant success. The LAS has been successful in prioritizing the sickest candidates and reducing waitlist mortality in line with the Final Rule mandates. However, the LAS model did not address geographic variability in donor lung supply and demand, leading to disparities in waiting list survival based on a patient’s listing location, which was inconsistent with the Final Rule. In an urgent response to a lawsuit filed by a patient demanding broader geographic access to lungs in November 2017, the second major change in lung allocation occurred when the primary allocation unit for donor lungs expanded from the local donation service area (DSA) to a 250-nautical mile radius around the donor hospital. The Organ Procurement and Transplantation Network has since undergone a review of the current organ allocation systems and has approved a continuous organ distribution framework to guide the creation of a new organ allocation system without rigid geographic borders. In this review, we will describe the history of lung allocation, the changes to the allocation system and their consequences, and the potential future of lung allocation policy in the U.S.

Outcomes following lung re-transplantation in patients with cystic fibrosis

PURPOSE

We examined cystic fibrosis (CF) patients and compared their clinical status at the time of primary versus double lung re-transplantation (re-DLTx) in order to better understand lung retransplant practice patterns.

METHODS

We performed a retrospective analysis of the UNOS Database identifying CF patients ≥18 years old undergoing re-DLTx (5/4/2005 and 12/4/2020). Baseline and clinical variables at the primary and re-DLTx were compared utilizing the paired student t-test. Graft survival was defined as time from surgery to retransplant and analyzed using Kaplan-Meier estimates.

RESULTS

277 CF patients who underwent re-DLTx experienced a significantly worse 5-year survival when compared to the primary DLTx cohort (47.9% vs 58.8%, p = 0.00012). The following differences were observed comparing CF re-DLTx group to their primary DLTx: higher LAS score at the time of listing (50.66 vs 42.15, p < 0.001) and transplant (62.19 vs 48.20, p < 0.001), and increase LAS from the time of listing to transplant (+12.22 vs +7.23, p = 0.002). While serum albumin and total bilirubin were similar, CF patients had a higher creatinine (1.05 vs 0.74, p < 0.001), dialysis (4.4% vs 0.6%, p < 0.001), ECMO bridge to transplant rates (7.6% vs 4.0%, p < 0.001), and higher oxygen requirements (5.95 vs 3.93, p < 0.001) at the time of listing for a re-DLTx.

CONCLUSION

Compared to their initial transplant, CF patients experience significant clinical decline in renal, cardiac, and pulmonary function at the time of lung retransplantation. This may indicate that an earlier evaluation and rehabilitation process may be necessary to identify patients earlier for lung retransplantation prior significant clinical decline.

A revealed preference analysis to develop composite scores approximating lung allocation policy in the U.S

BACKGROUND

The patient ranking process for donor lung allocation in the United States is carried out by a classification-based, computerized algorithm, known as the match system. Experts have suggested that a continuous, points-based allocation framework would better serve waiting list candidates by removing hard boundaries and increasing transparency into the relative importance of factors used to prioritize candidates. We applied discrete choice modeling to match run data to determine the feasibility of approximating current lung allocation policy by one or more composite scores. Our study aimed to demystify the points-based approach to organ allocation policy; quantify the relative importance of factors used in current policy; and provide a viable policy option that adapts the current, classification-based system to the continuous allocation framework.

METHODS

Rank ordered logistic regression models were estimated using 6466 match runs for 5913 adult donors and 534 match runs for 488 pediatric donors from 2018. Four primary attributes are used to rank candidates and were included in the models: (1) medical priority, (2) candidate age, (3) candidate's transplant center proximity to the donor hospital, and (4) blood type compatibility with the donor.

RESULTS

Two composite scores were developed, one for adult and one for pediatric donor allocation. Candidate rankings based on the composite scores were highly correlated with current policy rankings (Kendall's Tau ~ 0.80, Spearman correlation > 90%), indicating both scores strongly reflect current policy. In both models, candidates are ranked higher if they have higher medical priority, are registered at a transplant center closer to the donor hospital, or have an identical blood type to the donor. Proximity was the most important attribute. Under a points-based scoring system, candidates in further away zones are sometimes ranked higher than more proximal candidates compared to current policy.

CONCLUSIONS

Revealed preference analysis of lung allocation match runs produced composite scores that capture the essence of current policy while removing rigid boundaries of the current classification-based system. A carefully crafted, continuous version of lung allocation policy has the potential to make better use of the limited supply of donor lungs in a manner consistent with the priorities of the transplant community.

Veno-venous extracorporeal membrane oxygenation bridged living-donor lung transplantation for rapid progressive respiratory failure with pleuroparenchymal fibroelastosis after allogeneic hematopoietic stem cell transplantation

Cases of extracorporeal membrane oxygenation (ECMO) bridged lung transplantation (LTx) are rare in Japan because an allocation system to prioritize patients based on urgency remains to be established. For critically ill patients who cannot wait for a brain-dead donor LTx, ECMO bridge to living-donor LTx may be the only practical option. A 21-year-old woman with pleuroparenchymal fibroelastosis after hematopoietic stem cell transplantation was admitted to our hospital with rapidly progressive respiratory failure. She was waitlisted for 6 months before admission, but veno-venous ECMO was initiated. She was transported under ECMO support via a jet plane and underwent successful living-donor LTx.