Projection suggests lung waiting list mortality could be cut by a third by extending geographical sharing zones …

A 2019 paper questions why the geographic sharing zone for lungs should be limited to 250 miles in the United States, when cold ischemic time is no longer a risk factor for primary graft dysfunction or early mortality.

The United States lung allocation system (LAS) prioritizes allocation based on medical urgency and transplant benefit. Originally giving primacy to donors in the local Donor Service Agency (DSA), in 2017 the sharing zone was extended out to 250 miles.

A thought-provoking paper published this year(8) explores the intriguing question of why the sharing zone was limited to 250 miles. A microsimulation model was used to investigate the effects of extending it to 500 or even 1000 miles – and to examine what impact such broader geographic sharing zones might have on wait-list mortality.

They computed that extending the sharing zone to 500 miles could reduce wait-list mortality by 21%, and a further extension to 1000 miles could cut mortality by 32%. The potential change was greatest in patients with pulmonary fibrosis, or those urgently listed. The calculated effect on post-transplant survival was negligible. Interestingly, prolonged waiting time for stable, low-risk recipients – a likely consequence of the calculation – was not mentioned.

An accompanying editorial by Professor Tom Egan(9) added some very pertinent comments: he notes in particular that the choice of 250 miles was made because of perceived ischemic time constraints. But the Mooney paper(8) cites studies showing no effect of ischemic time from US registry data.

Egan comments that: “Since the adoption of Perfadex as a cold lung preservation solution, duration of cold ischemic time is no longer a risk factor for primary graft dysfunction or early mortality, according to ISHLT annual registry reports. Increasing the distance from the donor would increase transportation costs, but, as pointed out by Mooney et al, allocation within 1,000 miles would likely diminish waitlist deaths substantially.”

References:

8. Mooney JJ, et al, Effect of broader geographic sharing of donor lungs on lung transplant waitlist outcomes. J Heart Lung Transplant. 2019 Feb;38(2):136-144. doi: 10.1016/j.healun.2018.09.007 (link to abstract)

9. Egan TM, On broader geographic sharing of donor lungs J Heart Lung Transplant. 2019 Feb;38(2):127-129.
doi: 10.1016/j.healun.2018.11.010

Xvivo Insights PB-2019-03-26