Compare Apples to Apples

Although ex vivo lung perfusion (EVLP) has been around since the early 2000s, its clinical use did not become widespread until 2011 with the landmark publication of Cypel et al.1 Since then, there have been several studies that show that EVLP can increase the donor pool for transplantation programs, as well as provide extended evaluation time to give providers more comfort and transplanting potential lung allograft.2,3 And what was originally thought of as science fiction, these organs are now procured and transported to third-party perfusion centers,4,5 in which they undergo evaluation by perfusion experts, and transplant providers can access minute-by-minute data concerning oxygenation, compliance, and pulmonary artery, as well as left atrial pressures to determine suitability for transplantation as a potential donor allograft candidate. Although EVLP use in donation after brain death (DBD) donors is widely accepted, its role in donation after circulatory death (DCD) allografts is less certain.2 Additionally, because external perfusion centers are relatively new, the literature on their overall effectiveness and outcomes regarding US transplants is sparse.4,5 Alzahrani et al in their most recent publication6 answered several important and extremely clinically relevant questions regarding EVLP and its further expansion and use across the United States. Notably, they characterize current DCD use within the United States, which, according to their study, accounts for ~32% of non-EVLP transplants, 30%–40% of EVLP performed by hospitals, as well as about 30% through external perfusion centers. This is a significant increase in DCD transplants, which only a few years ago accounted for about 5% of total transplants.7 This adoption speaks to the increase in comfortability of current transplant providers and the evolution of donor care throughout the United States. Although several studies have questioned outcomes with DCD EVLP transplants,8 this study includes a propensity score matching, which is based on several extended criteria donor (ECD) characteristics to include Center of Disease Control high risk and on chest x-rays, bronchoscopies, as well as donor pO2. Previous studies have not considered ECD criteria for propensity score matching, and when comparing EVLP and DCD transplants to a standard DBD cohort, they missed the mark on a true comparison. These studies compare apples to oranges when analyzing EVLP transplants, which overlooks EVLP’s main role in evaluating potential ECD allografts against a standard donor static cold storage (SCS) cohort. Importantly, Alzahrani et al again confirmed no difference between short-term or long-term survival between standard DCD and DCD EVLP allografts. Although there is an increase in short-term morbidity noted in several studies,2,3 Alzahrani et al importantly demonstrated through multivariable adjustment that there is no relationship between EVLP and primary graft dysfunction incidence. Perhaps the biggest hurdle of EVLP to overcome is evaluating allografts that are truly extended criterion in today’s day and age and selecting the appropriate donor for transplantation to make postoperative outcomes truly equal to standard donors. Although this study shows DCD and DCD EVLP allografts, when matched for appropriate ECD criteria, are equivalent in terms of survival—it does not evaluate DCD EVLP versus DBD in a matched cohort to determine to a higher standard if this subsection of allografts is equivocal, or at least in terms of survival, for recipients. Further studies will be needed to clarify this relationship, which is of great importance currently to the transplantation community. The next evolution of the EVLP, and the current area of focus, is the further continuation and expansion of external perfusion centers, which can overcome some of the logistic barriers that smaller transplant programs face when wishing to adopt EVLP into their current practice. Although the United Network for Organ Sharing (UNOS) database has been collecting data on who and where these allografts have been perfused since 2018, it was not until recently that this practice has been explored within UNOS database studies.5,9,10 It is important to first clarify how these variables are reported within the UNOS database. First, one can determine where the organ was perfused: donor hospital, organ procurement organization, transplant hospital, or external perfusion center. Second, one can also determine who perfused the organ, organ procurement organization, transplant program, or an external perfusion center. Finally, one can determine whether the organ numbers were received on SCS after EVLP or received on the pump. Using a combination of clinical knowledge, as well as how the organ was received (on SCS or on pump10), one can determine whether it is a portable platform or a static platform. It is extremely important to clarify that one cannot determine with exactness what platform was used or what perfusate type was used. Therefore, it may be too big of a reach to state that these mobile EVLP transplants were all blood-based or designated a certain platform, as well as insinuating an acellular perfusate/close left atrium with the hospital-based EVLP. Ultimately, it is important to review these results within the context that the UNOS database is not granular, and additional multicenter studies are needed to determine the optimal perfusion, procurement, and preservation strategies for the type of donor assessed. However, this study still gives valuable insight into hospital-based and external perfusion center-based perfusion. Currently, there is no noticeable difference at 3 y between unadjusted survival for all procurement/perfusion techniques, as noted in Figure 4. Although in Figure 5 with the DCD subanalysis, there is no statistically significant difference, there seems to be a large difference in external perfusion center EVLP compared with hospital-based/mobile EVLP even at 1 y and extending to 3 y. Clearly, further studies are needed to clarify this relationship and additional propensity score–matched analysis. As a final parting thought, it ultimately falls on the transplant centers and data abstractors of the UNOS database to accurately and adequately communicate posttransplant outcomes and morbidity mortality of the several different procurement and perfusion techniques that dominate lung transplant today. It is of the utmost importance to compare apples to apples and oranges to oranges to adequately convey contemporary EVLP and DCD practices and outcomes so that we all may make transplantation a viable and equitable therapy for all.