Editorial Comment: Growing experience with ex vivo lung perfusion: many ways leading to the same goal

Abstract

Ex vivo lung perfusion (EVLP) has gained enormous interest, and a substantial number of lung transplant centres are using EVLP to increase the donor pool. The most widespread approach currently is the optimization and second evaluation of initially unacceptable donor organs with reversible impairments or donors after circulatory death. In this issue, the Sahlgrenska group presents an update of their experience with 5 additional cases [1] compared with the intial report from 2012 [2]. The results of this paper confirm the satisfying outcome achieved with the use of EVLP lungs. During the additional 10 months reported in this paper, 20% of all transplanted lungs were evaluated with EVLP. This represents a substantial increase in the transplant activity compared with if these lungs had all been otherwise rejected. The 100% acceptance rate after EVLP (with the exception of two single lungs while still using the contralateral side) suggests a careful preselection of EVLP cases. There are several different technical EVLP solutions available on the market, and there are distinct differences in the way EVLP is performed and in the interpretation of results obtained during EVLP. To accept a lung after EVLP, the Sahlgrenska group relies on a single measurement of venous pO2 and functional parameters if the initial values are fine. Due to variabilities in gas flow to the deoxygenator and differences in the oxygen content in the inflow, the pO2 difference between the arterial inflow and venous outflow (ΔpO2) is used by the majority of centres to judge oxygenation on EVLP. Using venous pO2 as the main parameter blinds out this potentially valuable additional information and might be insufficient to completely assess the oxygenation capacity; however, no direct comparison between these two parameters has been performed in the clinical setting. The largest EVLP experience so far has been reported by centres using acellular Steen solution [3–6] with consistent results regarding the recipient outcome. In contrast to this, the Sahlgrenska group advocates the use of red cells in addition to the Steen solution with a haematocrit of 10–15%. So far, it remains unclear if the initial oxygenation measurements obtained on EVLP directly correspond with the values obtained in the donor. Since absolute oxygen values in an acellular solution are not equal to the values obtained in the donor, the development of functional parameters and oxygenation levels during EVLP are additional major parameters in deciding about the acceptance of a lung. If the addition of red cells enhances the direct comparability to the donor is unclear and the interpretation of a single measurement of the venous pO2 seems doubtful. If the first measurement is already satisfying and the authors speculate on direct comparability with the donor, there is a high likelihood that the increase in pO2 is rather due to a full recruitment than a true improvement. In this aspect, EVLP could be seen as a rather time-consuming and sophisticated method for what could have been easily achieved by further optimization in the donor. No detailed figures on the comparability between donor and recipient values are provided in the current paper. Even though the clinical results are convincing, there are still questions remaining on the exact interpretation of the results that might receive answers once higher patient numbers have been recruited. It is very exciting to see the different ways in which EVLP is developing and to compare the advantageous aspects of individual approaches. EVLP has the potential to completely alter our current practice of organ preservation, serve as a platform for a multitude of therapeutic interventions and improve outcome after lung transplantation.