*Purpose: Identifying good quality grafts within the donor pool, ex vivo lung perfusion (EVLP) opens another window to evaluate grafts initially declined with marginal quality and allows potentially safe transplantation of those grafts. Dynamic graft assessments are available during EVLP, however, no reliable biological indicators exist. Oxidative stress is involved in development of various organ diseases and triggers inflammatory cascade which affects posttransplant outcomes. Thus, we performed noninvasive reactive oxygen species (ROS) detection in perfusate during EVLP to assess graft oxidative status and analyze how it may impact donor graft viability.

*Methods: Cases of clinical EVLP performed at our institute between September 2017 and April 2019 were included. The perfusate samples during EVLP were collected and analyzed by electron paramagnetic resonance (EPR) to detect circulating ROS. CMH. Hydrochloride was used as an EPR spin probe. EPR spectra were recorded using a Bruker X-band EMX premiumX spectrometer. All data were compared between lungs accepted or declined for transplantation on EVLP.

*Results: 32 cases of EVLP were performed in the study term and the data of 22 cases were available for analysis. Out of 22 lungs, 15 were transplanted (conversion rate: 68.1%). No significant difference was observed on the absolute value of physiologic parameters and their changes with time between transplanted and declined lungs. However, there was significant difference in PaO2/FiO2 and lab analysis for perfusate showed glucose consumption and lactate production of declined lungs were significantly higher than those of accepted lungs. Also, markedly higher EPR signal increase was detected in the perfusate from declined lungs compared to those from accepted lungs, and these data had positive correlation with lactate production (R²=0.306, p=0.011).

*Conclusions: The assessment of oxidative status of grafts on EVLP using EPR spectroscopy suggested that declined lungs had higher oxidative stress. This may induce graft damage and edema thus leading to an unacceptable EVLP lung. Future interventions addressing inherent oxidative stress may afford improved graft condition during EVLP thereby potentially leading to successful lung transplantation.

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