How Much Is Too Much? Determining the Optimal Oxygen Concentration for Early Hypothermic Oxygenation of Liver Grafts in Rodents

Introduction: Ischaemia is inevitable during organ preservation and contributes to graft dysfunction after liver transplantation. Early oxygenation of grafts during organ preservation, such as oxygenated washout (OW), has been shown to reduce ischaemic injury. However, the optimal oxygen concentration for OW is unknown. Hyper-oxygenation can induce reactive oxygen species and graft injury. This study compared non-oxygenated preservation with moderate and high oxygen concentrations during OW in rat livers. Methods: Donation after circulatory death livers were procured from 10 rats. Grafts were randomised to three groups: control (non-oxygenated University of Wisconsin Solution (UW)), moderate concentration OW (Mod-OW) (25-28mg dissolved oxygen/L) and high concentration OW(High-OW) (>50mg dissolved oxygen/L). Livers were flushed and stored at 4℃. After 24 hours of cold storage, livers were placed on isolated liver-reperfusion (ILRP) for 120 minutes. Dissolved oxygen in preservation fluid was measured throughout cold storage. Tissue ATP, as a marker of graft viability, was measured at 0, 6 and 24H cold storage, and after ILRP. Liver biochemistry and graft oxygen consumption were measured during ILRP. Results: The control group had lower dissolved oxygen in the preservation fluid than OW groups at 0H and 6H (all p<0.05) (Figure 1A-B). Tissue ATP was similar between groups at 0H. By 6H, grafts in the Mod-OW group had greater tissue ATP than the High-OW group (15.7 vs 8.4 ug/mg, p = 0.01) (Figure 1C). After 24H cold storage, preservation fluid oxygenation and tissue ATP were similar between all groups. During 120 minutes ILRP, the mean oxygen consumption of the Mod-OW group was greater than the High-OW group (47.2 vs 24.4 uL/min/g-liver, p = 0.048) (Figure 1D). No difference in liver biochemistry was observed (Figure 1E-F). Conclusion: Rat livers receiving Mod-OW had increased tissue viability at 6h and oxygen consumption on ILRP compared to High-OW. Our findings suggest that high oxygen concentrations may lead to reduced graft viability. Although OW may be beneficial for organ preservation, oxygen concentrations should be closely monitored to prevent hyper-oxygenation.