A. M. Jacques1,2, M. Crawford1,2, G. M. McCaughan1,2, C. Pulitano1,2 1Royal Prince Alfred Hospital,Transplantation Surgery,Sydney, NSW, Australia 2University of Sydney,Faculty Of Health And Medicine,Sydney, NSW, Australia
Introduction:
The shortage of quality donor organs has resulted in the widespread use of sub-optimal livers in clinical transplantation. Marginal grafts are particularly susceptible to injury after procurement during the period of static cold storage. Normothermic machine perfusion (NMP), where metabolic activity is maintained, is a potential alternative to impove the preservation of marginal grafts. If the safe preservation of metabolically active grafts can be extended for multiple days, an opportunity arises to introduce therapeutic agents and further optimise these organs. The accumulation of metabolic waste, however, limits the current utilisation of NMP beyond 24 hours. It is the aim of this study to evaluate the technical feasibility of prolonged (5-day) normothermic perfusion of discarded liver grafts with modifications to our current NMP system.
Methods:
Six discarded human liver grafts were perfused for 120 hours after the development of a newly adopted perfusion system incorporating: 1) long-life oxygenators; 2) a dialysis membrane; and 3) continuous parenteral nutrition. Perfusate volume consisted of packed red blood cells, fresh frozen plasma, concentrated albumin and crystalloid. In addition to homogenous perfusion and stable vascular flows, the viability of the grafts was assessed at 4 hours, and then every 24 hours for five days using: 1) maintenance of pH; 2) lactate <2.5mmol/L; 3) production of bile; and 4) biliary pH >7.4. Hepatocellular injury, protein synthesis, and clearance of water-soluble by-products were assessed using alanine transferase (ALT), coagulation factor V and urea levels respectively.
Results:
Five of six livers met all viability criteria after 72 hours, and three of six at 120 hours. One organ failed to reach viability criteria at all time points. Two livers initially failed to meet criteria due an inability to produce alkaline bile that that resolved over the perfusion duration. Five of six livers demonstrated a down-trending ALT after a peak within 24 hours. Initially low levels of factor V increased to >75% in five of six livers during perfusion. Clearance of water-soluble metabolic by-products was evident by a stable urea concentration from day 1 to 5 across all grafts. Macroscopic pressure necrosis was evident to varying extents in all grafts at the conclusion of perfusion. Two grafts demonstrated macroscopic evidence of fungal infection.
Conclusion:
This study sucessfully demonstrates the technicaly feasibility of preserving metabolically active human livers for 5 days using NMP. The sensitivity of current real-time viability criteria, however, have significant limitations that create challenges in the assessment of therapeutic agents that may be introduced in the future. Prior to this approach transitioning to clinical transplantation the validation of alternative viability criteria and alternative strategies to overcome both pressure necrosis and infection must be overcome.