Sources and prevention of graft infection during long term ex situ liver perfusion.

INTRODUCTION The use of normothermic machine liver perfusion to repair injured grafts ex situ is a hot topic. A major concern is microbial contamination in absence of a fully functional immune system ex situ. Here we report a standardized approach for maintenance of sterility during normothermic liver machine perfusion for one week in a porcine model. METHODS Porcine livers (n=42) were procured following aseptic rules and perfused with blood at 34 C°. The antimicrobial prophylaxis was adapted and improved in a step-wise manner taking into account the detected pathogens during development phase. Piperacillin-Tazobactam was applied as single doses initially and modified to continuous application in the final protocol. The perfusion machine was optimised also to recapitulate partially the host's defence system. The final protocol was tested for infection prevention during one week of perfusion. RESULTS During development phase, growth occurred in 27/39 (69%) porcine livers with a mean occurrence of growth on 4±1.6 perfusion days. The spectrum of recovered microorganisms mainly suggested an exogenous source of microbial contamination. Minimal inhibitory doses (8 mg/l) of Piperacillin-Tazobactam could be maintained only with continuous application. With continuous Piperacillin-Tazobactam application, partial recapitulation of host immune system ex situ accompanied by strict preventive measures for contact and air contamination sterility was maintained during one week of perfusion. CONCLUSION The work demonstrates feasibility of sterility maintenance for one week ex situ with normothermic liver perfusion.