Ex situ normothermic machine perfusion (NMP) of the liver has emerged as a dynamic preservation strategy, enabling the maintenance of metabolic activity and assessment of grafts prior to transplantation. Prolonged perfusions, however, are limited by the accumulation of metabolic waste, electrolyte imbalances, and inflammatory mediators that can compromise graft function. Continuous renal replacement therapies (CRRT), especially continuous venovenous hemodiafiltration (CVVHDF), offer a potential means to support solute clearance and homeostatic regulation during extended perfusion periods.

In this protocol, we describe a reproducible and safe method for integrating CVVHDF into an ex situ liver NMP system by connecting the filtration circuit independently from the main organ perfusion circuit. This configuration supports hemodynamic stability, helps prevent excessive intravascular pressures, and may reduce the risk of tissue edema. The physical connection, priming, and monitoring of the CRRT circuit are explained in detail, along with instructions on how to utilize a Hoffman clamp to simulate physiological venous pressure. When compared to direct in-line circuit integration, representative results suggest that the out-of-circuit approach is associated with reduced graft edema, while maintaining stable circuit pressure and solute clearance. This approach can be easily integrated into other similar perfusion devices in order to improve solute handling while maintaining stable perfusion dynamics.