Extracorporeal albumin dialysis

Patients with liver failure still present a high mortality. It can only be significantly improved by the rare resource of liver transplantation. Extracorporeal liver support devices have been developed to temporarily support liver detoxification. Artificial devices without hepatocytes ("liver dialysis" or "albumin dialysis") are already widely used in Europe. The two best-known systems, MARS and Prometheus, use a different technical approach to remove water-soluble as well as albumin-bound toxins from the blood. In MARS, toxins diffuse along a concentration gradient through an albumin-impermeable membrane into a secondary circuit that is pre-filled with an albumin solution. The albumin is continuously "recycled" inside the secondary circuit by different adsorber and low flux dialysis. In contrast, Prometheus includes an albumin-permeable filter allowing separation of the albumin fraction into the secondary circuit where the albumin-bound toxins are directly removed by two adsorbers. Thereafter, high flux dialysis is performed inside the primary circuit. For both extracorporeal systems, an improvement of hepatic encephalopathy and biochemical markers such as bilirubin is consistently reported. In-vivo comparisons of both systems showed significantly higher extraction capacities for protein-bound and water-soluble substances under Prometheus than under MARS treatment. Possible pathophysiological mechanisms could be a reduction of portal pressure or a removal of vasoactive cytokines. However, only few randomised controlled trials with low patient numbers and conflictive results regarding patient survival exist. Nevertheless, a Cochrane meta-analysis revealed a significant survival benefit for extracorporeal liver support devices in patients with acute-on-chronic liver failure. Other promising indications are severe refractory cholestatic pruritus, intoxication with protein-bound substances and graft dysfunction after liver transplantation. As large randomised controlled multi-center trials are currently underway, better evidence will be available soon to define the clinical role of extracorporeal liver support devices.