[Liver support systems today]

Abstract

Liver failure carries a high mortality, both the acute type with no pre-existing liver disease (acute liver failure) and the acute decompensation superimposed on a chronic liver disorder (acute on chronic liver failure). Today, liver transplantation still represents the only curative treatment for liver failure due to end-stage liver diseases. Donor organ shortage is still the major limitation and many patients die while awaiting transplantation. Due to the scarcity of donor organs, liver support technologies are being developed to support patients with severe liver failure until either an organ becomes available for transplantation or their livers recover from injury. Early devices including hemodialysis, hemoperfusion, exchange transfusion, cross-hemodialysis, cross-circulation and plasmapheresis appeared inefficient. In the present day, liver support systems' designs fall into two main categories: cell-based, so-called bioartificial and non-cell-based, also known as artificial systems. Bioartificial liver support systems use either porcine hepatocytes or human hepatoma cell lines housed within a hollow-fiber bioreactor. The system perfuses the patient's whole blood or separated plasma through the luminal space in the bioreactor. Theoretically, these methods should optimally resemble normal hepatic tissue structure and function. However, the existing bioartificial systems are far from ideal solution in terms of immunological, infectological, oncological and financial problems and must still be thought of as experimental. The artificial systems are already available for the clinicians in limited quantities. These non-cell-based devices are intended to remove protein-bound and water-soluble toxins without providing synthetic function, which can be partially replaced with substitution of the failing substances (plasma proteins, coagulation factors). These systems include the hemodiabsorption (Liver Dialysis Unit) which is commercially available in the United States, the albumin dialysis which is available in Europe and the newly developed fractionated plasma separation and adsorption (FPSA) system. The simple method of albumin dialysis is "single pass albumin dialysis" (SPAD), which evolved into the so-called "molecular adsorbent recirculating system"(MARS). Prometheus system combines the FPSA method with high-flux hemodialysis. Although the results of many experimental and clinical trials prove the efficacy of the above mentioned methods, large randomized controlled trials are mandatory to establish the impact on survival benefit of artificial and bioartificial support systems versus standard therapy.