**5.1 Auxiliary liver transplantation**

An alternative to traditional orthotopic liver transplantation for patients with ALF is that of auxiliary transplant, based on the well-established regenerative capacity of hepatocytes. Unlike traditional transplantation, where native hepatectomy is performed simultaneously with donor engraftment, in auxiliary transplants, the patient's native liver is left surgically intact, while a partial or smaller sized donor graft is transplanted. This procedure allows assumption of hepatic functions by the donor graft, resolution of multiorgan failure, and clinical stabilization of the patient. In turn, the native liver benefits both from additional time, as well as improved physiological conditions, thus maximizing the opportunity for hepatic regeneration. Younger patients (below 40 years of age) with ALF due to viral hepatitis or acetaminophen toxicity appear to have the best outcome with this strategy. After native hepatic function is demonstrated, the auxiliary graft can be removed, but is most frequently allowed to atrophy by withdrawal of immunosuppression. Complete cessation of immunosuppression can be achieved in many patients (*Boudjema et al., 1995*).

#### **5.2 Artificial and bioartificial hepatic support systems**

Mechanical hepatic support systems serve as a bridge to transplant in patients with ACLF, and as a bridge to transplant or spontaneous recovery in patients with ALF. These systems are designed to reproduce the detoxifying functions of the liver, and mimic the principles upon which renal replacement therapy is based. While conventional renal dialysis removes small toxins and water-soluble toxins, the liver detoxifies larger toxins and protein-bound toxins. Dialysis of these larger and protein-bound toxins through unbound human albumin solutions allows the removal from the patient's circulation.

Several artificial systems have been developed utilizing albumin dialysis. The Molecular Adsorbent Recirculating System (MARS), Single Pass Albumin Dialysis (SPAD), and Prometheus are examples; of these, MARS has been the most widely studied. MARS has been utilized for management of hepatic encephalopathy, cerebral edema, hepatorenal syndrome, treatment of drug overdoses, and as a bridge to transplantation (*Mitzner, 2011*). MARS has been shown to improve hemodynamic parameters and organ perfusion during circulatory collapse, and has been associated with improvement in hepatic synthetic function. For patients with ACLF, MARS can provide temporarily relief of intractable pruritis and fatigue.

Bioartificial systems work similarly to artificial systems to remove toxins by albumin dialysis, but additionally utilize human or porcine hepatocytes to mimic hepatic synthetic function. Advances in the development of bioartificial systems have been limited by the challenges in maintaining hepatocyte viability.
