Ammonia plays a major role in the pathogenesis of hepatic encephalopathy (HE). Systemic hyperammonemia has been largely found in patients with HE with underlying cirrhosis and acute liver failure. HE is associated with a poor prognosis of both acute and chronic liver disease (Bustamante, Rimola et al. 1999; Hui, Chan et al. 2002). Cirrhosis is the major cause of chronic liver dysfunction and affects 6.5 million people worldwide (Eurostat. 2010, as cited in Albrecht, 2010). HE is the hallmark for acute liver failure (ALF), a syndrome with very high mortality in which liver transplant is the often the only effective treatment.