Hepatic encephalopathy is a complication of liver failure, whether chronic as in cirrhosis, or acute as result of, say, fulminant hepatic necrosis due to acetaminophen poisoning. With severe liver impairment, toxic substances normally removed by the liver accumulate in the blood and impair the function of brain cells. If there is also portal hypertension, and subsequent bypassing of the liver filtration system of blood flowing in from the intestines, these toxic substances can travel directly to the brain, without being modified or purified.