 One scheme defines "acute hepatic failure" as the development of encephalopathy within 26 weeks of the onset of any hepatic symptoms.This is sub-divided into "fulminant hepatic failure", which requires onset of encephalopathy within 8 weeks, and "subfulminant", which describes onset of encephalopathy after 8 weeks but before 26 weeks.Another scheme defines "hyperacute" as onset within 7 days, "acute" as onset between 7 and 28 days, and "subacute" as onset between 28 days and 24 weeks.