Why do you get small dark urine output in acute liver failure?

I have a 40 year old female patient with acute liver failure. She has ascites, starting phase of hepatic encephalopathy etc.
She's also been put on furosemide/frusemide (lasix) and lactulose.

Why does she have small dark urine output??
The urine is dark because the kidneys are excreting billirubin.

aside from that you can also expect clay colored or pale colored stools since the bilirubin needed for its color is excreted in the urine..