Why is lactulose used for a patient who has azotemia?

If liver problems: Lactulose is a poorly absorbable carbohydrate, causes gas, bloat, diarrhea; changes pH in bowel, affects bacteria; causes less ammonia production which somehow affects thought process, mentation in patients with chronic liver disease who can't clear these chemicals as well as norm. Sometimes given for chronic constipation. Sorbitol works similarly, cheaper, found in sugarless candies, mints, gu.