Friend With Stage 4 Liver Cancer, Hep C And B,

friend with stage 4 liver cancer, Hep C and B, at the end of life pretty much. He has a drainage cath to drain off fluid every other day or so but has to take "ammonia meds" that requires him to empty bowels but sometimes takes 4-5 days for that and he just zones out. we were told the ammonia buildup would cause dementia or some type of problems with his brain. is that what causes him to zone out or is that just a part of his end of life> thank you.