Care Plan help please!

I had a patient recently that I am trying to find a second nursing dx for ... she had dementia, so she didn't even know why she was there, but she came in with a dx of UTI and acute renal failure. I already have a nursing dx of impaired memory r/t Central nervous changes secondary to degenerative brain disease as evidenced by Forgetting and inability to recall recent events (borrowed from another site) ... I am stuck however on another nursing diagnosis b/c I need 2 for class. the acute renal failure was said to be most likely secondary to volume depletion. I would like to find a nursing diagnosis that I could use for the volume depletion, I know that since she has dementia she may not remember to drink enough fluid. I was thinking deficient fluid volume. Any help/direction/pointers about how to most efficiently do a nursing care plan would be greatly appreciated - I am having such a difficult time with these things!! Thank you in advance for any help!