Is your Stan diabetic? I am and find that if my sugar is too high, then the process won't work correctly. I need to have a difference between me and the solution for the filtration to work. If my blood sugar is too high, I won't untrafiltrate. Hope this helps.
I had a negative UF the other day (not as huge as that one you mentioned though... it was -93) and I asked my nurse and she said that since I'm still urinating that sometimes I won't need to have fluids taken off. Thus, the machine doesn't pull anything. Does your husband still have a little function left?