Dehydration also makes the blood thicker.

For people with PN this is definitely not good. In fact some
PNers have increased proteins in the blood already making it thick to begin with. (MGUS etc)

Thick serum does not flow in the little end capillaries very well.
And there is increased risk of blood clotting.

So drinking lots of water is important for this reason.
Eating high fat diets also clog the blood up. This was demonstrated in normal volunteers in studies not to long ago.
Too low a fat diet will starve the nerve repair systems. So only consume moderate amounts of "good fats". Avoid things like ice cream binges...or huge meals of ribs, bacon, etc. Try to get that saturated fat intake down as much as possible.

Dehydration will raise BUN-- blood urea nitrogen... this is seen when people have long fasts, before blood work.