FLUID VOLUME

It's all about cause and effect. Yes, dehydration will make your BUN higher -- less circulating blood volume but the same amount of urea nitrogen. It's like putting a package of Crystal Lite in an 8 ounce bottle of water vs. a 16 ounce bottle. (Hopefully that made sense.). That doesn't say anything at all about your patient's renal function.

With a BUN and creatinine as high as your patient's, it's indicative of renal failure (either acute or chronic.). In renal failure, the kidneys don't do their job. They don't filter out the waste products and they don't make enough urine. Because the patient isn't able to pee off the volume he gets, he will become more and more fluid overloaded. Ultrafiltration will remove the excess volume; dialysis will remove the waste products. (Hint -- if you have access to the patient's chart, read the notes the renal team left -- that will tell you what they're thinking about what exactly caused the renal failure, whether they think it's acute or likely to become chronic and what they intend to do about it. It will also give recommendations for renal dosing of the patient's meds.)

I hope that (a) this made sense and (b) that it gives you a starting place for further research. I believe you need to be looking into renal failure as the problem rather than increased BUN/Creatnine. The BUN and creatinine are high because your patient's kidneys are failing. Dehydration would lead to a (much less) elevation in BUN in patients with normal kidney function.