Renal Pathophysiology

So, I've been researching this, and I currently work on a tele floor where a good portion (50% or so) of our pts are ckd/aki pts. I'm fuzzy on renal labs to some extent and wanted to know if there's a good delineation between dehydration and actual kidney disease. Or, is it that you would suspect dehydration as a cause of aki, rule it out with volume repletion, and continue BMPs/CMPs to reassess daily?

I guess what I'm asking is, I routinely get pt's w/ decreased GFRs, elevated BUNs, etc. I usually look for minimally abnormal GFR/BUN, combined w/ evidence of hemoconcentration to decipher dehydration on my own. Is there a cheat sheet for dehydration? Or are there just too many variables to look at to diagnose dehydration vs. some other form of aki?

Fifty percent of your tele patients are ARF/CKF? Am I reading that right??? Holy smokes...

Anyway, you ask all the right questions and it is obvious you've done a little digging. Good for you.

The title of your thread is "renal pathophysiology" which as you've figured out by now, is extremely complex. The only way to defnitively diagnose and rule out dehydration (as BUN/Creat/Na++ levels and ratios can be influenced by so many predicating factors) aside from the obvious "little old guy that hasn't been eating syndrome and his lips are cracked", is by fluid challenge.

Fluid challenges are not only instigated for cases of suspected dehydration, but if they fail, they also help rule out other underlying causes of renal insufficiency/failure as well.

Yes, you are correct in that there are too many variables to definitively diagnose dehydration as the cause of any patient's acute or chronic renal impairment. Remember, BUN and Creatinine are clues and diagnostic tools only, not diagnoses!

To keep it simple, remember these terms:

1.) Chronic Renal Insufficiency: multiple etiologies leading to chronically decreased renal function which include diabetes, HTN, autoimmune disorders that attack the functional units of the kidney (Wegener's Granulomatosis, Lupus)

2.) End Stage Renal Failure/Disease: multiple etiologies, all of which lead to irreversible renal disease requiring long term dialysis.

3.) Acute Renal Failure/Disease: multiple etiologies including dehydration/volume depletion, drug overdoses, burns, Hemolytic Uremic Syndrome (as in E-coli) Rhabdomyolosis (as in crush injuries and over-exertion...quite common actually), and heart failure.

4.) Acute-on-Chronic Renal Failure: a combo of #1 and #3 (and much more! :)). i.e., a patient with underlying diabetes and/or HTN may present with "Acute Renal Failure" but has baseline Chronic Renal Insufficiency, and, with a few interventions inlculding medications and fluids... may be able to regain sufficient renal function to keep them off of dialysis for a while.

5.) Pre-Renal: indicating renal failure outside of the functional portions of the kidney itself. Hint: dehydration, would be a "pre-renal" cause of kidney failure.

As far as acute renal failure causes in your patients, including dehydration considerations, here is a great flip chart that is easy to print and keep handy for yourself or on your unit:

http://www.physicianeducation.org/downloads/PDF%20Downloads%20for%20website/Acute%20Renal%20Failure.pdf

GREAT explanation Guttercat! Thanks so much! I actually asked my boss yesterday too and she gave me some of the same information you just gave me, but not so much detail. I LOVE pathophys, and yes, renal pathophys has definitely been the most difficult for me!

GREAT explanation Guttercat! Thanks so much! I actually asked my boss yesterday too and she gave me some of the same information you just gave me, but not so much detail. I LOVE pathophys, and yes, renal pathophys has definitely been the most difficult for me!

Thanks vwde.

In actuality any good neph clinician worth his or her salt, could poke numerous holes in my post...i.e., Lupus and Wegener's can't be lumped in under Chronic Renal Insufficiency as they fall more under the Nephritic Syndrome umbrella, rather than Nephrotic (and hence present as a sudden onset/Acute).

The link I gave you on the Acute Renal Failure flip-chart is excellent, however.

So go with that. :)