An 80-year-old woman was admitted from a nursing home because of somnolence, anorexia, and a 5-day history of watery diarrhea. One week prior to admission she was ambulatory, ate adequately, and cared for a small garden. Physical examination revealed a BP of 100/50, pulse of 110 while supine but BP of 60/30 and pulse of 122 on standing. Skin and mucous membranes were dry, eyeballs were sunken. Chest and abdominal examination were normal. She answered simple questions and had no other neurological abnormalities. Urine output for the first 8 hours in the hospital was 75 ml.

Laboratory Data:

Hct 56, BUN 98, Cr 2.6, Na 149, K 5.8, Cl 112, HCO3 21

Urinalysis: specific gravity 1.022, pH 5, protein - negative, occ WBC, 1-2 granular casts/LPF

UNa = 6 meq/L, UCr = 50, Uosm 760 mOsm/L, Posm 300 mOsm/L

1. Calculate and interpret the FENa.

FENa= 0.21% -- prerenal azotemia

2. What is the cause of the oliguria and azotemia?

Severe prerenal azotemia secondary to hypovolemia.

3. Why did the patient develop this disorder?

Diarrhea

4. What is the treatment for the oliguria/azotemia?

Restoration of intravascular volume and renal blood flow with IV saline.

5. How does this condition pathophysiologically and clinically differ from the ATN type of ARF?

The renal tubules are functioning normally and maximally reabsorbing sodium and maximally concentrating in response to low renal blood flow. With ATN, the tubules cannot respond.