Low Urine Output
1. Normal urine output is typically at least 0.5 cc/kg/hr. Oliguria is defined as urine output < 400 cc/day, and anuria is < 100 cc/day.
2. First, do you believe the numbers?
- If patient has a Foley, flush tubing to make sure it is not clogged.
- If patient does not have Foley, ask about urine output. Look for daily weights.
3. Examine the patient and assess volume status. Some places to look especially:
- Mucous membranes, skin pallor/dryness, edema, complaints of thirst
- Neck veins (to assess CVP), crackles in lungs (pulmonary edema)
- Bladder palpable on abdominal exam
- Prostate exam
4. The abrupt absence of urine output altogether (anuria) most often suggests obstructive uropathy. Other causes to consider if obstruction is not the case are:
- Progression of preexisting renal failure
- Renal cortical necrosis
- Necrotizing glomerular disease (RPGN)
5. Rule out obstructive uropathy early by checking a post-void residual by inserting Foley after patient voids. If volume > 200 cc then leave the Foley in; this indicates significant residual bladder volume indicating urinary retention. Some reasons for urinary retention include prostatic hypertrophy, anticholinergic side-effects of medications (narcotics, Benadryl, anesthetics, etc.).
6. Work-up: Renal failure is caused by prerenal, renal, and postrenal causes. Many laboratory indices exist to differentiate these (see Renal: Acute Reversible Renal Dysfunction), but if patient is not volume overloaded or obstructed and has no history of CHF, then a fluid challenge is usually appropriate (250-500 cc NS IV bolus). If they respond, however, your job is not quite done yet. Do the workup described under the Renal section.
- Always consider hypovolemia, decreased cardiac output, infection or sepsis, contrast nephropathy, and drug toxicity as potential causes because they are very common
- Beware of associated volume overload, acidosis, and hyperkalemia
- Consider increasing the frequency of labs and adjust drug dosages for renal failure as needed
7. If patient is in CHF or is volume overloaded, initiate diuresis. Remember, though, that unless the patient is truly volume overloaded, diuresis just for the sake of increasing urine output is pointless - treat the patient, not the numbers.
- Patients with working kidneys and overaggressive hydration usually will diurese themselves just by lowering the IV fluid rate.
- If in CHF or with symptoms, use furosemide 20-80 mg IV.
- If in renal failure, may require dialysis. Sometimes patients in renal failure can still respond to high dose furosemide while waiting for the renal consult (160-240 mg IV slowly).
8. Complications: acute oliguria is associated with higher rates of infection, gastritis, GI bleeding, AMS, and arrhythmias. Consider prophylaxis and/or closer monitoring of these possibilities.
Klahr S, Miller SB. Acute oliguria. N Engl J Med 1998; 338:671-5.
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