Oliguria

Oliguria is the decreased production of urine.^[1] The decreased production of urine may be a sign of dehydration, renal failure, hypovolemic shock or urinary obstruction/urinary retention.

It can be contrasted with anuria, which represents a more complete suppression of urination.

Definition

Oliguria is defined as a urine output that is less than 1 mL/kg/h in infants, less than 0.5 mL/kg/h in children, and less than 400 mL/day (equals 17mL/hour) in adults.^[2]

Olig- (or oligo-) is a Greek prefix meaning small or few.^[3]

Anuria is defined as less than 50mL urine output per day.

Testing

Perform ultrasound examination of the kidney to rule out obstructive processes.

Pathophysiology

The pathophysiologic mechanisms causing oliguria can be categorized globally in three different categories:

• Prerenal: in response to hypoperfusion of the kidney (e.g. as a result of dehydration by poor oral intake, cardiogenic shock, diarrhea, massive bleeding or sepsis)
• Renal: due to kidney damage (severe hypoperfusion, rhabdomyolysis, medication)
• Postrenal: as a consequence of obstruction of the urine flow (e.g. enlarged prostate, tumour compression urinary outflow, expanding hematoma or fluid collection)

Postoperative oliguria

Patients usually have decrease in urine output after a major operation that may be a normal physiological response to:

• fluid/ blood loss – decreased glomerular filtration rate secondary to hypovolemia and/or hypotension
• response of adrenal cortex to stress -increase in aldosterone (Na and water retention) and antidiuretic hormone (ADH) release

Oliguria in infants

Oliguria, when defined as less than 1 mL/kg/h, in infants is not considered to be a reliable sign of renal failure.^[4]

References

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