Oliguria

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Overview
Oliguria and anuria are the decreased or absent production of urine, respectively.

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.

Differential Diagnosis of Underlying Causes of Oliguria
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, 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)

The decreased production of urine may be a sign of dehydration, renal failure or urinary obstruction/urinary retention.

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.