Oliguria

Oliguria is the low output of urine,^[1] It is clinically classified as an output below 300-500ml/day^[2]. The decreased output of urine may be a sign of dehydration, renal failure, hypovolemic shock, HHNS Hyperosmolar Hyperglycemic Nonketotic Syndrome, multiple organ dysfunction syndrome, urinary obstruction/urinary retention, and Urinary tract infections.

It can be contrasted with anuria, which represents an absence of urine, clinically classified as below 50ml/day^[3].

Definition

Oliguria is defined as a urine output that is less than 1 mL/kg/h in infants,^[4] less than 0.5 mL/kg/h in children,^[4] and less than 400 mL^[4] or 500 mL^[5] per 24h in adults - this equals 17 or 21 mL/hour. For example, in an adult weighing 70kg it equals 0.24 or 0.3 ml/hour/kg. Alternatively, however, the value of 0.5 mL/kg/h is commonly used to define oliguria in adults as well.^[5]

Olig- (or oligo-) is a Greek prefix meaning small or few.^[6]

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^[7]:

• 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.^[8]

References

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