Oliguria


Oliguria or hypouresis is the low output of urine: specifically, more than 80 ml/day, but less than 400ml/day. The decreased output of urine may be a sign of dehydration, kidney failure, hypovolemic shock, hyperosmolar hyperglycemic nonketotic syndrome, multiple organ dysfunction syndrome, urinary obstruction/urinary retention, diabetic ketoacidosis, pre-eclampsia, and urinary tract infections, among other conditions.
Beyond oliguria is anuria, which represents an absence of urine, clinically classified as below 80 or 100 ml/day.
The term oliguria is derived from oligo-meaning "small, little," + -uria, from the Greek word ouron, meaning "urine".

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 or 500 mL per 24h in adults - this equals 17 or 21 mL/hour. For example, in an adult weighing 70 kg it equals 0.24 or 0.3 mL/kg/h. Alternatively, however, the value of 0.5 mL/kg/h is commonly used to define oliguria in adults as well.

Diagnostic approach

Perform ultrasound examination of the kidney to rule out obstructive processes.
The mechanisms causing oliguria can be categorized globally in three different categories:
  • Prerenal: in response to hypoperfusion of the kidney
  • Renal: due to kidney damage
  • Postrenal: as a consequence of obstruction of the urine flow

    Postoperative oliguria

Patients usually have a decrease in urine output after a major operation that may be a normal physiological response to:
Oliguria, when defined as less than 1 mL/kg/h, in infants is not attributed to kidney failure.