Oliguria
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Oliguria and anuria are the decreased or absent production of urine, respectively. The decreased production of urine may be a sign of dehydration, renal failure or urinary obstruction/urinary retention.
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/d in adults.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, diarrhoea, 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 hypovolumia and/or hypotension
- response of adrenal cortex to stress -increase in aldosterone (Na and water retention) and antidiuretic hormone (ADH) release
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