Oliguria refers to a clinical condition characterized by a low volume of urine. The medical definition of oliguria is an output below 500 ml per day but greater than 50 ml per day. Output below 50 ml per day is referred to as anuria, or the absence of urine. Low urine volume is a danger to health because of the need to remove waste materials from the body, along with excess water (although in many cases oliguria is caused by dehydration so that last may not be an immediate condern). It can be a sign of renal disease, although it can also arise from other sources.
Causes
Oliguria can be caused by dehydration, acute renal failure, hypovolemia (a severe and sudden reduction in the blood supply, as in severe blood loss, e.g. from an injury with severe bleeding), urinary obstruction or retention, urinary tract infections, and pre-
Although not all of these causes of oliguria involve the kidneys directly, the kidneys produce urine and so a shortage of urinary flow always indicates a condition that impacts the kidneys at least indirectly.
Pathophysiology
The causes of oliguria are classified medically, as are those of many other disorders involving the kidneys, as being either prerenal, renal, or postrenal, which means, literally, before the kidneys, in or involving the kidneys, and after the kidneys.
Prerenal
Prerenal oliguria is caused by circulatory shock involving the kidneys and usually arising from dehydration (which may be a result of cardiogenic shock, diarrhea and resulting dehydration, massive blood loss as from an injury, infections, or simply not drinking enough water).
Renal
Renal oliguria is a result of damage to the kidneys themselves, which can occur due to injury, high blood pressure, dehydration, side effects of medications, and other causes.
Postrenal
Postrenal oliguria occurs due to an obstruction of the urinary tract, and can arise due to an enlarged prostate, various cancers including cancer of the bladder, compression of urinary outflow by a tumor (cancerous or benign), and several other causes.
When oliguria is diagnosed, ultrasound is used to examine the kidneys and the urinary tract to identify or rule out urinary tract obstruction, as this is treated differently from other causes of oliguria. Other tests may be performed to narrow the cause of non-
Treatment
In clinical or surgical situations where the doctors expect renal shock or toxic injury as a complication, counter-
This therapy does not treat damage to the kidneys as such but it does make it easier to manage, as oliguria can narrow the therapeutic choices in regard to fluid control and nutritional support.
In cases other than urinary tract obstruction, the main concern in treating oliguria is to use bodily fluid management to maintain or restore blood volume.
Some drugs have proven useful in treatment of nonobstructive oliguria: furosimide, torsemide, and ethacrynic acid, all of which are loop diuretics (diuretics that operate on the ascending loop of Henle in the kidney). Although these are not as effective as thiazide diuretics in patients with normal kidney function, they are more effective in cases of renal failure.
When oliguria arises due to an obstruction in the urinary tract, i.e. postrenal oliguria, the preferred treatment is completely different and involves correcting the impairment by removing the cause of it. This may involve surgery or other treatment to free the outflow of urine from the kidneys and through the urinary tract.