Oliguria is a condition where too little urine is produced, caused by inadequate fluid to the kidneys, damaged kidneys, or obstruction. Treatment involves identifying and correcting underlying causes, and dialysis may be necessary. Prerenal causes, such as dehydration, are the most common. Postrenal causes involve urinary obstruction, often due to catheter blockage. Acute tubular necrosis is a renal cause of oliguria, where there is damage to the kidneys themselves.
Oliguria is a condition in which too little urine is produced. Low urine output can be the result of not enough fluid to the kidneys, damaged kidneys that are unable to produce urine, or an obstruction that prevents urine from leaving the body. The most common causes of oliguria are those, such as dehydration, that result in inadequate fluid supply to the kidneys, and these are known as prerenal causes. Treatment of oliguria generally involves correcting any of the underlying causes if possible. If there is a risk of kidney failure, dialysis may be needed, in which an artificial filter is used instead of the kidneys to remove waste products from the blood.
Where decreased urine output results from prerenal causes, there is not a large enough volume of fluid reaching the kidneys. This can occur due to dehydration, heart disorders, such as heart failure, in which blood is not pumped efficiently around the body, or the collapse of the circulatory system, known as hypovolemic shock, due to problems such as bleeding . Low fluid volume can cause kidney failure, resulting in decreased output from the urinary system.
In the early stages of kidney failure, also known as acute kidney injury, the kidneys respond to their reduced fluid intake by storing extra salt and water, and if the situation is reversed, urine output can return to normal. If the situation persists, some kidney cells die in a condition called acute tubular necrosis. Where the damage is too extensive, the kidneys may not be able to produce normal urine output even if the fluid load subsequently increases.
Acute tubular necrosis is known as a renal cause of oliguria, in which there is damage to the kidneys themselves. Diseases that cause kidney damage, some drugs that are toxic to the kidneys, and blood infection can lead to acute tubular necrosis. Some of the causes lead to more severe kidney damage than others, and oliguria is associated with only the most severe forms. For both prerenal and renal causes of oliguria, the underlying problems are identified and treated to give the kidneys the best chance of recovery. Any fluid loss is replaced and dialysis is used if necessary.
Postrenal causes of oliguria, where there is urinary obstruction, commonly involve problems such as catheter blockage. Catheters are flexible tubes used to drain urine from the bladder. In the case of a blockage, urinary retention occurs, in which the person usually feels the need to urinate but cannot, and the onset of oliguria is relatively sudden. A blockage can be caused by placing the urine collection bag higher than the bladder or by a kink in the tube, in which case a simple repositioning can correct the problem. If the inside of the tube is blocked by sediment or a blood clot, the catheter may need to be replaced.
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