The kidneys control the amount of urine the body makes, keeping electrolytes and fluid volumes in balance. When the kidneys stop producing enough urine, various problems can develop. Oliguria is the production of fewer than 500 milliliters of urine in 24 or fewer hours in adults or less than 0.5 milliliters per kilogram per hour in an adult or child. Sometimes, there is a simple explanation and treatment for decreased urine output, though it often indicates a serious underlying health condition.
Dehydration can quickly lead to oliguria. If the body is not taking in enough water, it cannot produce enough urine. Feeling thirsty is not always a reliable indicator of hydration status. Young infants and children may have fewer wet diapers, stop producing tears when crying, or have a sunken soft spot of the top of the head. Adults may present with confusion, dizziness, and fatigue. Any urine output will be dark yellow.
Believe it or not, burn injuries can lead to dehydration, which can, in turn, lead to oliguria. The skin is the largest organ in the body. One of its most essential functions is protecting the body against fluid and electrolyte loss. A burn that covers a large area can result in significant fluid loss.
It is not surprising that oliguria can be caused by problems with the kidneys. Causes related to this organ are commonly separated into three types. Pre-renal issues affect kidney blood supply. Renal problems describe issues within the kidney itself. Post-renal complications refer to obstructions below the kidney that prevent urination.
When something disrupts blood flow to the kidneys, oliguria occurs because the organs cannot work properly and cannot make urine. Blood loss, heart disease, heart attack, some infections, liver failure, and severe allergic reactions can all block or slow blood flow. Dehydration and severe burns also fit into this category. Anything that lowers blood volume or leads to ineffective cardiac function can cause pre-renal kidney failure.
Renal failure also leads to oliguria because of loss of kidney function but in a different way than pre-renal kidney failure. In these cases, the damage occurs in the kidney itself. Many factors can cause renal damage, including blood clots in and around the kidneys, lupus, infection, toxins, medications, and scleroderma. Prolonged loss of blood flow (more than four hours) from pre-renal causes can also damage the kidneys.
In post-renal kidney failure, oliguria happens because the body cannot eliminate urine properly. In this case, the kidneys can produce the waste product, but a blockage prevents it from leaving the body, decreasing urine output. Causes of post-renal kidney failure include bladder, prostate, colon, or cervical cancer, kidney stones, or blood clots in the urethra. Urine that cannot be excreted can back up into the kidneys and cause infection and significant kidney damage.
Dehydration can occur from excessive heat and sun exposure without proper hydration, vomiting, and diarrhea. As for oliguria caused by renal failure, it usually occurs in conjunction with another medical condition. Risk factors include a previous or current diagnosis of peripheral artery disease, diabetes, high blood pressure, heart failure, and certain cancers. Advanced age and hospitalization in an intensive care unit for a serious condition can also lead to oliguria.
There are multiple ways to diagnose the underlying cause of oliguria. One is a 24-hour urine collection to measure exactly how much urine the patient produces in a day. A doctor may also take urine samples for analysis and blood tests to measure creatinine and urea, two markers that measure kidney function. If the physician suspects kidney damage, an ultrasound or CT scan can evaluate the severity. Some cases may also require a biopsy.
Without early treatment, complications of oliguria can be severe. When the kidneys are not working properly, excess fluid can build up in the lungs and heart. Oliguria also affects electrolyte balances, which can cause muscle weakness and irregular cardiac rhythms. If the underlying cause of renal failure and oliguria persists untreated, permanent damage and loss of kidney function can occur.
Treatment of oliguria and kidney failure depends on the cause. If dehydration is the culprit, IV fluids can rehydrate the patient. If fluid has begun to build up in the tissue, the doctor may prescribe diuretics to help the kidneys eliminate the fluid buildup. Medications can also correct electrolyte imbalances, particularly blood potassium levels. If kidney failure and the associated oliguria persist, the patient may require dialysis to restore his or her electrolyte balance.
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