Oliguria - Causes, Diagnosis, and Treatment

Introduction:

Oliguria is a decrease in urine output. The urine output ranges from 800 to 2000 milliliters per day for adults with a water intake of around two liters. Oliguria occurs when the urine output is less than 400 milliliters per day or less than 20 mL/hour. In the case of children and infants, it depends on their weight. An infant with a urine output of less than one ml/kg/hour while a child with an output lesser than 0.5 mL/kg/hour is considered to have oliguria. It is one of the earliest signs of decreased kidney function. People with certain kidney diseases are prone to oliguria which could lead to kidney failure. It is also common among people on dialysis.

What Causes Oliguria?

Oliguria is considered to be one of the earliest signs of kidney failure. It is multifactorial and can result from a kidney or urinary tract pathology. When one loses blood or water, the body tries to conserve it with the help of neurohormonal control. Oliguria can occur due to prerenal, renal, or post-renal abnormalities.

Prerenal Factors:

• Hypovolemia or a decrease in the volume of blood or fluids in the body. This can happen due to less fluid intake, bleeding, diarrhea, vomiting, use of diuretics, presence of excess sugar in the urine, fluid accumulation in the abdomen, chest cavity, and lungs, injury, burns, surgery, sepsis after an infection or surgery, liver failure, certain drugs, anesthetic conditions, certain kidney disorders, or shock.

• Heart failure secondary to a heart attack.

• Pulmonary embolism is when a blood clot gets stuck in a blood vessel in the lungs, causing a blockage in the blood supply to that part of the lung.

• Cardiac tamponade is a condition in which fluid or blood fills the space between the sac containing the heart and the heart muscles.

• Heart failure.

• Blockage of the kidney vein or artery due to a blood clot.

• Stenosis or narrowing of one or more spaces within the spine.

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• Disturbance in the regulatory mechanism of kidney blood flow due to the administration of ACE (angiotensin-converting enzyme) inhibitors. ACE Inhibitors are medicines that relax the blood vessels to lower blood pressure.

Medications that cause oliguria include:

• Non-steroidal anti-inflammatory drugs like Aspirin or Ibuprofen.

• Certain antibiotics.

• Certain chemotherapy drugs.

• Medications that are used for treating bladder overactivity.

• Dyes are injected into the body as a part of certain diagnostic procedures.

Renal Factors:

• Vasculitis - Inflammation of the blood vessels.

• Glomerulonephritis - Inflammation of the glomerulus, tiny filters of the kidney.

• Scleroderma - Tightening and hardening of the joints, skin, and tissue.

• Malignant Hypertension - Very high and fluctuating blood pressure.

• Interstitial Nephritis - A kidney disorder in which the spaces between the kidney tubules become swollen.

• Damage to the Tubular Cells of the Kidneys or Acute Tubular Necrosis - It occurs due to compromised blood supply or toxic substances, such as certain drugs or contrast media.

Post-Renal Causes:

• Obstructing the upper urinary tract is due to obstruction of one or both of the tubes connecting the urinary bladder to the kidneys.

• Lower urinary tract obstruction due to the blockage of the bladder outlet because of the tumor, enlargement of the prostate gland in men, or certain drugs.

• After surgery, oliguria can occur for some time due to the release of vasopressin, causing the kidneys to retain water.

How Oliguria Occurs?

Urine output is a function of glomerular filtration with tubular secretion and resorption. Glomerular filtration is the first step in making urine, by which the kidneys filter excess fluid and waste out of the blood. Glomerular filtration is directly dependent on the kidney's blood flow. Good kidney blood flow is a function of the pressure and resistance of the kidney blood vessels. The blood vessels within the kidney preserve the glomerular filtration rate through the autoregulatory mechanism of the neurohormones. In oliguria, there is a decrease in glomerular filtration rate or mechanical obstruction to urine outflow.

A Decrease in Glomerular Filtration Rate May Occur When There Is:

• A decrease in blood volume, like in cases of trauma, hemorrhage, surgery, burn, diarrhea, etc.

• A decrease in the blood volume also occurs because of the widening of the blood vessels (vasodilation) commonly seen in sepsis, liver failure, nephrotic syndrome, and vasodilating drugs.

• The decrease in kidney blood flow is due to structural causes like embolism (blockage of a blood vessel by clots, particles, etc.), atherosclerosis, and inflammation affecting the blood flow within or outside the kidney.

• Renal atheroemboli (small hardened cholesterol particles that block the kidney blood vessels). It usually affects older people. It is mostly seen after the manipulation of larger blood vessels during surgery. This can also occur independently after treatment with Heparin, Warfarin, or thrombolytic agents (anti-blood clotting drugs).

• ACT (acute tubular necrosis), often a result of the above factors, can also occur due to kidney toxicity caused by substances such as antibiotics, heavy metals, solvents, dyes, uric acid, or oxalate crystals.

Oliguria According to the Site of Obstruction:

• Tubular ureteral obstruction is caused by stones, dead kidney tissues, crystals, or pigments.

• Obstruction of the urethra or the neck of the bladder by cancer.

• Malpositioned or obstructed urinary catheter.

How Is Oliguria Diagnosed?

A detailed history is taken about the onset of oliguria, whether it was sudden or worsened in due course. The amount of water intake is also taken into consideration. A detailed urine analysis is done to determine the color, presence of protein, uric acid levels, or presence of any kind of infection. Additional tests such as blood tests, CT scans to check for any kidney obstruction, renal scans, abdominal ultrasounds, or cystoscopy (a procedure involving a small camera to view) can be performed.

How Is Oliguria Treated?

The treatment of oliguria depends on its cause.

• Increasing Fluid Intake - This is the most common line of treatment if no other underlying pathology is present. Simply increasing the intake of water or fluids in the form of electrolytes can increase urine outflow. In case of severe dehydration, intravenous administration of fluids can be advised.

• Medications - If rehydration is not solving the problem or there is any other underlying cause, certain medications can be given to treat the condition.

• Antimicrobial Drugs - To treat infections causing diarrhea and vomiting.

• Diuretics - If given in small amounts, they can help the body produce more urine. But in higher doses, they can worsen the condition.

• Renal-Dose Dopamine - It is used to treat kidney injury by expanding the kidney blood vessels, thus increasing urine output.

• Surgeries are recommended to remove bigger stones or any kind of kidney obstruction.

• Medications - If certain medications cause the problem, tapering the medicine dose might treat the condition.

• Dialysis or Transplant - In severe cases where the kidneys cannot perform their function, a transplant or dialysis can be done to eliminate toxins from the body.

Conclusion:

Oliguria is a common clinical condition with multiple causes. The management depends on the underlying cause. Keeping a record of the number of times one is urinating can help to monitor the condition. If the urine output decreases or there is an underlying disease, one must go to the physician and get examined. Oliguria is not serious and can be reversed if diagnosed and treated early. If left untreated, it can lead to anuria, which means no urine output. Anuria can be fatal.