Oliguria

What is Oliguria?

Oliguria is a medical term that means a person is not producing enough urine. It is specifically defined as producing less than 400 milliliters of urine in a whole day, or producing less than 20 milliliters every hour. This is often one of the first signs that the kidneys are not working as they should. This connection between urine production and kidney function goes back to the time of the ancient Greek doctor, Hippocrates, who highlighted the importance of urine production for health. Later, in the second century, another doctor named Galen also highlighted the relevance of urine production to kidney health. A man named Heberden later used the term ‘ischuria renalis’ to describe what happens when kidney failure is linked with low urine production.

According to a group called the Acute Dialysis Quality Initiative, a person who is producing less than 0.3 milliliters of urine per kilogram of their body weight every hour, for a total of 24 hours, can be said to have oliguria.

What Causes Oliguria?

Oliguria, which is when a person produces less urine than normal, can have many different causes. Some of these are obvious, while others are more underlying or hidden. Oliguria can be a normal response from the body, or it can be due to an issue with the kidney or urinary tract.

Your body naturally retains fluids and electrolytes when there’s a drop in blood volume, which can lead to oliguria. This type of mechanism is controlled by hormones and can be reversed without causing kidney damage. The causes of oliguria usually fall into three categories: prerenal, renal (or intrinsic), and postrenal, each relating to different parts of the body.

Prerenal causes are related to the blood supply before it reaches the kidney. They include:

• Hypovolemia: Lower than usual blood volume due to things like not drinking enough fluids, bleeding, loss of fluids from the digestive system (like diarrhea or vomiting), kidney loss (from diuretics or high blood sugar), movement of fluid into body cavities (from conditions like liver disease or inflammation), trauma, surgery, and certain drugs.
• Pump Failure: Failure of the heart to pump blood properly due to heart attack, blood clot in the lungs, restricted filling of the heart, or heart failure.
• Vascular: Blockage of the artery or vein to the kidney due to blood clots or narrowing, or issues with the kidney’s ability to self-regulate, perhaps caused by certain medications.

Renal, or intrinsic, causes are related to problems within the kidneys themselves. They include:

• Blood vessel inflammation, inflammation of the kidney filters, hardening of the skin, very high blood pressure, or inflammation around the kidney tubules.
• Acute tubular necrosis (ATN): Damage to the kidney tubules due to lack of oxygen or exposure to harmful substances, including certain drugs and contrast agents used for medical imaging.

Postrenal causes are connected to problems with the flow of urine after it leaves the kidneys. They include:

• Upper urinary tract obstruction: Blockage of the tubes that carry urine from the kidneys caused by blockages on one or both sides.
• Lower urinary tract obstruction: Blockage of urine outflow from the bladder, often due to an enlarged prostate, tumor, or certain drugs.

After a surgery, it’s common for a person to have temporary oliguria. This is due to the release of certain hormones and stimulation of the nervous system in response to the surgical stress.

Risk Factors and Frequency for Oliguria

Oliguria, or the condition of producing less urine, is quite common in hospital patients and demands careful monitoring. It’s seen in about half of the patients in intensive care units (ICUs). Furthermore, people who have been on dialysis for a long time often experience chronic oliguria.

• Oliguria is a condition that is common among hospitalized patients and needs to be closely monitored.
• About half of the patients in intensive care units (ICUs) experience episodes of oliguria.
• Chronic oliguria is often seen in people who have been on long-term dialysis.

Signs and Symptoms of Oliguria

Oliguria is a condition where a person produces less urine than usual. If you’re a patient experiencing this condition, your doctor will likely ask you about your past medical history – including things like whether you have diabetes, high blood pressure, heart disease, or an autoimmune disease, among others. They will also be interested in your family’s medical history and what medications you’re currently taking. This is because some medications can potentially cause harm to the kidneys.

Additionally, your doctor may want to know about your job, any hobbies you might have, and whether you’ve been travelling recently. As part of their examination, they’ll check your hydration status by looking at the elasticity of your skin when it’s pinched (skin turgor) and the condition of your mucous membranes. Your body’s ability to regulate blood flow can give clues about whether the cause of oliguria is due to issues coming before the kidneys (pre-renal).

If you’ve been experiencing instances of both oliguria and excess urination (polyuria), it could suggest that there’s an intermittent blockage in your urinary tract. By performing a physical examination of your bladder, doctors can identify if it’s enlarged, which could indicate that urine is building up due to acute urinary retention. A quick bedside ultrasound of your bladder can also confirm whether there’s any retained urine.

Testing for Oliguria

When a doctor suspects you might have a condition involving your kidneys – like decreased urine production, they begin with a thorough review of your medical history and perform a physical examination. They may also order a series of tests to gain more information about your condition.

Blood tests can provide important information about kidney health. For example, the doctor may order a test for serum creatinine, urea, serum electrolytes, and blood urea nitrogen. High levels of these substances in your blood may indicate that your kidneys aren’t working properly.

Another important test is a urine analysis, which is usually done before other treatments are started. A urine test can give information about your kidney function and any potential reversible factors that may be affecting it. The quicker these factors are found and addressed, the less likely you are to have severe kidney failure, which comes with its own risks and can cause serious illness or even death.

In some severe cases, the doctor might need to measure your central venous pressure or the pressure in the pulmonary capillaries. This is typically done in very sick patients when non-invasive methods (tests that don’t involve entering the body) aren’t enough.

Urine tests can also help determine the cause of reduced urine production. Certain values, like the specific gravity of the urine or the urinary sodium concentration, can suggest where the problem might be happening. In addition, the pattern of urinary sediments (particles in urine) can also provide clues as to what might be the underlying cause of decreased urine production.

Imaging tools like a renal tract ultrasound and a CT scan of the abdomen can identify blockages in your urinary tract, a common cause of decreased urine output. The presence (or lack) of urinary tract dilation (widening) can help identify more specific causes, such as cancer, severe dehydration, or if the patient sought medical attention promptly.

Treatment Options for Oliguria

Oliguria is the medical term for producing less urine than usual. The approach to diagnosing and treating this condition depends mostly on what’s causing it.

For example, if the cause is some type of blockage in the urinary system (a post-renal cause), solutions may be as simple as removing a blockage in a urinary catheter or drainage tube. Sometimes, a bladder ultrasound at the bedside can be useful to identify urinary retention and guide the insertion of a urinary cathetar. If the cause is related to prostate enlargement, tumors, or kidney stones, then a urologist might need to assess the patient and suggest treatment.

Managing the patient’s fluid and blood flow (hemodynamic stabilization) is the first step. Each patient’s fluid needs are calculated individually – it’s important to balance having enough fluid, but not too much. If the patient gets too much fluid, a condition called volume overload, they might need medicine to increase urine production or treatment to filter the blood (renal replacement therapy). Special fluids, called balanced crystalloids, are often used for this purpose. The goal is to maintain stable blood pressure, and carefully monitor urine output to adjust treatment as needed.

Should fluid replacement not lead to increased urine production, the next step is to use medications that encourage the kidneys to produce more urine (diuretics) using a standard procedure. One method to assess the effect of these drugs is the furosemide stress test (FST). This test looks at the response of urine production to a specific dose of a diuretic medication, in this case, furosemide. Using the result, doctors can estimate the severity of kidney damage and guide treatment. However, the patient’s volume status (whether dehydrated or overloaded) and vital signs must be closely watched during this test, as it may worsen the patient’s condition in case of hypovolemia (lower than normal blood volume).

If diuretic therapy is not effective, the patient might then need renal replacement therapy. This therapy, also known as dialysis, helps to manage fluid and electrolyte balance and prevent complications.

Other considerations for patients with oliguria include ensuring they get enough protein and calories in their diet, as these patients have higher protein requirements. Also, all medications that could potentially harm the kidneys (nephrotoxic drugs) need to be stopped, and the dosages of medications that are metabolized by the kidneys need to be adjusted.

While increasing a person’s hydration levels is an essential part of treating oliguria, overdoing it can cause the kidneys to become even more damaged – a condition called acute kidney injury – and can increase the risk of death. Fluid overload signs include swelling in the arms and legs, increased pressure in the veins, and a size increase in a large vein in the stomach called the inferior vena cava. In patients who respond well to diuretics, these medicines can be used to help manage fluid overload. Those who don’t respond might need renal replacement therapy.

What else can Oliguria be?

When a patient has oliguria (low urine output), the doctor needs to consider several possible diagnoses. These are:

• Pre-renal azotemia: This can be checked by evaluating the patient’s blood circulation, examining their urine, and using a Doppler ultrasound to view their kidneys.
• Acute glomerulonephritis: This is typically diagnosed through a kidney biopsy and by measuring complement levels in the blood (proteins that help the immune system).
• Oliguric acute tubular necrosis: This is a condition where the tubules in the kidney are damaged. It is diagnosed using urine analysis.
• Non-oliguric acute tubular necrosis: Similar to the oliguric variant but the patient still has some urine output. It’s also diagnosed using urine output measurement and urine analysis.
• Urinary tract obstruction: This is diagnosed through a combination of examining the patient’s urine, performing a renal ultrasound, and taking a non-contrast CT scan.

What to expect with Oliguria

Oliguria, or producing less urine than usual, can be one of the first signs of sudden kidney injury. When this happens outside of the hospital, it’s typically due to a single cause and is often reversible with generally good outcomes. However, patients who arrive at the hospital producing less urine typically have a more severe kidney issue because of multiple underlying factors. This means they often have more serious outcomes than those who aren’t hospitalised.

Patients in the intensive care unit usually experience oliguria later on in their illness and it’s often due to multiple organ failure. People in the hospital producing less urine generally have a higher chance of sickness and death.

Those making less urine are at a greater risk of developing sudden severe kidney failure. In fact, 30 to 70 percent of patients with sudden severe kidney failure develop infections, which can lead to an increased chance of disease and death. Yet, the risk of death due to producing less urine isn’t only due to the development of severe kidney failure.

The length and severity of oliguria can significantly influence the outcomes. As the severity of oliguria becomes worse, to a level of less than 0.5 ml per kg per hour, the risk of death significantly increases.

Possible Complications When Diagnosed with Oliguria

People with acute oliguria, a condition where the body produces less urine than usual, often experience a sudden decrease in GRF (Glomerular filtration rate) that causes acute kidney failure. This issue increases the levels of urea and creatinine in the plasma rapidly, leads to metabolic acidosis with high potassium levels, other electrolyte irregularities, and an excess of body fluids. This condition is critical, and quick hospital admission is necessary to avoid dangerous health events. Some of the dangerous complications include:

• Electrolyte Imbalances: High potassium levels, metabolic acidosis, salt and water retention leading to lung water accumulation, abdominal fluid buildup, or fluid in the lungs, higher phosphorus levels, or low calcium levels.
• Neurologic Issues: Drowsiness, confusion, excessive sleepiness, overactive reflexes, seizures, and even coma.
• Cardiovascular Problems: Heart disease, fluid in the lungs, and high blood pressure due to fluid and salt imbalances. In some cases, low blood pressure which could be due to other serious illnesses like sepsis. Changes in heart activity due to high potassium levels. Electrolyte imbalances can also cause irregular heart rhythm in some cases. Rarely pericarditis, inflammation of the pericardium.
• Gastrointestinal Issues: Nausea, vomiting, bowel obstruction, gastrointestinal bleeding, and gastritis.
• Respiratory Issues: Accelerated and deep breathing due to metabolic acidosis.
• Musculoskeletal Problems: Weakness or paralysis of the muscles.
• Drug Responses: Kidney issues often reduce the body’s ability to break down certain medications, increasing the risk of drug toxicity and requiring dosage adjustments for some drugs.
• Infectious Complications: An increased risk of infections of the urinary tract and respiratory system due to damaged protective barriers, uremia, and inappropriate use of antibiotics.
• Blood-Related Complications: Acute kidney failure can cause anemia, which is a decrease in red blood cell production. This can partly be due to the destruction of red blood cells, with hematocrit (the portion of your blood that’s made up of red blood cells) levels between 20 and 30 percent.

It is crucial to detect these complications early through careful monitoring to prevent the development of life-threatening complications.

Preventing Oliguria

It’s essential for patients to stay well-hydrated and not take any medication without first consulting their doctor. This includes ‘over the counter’ pain relief medicines like NSAIDs which are easily accessible without prescription. Patients should also be sure to follow their doctor’s advice and regularly check-in with their doctor. If your doctor suggests, you may also need to see a kidney specialist, known as a nephrologist.

Avoid fasting for long periods and avoid extreme exercise, as these actions can make the condition of producing less-than-normal amount of urine, called oliguria, worse and can even lead to a dangerous condition called rhabdomyolysis. This condition occurs when muscle tissue breaks down, leading to the release of muscle fiber contents into the blood.

If you have a catheter, make sure to take proper care of it. A key indicator of your condition will be your urine output. You should pay attention to the amount and appearance of your urine. If you notice any changes in color, frothing, or formation of sediment in your urine, be sure to let your doctor know.

Besides focusing on managing your fluid intake and maintaining a balance of salts, minerals and chemicals in your body (known as electrolytes), it’s also important to ensure you’re getting enough protein and calories in your diet.