An Overview of Acute Renal Failure

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Acute renal failure is caused by damage to the kidneys, which can occur as a result of blood loss, toxins, or physical damage to the kidneys. Acute renal failure occurs rapidly, causing generalized symptoms, such as loss of appetite and confusion. It is a serious condition, but it can be treated. With proper treatment, most people can survive an episode without long-term consequences. 

Symptoms

The kidney monitors the amount of fluid, electrolytes, and waste in the body and sends the excess materials to be eliminated in the urine. The symptoms of acute renal failure occur because these substances accumulate in the body when the kidney does not work the way it should.

Normal fluid and electrolyte levels are necessary for the whole body to function optimally. Waste materials are toxic to most of the body's cells and tissues, which results in wide-ranging symptoms.

Symptoms of acute renal failure develop quickly, over several hours or days. The most common symptoms of are:

  • Lack of energy and fatigue: This is the result of early dysfunction of the organs in your body, which do not have the right concentration of electrolytes to function as they should.
  • Loss of appetite, nausea, and vomiting: This feeling occurs because your digestive system—which requires healthy digestive enzymes, muscles, and nerves to function properly—can slow down and be unable to maintain normal activity if your kidney does not properly regulate the substances in your body.
  • Generalized muscle weakness: Your muscles require electrolytes to be able to function. When you have renal failure, this causes muscle function to suffer. 
  • Rapid, slow or irregular heartbeats: Your heartbeat is controlled by your cardiac (heart) muscles which rely on a number of important electrolytes to function properly. Your body attempts to preserve heart function for as long as possible. If your body cannot compensate for the effects of acute renal failure, your heart function can suffer, producing irregular heart rhythms. This can ultimately result in a lack of adequate blood supply throughout the body. 
  • Confusion: A serious symptom of acute renal failure, confusion means that your brain is not getting adequate blood supply. If you experience confusion as a result of acute renal failure,  you could quickly progress to a loss of consciousness or coma. 
  • Loss of consciousness or coma: This symptom means that the brain is lacking adequate blood supply and may result in permanent damage unless you get urgent medical care. 

Causes

The kidneys are impacted by many factors, such as blood pressure, medications, overall health, diet, and the amount of water a person drinks. There are a number different ways that acute renal failure can occur. Anything that rapidly damages the kidneys will decrease the amount of work they are able to do. Acute kidney failure can be temporary or may be the sign of a larger problem.

There are three main categories of causes of acute renal failure:

Prerenal

This describes causes of kidney failure that begin before blood reaches the kidneys. Low blood pressure, for example, will occur if your heart is not working efficiently or if you become severely dehydrated.

In this case, the kidneys themselves are not the main problem, but they are being affected by low blood supply. This makes it hard for the kidneys to do their job of filtering blood. A severe infection may even progress to septic shock, a condition that can cause an acute kidney injury because the blood pressure falls to such a low level that the kidneys cannot work efficiently.

Intrinsic

This describes causes of kidneys failure in which the kidneys themselves are harmed. Toxins, including chemicals, illegal drugs, and even some prescribed medications, have to pass through the kidneys and can damage them.

Examples of medications that may cause acute renal failure include contrast materials for imaging tests. These types of medications do not cause everyone who takes them to have acute renal failure or else no one would ever use them. But they can cause acute renal failure for some people and it can be hard to predict if you will have this reaction. Sometimes, you might need blood tests that measure your kidney function before you can take medications that are more likely to cause acute renal failure. 

Other situations that can cause acute renal failure in the intrinsic category include a lack of oxygen in the bloodstream, kidney infection, inflammation of the kidneys, and kidney diseases. A very large kidney stone can also cause intrinsic damage to the kidney.

Postrenal

This describes causes of kidney failure that are rooted in the urinary tract, which is where urine flows after it has been processed by the kidneys. These causes include problems involving the ureters (the tubes that carry urine to the bladder), the bladder, or the urethra (the tube that carries urine from the bladder out of the body).  

A large kidney stone or a tumor, for example, can be located in the bladder or the urethra. If it is large enough that urine cannot pass through, the urine can begin to back up—eventually up into the kidneys. This pressure and the backward flow of urine can cause an acute injury to the kidney.

Diagnosis 

There are certain criteria for the diagnosis of acute renal failure. If you have one of the following three criteria in the course of 48 hours, this means that you have acute renal failure:

  1. If your serum creatinine (a blood test that measures kidney function) rises by .3 mg/dl
  2. If your serum creatinine rises by 50 percent or more from normal levels
  3. If your urine output falls to .5 milliliters per kilogram of body weight per hour for more than six hours

Urine Production

If you have acute kidney injury, you may be making adequate amounts of urine or very little urine. You can even have a significant increase in your creatinine level, which indicates an acute kidney injury but still make a normal level of urine. Over half of all people who have acute renal failure continue to make urine in what appears to be a normal fashion. 

  • For adults, normal urine output is 0.5 to 1 milliliter per hour per kilogram of body weight or one to two liters per day. 
  • For children, approximately 1 milliliter per hour per kilogram is normal.
  • For infants, 2 milliliters per hour per kilogram of body weight is considered normal. 

(For reference, 30 milliliters is approximately one ounce of urine.)

There are three categories that describe the amount of urine output during acute kidney injury:

  1. Non-oliguric: This describes a situation in which a person continues to make an adequate amount of urine, which is generally more than 400 milliliters per day, or more, depending on health status and fluid intake. 
  2. Oliguric: This describes a situation in which a person makes 400 milliliters of urine or less per day. 
  3. Anuric: This describes a situation in which a person makes less than 100 milliliters of urine per day.

Treatment

The treatment of acute renal failure depends on the cause of the problem, as well as the severity of the situation. Many people improve with treatment and do not experience long-term problems or chronic renal failure.

Identifying the problem, and obtaining treatment as quickly as possible, is the best way to prevent kidney damage that causes a lifetime of kidney issues or requires dialysis treatments. Treatments can include:

  • Intravenous (IV) fluids: A person who has acute renal failure due to severe dehydration after experiencing heat stroke may improve with IV fluids. When a low fluid volume is a reason for the acute renal failure, providing the body with fluids can help restore fluid levels
  • Electrolyte management: If your fluids and electrolytes are not within the optimal range, your doctors may give you electrolyte supplements or give you medications that can get rid of some excess electrolytes. 
  • Stopping the use of toxins: If acute renal failure is caused by a medication or supplement, the treatment should include stopping the medication.
  • Dialysis: When toxins are not expected to be eliminated efficiently if you simply stop taking them, treatment of acute renal failure requires ridding the body of the chemical as quickly as possible. Sometimes dialysis is needed, a method through which a machine can do the work of the kidney by removing toxins and regulating fluid and electrolyte balance. 

Kidney Function Tests

Kidney function tests are a group of tests that examine your kidney function. These tests are not used to diagnose acute renal failure, but they are used to monitor whether your kidney failure is improving or worsening. 

Often, kidney function tests can determine how severe the problem is, provide some insight into what the cause of the problem is, and be repeated to show if the kidneys are responding to treatment. Kidney function tests include:

  • Creatinine: A waste product produced by muscle breakdown, the creatinine level in your blood provides an idea of how well your kidneys are functioning because the kidneys should remove creatinine from the blood. A level above 1.21 mg/dL is considered high and is an indication that the kidneys are not functioning as they should. 
  • Blood urea nitrogen (BUN): Urea nitrogen, also measured in the blood, is removed by the kidneys. Levels above 25 mg/dL are suggestive of kidney failure.  
  • Glomerular filtration rate (GFR): This number is calculated based on the creatinine level in your blood, with a calculation that accounts for age, height, weight, and other factors that account for anticipated individual changes. A normal GFR should be above 60. A GFR below 20 often means that a person has kidney failure. 
  • Urinalysis: A urinalysis can identify blood, proteins, infections, inflammation, and drugs. This information provides insight into the cause, and sometimes the progression, of acute renal failure. 
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