Section 11. Kidney and Urinary Tract Disorders

Chapter 143. Kidney Failure

Topics: Introduction | Acute Kidney Failure | Chronic Kidney Failure | Dialysis

Acute Kidney Failure

Acute kidney failure is a rapid decline (days to weeks) in the kidneys' ability to filter metabolic waste products from the blood.

Acute kidney failure can result from any condition that decreases the blood supply to the kidneys or that obstructs urine flow anywhere along the urinary tract. Kidney failure may also result from disease affecting the kidneys themselves. In many people, no cause of acute kidney failure can be identified.

See the table Major Causes of Acute Kidney Failure.

Symptoms

Symptoms depend on the severity of kidney failure, its rate of progression, and its underlying cause.

In some people, the first symptom of acute kidney failure is fluid retention, with swelling of the feet and ankles or puffiness of the face and hands. The person may notice the passage of cola-colored urine, which may indicate a number of kidney diseases. The amount of urine (which for most healthy adults is between 3 cups and 2 quarts per day) often decreases to less than 1 pint per day or stops completely. Very little urine production is called oliguria, and no urine production is called anuria. However, some people with acute kidney failure continue to produce normal amounts of urine.

As acute kidney failure persists and metabolic waste products accumulate in the body, a person may experience fatigue, a decreased ability to concentrate on mental tasks, loss of appetite, nausea, and overall itchiness (pruritus). A person with acute kidney failure may experience a rapid heart rate (tachycardia) and lightheadedness.

If the cause is an obstruction, the backup of urine within the kidneys causes the drainage system to stretch (a condition called hydronephrosis). Urinary obstruction may produce crampy pain--ranging from mild to excruciating--usually along the sides (flanks) of the body. Some people with hydronephrosis have blood in their urine. If the obstruction is located below the bladder, the bladder will enlarge. If the bladder enlarges rapidly, the person is likely to feel severe pain. If the bladder enlarges slowly, pain may be minimal, but the lower part of the abdomen may swell from the markedly distended bladder.

If acute kidney failure develops during hospitalization, the condition often relates to some recent injury, surgical event, drug, or medical illness such as infection. The symptoms of the underlying cause of the acute kidney failure may predominate. For example, high fever, life-threatening low blood pressure (shock), and symptoms of heart failure or liver failure may occur before symptoms of kidney failure and be more obvious and urgent.

Some of the conditions that cause acute kidney failure also affect other parts of the body. For example, Wegener's granulomatosis (see Section 5, Chapter 69), which damages blood vessels in the kidneys, may also damage blood vessels in the lungs, causing a person to cough up blood. Skin rashes are typical of some causes of acute kidney failure, including polyarteritis nodosa, systemic lupus erythematosus, and some toxic drugs.

Diagnosis

Blood tests that measure levels of creatinine and blood urea nitrogen in the blood are needed to confirm the diagnosis. A progressive daily rise in creatinine indicates acute kidney failure. The level of creatinine is also the best indicator of the degree or severity of kidney failure; the higher the level, the more severe the failure is likely to be. Other blood tests detect metabolic imbalances that occur as kidney failure persists, such as a high acid level (acidosis), a high potassium level (hyperkalemia), a low sodium level (hyponatremia), and a high phosphorus level (hyperphosphatemia).

The physical examination may help the doctor identify the cause of the acute kidney failure. Enlarged or tender kidneys give clues to the cause, such as obstruction with hydronephrosis. Urine tests, such as a urinalysis and a measurement of certain electrolytes, may enable the doctor to categorize the cause of kidney failure.

Imaging of the kidneys using ultrasound or computed tomography (CT) is helpful, sometimes by providing such basic information as the size of the kidneys. For example, an ultrasound can be used to identify hydronephrosis or to detect an enlarged bladder. X-rays of the renal arteries or veins (angiography) may be performed if obstruction of blood vessels is the suspected cause. Alternatively, magnetic resonance imaging (MRI) can be used. If these studies do not reveal the cause of kidney failure, a biopsy may be necessary to determine the diagnosis and the prognosis.

Prognosis and Treatment

Acute kidney failure and its immediate complications, such as fluid retention, high acid and potassium levels in the blood, and increased urea in the blood, can often be treated successfully. The overall survival rate is about 60%. Survival is less than 50% for people who have several organs failing at the same time. Yet, survival is about 90% for people whose kidney failure is due to decreased blood flow because body fluids have been lost through bleeding, vomiting, or diarrhea--conditions that are reversible with treatment.

Any treatable cause of kidney failure is addressed as soon as possible. For example, if obstruction is the cause, endoscopy or surgery may be needed to relieve the obstruction.

Often, simple but meticulous supportive care is all that is needed for the kidneys to heal themselves, especially if the kidney failure has existed for less than 5 days and has been uncomplicated by other problems such as infection.

The doctor strictly limits the person's intake of all substances that are eliminated through the kidneys, including many drugs, such as digoxin, and many antibiotics. Water intake is restricted to replacing the amount lost from the body, unless hydration is needed. A person's weight is measured every day to monitor fluid intake because measured intake may be inaccurate. A weight gain from one day to the next indicates that the person is receiving excessive fluid.

In addition to receiving nutrients such as glucose, a person with acute kidney failure receives certain amino acids (the building blocks of protein) by mouth or intravenously to maintain adequate protein levels. Salt (sodium) and potassium intake is usually restricted.

Sodium polystyrene sulfonate is sometimes given by mouth or rectally to treat a high level of potassium in the blood. Calcium salts (calcium carbonate or calcium acetate) may be given to prevent or treat a high level of phosphorus in the blood.

Fluids are not restricted in a person who is recovering from acute kidney failure caused by obstruction. During this time, the kidneys are unable to reabsorb sodium and water normally, and a large amount of urine is produced for a period of time after the obstruction is relieved. Such a person may also need replacement of fluids and electrolytes, such as sodium, potassium, and magnesium.

Acute kidney failure may be prolonged, necessitating that waste products and excess water be removed through dialysis, usually hemodialysis (see Section 11, Chapter 143). In these cases, dialysis is started as soon as possible after diagnosis. Dialysis may be needed only temporarily, until the kidneys recover their function, usually in several days to several weeks. If the kidneys are too badly damaged to recover, then the acute kidney failure will become chronic.