| Definition Acute kidney
failure occurs when illness, infection, or injury
damages the kidneys. Temporarily, the kidneys cannot
adequately remove fluids and wastes from the body or
maintain the proper level of certain kidney-regulated
chemicals in the bloodstream.
Description
The kidneys are the body's natural filtration system.
They perform the critical task of processing
approximately 200 quarts of fluid in the bloodstream
every 24 hours. Waste products like urea and toxins,
along with excess fluids, are removed from the
bloodstream in the form of urine. Kidney (or renal)
failure occurs when kidney functioning becomes impaired.
Fluids and toxins begin to accumulate in the
bloodstream. As fluids build up in the bloodstream, the
patient with acute kidney failure may become puffy and
swollen (edematous) in the face, hands, and feet. Their
blood pressure typically begins to rise, and they may
experience fatigue and nausea.
Unlike chronic kidney failure, which is long term and
irreversible, acute kidney failure is a temporary
condition. With proper and timely treatment, it can
typically be reversed. Often there is no permanent
damage to the kidneys. Acute kidney failure appears most
frequently as a complication of serious illness, like
heart failure, liver failure, dehydration, severe burns,
and excessive bleeding (hemorrhage). It may also be
caused by an obstruction to the urinary tract or as a
direct result of kidney disease, injury, or an adverse
reaction to a medicine.
Causes and symptoms
Acute kidney failure can be caused by many different
illnesses, injuries, and infections. These conditions
fall into three main categories: prerenal,
postrenal, and intrarenal conditions.
Prerenal conditions do not damage the kidney, but can
cause diminished kidney function. They are the most
common cause of acute renal failure, and include:
- dehydration
- hemorrhage
- septicemia, or sepsis
- heart failure
- liver failure
- burns
Postrenal conditions cause kidney failure by
obstructing the urinary tract. These conditions include:
- inflammation of the prostate gland in men
(prostatitis)
- enlargement of the prostate gland (benign
prostatic hypertrophy)
- bladder or pelvic tumors
- kidney stones (calculi)
Intrarenal conditions involve kidney disease or
direct injury to the kidneys. These conditions include:
- lack of blood supply to the kidneys (ischemia)
- use of radiocontrast agents in patients with
kidney problems
- drug abuse or overdose
- long-term use of nephrotoxic medications, like
certain pain medicines
- acute inflammation of the glomeruli, or filters,
of the kidney (glomerulonephritis)
- kidney infections (pyelitis or pyelonephritis).
Common symptoms of acute kidney failure include:
- anemia. The kidneys are responsible for
producing erythropoietin (EPO), a hormone that
stimulates red blood cell production. If kidney
disease causes shrinking of the kidney, red blood
cell production is reduced, leading to anemia.
- bad breath or bad taste in mouth. Urea in the
saliva may cause an ammonia-like taste in the mouth.
- bone and joint problems. The kidneys produce
vitamin D, which helps the body absorb calcium and
keeps bones strong. For patients with kidney
failure, bones may become brittle. In children,
normal growth may be stunted. Joint pain may also
occur as a result of high phosphate levels in the
blood. Retention of uric acid may cause gout.
- edema. Puffiness or swelling in the arms, hands,
feet, and around the eyes.
- frequent urination.
- foamy or bloody urine. Protein in the urine may
cause it to foam significantly. Blood in the urine
may indicate bleeding from diseased or obstructed
kidneys, bladder, or ureters.
- headaches. High blood pressure may trigger
headaches.
- hypertension, or high blood pressure. The
retention of fluids and wastes causes blood volume
to increase. This makes blood pressure rise.
- increased fatigue. Toxic substances in the blood
and the presence of anemia may cause the patient to
feel exhausted.
- itching. Phosphorus, normally eliminated in the
urine, accumulates in the blood of patients with
kidney failure. An increased phosphorus level may
cause the skin to itch.
- lower back pain. Patients suffering from certain
kidney problems (like kidney stones and other
obstructions) may have pain where the kidneys are
located, in the small of the back below the ribs.
- nausea. Urea in the gastric juices may cause
upset stomach.
Diagnosis
Kidney failure is diagnosed by a doctor. A
nephrologist, a doctor that specializes in the kidney,
may be consulted to confirm the diagnosis and recommend
treatment options. The patient that is suspected of
having acute kidney failure will have blood and urine
tests to determine the level of kidney function. A blood
test will assess the levels of creatinine, blood urea
nitrogen (BUN), uric acid, phosphate, sodium, and
potassium. The kidney regulates these agents in the
blood. Urine samples will also be collected, usually
over a 24-hour period, to assess protein loss and/or
creatinine clearance.
Determining the cause of kidney failure is critical
to proper treatment. A full assessment of the kidneys is
necessary to determine if the underlying disease is
treatable and if the kidney failure is chronic or acute.
X rays, magnetic resonance imaging (MRI), computed
tomography scan (CT), ultrasound, renal biopsy, and/or
arteriogram of the kidneys may be used to determine the
cause of kidney failure and level of remaining kidney
function. X rays and ultrasound of the bladder and/or
ureters may also be needed.
Treatment
Treatment for acute kidney failure varies. Treatment
is directed to the underlying, primary medical condition
that has triggered kidney failure. Prerenal conditions
may be treated with replacement fluids given through a
vein, diuretics, blood transfusion, or medications.
Postrenal conditions and intrarenal conditions may
require surgery and/or medication.
Frequently, patients in acute kidney failure require
hemodialysis, hemofiltration, or
peritoneal dialysis to filter fluids and wastes from
the bloodstream until the primary medical condition can
be controlled.
Hemodialysis
Hemodialysis involves circulating the patient's blood
outside of the body through an extracorporeal circuit
(ECC), or dialysis circuit. The ECC is made up of
plastic blood tubing, a filter known as a dialyzer (or
artificial kidney), and a dialysis machine that monitors
and maintains blood flow and administers dialysate.
Dialysate is a sterile chemical solution that is used to
draw waste products out of the blood. The patient's
blood leaves the body through the vein and travels
through the ECC and the dialyzer, where fluid removal
takes place.
During dialysis, waste products in the bloodstream
are carried out of the body. At the same time,
electrolytes and other chemicals are added to the blood.
The purified, chemically-balanced blood is then returned
to the body.
A dialysis "run" typically lasts three to four hours,
depending on the type of dialyzer used and the physical
condition of the patient. Dialysis is used several times
a week until acute kidney failure is reversed.
Blood pressure changes associated with hemodialysis
may pose a risk for patients with heart problems.
Peritoneal dialysis may be the preferred treatment
option in these cases.
Hemofiltration
Hemofiltration, also called continuous renal
replacement therapy (CRRT), is a slow, continuous blood
filtration therapy used to control acute kidney failure
in critically ill patients. These patients are typically
very sick and may have heart problems or circulatory
problems. They cannot handle the rapid filtration rates
of hemodialysis. They also frequently need antibiotics,
nutrition, vasopressors, and other fluids given through
a vein to treat their primary condition. Because
hemofiltration is continuous, prescription fluids can be
given to patients in kidney failure without the risk of
fluid overload.
Like hemodialysis, hemofiltration uses an ECC. A
hollow fiber hemofilter is used instead of a dialyzer to
remove fluids and toxins. Instead of a dialysis machine,
a blood pump makes the blood flow through the ECC. The
volume of blood circulating through the ECC in
hemofiltration is less than that in hemodialysis.
Filtration rates are slower and gentler on the
circulatory system. Hemofiltration treatment will
generally be used until kidney failure is reversed.
Peritoneal dialysis
Peritoneal dialysis may be used if an acute kidney
failure patient is stable and not in immediate crisis.
In peritoneal dialysis (PD), the lining of the patient's
abdomen, the peritoneum, acts as a blood filter. A
flexible tube-like instrument (catheter) is surgically
inserted into the patient's abdomen. During treatment,
the catheter is used to fill the abdominal cavity with
dialysate. Waste products and excess fluids move from
the patient's bloodstream into the dialysate solution.
After a certain time period, the waste-filled dialysate
is drained from the abdomen, and replaced with clean
dialysate. There are three type of peritoneal dialysis,
which vary according to treatment time and
administration method.
Peritoneal dialysis is often the best treatment
option for infants and children. Their small size can
make vein access difficult to maintain. It is not
recommended for patients with abdominal adhesions or
other abdominal defects (like a hernia) that might
reduce the efficiency of the treatment. It is also not
recommended for patients who suffer frequent bouts of an
inflammation of the small pouches in the intestinal
tract (diverticulitis).
Prognosis
Because many of the illnesses and underlying
conditions that often trigger acute kidney failure are
critical, the prognosis for these patients many times is
not good. Studies have estimated overall death rates for
acute kidney failure at 42-88%. Many people, however,
die because of the primary disease that has caused the
kidney failure. These figures may also be misleading
because patients who experience kidney failure as a
result of less serious illnesses (like kidney stones or
dehydration) have an excellent chance of complete
recovery. Early recognition and prompt, appropriate
treatment are key to patient recovery.
Up to 10% of patients who experience acute kidney
failure will suffer irreversible kidney damage. They
will eventually go on to develop chronic kidney failure
or end-stage renal disease. These patients will require
long-term dialysis or kidney transplantation to replace
their lost renal functioning.
Prevention
Since acute kidney failure can be caused by many
things, prevention is difficult. Medications that may
impair kidney function should be given cautiously.
Patients with pre-existing kidney conditions who are
hospitalized for other illnesses or injuries should be
carefully monitored for kidney failure complications.
Treatments and procedures that may put them at risk for
kidney failure (like diagnostic tests requiring
radiocontrast agents or dyes) should be used with
extreme caution.
Key Terms
- Blood urea nitrogen (BUN)
- A waste product that is formed in the liver
and collects in the bloodstream; patients with
kidney failure have high BUN levels.
- Creatinine
- A protein produced by muscle that healthy
kidneys filter out.
- Extracorporeal
- Outside of, or unrelated to, the body.
- Ischemia
- A lack of blood supply to an organ or
tissue.
- Nephrotoxic
- Toxic, or damaging, to the kidney.
- Radiocontrast agents
- Dyes administered to a patient for the
purposes of a radiologic study.
- Sepsis
- A bacterial infection of the bloodstream.
- Vasopressors
- Medications that constrict the blood
vessels.
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