Acute Renal Failure
Doç. Dr. Mehmet Cansev
Acute Renal Failure
Acute renal failure (ARF) is the rapid breakdown of renal (kidney) function
that occurs when high levels of uremic toxins accumulate in the blood. ARF occurs
when the kidneys are unable to excrete the daily load of toxins in the urine.
Based on the amount of urine that is excreted over a 24-hour period, patients
with ARF are separated into two groups:
- Oliguric: patients who excrete less than 500 milliliters per day (< 16 oz/day)
- Nonoliguric: patients who excrete more than 500 milliliters per day (> 16 oz/day)
In nonoliguric patients, the urine is of poor quality (i.e., contains little waste)
because the blood is not well filtered, despite the fact that an adequate
volume of urine is excreted.
Types of Acute Renal Failure
The three types of ARF are named for their location within the renal (kidney) system:
- Prerenal ARF
- Postrenal ARF
- Intrinsic renal ARF
Incidence of Acute Renal Failure
ARF affects approximately 1% of patients on admission to the hospital, 2 to 5% during
the hospital stay, and 4% to 15% after cardiopulmonary bypass surgery.
ARF Signs and Symptoms
Acute renal failure does not produce a classic set of symptoms.
The most common symptom is decreased urine output, which occurs in 70% of patients.
ARF Diagnosis
ARF is most easily diagnosed by an increase in blood levels of creatinine and
blood urea nitrogen (BUN). The blood level of creatinine typically increases
by 0.5 milligrams per tenth of a liter (mg/dL) every day.
ARF Treatment
There are several modalities of renal replacement therapy (RRT) for patients
with acute renal failure:
- Intermittent hemodialysis
- Continuous hemodialysis (used in critically ill patients)
- Peritoneal dialysis (rarely used)
ARF Prognosis
Before the development of RRT, many people with ARF died from severe electrolyte
imbalance (hyperkalemia, acidosis) or from the uremic toxins themselves. Patients
with ARF are at risk for numerous complications that may lead to death, such as
seizures, bleeding, and coma. Since dialysis treats the life-threatening complications
of ARF, advanced age and underlying diseases are more likely to determine the risk
for a patient's dying from ARF.
Oliguric ARF patients have a high mortality rate, despite the availability of RRT. Almost
uniformly, these patients have other acute and/or chronic medical problems. Patients
with nonoliguric ARF tend to have a more favorable prognosis and are often easier to
treat. Nonoliguric ARF patients often have fewer systemwide complications because
their condition typically is caused by drug-related toxicity and interstitial nephritis.
Prerenal ARF Overview
Prerenal ARF is characterized by inadequate blood circulation (perfusion) to the
kidneys, which leaves them unable to clean the blood properly. Many patients
with prerenal ARF are critically ill and experience shock (very low blood pressure).
There often is poor perfusion within many organs, which may lead to multiple
organ failure.
Prerenal ARF Causes
Some of the most notable causes of prerenal ARF are dehydration, heart failure,
sepsis (severe infection), and severe blood loss.
Prerenal ARF is associated with a number of preexisting medical conditions,
such as atherosclerosis ("hardening" of the arteries with fatty deposits), which
reduces blood flow. Dehydration caused by drastically reduced fluid intake or
excessive use of diuretics (water pills) is a major cause of prerenal ARF.
Many people with severe heart conditions are kept slightly dehydrated by the
diuretics they take to prevent fluid buildup in their lungs, and they often have
reduced blood flow (underperfusion) to the kidneys.
Prerenal ARF Signs and Symptoms
Symptoms of prerenal ARF include the following:
- Dizziness
- Dry mouth
- Low blood pressure (hypotension)
- Rapid heart rate
- Slack skin
- Thirst
- Weight loss
Urine output is usually low in people with prerenal ARF.
The patient also may have symptoms of heart or liver disease.
Prerenal ARF Complications
Many prerenal ARF patients are critically ill and require admission to an intensive
care unit. They may suffer from severe infection, such as viral hepatitis.
Decreased perfusion can cause acute organ failure, such as cardiac or liver failure.
Symptoms of heart failure include:
- Dyspnea (shortness of breath)
- Edema (fluid retention and swelling)
- Venous engorgement
- Symptoms of liver failure include:
- Confusion, disorientation, stupor
- Sweet, ammoniacal odor
Prerenal ARF Diagnosis
A complete physical examination and a medical history help the physician to diagnose
prerenal ARF. In addition, laboratory studies often reveal a high BUN to Cr ratio
(BUN:Cr > 20:1), along with abnormal urine chemistry. The physician often must rule
out postrenal and intrinsic renal causes of acute renal failure.
Prerenal ARF Treatment
The goal of treatment is to improve of kidney perfusion. This usually involves treating
the underlying condition (e.g., infection, heart failure, liver failure).
Intravenous (IV) fluids are administered to most patients to treat dehydration.