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 FailureARF 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.