What is acute renal failure (ARF)?
This is when an abrupt deterioration of renal function develops within hours or days. It is a very serious condition with a high mortality and must be prevented in patients at risk.
Acute renal failure often develops in patients that are in hospital for other conditions, like surgery, major burns or due to a motor vehicle accident. Urine production slows or stops and waste products and excess water build up. Blood levels of urea and creatinine rise rapidly and these waste products are the diagnostic indicators of ARF. The disturbance of fluid and electrolyte balance, especially elevated potassium, is potentially life threatening.
ARF affects the functioning of the whole body including the heart, brain, lungs and digestive system. The current tendency is to dialyze patients with acute renal failure early in order to prevent complications. This also simplifies their fluid and electrolyte management and allows for better nutritional support.
Causes of ARF
This condition is classified into three groups according to the underlying causative mechanisms. It influences the management plan and treatment given.
Decreased bloodflow to the kidneys: (pre-renal ARF)
A severe drop in blood pressure or blood volume can lead to ARF. Both cause a reduction in the perfusion or bloodflow to the kidney. This accounts for 50 to 60 percent of cases. Decreased blood pressure can occur during major surgery or as result of a heart attack or serious infection in the blood. A reduction in bloodflow can occur with massive bleeding and cause renal failure in this way. Dehydration caused by vomiting and diarrhoea is the commonest cause of prerenal ARF in children who suffer from gastroenteritis. Prerenal ARF may also occur in burn victims. Blood clots to the kidney can also interrupt the normal bloodflow to the kidneys, but are rare.
Damage to the kidney: (renal ARF)
This is when the kidney cells or its filtering units are damaged directly. It may be due to a sudden illness, inflammation of the kidneys, and injury or certain drugs and toxins. About 30 to 40 percent of ARF fall in this category. It is most often caused by acute tubular necrosis (ATN), where the filtering tubes of the kidney are damaged. Decreased bloodflow to the kidney during surgery, trauma or major infections can lead to ATN. Kidney diseases like glomerulonephritis can also cause kidney damage and lead to ARF. Sometimes medication can be toxic to the kidneys including certain antibiotics, anti-inflammatory drugs and contrast agents used in specific X-ray tests. The elderly, diabetic and other patients with underlying kidney disease are most at risk.
Blockage of the urine flow
Obstruction of the urine flow from the kidney, or within the kidney can also lead to ARF and accounts for about 5 percent of cases. The blockage can be caused by kidney stones, mass lesions like a tumor or an enlarged prostate. Doing a rectal or vaginal examination can reveal tumors of the reproductive organs and prostate. It is very important to exclude obstruction as a cause of renal failure because the treatment is considerably different. Special investigations like sonar of the kidney or pyelogram are used to determine the diagnosis. Pyelogram is an X-ray of the kidney taken after giving a contrast agent or “dye”.
Symptoms and signs of ARF
In patients who develop ATN, other features of disease or illness are often present: the patient may have dehydration, or the patient may be receiving treatment for infection or has been involved in an accident. In patients who develop glomerulonephritis, there is often acute onset of facial swelling and the presence of “coke” coloured urine. Urine production may slow down or (rarely) stop completely. The excess fluid leads to elevated blood pressure and fluid buildup in the lungs. This leads to shortness of breath especially when lying down. Distented neck veins and a fast or irregular heartbeat can be present. Depending on the cause of the renal failure, dehydration may be present and must be looked for and corrected promptly.
The toxic effects of the waste products on brain function can cause nausea, vomiting and tiredness. Patients lose their appetite and acid buildup in the blood leads to deep breathing and headaches. If untreated, the fluid and waste overload can lead to heart failure, altered brain functioning like lethargy, seizures and coma.
The chemical balance of the blood is derailed and high levels of electrolytes like potassium can be very dangerous and lead to abnormal heart rhythm. The heart may become inflamed from the toxins (pericarditis). This is a serious complication and can be treated by dialysis. Muscle cramps and confusion are often found.
Dialysis can be life saving when serious chemical abnormalities, fluid overload, congestive heart failure or severe hypertension are developed. Dialysis is when a sophisticated filter, connected to a machine, is used to take over the function of the failed kidneys temporarily.
Diagnosis of ARF
Patients who develop ARF are often in hospital for another condition that puts them at risk for the condition. This includes major surgery, heart attack, crush injury and severe burns. Urine and blood tests are done and the volume of urine produced is monitored. An abrupt rise in the blood levels of urea and creatinine characterises ARF. Urine production may be slowed down but often patients continue to pass more than one litre of urine per day. Sophisticated urine and blood tests are done to determine the renal function.
It is important to determine if the patient might have underlying chronic kidney failure that can slowly progress for years, without causing symptoms. In this case, acute deterioration of the chronic condition can be difficult to differentiate from ARF. Small scarred kidneys on sonar or special X-ray of the kidneys, suggest the disease is of a chronic nature.
Taking a thorough history, careful physical examination, urine and special tests will help the doctors establish whether the cause is pre-renal, renal or post-renal. Obstruction of the urine flow is an important post-renal cause and should be excluded because the management is different from the other forms of ARF. Dehydration is a common cause of pre-renal ARF and correcting the patient’s fluid balance is a priority.
The first principle of the treatment of ARF is to identify any potentially reversible causes. Therefore, dehydration should be corrected, offending drugs discontinued, obstruction relieved and infection treated.
Further treatment is tailored according to the underlying cause of the ARF and the fluid and electrolyte disturbances. Patients with ARF are monitored closely. The volume of urine produced and other clinical indicators are charted, and regular blood tests are done. Treatment may include intravenous fluids in dehydrated patients or restriction of fluids if overloaded. Blood levels of electrolytes are corrected and medication to decrease potassium may be necessary. High blood pressure is treated if necessary. A diet low in protein and high in carbohydrates is generally recommended.
Tests to identify and manage the complications of ARF may also be done, for example, chest X-rays to exclude heart failure. The current tendency is to dialyze patients with ARF early in order to prevent complications. This also simplifies their fluid and electrolyte management and allows for better nutritional support.
Course of the disease
ARF is a serious condition and its complications can lead to death. It may resolve in time and sometimes within days. Recovery also depends on the underlying cause and the treatment given. Mortality is highest in surgical patients and the leading causes of death are infection, bleeding of the digestive tract and fluid/electrolyte disturbances. Children tend to have a better chance of regaining their kidney function than adults. Only a minority of patients with ARF are left with permanent residual kidney damage.
Incidence / people at risk
ARF must be prevented in high-risk patients. This includes those with chronic diseases that can affect the kidneys like diabetes, hypertension and heart disease. Heart attack can lead to cardiogenic shock and must be treated early. Pregnant patients who suffer from eclampsia, a hypertensive condition, have a high risk for kidney damage.
Patients with major injuries due to accidents require optimal treatment to maintain bloodflow to the kidneys and should be aggressively resuscitated.
Some drugs are nephrotoxic (poisonous to the kidney), and therefore damaging to the kidneys. This includes certain antibiotics called aminoglycosides, anti-inflammatory drugs and the contrast media used in specific X-ray tests of the urinary tract.
Written by Dr K. Coetzee, reviewed by Dr R. Moosa, head of the Renal Unit, Tygerberg Academic Hospital