Chronic Kidney Failure
Chronic kidney failure is a slowly progressive decline (months to years) in the kidneys' ability to filter metabolic waste from the blood.
Many diseases can irreversibly damage or injure the kidneys. Acute kidney failure can become chronic if kidney function does not recover after treatment. Therefore, anything that can cause acute kidney failure can cause chronic kidney failure. However, the most common cause of chronic kidney failure is diabetes mellitus, followed by high blood pressure (hypertension). Both of these conditions directly harm the kidneys' small blood vessels. Other causes of chronic kidney failure include urinary tract obstruction; kidney abnormalities (such as polycystic kidney disease and glomerulonephritis); and autoimmune disorders (such as systemic lupus erythematosus), in which antibodies damage the tiny blood vessels (glomeruli) and the tiny tubes (tubules) of the kidneys.
Symptoms
Symptoms may develop slowly or evolve from acute kidney failure. A person with mild to moderate kidney failure may have only mild symptoms despite the increase in the levels of urea and other metabolic waste products in the blood. At this stage, the person may need to urinate several times during the night (nocturia), because the kidneys cannot absorb water from the urine to reduce the volume and concentrate it as normally occurs during the night.
As kidney failure progresses and metabolic wastes build up in the blood, the person may feel fatigued and generally weak and may become less mentally alert. These symptoms progress as the blood becomes more acidic, a condition called acidosis. A loss of appetite and shortness of breath can result. Fatigue and generalized weakness may also be attributed in part to a decline in red blood cell production and the resulting anemia. People with chronic kidney failure tend to bruise easily or bleed for an unusually long time after cuts or other injuries. Chronic kidney failure also diminishes the body's ability to fight infections.
As metabolic wastes build up in the blood, damage to muscles and nerves can cause muscle twitches, muscle weakness, cramps, and pain. The person may also feel a pins-and-needles sensation in the arms and legs and may lose sensation in certain areas of the body. Encephalopathy, a condition in which the brain malfunctions, may ensue from the buildup of metabolic waste products in the blood. This condition may lead to confusion, lethargy, and seizures.
High blood pressure often develops in people who have kidney failure, because the diseased kidneys produce hormones that raise blood pressure. In addition, diseased kidneys cannot excrete excess salt and water. Salt and fluid retention can lead to heart failure, which may cause shortness of breath. The sac that surrounds the heart (pericardium) may become inflamed (pericarditis) as metabolic waste products accumulate. This complication may cause chest pain and low blood pressure. The level of triglycerides in the blood is often elevated, which, along with hypertension, increases the risk for atherosclerosis. The buildup of metabolic waste in the blood also causes nausea, vomiting, and an unpleasant taste in the mouth, which may lead to malnutrition and weight loss. People who have advanced chronic kidney failure commonly develop gastrointestinal ulcers and bleeding. The skin may turn yellow-brown, and occasionally, the concentration of urea is so high that it crystallizes from sweat, forming a white powder on the skin. Some people with chronic kidney failure itch all over their body.
The formation and maintenance of bone tissue may be impaired (renal osteodystrophy) if certain conditions that accompany chronic kidney failure are present for a long time. These conditions include a high level of parathyroid hormone, low concentration of calcitriol (the active form of vitamin D) in the blood, impaired absorption of calcium, and a high concentration of phosphate in the blood. Renal osteodystrophy may lead to bone pain and an increased risk of fractures.
Diagnosis
Blood tests are essential and show increased levels of urea and creatinine, metabolic waste products that are normally filtered out by the kidneys. Typically, the blood becomes moderately acidic. The level of potassium in the blood is normal or only slightly increased but can become dangerously high when kidney failure reaches an advanced stage or if a person ingests large amounts of potassium. Usually, the person has some decline in red blood cell count (anemia). The level of triglycerides in the blood is likely to be elevated. The calcium and calcitriol levels decrease, and the phosphate and parathyroid hormone levels increase.
Urine volume often stays about the same, regardless of the amount of fluid consumed. Analysis of the urine may detect many abnormalities, including protein and abnormal cells.
Determining a precise cause becomes increasingly difficult as the kidney failure reaches an advanced stage. A kidney biopsy may be the most accurate test, but it is not recommended if results of an ultrasound show that the kidneys are small and scarred.
Prognosis and Treatment
Ultimately, chronic kidney failure progresses in most people regardless of treatment. It is fatal if not treated. Survival when kidney failure is severe (sometimes called end-stage kidney failure) is usually limited to several months in people who are not treated, but those who are treated with dialysis can live many years. The doctor must pay attention to conditions that can cause or worsen kidney failure and consequences of the kidney failure that might adversely affect overall health. For example, infections are treated promptly with antibiotics, and any obstructions in the urinary tract are removed or relieved.
The rate of decline in kidney function depends somewhat on the underlying disorder causing the kidney failure. For example, controlling the level of sugar in the blood as well as hypertension in people with diabetes substantially slows deterioration in kidney function. Drugs called angiotensin-converting enzyme (ACE) inhibitors and also angiotensin receptor blockers may decrease the rate of decline in kidney function in some people with chronic kidney failure.
Meticulous attention to diet helps control a number of potential problems. Sometimes mild acidosis can be controlled by increasing the intake of carbohydrates and reducing proteins. However, moderate or severe acidosis may require treatment with sodium bicarbonate. The decline in kidney function can be slowed slightly by restricting the amount of protein consumed daily. The person needs to consume sufficient carbohydrates to offset the reduction in protein. The triglyceride level may be lowered somewhat by limiting fat in the diet. Drugs such as gemfibrozil may be required to reduce the triglyceride level.
The intake of salt (sodium) usually does not have to be restricted unless fluid accumulates and is retained in the tissues or high blood pressure develops. A person with heart failure needs to restrict the intake of sodium. Diuretics may also relieve symptoms of heart failure, even when kidney function is poor, but dialysis may be needed to remove the excess fluid.
During chronic kidney failure, changes in thirst usually determine how much water is consumed. Occasionally, water intake needs to be restricted to prevent the sodium concentration in the blood from becoming too low. Foods that are extremely high in potassium, such as salt substitutes, must be avoided, and foods that are somewhat high in potassium, such as dates and figs, should not be consumed in excess. A high potassium level in the blood increases the risk of abnormal heart rhythms and cardiac arrest. If the potassium level becomes too high, drugs may help, but emergency dialysis may be required.
The elevated phosphorus level in the blood can cause deposits of calcium and phosphorus to form in tissues, including the blood vessels. Restricting the intake of foods high in phosphorus, such as dairy products, liver, legumes, nuts, and most soft drinks, lowers the phosphate concentration in the blood. Drugs that bind phosphate, such as calcium carbonate and calcium acetate, taken by mouth, may also lower the phosphorus level in the blood.
The anemia caused by kidney failure responds to the drugs erythropoietin or darbepoietin. Blood transfusions are given only if the anemia is severe, is causing symptoms, and does not respond to erythropoietin or darbepoietin. Doctors also look for and treat other causes of anemia, particularly dietary deficiencies of iron, folic acid (folate), and vitamin B12 or excesses of aluminum in the body. Most people receiving erythropoietin or darbepoietin regularly need to be given iron intravenously to prevent iron deficiency, which impairs the body's response to these drugs. Anemia often requires more aggressive treatment in older people, because they are more likely to have heart disease, which can be aggravated by the anemia. The tendency to bleed can be temporarily suppressed by transfusions of platelets or fresh frozen plasma or by such drugs as desmopressin or estrogens. Such treatment may be needed after an injury or before a surgical procedure or a tooth extraction.
A moderate or severe increase in blood pressure is treated with blood pressure drugs to prevent further impairment of heart and kidney function.
When the treatments for chronic kidney failure are no longer effective, the only option is long-term dialysis or kidney transplantation (see Section 16, Chapter 187). Despite the advent of dialysis, most people with advanced kidney failure die within 5 to 10 years. End-of-life care is important (see Section 1, Chapter 8).
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