Potassium, a necessary electrolyte, facilitates nerve impulse conduction andthe contraction of skeletal and smooth muscles, including the heart. It alsofacilitates cell membrane function and proper enzyme activity. Levels must bekept in a proper (homeostatic) balance for the maintenance of health. The normal concentration of potassium in the serum is in the range of 3.5 to 5.0 mM. Hyperkalemia refers to serum or plasma levels of potassium ions above 5.0 mM. Hypokalemia means serum or plasma levels of potassium ions that fall below3.5 mM. The concentration of potassium is often expressed in units of milliequivalents per liter (mEq/L), rather than in units of millimolarity (mM). Both units mean the same thing when applied to concentrations of potassium ions.
A normal adult who weighs about 154 lbs (70 kg) contains a total of about 3.6moles of potassium ions in the body. Most of this potassium (about 98%) occurs inside various cells and organs, where its concentration is about 150 mM.This level is in contrast to the much lower concentration found in the bloodserum, where only about 0.4% of the body's potassium resides. Hyperkalemia can be caused by an overall excess of body potassium, or by a shift from insideto outside cells. For example, hyperkalemia can be caused by the sudden release of potassium ions from muscle into the surrounding fluids.
Hypokalemia can result from two general causes: either from an overall depletion in the body's potassium or from excessive uptake of potassium by muscle from surrounding fluids. Hypokalemia due to overall depletion tends to be a chronic phenomenon, while hypokalemia due to a shift in location tends to be atemporary disorder.
In a normal person, hyperkalemia from too much potassium in the diet is prevented by at least three types of regulatory processes. First, various cells and organs act to prevent hyperkalemia by taking up potassium from the blood. It is also prevented by the action of the kidneys, which excrete potassium into the urine. A third protective mechanism is vomiting. Consumption of a largedose of potassium ions, such as potassium chloride, induces a vomiting reflex to expel most of the potassium before it can be absorbed.
Hyperkalemia can occur from a variety of causes, including the consumption oftoo much of a potassium salt; the failure of the kidneys to normally excretepotassium ions into the urine; the leakage of potassium from cells and tissues into the bloodstream; and from acidosis. The most common cause of hyperkalemia is kidney (or renal) disease, which accounts for about three quarters ofall cases.
Hyperkalemia can also be caused by a disease of the adrenal gland called Addison's disease. The adrenal gland produces the hormone aldosterone that promotes the excretion of potassium into the urine by the kidney.
Hyperkalemia can also result from injury to muscle or other tissues. Since most of the potassium in the body is contained in muscle, a severe trauma thatcrushes muscle cells results in an immediate increase in the concentration ofpotassium in the blood. Hyperkalemia may also result from severe burns or infections.
Acidic blood plasma, or acidosis, is an occasional cause of hyperkalemia. Acidosis, which occurs in a number of diseases, is defined as an increase in theconcentration of hydrogen ions in the bloodstream. In the body's attempt tocorrect the situation, hydrogen is taken up by muscle cells out of the bloodin an exchange mechanism involving the transfer of potassium ions into the bloodstream. This can abnormally elevate the plasma's concentration of potassium ions. When acidosis is the cause of hyperkalemia, treating the patient foracidosis has two benefits: a reversal of both the acidosis and the hyperkalemia.
Symptoms of hyperkalemia include abnormalities in the behavior of the heart.Heart abnormalities of mild hyperkalemia (5.0 to 6.5 mM potassium) can be detected by an electrocardiogram (ECG or EKG). With severe hyperkalemia (over 8.0 mM potassium), the heart may beat at a dangerously rapid rate (fibrillation) or stop beating entirely (cardiac arrest). Patients with moderate or severehyperkalemia may also develop nervous symptoms such as tingling of the skin,numbness of the hands or feet, weakness, or a flaccid paralysis, which is characteristic of both hyperkalemia and hypokalemia (low plasma potassium).
Hypokalemia is most commonly caused by the use of diuretics. Diuretics are drugs that increase the excretion of water and salts in the urine. Diuretics are used to treat a number of medical conditions, including hypertension (highblood pressure), congestive heart failure, liver disease, and kidney disease.However, diuretic treatment can have the side effect of producing hypokalemia. In fact, the most common cause of hypokalemia in the elderly is the use ofdiuretics. The use of furosemide and thiazide, two commonly used diuretic drugs, can lead to hypokalemia. In contrast, spironolactone and triamterene arediuretics that do not provoke hypokalemia.
Other commons causes of hypokalemia are excessive diarrhea or vomiting. Diarrhea and vomiting can be produced by infections of the gastrointestinal tract.Due to a variety of organisms, including bacteria, protozoa, and viruses, diarrhea is a major world health problem. It is responsible for about a quarterof the 10 million infant deaths that occur each year. Although nearly all ofthese deaths occur in the poorer parts of Asia and Africa, diarrheal diseases are a leading cause of infant death in the United States. Diarrhea resultsin various abnormalities, such as dehydration (loss in body water), hyponatremia (low sodium level in the blood), and hypokalemia.
Because of the need for potassium to control muscle action, hypokalemia can cause the heart to stop beating. Young infants are especially at risk for death from this cause, especially where severe diarrhea continues for two weeks or longer. Diarrhea due to laxative abuse is an occasional cause of hypokalemia in the adolescent or adult. Enema abuse is a related cause of hypokalemia.Laxative abuse is especially difficult to diagnose and treat, because patients usually deny the practice. Up to20% of persons complaining of chronic diarrhea practice laxative abuse. Laxative abuse is often part of eating disorders, such as anorexia nervosa or bulimia nervosa. Hypokalemia that occurswith these eating disorders may be life-threatening.
Alcoholism occasionally results in hypokalemia. About one half of alcoholicshospitalized for withdrawal symptoms experience hypokalemia. The hypokalemiaof alcoholics occurs for a variety of reasons, usually poor nutrition, vomiting, and diarrhea. Hypokalemia can also be caused by hyperaldosteronism; Cushing's syndrome; hereditary kidney defects such as Liddle's syndrome, Bartter'ssyndrom, and Franconi's syndrome; and eating too much licorice.
Mild hypokalemia usually results in no symptoms, while moderate hypokalemia results in confusion, disorientation, weakness, and discomfort of muscles. Onoccasion, moderate hypokalemia causes cramps during exercise. Another symptomof moderate hypokalemia is a discomfort in the legs that is experienced while sitting still. The patient may experience an annoying feeling that can be relieved by shifting the positions of the legs or by stomping the feet on thefloor. Severe hypokalemia results in extreme weakness of the body and, on occasion, in paralysis. The paralysis that occurs is "flaccid paralysis," or limpness. Paralysis of the muscles of the lungs results in death. Another dangerous result of severe hypokalemia is abnormal heart beat (arrhythmia) that canlead to death from cardiac arrest (cessation of heart beat). Moderate hypokalemia may be defined as serum potassium between 2.5 and 3.0 mM, while severehypokalemia is defined as serum potassium under 2.5 mM.
Insulin injections are used to treat hyperkalemia in emergency situations. Insulin is a hormone well known for its ability to stimulate the entry of sugar(glucose) into cells. It also provokes the uptake of potassium ions by cells, decreasing potassium ion concentration in the blood. When insulin is used to treat hyperkalemia, glucose is also injected. Serum potassium levels beginto decline within 30 to 60 minutes and remain low for several hours. In non-emergency situations, hyperkalemia can be treated with a low potassium diet. If this does not succeed, the patient can be given a special resin to bind potassium ions. One such resin, sodium polystyrene sulfonate (Kayexalate), remains in the intestines, where it absorbs potassium and forms a complex of resinand potassium. Eventually this complex is excreted in the feces. A typical dose of resin is 15 grams, taken one to four times per day. The correction ofhyperkalemia with resin treatment takes at least 24 hours.
In emergency situations, when severe hypokalemia is suspected, the patient should be put on a cardiac monitor, and respiratory status should be assessed.If laboratory test results show potassium levels below 2.5 mM, intravenous potassium should be given. In less urgent cases, potassium can be given orallyin the pill form. Potassium supplements take the form of pills containing potassium chloride (KCl), potassium bicarbonate (KHCO3), and potassium acetate. Oral potassium chloride is the safest and most effective treatmentfor hypokalemia. Generally, the consumption of 40-80 mmoles of KCl per day is sufficient to correct the hypokalemia that results from diuretic therapy. For many people taking diuretics, potassium supplements are not necessary as long as they eat a balanced diet containing foods rich in potassium.