[L. potassa, potash + -ium]
SYMB: K A metallic chemical element, atomic weight (mass) 39.0983, atomic number 19. It serves as both the principal cation in intracellular fluid and as an important electrolyte in extracellular fluid. Intracellular potassium concentrations are about 70 mmol/L, but the normal range of extracellular potassium is maintained by the body between only 3.5 and 5 mmol/L. Along with other electrolytes (such as sodium, magnesium, calcium, and chloride), potassium participates in many functions, including cell membrane homeostasis, nerve impulse conduction, and muscle contraction.
Potassium, which constitutes 0.35% of body weight, is found in most foods, including cereals, dried peas and beans, fresh vegetables, fresh or dried fruits, fruit juices, sunflower seeds, nuts, molasses, cocoa, and fresh fish, beef, ham, or poultry. The usual dietary intake of potassium is 50 to 150 mEq/day. In healthy people, the kidneys excrete any potassium excess consumed in the diet. In patients with renal failure, congestive heart failure, hypertension, and many other illnesses, serum potassium levels must be adjusted carefully to avoid adverse consequences of deficiency or excess.
Muscle weakness, dizziness, thirst, confusion, changes in the electrocardiogram, and life-threatening arrhythmias may develop during potassium deficiency (hypokalemia).
Extracellular potassium is increased in renal failure; in destruction of cells with release of intracellular potassium in burns, crush injuries, or severe infection; in adrenal insufficiency; in overtreatment with potassium salts; and in metabolic acidosis. This causes weakness and paralysis, impaired electrical conduction in the heart, and eventually ventricular fibrillation and death. Hyperkalemia can be treated by withholding potassium, by using drugs such as sodium polystyrene sulfonate, a cation exchange resin, to lower the potassium concentration in cells, and by using calcium gluconate to counteract the effects on the heart.
Rapid infusion of potassium is painful and may cause severe hyperkalemia, complicated by cardiac arrhythmias. Institutional protocols for the use of intravenous potassium should be followed carefully.
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