Significance of Potassium

SIGNIFICANCE OF POTASSIUM

Potassium is the major intracellular electrolyte; in fact, 98% of the body’s potassium is inside the cells. The remaining 2% is in the ECF, and it is this 2% that is important in neuromuscular func-tion. Potassium influences both skeletal and cardiac muscle activ-ity. For example, alterations in its concentration change myocardial irritability and rhythm. Under the influence of the sodium– potassium pump and based on the body’s needs, potassium is con-stantly moving in and out of cells. The normal serum potassium concentration ranges from 3.5 to 5.5 mEq/L (3.5–5.5 mmol/L), and even minor variations are significant. Potassium imbalances are commonly associated with various diseases, injuries, medica-tions (diuretics, laxatives, antibiotics), and special treatments, such as parenteral nutrition and chemotherapy (Cohn et al., 2000).

To maintain potassium balance, the renal system must func-tion because 80% of the potassium is excreted daily from the body by way of the kidneys; the other 20% is lost through the bowel and in sweat. The kidneys are the primary regulators of potassium balance and accomplish this by adjusting the amount of potassium that is excreted in the urine. As serum potassium levels increase, so does the potassium level in the renal tubular cell. A concentration gradient occurs, favoring the movement of potassium into the renal tubule with the loss of potassium in the urine. Aldosterone also increases the excretion of potassium by the kidney. Because the kidneys do not conserve potassium as well as they conserve sodium, potassium may still be lost in urine in the presence of a potassium deficit.