Potassium imbalance
Potassium, a cation that’s the dominant cellular electrolyte, facilitates contraction of both skeletal and smooth muscles—including myocardial contraction—and figures prominently in nerve impulse conduction, acid-base balance, enzyme action, and cell-membrane function. Because the normal serum potassium level has such a narrow range (3.5 to 5 mEq/L), a slight deviation in either direction can produce profound clinical consequences.
Paradoxically, both hypokalemia (potassium deficiency) and hyperkalemia (potassium excess) can lead to muscle weakness and flaccid paralysis because both create an ionic imbalance in neuromuscular tissue excitability. Both conditions also diminish excitability and conduction rate of the heart muscle, which may lead to cardiac arrest.
Causes
There are a number of possible causes of potassium imbalance.
Hypokalemia
Because many foods contain potassium, hypokalemia rarely results from a dietary deficiency. Instead, potassium loss results from:
excessive GI or urinary losses, such as vomiting, gastric suction, diarrhea, dehydration, anorexia, or prologed laxative use
trauma (injury, burns, or surgery), in which damaged cells release potassium, which enters serum or extracellular fluid to be excreted in the urine
chronic renal disease, with tubular potassium wasting
certain drugs, especially potassium-wasting diuretics, steroids, and certain sodium-containing antibiotics (carbenicillin)
acid-base imbalances, which cause potassium shifting into cells without true depletion in alkalosis
prolonged potassium-free I.V. therapy
hyperglycemia, causing osmotic diuresis and glycosuria
Cushing’s syndrome, primary hyperaldosteronism, excessive ingestion of licorice, and severe serum magnesium deficiency.
Hyperkalemia
Generally, hyperkalemia results from the kidneys’ inability to excrete excessive amounts of potassium infused I.V. or administered orally; from decreased urine output, renal dysfunction, or renal failure; or from the use of potassium-sparing diuretics such as triamterene by patients with renal disease. It may also result from any injuries or conditions that release cellular potassium or favor its retention, such as burns, crushing injuries, failing renal
function, adrenal gland insufficiency, dehydration, or diabetic acidosis.
function, adrenal gland insufficiency, dehydration, or diabetic acidosis.
Clinical features of potassium imbalance
| Dysfunction | Hypokalemia | Hyperkalemia |
|---|---|---|
| Acid-base balance |
|
|
| Cardiovascular |
