Causes of low potassium (hypokalemia)

With normal blood pH, normal serum potassium concentration may mask an actual overall deficiency in the body (up to 200 mmol). A decrease in serum potassium concentration by every 1 mmol/L usually corresponds to an overall deficiency of approximately 350 mmol. A serum potassium concentration below 2 mmol/L indicates an overall deficiency in the body exceeding 1000 mmol.

The following situations lead to hypokalemia.

• The loss of gastrointestinal fluids and the accompanying loss of chlorides deepen the metabolic alkalosis.
• Long-term treatment with osmotic diuretics or saluretics (mannitol, furosemide), as well as diabetic glucosuria.
• Stressful conditions accompanied by increased activity of the adrenal glands, Cushing's disease.
• Decreased potassium intake in the postoperative and post-traumatic periods in combination with sodium retention in the body (iatrogenic hypokalemia).
• Prolonged acidosis or alkalosis, resulting in impaired renal function and kaliuria.
• Pre-existing potassium deficiency caused by severe chronic disease and aggravated by the postoperative period.
• Long-term use of glucocorticosteroids.
• Dilutional hypokalemia in the rehydration phase after acute or chronic dehydration.
• Chronic renal failure.
• Bartter's syndrome.
• Low-renin hyperaldosteronism.

All the above causes of hypokalemia are based on four main mechanisms: decreased potassium intake, increased potassium transfer from the extracellular fluid into the cell, decreased potassium exit from the cell, and increased potassium loss. However, the main mechanism of hypokalemia is increased potassium loss, which occurs in two ways - through the gastrointestinal tract and kidneys (hypokalemia of "exhaustion"). Intestinal and biliary fistulas, as well as extensive burns, are two secondary ways of potassium loss. The most massive potassium losses occur with repeated vomiting (in this regard, hyperkalemia is often absent in patients with acute renal failure), intestinal obstruction, and all diseases accompanied by diarrhea.

The main causes of increased potassium transfer from the extracellular space into the cell include insulin administration (or the presence of insulinoma), thyrotoxicosis, and alkalosis. Hypokalemia associated with alkalosis is caused, firstly, by potassium transferring from the extracellular fluid (plasma) to the intracellular fluid in exchange for hydrogen ions entering to lower the blood pH; secondly, there is increased excretion of potassium in the urine, with potassium being lost and hydrogen ions being reabsorbed to correct the alkalosis.

A decrease in potassium intake is possible in patients with poor nutrition (with alcoholism, anorexia), as well as with long-term intravenous administration of potassium-free solutions.

Symptoms of potassium deficiency include nausea, vomiting, muscle weakness (including respiratory muscles - shallow breathing), intestinal and bladder atony, and cardiac weakness. When the serum potassium concentration is below 3 mmol/l, changes are noted on the ECG indicating a disturbance and weakening of excitability and conductivity in the heart muscle. In some cases, the relationship between the concentration of potassium in the blood and the occurrence of such serious consequences as cardiac arrhythmia is not observed.