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Hypokalemia is a plasma potassium (K) concentration of less than 3.5 mEq/L caused by a deficit in total body potassium stores or abnormal movement of potassium into cells. It may be caused by a decreased intake of potassium or usually by excessive losses of potassium from the kidneys or from the gastrointestinal tract. Drugs known to cause hypokalemia include diuretics, laxatives, antimicrobials, mineralo -and glucocorticoids, and beta-2 receptor agonists. Clinical signs are dependent on the degree of potassium depletion and may include muscle weakness, muscle cramping, fasciculations, and paralytic ileus. Hypoventilation and hypotension occur when hypokalemia is severe. ECG changes typically occur when serum potassium is < 3 mEq/L, and include ST segment sagging, T wave depression, and U wave elevation. With marked hypokalemia, the T wave becomes progressively smaller and the U wave becomes increasingly larger. Hypokalemia may cause arrhythmias including premature ventricular and atrial contractions, ventricular and atrial tachyarrhythmias, and 2nd- or 3rd-degree atrioventricular block; eventually, ventricular fibrillation may occur. Treatment is with oral potassium replacement, giving 20 to 80 mEq/day unless patients have ECG changes or severe symptoms. For hypokalemic arrhythmias, intravenous potassium chloride is given through a central vein, at a maximum of 40 mEq/h and only with continuous cardiac monitoring; routine IV infusion should be no more than 10 mEq/h.
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