endocrine and metabolic disorders
Hypokalemia
Key Points
Hypokalemia can be caused by decreased intake of potassium or shift of extracellular potassium into cells, but it is usually caused by excessive losses of potassium in the urine or from the gastrointestinal tract. Clinical signs include muscle weakness, cramping, fasciculations, paralytic ileus, and when hypokalemia is severe, hypoventilation, and hypotension. ECG changes typically occur when serum potassium is<3 mEq/L (< 3 mmol/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 premature ventricular and atrial contractions, ventricular and atrial tachyarrhythmias, and 2nd- or 3rd-degree atrioventricular block; eventually, ventricular fibrillation may occur. Replace potassium orally, giving 20 to 80 mEq (20 to 80 mmol)/day unless patients have ECG changes or severe symptoms. For hypokalemic arrhythmia, give IVpotassium chloridethrough a central vein at a maximum of 40 mEq (40 mmol)/hour and only with continuous cardiac monitoring; routine IV infusion should be no more than 10 mEq (10 mmol)/hour. 