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  1. Problem. A serum potassium value is 2.8 mEq/L. Normal serum potassium values vary with technique used by the laboratory but are usually between 3.5 and 5 mEq/L. Moderate hypokalemia is 2.5–3.0 mEq/L; severe hypokalemia is <2.5 mEq/L.

  2. Immediate questions

      1. What is the central serum potassium? If a low value is obtained by heelstick, central values should be obtained because they may actually be lower than values obtained by heelstick because of the hemolysis of red blood cells.

      1. Are potassium-wasting medications or digitalis being given? Diuretics may cause hypokalemia. Hypokalemia may cause arrhythmias if digitalis is being administered.

      1. How much potassium is the infant receiving? Normal maintenance doses are 1–2 mEq/kg/day.

      1. Is diarrhea occurring, or is a nasogastric tube in place? Loss of large amounts of gastrointestinal (GI) fluids can cause hypokalemia.

  3. Differential diagnosis

      1. Inadequate maintenance infusion of potassium (Inadequate intake). For a further discussion, see Chapter 8.

      1. Abnormal potassium losses (GI and renal)

          1. Medications (most common cause of hypokalemia in the newborn). Diuretic use, especially long-term therapy, is the most common cause. Any thiazide diuretic may cause hypokalemia. High and continuous doses of spironolactone with hydrochlorothiazide (Aldactazide) have also resulted in hypokalemia. Amphotericin B can cause direct renal tubular damage with resulting hypokalemia. Gentamicin, carbenicillin, and corticosteroids are associated with potassium losses. β-Adrenergic agonists can cause hypokalemia with a case report of epinephrine overdose causing newborn hypokalemia and rhabdomyolysis.

          1. Gastrointestinal tract losses. Diarrhea, loss of fluid via nasogastric tube, and vomiting may cause hypokalemia. Pyloric stenosis with vomiting and ileostomy can cause hypokalemia.

          1. Primary or secondary hypermineralocorticoidism. Renal artery stenosis is a cause. In certain forms of congenital adrenal hyperplasia, hypokalemia may occur.

          1. Renal loss of potassium (other than induced by medications).

              1. Any cause of polyuria can be associated with hypokalemia.

              1. Excessive base administration.

              1. Bartter syndrome, a rare form of potassium wasting, secondary to chloride channels abnormality, is characterized by polyuria, hypokalemia, hyponatremia, and hypercalciuria with risk of nephrocalcinosis with elevated levels of aldosterone and renin.

              1. Hyperaldosteronism. Hypertension, hypokalemia, and suppressed renin activity are the three laboratory hallmarks of this disease, an increased potassium secretion from a primary defect of the adrenal gland.

              1. Cushing syndrome, hyperfunction of the adrenal cortex, in infants is usually caused by a functioning adrenocortical tumor.

              1. Proximal renal tubular acidosis type 2.

              1. Distal renal tubular acidosis type 1.

      1. Redistribution of potassium by an increase in intracellular uptake (movement of potassium from serum into the cells)

          1. Alkalosis (metabolic or respiratory). An increase in pH by 0.1 unit causes a decrease in the potassium level by 0.3–1.3 mEq/L. The decrease is less in respiratory than in metabolic alkalosis.

          1. Insulin. An increase in insulin causes intracellular uptake in potassium with hypokalemia.

          1. Medications cause an increase in intracellular uptake of potassium. These include terbutaline, albuterol, isoproterenol, and catecholamines.

  4. Database

      1. Physical examination. Mild hypokalemia may not cause any symptoms. Symptoms of clinically significant hypokalemia include muscle weakness and decreased tendon reflexes, but these are difficult to evaluate in an infant. In severe hypokalemia, the infant can have lethargy, an ...

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