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Key Features

Essentials of Diagnosis

  • Serum K+ < 3.5 mEq/L (< 3.5 mmol/L)

  • Severe hypokalemia may induce arrhythmias and rhabdomyolysis

  • Transtubular potassium concentration gradient (TTKG) can distinguish renal from nonrenal loss of potassium

General Considerations

  • Gastrointestinal loss due to infectious diarrhea is most common cause

  • Potassium shift into the cell is transiently stimulated by insulin and glucose and facilitated by β-adrenergic stimulation

  • α-Adrenergic stimulation blocks potassium shift into the cell

  • Aldosterone is an important regulator of body potassium, increasing potassium secretion in the distal renal tubule

  • Magnesium is an important cofactor for potassium uptake and for maintenance of intracellular potassium levels

  • Magnesium depletion should be suspected in persistent hypokalemia refractory to potassium repletion

Etiology

  • Potassium shift into cell (Table 21–3)

    • Insulin excess, eg, postprandial

    • Alkalosis

    • β-Adrenergic agonists

    • Trauma (via epinephrine release)

    • Hypokalemic periodic paralysis

    • Barium or cesium intoxication

  • Renal potassium loss (urine K+ > 40 mEq/L)

    • Increased aldosterone (mineralocorticoid) effects

      • Primary hyperaldosteronism

      • Secondary hyperaldosteronism (dehydration, heart failure)

      • Renovascular or malignant hypertension

      • Cushing syndrome

      • European licorice (inhibits cortisol)

      • Renin-producing tumor

      • Congenital abnormality of steroid metabolism (eg, adrenogenital syndrome, 17α-hydroxylase defect)

    • Increased flow of distal nephron

      • Diuretics (furosemide, thiazides)

      • Salt-losing nephropathy

    • Hypomagnesemia

      • Unreabsorbable anion

      • Carbenicillin, penicillin

    • Renal tubular acidosis (type I or II)

      • Fanconi syndrome

      • Interstitial nephritis

      • Metabolic alkalosis (bicarbonaturia)

    • Genetic disorder of the nephron

      • Bartter syndrome

      • Liddle syndrome

  • Extrarenal potassium loss (urine K+ < 20 mEq/L)

    • Vomiting, diarrhea, laxative abuse

    • Villous adenoma, Zollinger-Ellison syndrome

Table 21–3.Causes of hypokalemia.

Clinical Findings

Symptoms and Signs

  • Muscular weakness, fatigue, and muscle cramps are common in mild to moderate hypokalemia

  • Constipation or ileus may result from smooth muscle involvement

  • Flaccid paralysis, hyporeflexia, hypercapnia, tetany, and rhabdomyolysis may be seen in severe hypokalemia (serum K+ < 2.5 mEq/L)

  • Hypertension may result from aldosterone or mineralocorticoid excess

  • Renal manifestations include nephrogenic diabetes insipidus and interstitial nephritis

Diagnosis

Laboratory Tests

  • Serum K+ < 3.5 mEq/L (< 3.5 mmol/L)

  • Urinary potassium ...

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