Hypokalemia

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

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)

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