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Introduction ⬇

ECG effects of hypokalemia

Rhythm

  • Regular

Rate

  • Within normal limits

P wave

  • Normal size
  • Normal configuration
  • May be peaked in severe hypokalemia

PR interval

  • May be prolonged

QRS complex

  • Within normal limits
  • Possibly widened
  • Prolonged in severe hypokalemia

T wave

  • Has decreased amplitude
  • Becomes flat as potassium level drops, and U wave appears (the key finding, as shown in shaded area on strip)
  • Flattens completely in severe hypokalemia and may become inverted
  • May fuse with increasingly prominent U wave

QT interval

  • Usually indiscernible as T wave flattens

Other

  • Depressed ST segment
  • Increased amplitude and prominence of U wave as hypokalemia worsens; may fuse with T wave


What Causes It ⬆ ⬇

  • Potassium loss through abnormal routes
    • Continuous nasogastric drainage
    • Diarrhea
    • Drainage tubes
    • Intestinal fistulae
    • Laxative abuse
    • Vomiting
  • Increased secretion of potassium by the distal tubule
  • Low serum magnesium level
  • Excessive aldosterone secretion
  • Drugs
    • Antibiotics, such as amphotericin B or gentamicin
    • Diuretics
    • Corticosteroids
  • Increased entry of potassium into cells due to alkalosis, especially respiratory
  • Reduced potassium intake or dietary deficiency due to anorexia or nothing-by-mouth status

What to Look for ⬆ ⬇

  • Signs and symptoms of smooth-muscle atony
    • Anorexia
    • Constipation
    • Intestinal distention
    • Paralytic ileus
    • Nausea
    • Vomiting
  • Skeletal muscle weakness (first appearing in larger muscles of the arms and legs and eventually in the diaphragm, causing respiratory arrest)
  • Cardiac arrhythmias
    • Atrioventricular block
    • Bradycardia
    • Ventricular arrhythmias

How It's Treated ⬆

  • Identify and correct the underlying cause.
  • Correct acid–base imbalances.
  • Replace potassium losses and prevent further losses.
  • Encourage intake of potassium-rich foods and fluids.
  • Give oral or IV potassium supplements.
  • Monitor serum potassium levels closely.
  • Keep in mind that hypokalemia may result in digoxin toxicity. Monitor serum digoxin and potassium levels closely at the start of therapy and until maintenance doses are determined.
  • Identify and manage cardiac arrhythmias.
  • Monitor the patient closely for early evidence of skeletal muscle weakness because it may progress to respiratory arrest.