Lesson 6: Potassium

Potassium Overview

  • Normal serum potassium: 3.5 - 5.5 mEq/L
  • Most abundant intracellular cation.
  • Regulates resting membrane potential in nervous, skeletal, and cardiac muscle.

Effects of Potassium Levels

  • Hypokalemia (< 3.5 mEq/L): Hyperpolarizes membranes.
  • Hyperkalemia (> 5.5 mEq/L): Depolarizes membranes.

Potassium Regulation

  • The kidney is the primary regulator of potassium.
  • Decreased glomerular filtration (renal failure) increases serum potassium.

Causes of Hypokalemia

  • Poor Intake: Dietary deficiency.
  • GI Loss: Vomiting, diarrhea, nasogastric suction.
  • Renal Loss: Diuretics, metabolic alkalosis, licorice effects.
  • Redistribution: Insulin, beta-2 agonists, hyperventilation.

Presentation of Hypokalemia

  • Skeletal muscle cramps, weakness, paralysis.
  • Can worsen digoxin toxicity.

Causes of Hyperkalemia

  • Increased Intake: Potassium supplements, blood products.
  • Impaired Excretion: Renal failure, hypoaldosteronism, NSAIDs.
  • Redistribution: Acidosis, succinylcholine, beta-blockers.
  • Cellular Injury: Tumor lysis, hemolysis, burns, crush injury.

Presentation of Hyperkalemia

  • Cardiac rhythm disturbances (EKG changes):
    • Peaked T waves, prolonged PR and QT intervals, sine wave pattern at very high levels.

Treatment of Hyperkalemia

  • Cardiac Stabilization: IV calcium.
  • Redistribution: Insulin + D50, hyperventilation, bicarbonate, beta-2 agonists.
  • Elimination: Diuretics, kayexalate, dialysis.

Key Points on Treatment

  • Assess total body potassium: 98% stored intracellularly.
  • Treat hypokalemia only if low whole body potassium (not redistribution).
  • Administer potassium slowly:
    • Peripheral line: 10 mEq/hr.
    • Central line: 20 mEq/hr.
  • Always rule out pseudohyperkalemia due to lab errors before treating hyperkalemia.