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Potassium Shifts

Topic updated on 11/14/17 9:18pm

Snapshot
  • A 22-year-old man presents to the emergency department after a crush injury to his lower extremities. He reports muscular pain, weakness, and palpitations and noticed that his urine is "tea-colored." On physical exam, there is tenderness upon palpation of his lower extremities and 4-/5 power in the same area. Urinalysis is heme positive. Laboratory testing is significant for a potassium level of 6.5 mEq/L and creatinine kinase level of 1,500 units/L. An electrocardiogram is shown. (Rhabdomyolysis resulting in hyperkalemia)

Introduction
  • The major intracellular cation is potassium and magnesium
    • cells contain approximately 98% of the body's potassium
    • the sodium-potassium-ATPase (Na+/K+ -ATPase) pump within the cellular membrane maintains this potassium distribution between the intracellular and extracellular compartments
    • potassium is the major determinant of the resting membrane potential across the cell membrane
      • normal potassium homeostasis is essential for proper action potential generation in muscle and neural tissue
  • Normal potassium homeostasis
    • determined by
      • potassium intake
      • intracellular and extracellular potassium distribution
      • urinary excretion of potassium
        • mainly accomplished by principal cells in the nephron
  • Disruptions in potassium homeostasis can result in hyperkalemia or hypokalemia
    • these disruptions can have a number of clinical consequences
      • hyperkalemia
        • defined as a potassium level in the blood that is > 5.0-5.5 mEq/L
        • muscle and cardiac dysfunction
          • muscular symptoms
            • myalgias
            • muscle paralysis
            • chest pain
          • cardiac symptoms
            • arrhythmias and palpitations
        • nausea and vomiting
        • parasthesias
      • hypokalemia
        • defined as a potassium level in the blood that is < 3.5 mEq/L
        • muscle and cardiac dysfunction
          • muscular symptoms
            • abdominal cramping
            • muscle weakness and cramping
          • cardiac symptoms
            • palpitations
        • parasthesias
        • nausea and vomiting
 
Factors that Influence Potassium Shifts
Shifts out of Cells (Hyperkalemia)
Shifts into Cells (Hypokalemia)
  • Insulin deficiency
  • β2-adrenergic antagonists
  • Acidosis
    • cells attempt to buffer excess hydrogen ions to shift these ions into the cells
      • in exchange for this intracellular uptake of hydrogen, potassium is transferred out the cell
        • this attempts to achieve electroneutrality
  • Digitalis
    • secondary to dose-dependent Na+/K+ -ATPase pump inhibition
  • Cell lysis (e.g., rhabdomyolysis)
  • Exercise
  • Hyperosmolarity
  • Succinylcholine
  • ↑ insulin
  • Hyperglycemia
    • this stimulates endogenous insulin secretion from the pancreas in normal conditions
  • β2-adrenergic agonists
  • Alkalosis
  • Hyposmolality

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