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Updated: Jan 26 2020

Potassium Shifts

  • 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. 
  • 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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