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. (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