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