Upon completion of the chapter, the reader will be able to:
- 1. Describe the cellular distribution of potassium.
- 2. Identify the metabolic factors that regulate potassium balance.
- 3. Determine the etiology of hypo- and hyperkalemia.
- 4. Recognize the clinical signs and symptoms of hypo- and hyperkalemia.
- 5. Identify drug-related causes of hypo- and hyperkalemia.
- 6. Describe the various treatments for hypo- and hyperkalemia in terms of mechanism of action, place in therapy, dosage, route, frequency, onset-of-action, and monitoring.
- 7. Devise an appropriate pharmacotherapy and monitoring plan for patients exhibiting hypo- and hyperkalemia.
- 8. Describe the cellular distribution of magnesium.
- 9. Determine the etiology of hypo- and hypermagnesemia.
- 10. Devise an appropriate pharmacotherapy and monitoring plan for patients exhibiting hypo- and hypermagnesemia.
Potassium and magnesium are electrolytes that are responsible for numerous metabolic activities. Disorders of these electrolytes are frequently seen in both the acute care and community ambulatory care settings. Therefore, clinicians need a firm understanding of the etiology, pathophysiology, symptoms, pharmacotherapy, and monitoring of these disorders. This chapter describes the homeostatic mechanisms that are responsible for the maintenance of normal potassium and magnesium serum concentrations. The clinical disorders responsible for the development of hyperkalemia, hypermagnesemia, hypokalemia, and hypomagnesemia are also reviewed.
Potassium is the most abundant cation in the body, with estimated total-body stores of 3,000 to 4,000 mEq (3,000–4,000 mmol).1 Ninety-eight percent of this amount is contained within the intracellular compartment, and the remaining 2% is distributed within the extracellular compartment. The sodium potassium adenosine triphosphatase (Na+-K+-ATPase) pump located in the cell membrane is responsible for the compartmentalization of potassium. This pump is an active transport system that maintains increased intracellular stores of potassium by transporting sodium out of the cell and potassium into the cell at a ratio of 3:2. Consequently, the pump maintains a higher concentration of potassium inside the cell.
The normal serum concentration range for potassium is 3.5 to 5.0 mEq/L (3.5–5.0 mmol/L), whereas the intracellular potassium concentration is usually approximately 150 mEq/L (150 mmol/L).2 Approximately 75% ...