Electrolytes are involved in numerous metabolic and homeostatic processes throughout the body. Abnormalities are associated with excessive or reduced intake, altered absorption and excretion, or changes in hormonal and neurological homeostasis. Signs and symptoms of electrolyte disorders range from asymptomatic to life-threatening, depending on the speed of onset and degree of electrolyte loss or excess. The goals of therapy for electrolyte disorders are to prevent the development and/or treat life-threatening complications, identify and treat the underlying cause of the disturbance, correct concomitant abnormal electrolyte findings, and attain a normal electrolyte concentration while preventing overcorrection. The rapidity of development, severity of symptoms present, concomitant medical conditions, medications, dietary factors, and consideration for patient compliance should all be considered when selecting a treatment strategy. This chapter provides a review of the pathophysiology, clinical manifestations, and treatment of the most common electrolyte disorders. Listed in Table 39-1 are the normal serum concentrations of the common electrolytes.
TABLE 39-1Electrolyte Serum Concentrations ||Download (.pdf) TABLE 39-1Electrolyte Serum Concentrations
|Electrolytes ||Normal Values |
|Sodium (Na) ||135-145 mEq/L |
|Potassium (K) ||3.5-5.0 mEq/L |
|Magnesium (Mg) ||1.4-1.8 mEq/L |
|Calcium (Ca) ||8.5-10.5 mg/dL |
|Phosphate (PO4) ||2.6-4.5 mg/dL |
Sodium is the major extracellular cation and is responsible for the majority of the extracellular fluid (ECF) osmolality. Under normal conditions, the serum sodium concentration is maintained between 135 and 145 mEq/L. Disorders of sodium balance are the most common electrolyte disturbances encountered in clinical practice and occur in both inpatient and ambulatory patients. Hyponatremia can be classified by the patient’s serum osmolality and volume status (Figure 39-1). Pseudohyponatremia may be caused by hyperparaproteinemia, and hyperlipidemia (mainly hypertriglyceridemia). Hypernatremia always causes hypertonicity, and can be classified by the patient’s volume status (Figure 39-2). Common causes of sodium disorders are listed in Table 39-2.
Diagnosis of hyponatremia. Reproduced with permission from Chessman KH, Haney J. Disorders of Sodium and Water Homeostasis. In: DiPiro JT, Talbert RL, Yee GC, et al, eds. Pharmacotherapy: A Pathophysiologic Approach, 10e. McGraw-Hill; 2017.
Diagnosis of hypernatremia. Adapted from DiPiro JT, Talbert RL, Yee GC, et al: Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw Hill; 2017.
TABLE 39-2Causes and Contributing Factors for Electrolyte Disorders ||Download (.pdf) TABLE 39-2Causes and Contributing Factors for Electrolyte Disorders
|Electrolyte ||Decreased ||Increased |
|Sodium ||Hypovolemic hypotonic hyponatremia ||Hypovolemic hypernatremia |
| ||Excessive sweating ||Dermal losses |
| ||GI losses ||Vomiting |
| ||Renal losses ||NG suction |
| || ||Lactulose |
| ||Isovolemic hypotonic hyponatremia ||Osmotic diuresis—hyperglycemia, mannitol |
| ||SIADH secondary to malignancy, pulmonary disease, CNS disorders, iatrogenic sources |