Common electrolyte disorders (sodium, potassium, calcium, magnesium)

Introduction Serum sodium (Na) concentration is mediated by free water intake, circulating levels of antidiuretic hormone (ADH), and renal filtration of sodium. Hyponatremia is defined as serum sodium level of <135 mEq/L, and is due to a deficit of sodium relative to free water. It occurs most commonly in the setting of intravascular volume depletion, where increased secretion of ADH and volume replacement with free water will create a hypotonic state in the process of restoring volume. Hypernatremia is defined as a serum sodium level of >150 mEq/L, and is due to a deficit of free water relative to sodium. It occurs most commonly from loss of free water due to impaired access. Since most people are able to respond to their thirst stimulus with free water intake, hypernatremia is a rare condition, and is typically only seen in patients with limited mobility or impaired thirst mechanisms. Hypernatremia also occurs in the setting of diabetes insipidus, defined as a loss of free water due to either a deficiency of or insensitivity to ADH. Hyponatremia Classic presentation Signs and symptoms of moderate hyponatremia are nonspecific: generalized weakness, lethargy, nausea, vomiting, and muscle cramps are common.