Sodium disorders (ie, hyponatremia, hypernatremia) are common electrolyte disturbances in clinical medicine and are associated with increased rates of morbidity and mortality. Etiologies of hyponatremia are classified into four categories. The first is pseudohyponatremia, in which the sodium level is low due to hyperproteinemia, hyperlipidemia, or hyperglycemia. The other three categories are based on overall patient fluid status and include hypovolemic (commonly due to fluid loss), hypervolemic (commonly due to fluid retention from heart failure, cirrhosis, or renal failure), and euvolemic (most often because of syndrome of inappropriate secretion of antidiuretic hormone). Hypovolemic hyponatremia is managed by rehydration with isotonic saline. Hypervolemic hyponatremia is managed by addressing the underlying cause. Euvolemic hyponatremia is managed by restricting free water intake, addressing the underlying cause, and occasionally with drugs (eg, vasopressin receptor antagonists). Patients with severe or acutely symptomatic hyponatremia (eg, altered mental status, seizures), including those with acute symptomatic exercise-induced hyponatremia, require urgent treatment. This should consist of hypertonic saline administration along with monitoring of sodium levels to avoid overly rapid correction. Hypernatremia most often occurs because of water loss or inadequate water intake. Depending on severity, management involves oral or intravenous hypotonic fluids and addressing the underlying cause.
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