Figure 116

Diagnostic algorithm for hyponatremia. The next step in the evaluation of a hyponatremic patient is to assess volume status and identify it as hypovolemic, euvolemic or hypervolemic. The patient with hypovolemic hyponatremia has both total body sodium and water deficits, with the sodium deficit exceeding the water deficit. This occurs with large gastrointestinal and renal losses of water and solute when accompanied by free water or hypotonic fluid intake. In patients with hypervolemic hyponatremia, total body sodium is increased but total body water is increased even more than sodium, causing hyponatremia. These syndromes include congestive heart failure, nephrotic syndrome, and cirrhosis. They are all associated with impaired water excretion. Euvolemic hyponatremia is the most common dysnatremia in hospitalized patients. In these patients, by definition, no physical signs of increased total body sodium are detected. They may have a slight excess of volume but no edema [12]. (Modified from Halterman and Berl [12]; with permission.)

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