What causes hypernatremia?
Rapid administration of hypertonic fluid—as often occurs with administration of ampules of sodium bicarbonate during cardiopulmonary resuscitation—and baby formula mixing errors can result in hypernatremia from pure solute gain.
The overwhelming majority of cases, however, arise because thirst perception or access to water is impaired.
Outside of the hospital, hypernatremia occurs most commonly among the institutionalized elderly and infants, who at baseline depend on others for access to water. Increased insensible water losses in the setting of febrile illness can incite hypernatremia among the elderly. In other instances, urine-concentrating defects resulting from loop diuretics or diabetes insipidus (DI) (see below) contribute to hypernatremia.
Among hospitalized patients, iatrogenic hypernatremia is common and found among all age groups, particularly intubated patients and patients with increased enteral fluid losses from either diarrhea or nasogastric drainage whose fluid prescription contains an insufficient amount of hypotonic fluid.
Loop diuretics, by reducing the tonicity of the medulla, diminish ADH-mediated water reabsorption and predispose to hypernatremia.