The principles of correcting hypernatremia are similar to those for correcting hyponatremia. Sodium is a functionally impermeable solute, and thus, it is the main contributor to cellular osmolarity and causes shifts of water across cell membranes. These fluid shifts may cause cells to expand or shrink more rapidly than the body can withstand. Rapid decreases in brain cell size caused by hypernatremia can lead to brain injury due to brain tissue separation from the meninges, rupture of the bridging veins, and venous sinus thromboses. Rapid correction of severe hypernatremia can also lead to significant brain injury from increased intracranial pressure and herniation, caused by rapid cellular expansion within the fixed capacity of the intracranial vault. Often, rapid iatrogenic corrections of hypernatremia cause more serious complications than the original disorder. Studies suggest that a patient with chronic hypernatremia is at a high risk for cerebral edema when the sodium drops >0.5 mEq/L/hr. To manage the rate of sodium decline, the practitioner needs to be aware of the general fluid status of the patient, select the appropriate initial fluid concentration, and be prepared to frequently alter its rate and concentration based on frequent checks of the serum sodium concentration and ongoing fluid losses.

Hypernatremia is defined as a serum sodium concentration >145 mEq/L. It represents a deficit of water in relation to the body’s sodium stores and occurs as a result of a net water loss, or less commonly, a net sodium gain. It should be considered in patients who present with anorexia, restlessness, weakness, a high-pitched cry, hyperpnea, nausea, and vomiting. The greater and more rapid the water and salt disruption, the more significant the patient’s clinical manifestations. Patients with sodium concentrations >170 mEq/L may have severe neurologic symptoms, including stupor or coma. Practitioners should have a high index of suspicion for hypernatremia when evaluating infants and other patients who have an impaired ability to control their free water intake.