Hyponatremia is a serum sodium concentration < 135 mEq/L (< 135 mmol/L). Significant hyponatremia may cause seizures or coma. Treatment is cautious sodium replacement with IV 0.9% saline solution; rarely, 3% saline solution is required, particularly if seizures are occurring.
(Hyponatremia in adults is discussed elsewhere.)
Etiology of Neonatal Hyponatremia
The most frequent cause of neonatal hyponatremia is hypovolemic dehydration caused by vomiting, diarrhea, or both. When fluid losses are replaced with fluids that have little or no sodium (eg, some juices), hyponatremia can result.
A less frequent cause is euvolemic hyponatremia caused by inappropriate antidiuretic hormone (ADH) secretion and consequent water retention. Possible causes of inappropriate ADH secretion include intracranial hemorrhage, central nervous system (CNS) infection, and rarely CNS tumors.
Overdilution of infant formula can lead to water intoxication.
Finally, hypervolemic hyponatremia occurs in the setting of excess sodium retention with even more excessive water retention, such as in heart failure or renal failure.
Symptoms and Signs of Neonatal Hyponatremia
Symptoms and signs of neonatal hyponatremia include nausea and vomiting, apathy, headache, seizures, hypothermia, weakness, and coma.
Infants with hyponatremic dehydration may appear quite ill because hyponatremia causes disproportionate reductions in extracellular fluid volume. Symptoms and signs are related to duration and degree of hyponatremia.
Diagnosis of Neonatal Hyponatremia
Serum sodium concentration
Diagnosis of neonatal hyponatremia is suspected based on symptoms and signs and is confirmed by measuring serum sodium concentration.
In dehydration, an increase in blood urea nitrogen may be observed.
Treatment of Neonatal Hyponatremia
Rarely IV hypertonic (3%) saline solution
Treatment of neonatal hyponatremia is with 5% D/0.45% to 0.9% saline solution IV in volumes equal to the calculated deficit, given over as many days as it takes to correct the sodium concentration by no more than 10 to 12 mEq/L/day (10 to 12 mmol/L/day) to avoid rapid fluid shifts in the brain.
Neonates with symptomatic hyponatremia (eg, lethargy, confusion) require emergency treatment with 3% saline solution IV to prevent seizure or coma.
