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Hypernatremia in newborns
Last reviewed: 05.07.2025
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[ What causes hypernatremia in newborns?
Hypernatremia occurs when water losses exceed sodium losses (hypernatremic dehydration), when sodium intake exceeds sodium losses (salt poisoning), or both. The most common causes of water losses exceeding sodium losses are diarrhea, vomiting, or high fever. It may also occur due to feeding problems in the early days of life and may occur in very low birth weight (OHMT) infants born at 24 to 28 weeks' gestation. In OHMT infants, insensible water losses through the immature, water-permeable stratum corneum, combined with immature renal function and a reduced ability to concentrate urine, increase free water loss. Insensible water losses through the skin are also greatly increased by exposure to a radiant warmer and by phototherapy. In such conditions, VLBW infants may require up to 250 ml/(kg x day) of water intravenously in the first few days, after which the stratum corneum develops and imperceptible water losses decrease.
Excessive salt intake most often results from adding too much salt when preparing infant formula or from administering hyperosmolar solutions. Fresh frozen plasma and albumin contain sodium and can cause hypernatremia if given repeatedly to very premature infants.
Symptoms of hypernatremia in newborns
Symptoms of hypernatremia include lethargy, restlessness, hyperreflexia, muscle hypertonicity, and seizures. Major complications include intracranial hemorrhage, venous sinus thrombosis, and acute renal tubular necrosis.
The diagnosis of hypernatremia is suspected based on symptoms and signs and is confirmed by measuring serum sodium concentration. Additional laboratory changes may include elevated blood urea nitrogen, moderately elevated glucose, and, if potassium is low, decreased serum calcium.
Treatment of hypernatremia in newborns
Treatment is with intravenous glucose/0.3-0.45% sodium chloride solution in amounts equal to the fluid deficit, given over 2-3 days to avoid a rapid decrease in serum osmolality, which could cause rapid water influx into cells and potentially lead to cerebral edema. The goal of treatment is to reduce serum sodium by approximately 10 mEq/day. Body weight, serum electrolytes, and urine volume and specific gravity should be monitored regularly to allow fluid volume adjustment. Maintenance solutions should be given simultaneously.
Severe hypernatremia (sodium greater than 200 mEq/L) caused by salt poisoning should be treated with peritoneal dialysis, especially if the poisoning leads to a rapid increase in serum sodium.
How is hypernatremia prevented in newborns?
Prevention requires attention to the volume and composition of unusual fluid losses and solutions used to maintain homeostasis. Neonates and infants who are unable to effectively communicate thirst and need fluid replacement are at greatest risk of developing dehydration. The composition of the feeds, if diluted formulas are used (e.g., some infant formulas or concentrated formulas for tube feeding), requires special attention, especially when there is a high risk of dehydration, such as during episodes of diarrhea, low fluid intake, vomiting, or high fever.