Neonatal Hypernatremia

Hypernatremia develops when

• Water is lost in excess of sodium (hypernatremic dehydration)

• Sodium intake exceeds sodium losses (salt poisoning)

• Both

Water loss in excess of sodium intake is most commonly caused by diarrhea, vomiting, or high fever. It may also be caused by poor feeding in the early days of life (eg, when mother and infant are both learning to breastfeed) and may occur in very low-birth-weight (VLBW) infants born at 24 to 28 weeks. In VLBW infants, insensible water losses through an immature, water-permeable stratum corneum combine with immature renal function and a reduced ability to produce concentrated urine to lead to free water loss. Insensible water loss through the skin is also significantly increased by radiant warmers and phototherapy lights; exposed VLBW infants may require up to 250 mL/kg/day of water IV in the first few days, after which the stratum corneum develops and insensible water loss decreases. A rare cause is central or nephrogenic diabetes insipidus. Infants with hypernatremia and dehydration are often more dehydrated than is apparent by physical examination, because the increased osmolality helps maintain the extracellular fluid space (and hence circulating blood volume).

Solute overload

Symptoms and signs of hypernatremia include lethargy, restlessness, hyperreflexia, spasticity, hyperthermia, and seizures. Skin texture may be doughy rather than diminished.

Intracranial hemorrhage, venous sinus thrombosis, and acute renal tubular necrosis are major complications of hypernatremia.

• Serum sodium concentration

Diagnosis of hypernatremia is suspected by symptoms and signs and is confirmed by measuring serum sodium concentration.

• IV 0.9% saline, then hypotonic saline (0.3% or 0.45% saline)

treatment of dehydration in children), given over 2 to 3 days to avoid a rapid fall in serum osmolality, which would cause rapid movement of water into cells and potentially lead to cerebral edema. Maintenance fluids should be provided concurrently. The goal of treatment is to decrease serum sodium by about 10 mEq/L/day (10 mmol/L/day). Correcting the serum sodium too rapidly can have significant adverse consequences including cerebral edema. Body weight, serum electrolytes, and urine volume and specific gravity must be monitored regularly so that fluid therapy can be adjusted appropriately. Once adequate urine output is shown, potassium is added to provide maintenance requirements or replace urinary losses.

Extreme hypernatremia (sodium > 200 mEq/L [> 200 mmol/L]) caused by salt poisoning should be treated with peritoneal dialysis, especially if poisoning causes a rapid rise in serum sodium.

Prevention of hypernatremia requires attention to the volume and composition of unusual fluid losses and of solutions used to maintain homeostasis. In neonates and young infants, who are unable to signal thirst effectively and to replace losses voluntarily, the risk of dehydration is greatest. The composition of feedings whenever mixing is involved (eg, some infant formulas and concentrated preparations for tube feeding) requires particular attention, especially when the potential for developing dehydration is high, such as during episodes of diarrhea, poor fluid intake, vomiting, or high fever.