An interesting case of hypernatraemia in the neonate

Hypernatraemia is not uncommon in neonates and can have serious sequelae. Usual causes include water depletion due to inadequate intake, renal, GI and evaporative losses, however iatrogenic excessive sodium intake must be considered and there are documented cases in the literature. We present the case of a 25 week neonate with severe hypernatraemia. The infant was mechanically ventilated, required ionotropic suppport for the first 48 hours and developed a metabolic acidosis treated with sodium bicarbonate. On day 5 of life an arterial blood gas showed a sodium level of 199 mmol/L. The laboratory result was 217 mmol/L and a capillary sodium level was 169 mmol/L. 16 hours earlier the infants sodium level had been 136 mmol/L. The infant had gained 96 grams, had no clinical dehydration and neutral fluid balance. Sodium intake from TPN and heparin sodium totalled 5.3 mmol/kg/day and had not changed. The Heparin Sodium arterial infusion had been changed 10 hours earlier when sodium bicarbonate was discontinued. All infusions were stopped and the possibility that 30% sodium chloride had been infusing instead of Heparin Sodium (0.45%) was considered and confirmed by further detective work! We discovered that the two drugs were in similar ampoules and were stored close together. We also put the UAC infusion fluid through the gas machine to confirm its sodium levels. The arterial line solution was changed and the sodium levels gradually corrected over 48 hours. The infant's response to hypernatraemia was appropriate with increased urine output and urinary sodium of 177 mmol (26 mmol/kg/day). Cranial ultrasound scans which had previously been normal now showed a small left IVH. A previous case of unexplained neonatal hypernatraemia in the same unit was revisited and found to also coincide with the changing of Hepsal infusion. The incident was fully investigated resulting in several recommendations for improvement in practice. We feel it is of utmost importance to inform other healthcare professionals of this critical incident and share its learning points.