Early-onset non-oliguric hyperkalaemia in a moderate preterm infant following maternal magnesium sulfate therapy.

Early neonatal hyperkalaemia is uncommon but may cause life-threatening arrhythmias if untreated. While most cases occur in extremely low-birth-weight infants after 24 hours of life, hyperkalaemia within the first few hours after birth is unusual.Magnesium sulfate, commonly used for pre-eclampsia, crosses the placenta and can cause neonatal hypermagnesaemia, which may disrupt potassium balance by inhibiting sodium-potassium adenosine triphosphatase activity and renal outer medullary potassium channel-mediated distal tubular potassium secretion.A preterm infant born at 33+4 weeks' gestation developed severe hyperkalaemia, with serum potassium 7.65 mmol/L and hypermagnesaemia within 2 hours of life. Electrocardiography, urine output, acid-base status and renal ultrasonography were normal. Postpartum maternal evaluation showed hypermagnesaemia and hyperkalaemia, suggesting a possible maternal contribution. Following rapid recognition and treatment with salbutamol and insulin-dextrose, serum potassium normalised and no arrhythmias occurred.This case shows that early-onset neonatal hyperkalaemia can occur in moderately preterm infants after maternal magnesium sulfate exposure, highlighting the importance of early detection and management.