Incidence of hyponatraemia and hyponatraemic seizures in severe respiratory syncytial virus bronchiolitis

Aim: To document the incidence and early evolution of hyponatraemia (serum sodium <136 mmol l -1 ) associated with respiratory syncytial virus (RSV) bronchiolitis in infants requiring intensive care. Methods: In a retrospective review over two winter seasons, 130 infants were admitted with confirmed RSV infection, of whom 39 were excluded because of either pre-existing risk factors for hyponatraemia: diuretic therapy (n = 14), cardiac disease (n = 10), renal disease (n = 2) or lack of admission sodium data (n = 13). Results: The incidence of admission hyponatraemia in the remaining infants (median age 6 wk) was 33% (30/91), with 11% (10/91) exhibiting a serum sodium less than 130mmol l -1 . Hyponatraemic and normonatraemic infants were of a similar age (median 6 vs 7 wk, p = 0.82). With fluid restriction and diuretic therapy, the incidence of hyponatraemia at 48 h had decreased to 3.3%, odds ratio 0.07 (95% confidence interval 0.02-0.24, p < 0.001). Four infants (4%) suffered hyponatraemic seizures at admission (sodium 114-123 mmol l -1 ); three had received hypotonic intravenous fluids at 100-150 ml kg -1 d -1 before referral to intensive care. All four were managed successfully with hypertonic (3%) saline, followed by fluid restriction, resulting in immediate termination of seizure activity and normalization of serum sodium values over 48 h. Conclusion: Hyponatraemia is common among infants with RSV bronchiolitis presenting to intensive care. Neurological complications may occur and fluid therapy in vulnerable infants should be tailored to reduce this risk.