Hyponatremia is Associated with Increased Severity of Disease in Critically Ill Children with Bronchiolitis

INTRODUCTION: Hyponatremia is the most common electrolyte abnormality seen in the intensive care unit (ICU), and is associated with increased morbidity and mortality. Critically ill children with bronchiolitis are at risk of developing hyponatremia, due to impaired renal free water excretion and exogenous sources of excess free water intake. We hypothesize that the development of hyponatremia is associated with a more complicated clinical course in critically ill children with bronchiolitis. METHODS: A retrospective case-control study was conducted that included all children admitted to the ICU with bronchiolitis over a two year period (n = 59). Patients were divided into two clinical groups: those that were hyponatremic (serum sodium < 136 mmol/L) during their ICU stay and those that remained normonatremic (serum sodium ≥ 136 mmol/L). RESULTS: Forty-three children (73%) developed hyponatremia while in the ICU. Hyponatremic children were intubated more often than normonatremic children (OR 16.7; 95% CI 4.1-68.5); however, hyponatremia rarely developed before intubation (2%). Hyponatremic children also had a longer ICU length of stay (209 ± 137 hrs vs. 130 ± 85 hrs, p = 0.01). In a subset of intubated children (n = 44), thirty-eight (88%) developed hyponatremia. These intubated children had a lower mean serum sodium concentration (132.8 mmol/L vs. 137.3 mmol/L, p < 0.0001) than non-intubated children. CONCLUSIONS: Hyponatremia is a common comorbidity in children admitted to the ICU with bronchiolitis, and is associated with increased illness severity, as evidenced by a higher frequency of intubation and a longer ICU length of stay.