BRIEF REPORT Association Between Hyponatremia and Higher Bronchiolitis Severity Among Children in the ICU With Bronchiolitis

METHODS: We conducted a 16-center, prospective cohort study of hospitalized children aged ,2 years with bronchiolitis during the winters of 2007 through 2010. Patients were classified into 2 groups (normonatremic [135–145 mEq/L] and hyponatremic [,135 mEq/L]) based on the firstmeasured serum sodium concentration on the day of hospitalization. Outcomes were use of mechanical ventilation and ICU length of stay (LOS). To examine the association of sodium status with outcomes, we fit logistic and linear regression models with propensity score adjustment. RESULTS: Of 231 children hospitalized in the ICU for bronchiolitis, 193 (84%) were categorized into the normonatremic group and 38 (16%) into the hyponatremic group. Compared with children with normonatremia, those with hyponatremia had higher risks of mechanical ventilation use (40% vs 58%; P 5 .04) and longer ICU LOS (median, 3 vs 6 days; P 5 .007). Likewise, in the adjusted analyses, children with hyponatremia had significantly higher risks of mechanical ventilation use (odds ratio, 2.14 [95% confidence interval, 1.03–4.48; P 5 .04) and longer ICU LOS (b-coefficient, 2.21 days [95% confidence interval, 0.68–3.73; P 5 .005]). CONCLUSIONS: In this prospective, multicenter study of children hospitalized for bronchiolitis, hyponatremia on the day of hospitalization was associated with a higher severity of disease. Our data support hyponatremia as a prognostic factor that might improve the ability of clinicians to predict the disease course of children with severe bronchiolitis. aDepartment of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts; bDepartment of Pediatrics, University of Louisville, Louisville, Kentucky; cDepartment of Medicine, Boston Children’s Hospital, Harvard Medical School, Boston, Massachusetts; dDepartment of Pediatrics, Santa Clara Valley Medical Center, San Jose, California; and eDepartments of Molecular Virology and Microbiology, and Pediatrics, Baylor College of Medicine, Houston, Texas www.hospitalpediatrics.org DOI:10.1542/hpeds.2015-0022 Copyright © 2015 by the American Academy of Pediatrics Address correspondence to Kohei Hasegawa, MD, MPH, Department of Emergency Medicine, Massachusetts General Hospital, 326 Cambridge St, Suite 410, Boston, MA 02114. E-mail: [email protected] HOSPITAL PEDIATRICS (ISSN Numbers: Print, 2154-1663; Online, 2154-1671). FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose. FUNDING: Supported by grants U01 AI-67693 and K23 AI-77801 from the National Institutes of Health. Funded by the National Institutes of Health (NIH). POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose. The content of this manuscript is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Allergy and Infectious Diseases or the National Institutes of Health. HOSPITAL PEDIATRICS Volume 5, Issue 7, July 2015 385 Bronchiolitis is the leading cause of hospitalization in infants, accounting for 18% of all infant hospitalizations in the United States (ie, 129 000 hospitalizations) in 2009. Approximately 10% to 15% of these children require intensive care. Despite the substantial burden of this lifethreatening disease, clinicians continue to struggle with predictions about the disease course and the appropriate level of care for these children. Previous studies have documented marked variability in acute management, highlighting the need for evidence-based assessments. Two singlecenter retrospective studies of children hospitalized to the ICU reported unadjusted associations between hyponatremia (the most common electrolyte abnormality in ICUs) and more severe disease course. However, these earlier studies were potentially limited by small sample sizes (102 and 59 children, respectively), confounding, and potential problems with generalizability. In addition, earlier studies of children with pneumonia also suggested associations of hyponatremia with higher severity of illness, potentially through fluid shift to the lungs and syndrome of inappropriate secretion of antidiuretic hormone. Despite the clinical importance of hyponatremia, it remains unclear whether this condition independently predicts a higher severity in children with bronchiolitis. To address this knowledge gap in the literature, we used data from a multicenter prospective cohort study and investigated the association between hyponatremia and higher bronchiolitis severity, as measured by use of mechanical ventilation and ICU length of stay (LOS), among 231 children hospitalized in the ICU for bronchiolitis. METHODS Design and Setting This study was a planned secondary analysis of a prospective cohort study of children hospitalized with bronchiolitis. The study design, setting, participants, and methods of data collection have been reported previously. Briefly, this prospective cohort study was conducted at 16 sites across 12 US states during the 2007–2010 winter seasons, as part of MARC (Multicenter Airway Research Collaboration). MARC is a program of the Emergency Medicine Network (www.emnetusa.org), a collaboration with .225 participating hospitals. Site investigators enrolled a target number of consecutive patients from the inpatient wards and the ICU. We aimed to enroll 20% of the total sample from the ICU; to achieve this oversampling from the ICU, the ward and ICU enrollments were monitored separately. All patients were managed at the discretion of the treating physician. The institutional review board at all participating hospitals approved the study.