Hyponatraemia is independently associated with in-hospital mortality in patients with pneumonia

Background: Hyponatraemia on hospital admission has been shown to be a risk factor for illness severity in critically ill patients. The aim of the present study was to investigate whether hyponatraemia on emergency department (ED) admission independently influences in-hospital mortality, ICU admission, and/or length of hospitalisation in patients with pneumonia. Methods: 610 patients (64.4% male, median 66 years) diagnosed with pneumonia were identified by retrospective screening of electronic admission data (06/2011-06/2013). Patients were admitted to the ED of Bern University Hospital, Switzerland. Patient characteristics, potential confounders, and patient-centred clinical outcomes, including mortality, ICU admission, and length of hospitalisation, were analysed. Multivariate logistic analysis adjusted for typical confounders was performed to analyse the association of hyponatraemia with clinical outcomes. Results: In a large cohort of consecutive acutely admitted patients with pneumonia, the overall in-hospital mortality rate was 12.5%; 21.2% of patients required primary or secondary ICU admission, and the median length of hospital stay was 8 (IQR 5-13) days. At baseline, 47 patients (7.7%) were found to have concomitant hyponatraemia. Multivariate regression revealed a significant association between hyponatraemia and in-hospital mortality (adjusted OR: 2.7, 95% CI: 1.3-5.9, p = 0.010), but not with ICU admission (adjusted OR: 1.8, 95% CI: 0.9-3.6, p = 0.103) or length of hospitalisation (p = 0.493) after adjustment for age, neoplasia, COPD, suspected sepsis, and cardiac disease. The association was robust if controlled for other covariates, e.g. CRB-65 score. Conclusions: Hyponatraemia on admission predicts poor outcome and is an independent risk factor for in-hospital mortality in admitted patients diagnosed with pneumonia.