Highlights
- •Hyponatremia with acute heart failure has increased in internal medicine lately.
- •Hyponatremia was most frequently observed in patients with comorbidities.
- •Hyponatremia was associated to readmission and longer hospital stay.
- •Hyponatremia was an independent risk factor for mortality in acute heart failure.
Abstract
Objective
Hyponatremia is the most common electrolyte disorder seen in clinical practice. Numerous
studies have reported increased inhospital mortality associated to this condition,
which is also an independent predictor of comorbidity in patients admitted with heart
failure (HF). The objective of this study is to assess the incidence, average length
of stay, associated comorbidities, readmissions and mortality caused by hyponatremia
in admissions for acute heart failure from the Spanish national minimum basic data
set (MBDS).
Materials and methods
Data from the Spanish national minimum basic data set (MBDS) of discharged patients
who were initially diagnosed with heart failure (HF) from all internal medicine (IM)
departments of Spanish National Health System (SNS) hospitals between 2005 and 2011
were analysed (ICD-9: 428; DRGs 127 and 544). A descriptive data analysis was conducted
comparing the diagnosis codes and administrative variables of heart failure patients
with and without hyponatremia. The chi-square test was used for qualitative variables
and the Student's t test for quantitative variables. A bivariate analysis was used to detect statistical
differences in the mortality of both groups, as well as mean age, Charlson index,
average length of stay and readmissions. A multivariate logistic regression analysis
was performed, taking intrahospital mortality and hospital readmissions as dependent
variables, and age, gender, comorbidity according to the Charlson index and hyponatremia
as independent variables.
Results
A total of 504,860 patients with acute heart failure were identified, of whom 11,095
(2.2%) presented with HNa. A gradual year-on-year increase of hyponatremia codification
(both primary and secondary diagnosis) was observed at discharge throughout the study
period (from 1.6% in 2005 to 2.8% in 2011; p < 0.0001). Overall mortality due to any cause in patients with hyponatremia was 17%
(1937 patients) versus 11% in non-hyponatremic patients (53,820 patients). The probability
of readmission for patients with hyponatremia was 22% versus 17% in the non-hyponatremic
group. Hyponatremia was associated to a higher rate of mortality during hospitalisation
for acute heart failure with an odds ratio (OR) of 1.58, 95% CI, 1.50–1.66 (p < 0.05). Hyponatremia maintained statistical significance in the regression model after
adjusting for gender, OR 0.919 (95% CI 0.902–0.936); age, OR 1.061 (95% CI 1.060–1.062);
and Charlson index, OR 1.388 (95% CI 1.361–1.461).
Conclusions
Hyponatremia is associated to an increased rate of mortality and readmission in patients
admitted for acute heart failure in SNS hospitals. Our study identified a statistically
significant association between hyponatremia and increased intrahospital mortality
independent of age, gender and the Charlson comorbidity index. During the defined
follow-up period the discharge reports showed an increased codification of hyponatremia.
Keywords
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Article info
Publication history
Published online: June 25, 2015
Accepted:
June 16,
2015
Received in revised form:
May 31,
2015
Received:
March 22,
2015
Identification
Copyright
© 2015 European Federation of Internal Medicine. Published by Elsevier Inc. All rights reserved.
