Does hyponatremia increase the risk of overall mortality in hospitalized patients and specific disease cohorts?
Even a moderate decrease in serum sodium is independently associated with a significantly increased risk of mortality across various clinical conditions, including heart failure and myocardial infarction.
BACKGROUND: Hyponatremia is the most common electrolyte disorder in clinical practice, and evidence to date indicates that severe hyponatremia is associated with increased morbidity and mortality. The aim of our study was to perform a meta-analysis that included the published studies that compared mortality rates in subjects with or without hyponatremia of any degree. METHODS AND FINDINGS: An extensive Medline, Embase and Cochrane search was performed to retrieve the studies published up to October 1st 2012, using the following words: "hyponatremia" and "mortality". Eighty-one studies satisfied inclusion criteria encompassing a total of 850222 patients, of whom 17.4% were hyponatremic. The identification of relevant abstracts, the selection of studies and the subsequent data extraction were performed independently by two of the authors, and conflicts resolved by a third investigator. Across all 81 studies, hyponatremia was significantly associated with an increased risk of overall mortality (RR = 2.602.31-2.93). Hyponatremia was also associated with an increased risk of mortality in patients with myocardial infarction (RR = 2.832.23-3.58), heart failure (RR = 2.472.09-2.92), cirrhosis (RR = 3.341.91-5.83), pulmonary infections (RR = 2.491.44-4.30), mixed diseases (RR = 2.591.97-3.40), and in hospitalized patients (RR = 2.482.09-2.95). A mean difference of serum Na(+) of 4.8 mmol/L was found in subjects who died compared to survivors (130.1 ± 5.6 vs 134.9 ± 5.1 mmol/L). A meta-regression analysis showed that the hyponatremia-related risk of overall mortality was inversely correlated with serum Na(+). This association was confirmed in a multiple regression model after adjusting for age, gender, and diabetes mellitus as an associated morbidity. CONCLUSIONS: This meta-analysis shows for the first time that even a moderate serum Na(+) decrease is associated with an increased risk of mortality in commonly observed clinical conditions across large numbers of patients.
Corona et al. (2013) studied this question.