Impact of Hospital-Associated Hyponatremia on Selected Outcomes

BACKGROUND: Hyponatremia is the most common electrolyte disorder encountered in hospitalized patients. METHODS: We evaluated whether hospital-associated hyponatremia has an independent effect on all-cause mortality, hospital length of stay (LOS), and patient disposition. This cohort study included all adult hospitalizations at an academic medical center occurring between 2000-2007 for which an admission serum sodium concentration (Na(+)) was available (N = 53 236). We examined community-acquired hyponatremia (admission serum Na(+), <138 mEq/L to convert to millimoles per liter, multiply by 1.0), hospital-aggravated hyponatremia (community-acquired hyponatremia complicated by worsening in serum Na(+)), and hospital-acquired hyponatremia (nadir serum Na(+), <138 mEq/L with a normal admission serum Na(+)). The independent associations of these hyponatremic presentations with in-hospital mortality, LOS, and patient disposition were evaluated using generalized estimating equations adjusted for age, sex, race, admission service, and Deyo-Charlson Comorbidity Index score. RESULTS: Community-acquired hyponatremia occurred in 37.9% of hospitalizations and was associated with adjusted odds ratios (ORs) of 1.52 (95% confidence interval CI, 1.36-1.69) for in-hospital mortality and 1.12 (95% CI, 1.08-1.17) for discharge to a short- or long-term care facility and a 14% (95% CI, 11%-16%) adjusted increase in LOS. Hospital-acquired hyponatremia developed in 38.2% of hospitalizations longer than 1 day in which initial serum Na(+) was 138 to 142 mEq/L. Hospital-acquired hyponatremia was associated with adjusted ORs of 1.66 (95% CI, 1.39-1.98) for in-hospital mortality and 1.64 (95% CI, 1.55-1.74) for discharge to a facility and a 64% (95% CI, 60%-68%) adjusted increase in LOS. The strength of these associations tended to increase with hyponatremia severity. CONCLUSIONS: Hospital-associated hyponatremia is a common occurrence. All forms of hyponatremia are independently associated with in-hospital mortality and heightened resource consumption.