Background Abnormal serum
sodium levels have been associated with higher mortality among patients with
acute coronary syndromes and
heart failure. We sought to describe the association between
sodium levels and mortality among unselected cardiac intensive care unit (CICU) patients. Methods and Results We retrospectively reviewed consecutive adult patients admitted to our cardiac intensive care unit from 2007 to 2015.
Hyponatremia and
hypernatremia were defined as admission serum
sodium <135 and >145 mEq/L, respectively. In-hospital mortality was assessed by multivariable regression, and postdischarge mortality was evaluated by Cox proportional-hazards analysis. We included 9676 patients with a mean age of 68±15 years (37.5% females).
Hyponatremia occurred in 1706 (17.6%) patients, and
hypernatremia occurred in 322 (3.3%) patients; these groups had higher illness severity and a greater number of comorbidities. Risk of hospital mortality was higher with
hyponatremia (15.5% versus 7.5%; unadjusted odds ratio, 2.41; 95% CI, 2.06-2.82; P<0.001) or
hypernatremia (17.7% versus 8.6%; unadjusted odds ratio, 2.82; 95% CI, 2.09-3.80; P<0.001), with a J-shaped relationship between admission
sodium and mortality. After multivariate adjustment, only
hyponatremia was significantly associated with in-hospital mortality (adjusted odds ratio, 1.42; 95% CI, 1.14-1.76; P=0.002). Among hospital survivors, risk of postdischarge mortality was higher in patients with
hyponatremia (adjusted hazard ratio, 1.28; 95% CI, 1.17-1.41; P<0.001) or
hypernatremia (adjusted hazard ratio, 1.36; 95% CI, 1.12-1.64; P=0.002). Conclusions
Hyponatremia and
hypernatremia on admission to the cardiac intensive care unit are associated with increased unadjusted short- and long-term mortality. Further studies are needed to determine whether correcting abnormal
sodium levels can improve outcomes in cardiac intensive care unit patients.