The Association of Hyponatremia, Risk of Confusional State, and Mortality

Hyponatremia and delirium are frequent problems in older hospitalized patients. Although confusional states are considered to be a possible complication of hyponatremia, there has been no systematic study to date of the precise prevalence of delirium among patients with hyponatremia and its effect on long-term outcomes.

In a 13-month period in 2009/2010, all patients with a serum sodium level less than or equal to 130 mmol/L (the hyponatremia group) in a cohort of hospitalized older patients were studied and compared to a normonatremic control group of patients who were matched for age, sex, and diagnosis group. The prevalence of delirium was determined by two-stage examination. Inhospital mortality, mortality six months after initial examination, and functional status were prospectively analyzed.

179 patients were identified whose serum sodium level was less than or equal to 130 mmol/L (7.9% of all treated patients), of whom 141 were included in the hyponatremia group. The mean age of the participants was 83 (range, 63-102), and 84% were women. Patients with hyponatremia suffered more often from delirium (22.7% versus 8.5%; p = 0.002) and had a higher inhospital mortality (10.6% versus 2.1%; p = 0.005). The mortality six months after initial examination was 31.9% versus 22.7% (p = 0.080). 59.7% of patients in the hyponatremia group and 49% in the control group (p = 0.146) needed a higher level of chronic care after discharge than they had needed before the hospitalization.

Hyponatremia in hospitalized older patients is associated with a higher likelihood of delirium and an elevated in-hospital mortality.