Summary

Background and objectives Severe hyponatremia (120 mEq/L) in hospitalized patients has a high mortal-ity rate. We hypothesized that underlying diseases causing hyponatremia attribute to mortality rather than hyponatremia itself. Design, setting, participants, & measurements The relationship between mortality and serum sodium (sNa) was examined in 45,693 patients admitted to a single community teaching hospital between January 1996 and December 2007. We conducted a comprehensive retrospective review of the medical records of 53 pa-tients who died after developing sNa 120 mEq/L before or after admission and of 32 patients who sur-vived after developing sNa 110 mEq/L. Results Mortality rates tended to increase as the sNa fell from 134 to 120 mEq/L, rising above 10 % for pa-tients with sNa of 120 to 124 mEq/L. However, below sNa of 120 mEq/L, the trend reversed, such that the mortality rate progressively decreased as sNa fell. More than two thirds of patients who died after sNa 120mEq/L had at least two additional acute severe progressive illnesses, most commonly sepsis and mul-tiorgan failure. Three deaths (5.6%) in 12 years could plausibly be related to adverse consequences of hypo-natremia, and one (1.8 % of the fatal cases and 0.15 % of all patients with sNa 120 mEq/L) was from cere-bral edema. Most patients who survived with sNa 110 mEq/L had medication-induced hyponatremia. Severe underlying illnesses were uncommon in this group. Conclusions The nature of underlying illness rather than the severity of hyponatremia best explains mortal-ity associated with hyponatremia. Neurologic complications from hyponatremia are uncommon among pa-tients who die with hyponatremia