Sodium variability is associated with increased mortality in severe burn injury

Background: Dysnatremias are associated with increased mortality in critically ill patients. Hypernatremia in burn patients is also associated with poor survival. Based on these findings, we hypothesized that high plasma sodium variability is a marker for increased mortality in severely burn-injured patients. Methods: We performed a retrospective review of adult burn patients with a burn injury of 15% total body surface area (TBSA) or greater from 2010 to 2014. All patients included in the study had at least three serum sodium levels checked during admission. We used multivariate logistic regression analysis to determine if hypernatremia, hyponatremia, or sodium variability independently increased the odds ratio (OR) for death. Results: Two hundred twelve patients met entry criteria. Mean age and % TBSA for the study was 45 +/- 18 years and 32 +/- 19%. Twenty-nine patients died for a mortality rate of 14%. Serum sodium was measured 10,310 times overall. The median number of serum sodium measurements per patient was 22. Non-survivors were older (59 +/- 19 vs. 42 +/- 16 years) and suffered from a more severe burn injury (50 +/- 25% vs. 29 +/- 16% TBSA). While mean sodium was significantly higher for non-survivors (138 +/- 3 milliequivalents/liter (meq/l)) than for survivors (135 +/- 2 meq/l), mean sodium levels remained within the laboratory reference range (135 to 145 meq/l) for both groups. Non-survivors had a significantly higher median number of hypernatremic (> 145 meq/l) measurements (2 vs. 0). Coefficient of variation (CV) was significantly higher in non-survivors (2.85 +/- 1.1) than survivors (2.0 +/- 0.7). Adjusting for TBSA, age, ventilator days, and intensive care unit (ICU) stay, a higher CV of sodium measurements was associated with mortality (OR 5.8 (95% confidence interval (CI) 1.5 to 22)). Additionally, large variation in sodium ranges in the first 10 days of admission may be associated with increased mortality (OR 1.35 (95% CI 1.06 to1.7)). Conclusions: Increased variability in plasma sodium may be associated with death in severely burned patients.