Utility of Stewartʹs strong ion difference as a predictor of major injury after trauma in the ED

Introduction Base deficit (BD) is a validated surrogate for lactate in injured patients and correlates with trauma severity. Stewart proposed a more comprehensive measure of acidosis based on the strong ion difference (SID) (SID = Na + K + Mg + Ca − CL − lactate [mEq/L]). We compared operating characteristics of BD, anion gap (AG), and SID in identifying major injury in emergency department (ED) trauma patients. Methods This was a retrospective review. Major injury was defined as Injury Severity Score ≥15, blood transfusions, or significant drop in hematocrit. Receiver operating characteristic curves compared BD, AG, and SID in differentiating major from minor injuries. Results The study included 1181 patients. Both BD and SID were significantly (P = .0001) different after major vs minor injury (mean difference, 3.40; 95% confidence interval, 2.70-4.00 and mean difference, 2.50; 95% confidence interval, 1.90-3.10, respectively). Receiver operating characteristic curves were minimally different from one another (P = .0035). Conclusion Stewartʹs SID can identify major injury in the ED