Utility of Stewart's 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 > or =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: Stewart's SID can identify major injury in the ED.