All trauma is not created equal: Redefining severe trauma for combat injuries

Injury severity scores (ISS) and shock index (SI) are popular trauma scoring systems. We assessed ISS and SI in combat trauma to determine the optimal cut-off values for mortality and trauma outcomes. Retrospective analysis of the Department of Defense Trauma Registry, 2008–2016, was performed. Areas under receiver operating characteristic curves (AUROCs) were calculated for ISS and SI on mortality, massive volume transfusion (MVT), and emergent surgical procedure (ESP). Optimal cut-off values were defined using the Youden index (YI). 22,218 patients (97.1% male), median ages 25–29 years, ISS 9.4 ± 0.07, with 58.1% penetrating injury were studied. Overall mortality was 3.4%. AUROCs for ISS on mortality, MVT, and ESP were 0.882, 0.898, and 0.846, while AUROCs for SI were 0.727, 0.864, and 0.711 respectively. The optimal cut-off values for ISS on mortality, MVT, and ESP were 12.5 (YI = 0.634), 12.5 (YI = 0.666), and 12.5 (YI = 0.819), with optimal values for SI being 0.94 (YI = 0.402), 0.88 (YI = 0.608), and 0.81 (YI = 0.345) respectively. Classic values for severe ISS underrepresent combat injury while the SI values defined in this study are consistent with civilian data. •Classic definitions for major trauma do not accurately reflect combat trauma.•Shock Index may be used to predict combat trauma outcomes in similar fashions for combat and civilian trauma.•Injury Severity Score and Shock Index hold clinical and research value in combat trauma.