Use of Combat Casualty Care Data to Assess the US Military Trauma System During the Afghanistan and Iraq Conflicts, 2001-2017

Abstract

Importance: Although the Afghanistan and Iraq conflicts have the lowest US case-fatality rates in history, no comprehensive assessment of combat casualty care statistics, major interventions, or risk factors has been reported to date after 16 years of conflict.

Objectives: To analyze trends in overall combat casualty statistics, to assess aggregate measures of injury and interventions, and to simulate how mortality rates would have changed had the interventions not occurred.

Design, setting, and participants: Retrospective analysis of all available aggregate and weighted individual administrative data compiled from Department of Defense databases on all 56 763 US military casualties injured in battle in Afghanistan and Iraq from October 1, 2001, through December 31, 2017. Casualty outcomes were compared with period-specific ratios of the use of tourniquets, blood transfusions, and transport to a surgical facility within 60 minutes.

Main outcomes and measures: Main outcomes were casualty status (alive, killed in action [KIA], or died of wounds [DOW]) and the case-fatality rate (CFR). Regression, simulation, and decomposition analyses were used to assess associations between covariates, interventions, and individual casualty status; estimate casualty transitions (KIA to DOW, KIA to alive, and DOW to alive); and estimate the contribution of interventions to changes in CFR.

Results: In aggregate data for 56 763 casualties, CFR decreased in Afghanistan (20.0% to 8.6%) and Iraq (20.4% to 10.1%) from early stages to later stages of the conflicts. Survival for critically injured casualties (Injury Severity Score, 25-75 [critical]) increased from 2.2% to 39.9% in Afghanistan and from 8.9% to 32.9% in Iraq. Simulations using data from 23 699 individual casualties showed that without interventions assessed, CFR would likely have been higher in Afghanistan (15.6% estimated vs 8.6% observed) and Iraq (16.3% estimated vs 10.1% observed), equating to 3672 additional deaths (95% CI, 3209-4244 deaths), of which 1623 (44.2%) were associated with the interventions studied: 474 deaths (12.9%) (95% CI, 439-510) associated with the use of tourniquets, 873 (23.8%) (95% CI, 840-910) with blood transfusion, and 275 (7.5%) (95% CI, 259-292) with prehospital transport times.

Conclusions and relevance: Our analysis suggests that increased use of tourniquets, blood transfusions, and more rapid prehospital transport were associated with 44.2% of total mortality reduction. More critically injured casualties reached surgical care, with increased survival, implying improvements in prehospital and hospital care.

Figure 1.. Data Flow Diagram

Wounded in action (WIA), killed in action (KIA), died of wounds (DOW), and returned to duty (RTD) are administratively determined categories, not medically determined designations. Killed in action and DOW are designations meant to distinguish administratively between deaths occurring before a casualty reaches a treatment facility (KIA) and after reaching a treatment facility (DOW). CFR indicates case-fatality rate; DCAS, Defense Casualty Analysis System; DoDTR, Department of Defense Trauma Registry; and MTF, military treatment facility.

Figure 2.. Trends in Combat Casualty Care Statistics

Percentage survival for critically injured casualties (ISS [Injury Severity Score], 25-75 [ISS 25+]) for Afghanistan (A) and Iraq (B) by using cubic spline estimations smoothed over time from October 2001 through December 2017. The y-axis indicates percentage of casualties. The plot for ISS 25+ survival is truncated for Afghanistan after 2015 and for Iraq after 2009 owing to small sample sizes, which generated unstable spline estimates. The gap in data for Iraq between 2011 and 2016 reflects the absence of combat operations during this period. CFR indicates case-fatality rate; %KIA, percentage who were killed in action; and %DOW, percentage who died of wounds.