Refining the Trauma and Injury Severity Score (TRISS) to Measure the Performance of the UK Combat Casualty Care System

Introduction: The Trauma and Injury Severity Score (TRISS) methodology is used in both the UK and US Military trauma registries. The method relies on dividing casualties according to mechanism, penetrating or blunt, and uses different weighting coefficients accordingly. The UK Military Joint Theatre Trauma Registry uses the original coefficients devised in 1987, whereas the US military registry uses updated civilian coefficients, but it is not clear how either registry analyzes explosive casualties according to the TRISS methodology. This study aims to use the UK Military Joint Theatre Trauma Registry to calculate new TRISS coefficients for contemporary battlefield casualties injured by either gunshot or explosive mechanisms. The secondary aim of this study is to apply the revised TRISS coefficients to examine the survival trends of UK casualties from recent military conflicts.

Materials and methods: The Joint Theatre Trauma Registry was searched for all UK casualties injured or killed in Iraq and Afghanistan by explosive or gunshot mechanisms between January 1, 2003 and December 31, 2014. Details of these casualties including injuries and vital signs were reviewed. Logistic regression analysis was performed to devise new TRISS coefficients; these were then used to examine survival over the 12 yr of the study.

Results: Comparing the predictions from the gunshot TRISS model to the observed outcomes, it demonstrates a sensitivity of 98.1% and a specificity of 96.8% and an overall accuracy of 97.8%. With respect to the explosive TRISS model, there is a sensitivity of 98.6%, a specificity of 97.4%, and an overall accuracy of 98.4%. When this updated and mechanism-specific TRISS methodology was used to measure changes in survival over the study period, survival following these injuries improved until 2012 when performance was maintained for the last 2 yr of the study.

Conclusion: This study for the first time refines the TRISS methodology with coefficients appropriate for use within combat casualty care systems. This improved methodology reveals that UK combat casualty care performance appears to have improved until 2012 when this standard was maintained.