TRISS methodology: an inappropriate tool for comparing outcomes between trauma centers

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Abstract
Background: The TRISS methodology has been used for comparison of survival outcomes between trauma centers. The purpose of this study was to evaluate the role of TRISS in comparing outcomes between a small and a large trauma center and evaluate its usefulness in various groups of patients. Study Design: Trauma registry study that compared the survival outcomes between a large academic level I trauma center and a small community level II center. The comparison was made with the standard TRISS probability of survival, M value, and Z score. In the second part of the study the patients from the small center were matched for age, gender, injury severity score, Glasgow Coma Scale, head Abbreviated Injury Score, BP, prehospital respiratory assistance, and transport mode with an equal number of patients from the large center. The Z scores were calculated for each center. In the third part of the study the TRISS usefulness and limitations were evaluated in various subgroups of patients by calculating its sensitivity, specificity, positive predictive value, negative predictive value, and misclassification rate. Results: The Z value of the large center (3,315 patients) was 2.24, indicating a considerably higher mortality than expected when compared with the Major Trauma Outcomes Study population. The Z value of the small center (331 patients) was −0.92, indicating fewer than the Major Trauma Outcomes Study expected deaths. In the second part of the study, 297 patients from the small center were matched with an equal number from the large center. The Z scores were −0.40 and −0.95, respectively, indicating slightly better outcomes than those of the Major Trauma Outcomes Study. Additional evaluation of the TRISS prediction of survival in various subgroups of patients showed a high misclassification rate in severe trauma, in some groups higher than 25%. Conclusions: The TRISS methodology is not a reliable tool for comparing outcomes between trauma centers and has an unacceptably high misclassification rate in patients with severe trauma.

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