Outcome Prediction after Traumatic Brain Injury: Comparison of the Performance of Routinely Used Severity Scores and Multivariable Prognostic Models

Abstract

Objectives: Prognosis of outcome after traumatic brain injury (TBI) is important in the assessment of quality of care and can help improve treatment and outcome. The aim of this study was to compare the prognostic value of relatively simple injury severity scores between each other and against a gold standard model - the IMPACT-extended (IMP-E) multivariable prognostic model.

Materials and methods: For this study, 866 patients with moderate/severe TBI from Austria were analyzed. The prognostic performances of the Glasgow coma scale (GCS), GCS motor (GCSM) score, abbreviated injury scale for the head region, Marshall computed tomographic (CT) classification, and Rotterdam CT score were compared side-by-side and against the IMP-E score. The area under the receiver operating characteristics curve (AUC) and Nagelkerke's R² were used to assess the prognostic performance. Outcomes at the Intensive Care Unit, at hospital discharge, and at 6 months (mortality and unfavorable outcome) were used as end-points.

Results: Comparing AUCs and R²s of the same model across four outcomes, only little variation was apparent. A similar pattern is observed when comparing the models between each other: Variation of AUCs <±0.09 and R²s by up to ±0.17 points suggest that all scores perform similarly in predicting outcomes at various points (AUCs: 0.65-0.77; R²s: 0.09-0.27). All scores performed significantly worse than the IMP-E model (with AUC > 0.83 and R² > 0.42 for all outcomes): AUCs were worse by 0.10-0.22 (P < 0.05) and R²s were worse by 0.22-0.39 points.

Conclusions: All tested simple scores can provide reasonably valid prognosis. However, it is confirmed that well-developed multivariable prognostic models outperform these scores significantly and should be used for prognosis in patients after TBI wherever possible.

Keywords: Abbreviated injury scale; Glasgow coma scale; outcome; prognosis; traumatic brain injury.

Figure 1

Flow of participants through the study. GCSM: Glasgow coma scale motor score; GCST: Total GCS; AIS-H: Abbreviated Injury Scale for Head and Neck Regions; M-CT: Marshall CT classification, R-CT: Rotterdam CT score

Figure 2

Comparison of receiver operating characteristics curves of the analyzed prediction models to the gold standard (receiver operating characteristics curve of the IMPACT extended model). GCSM: Glasgow coma scale motor score; GCST: Total GCS; AIS-H: Abbreviated Injury Scale for head and neck; M-CT: Marshall CT classification, R-CT: Rotterdam CT score; IMP-E: IMPACT extended model. The thick curve represents the gold standard (receiver operating characteristics of the IMPACT extended model)