Performance of the IMPACT and CRASH prognostic models for traumatic brain injury in a contemporary multicenter cohort: a TRACK-TBI study

Abstract

Objective: The International Mission on Prognosis and Analysis of Clinical Trials in Traumatic Brain Injury (IMPACT) and Corticosteroid Randomization After Significant Head Injury (CRASH) prognostic models for mortality and outcome after traumatic brain injury (TBI) were developed using data from 1984 to 2004. This study examined IMPACT and CRASH model performances in a contemporary cohort of US patients.

Methods: The prospective 18-center Transforming Research and Clinical Knowledge in Traumatic Brain Injury (TRACK-TBI) study (enrollment years 2014-2018) enrolled subjects aged ≥ 17 years who presented to level I trauma centers and received head CT within 24 hours of TBI. Data were extracted from the subjects who met the model criteria (for IMPACT, Glasgow Coma Scale [GCS] score 3-12 with 6-month Glasgow Outcome Scale-Extended [GOSE] data [n = 441]; for CRASH, GCS score 3-14 with 2-week mortality data and 6-month GOSE data [n = 831]). Analyses were conducted in the overall cohort and stratified on the basis of TBI severity (severe/moderate/mild TBI defined as GCS score 3-8/9-12/13-14), age (17-64 years or ≥ 65 years), and the 5 top enrolling sites. Unfavorable outcome was defined as GOSE score 1-4. Original IMPACT and CRASH model coefficients were applied, and model performances were assessed by calibration (intercept [< 0 indicated overprediction; > 0 indicated underprediction] and slope) and discrimination (c-statistic).

Results: Overall, the IMPACT models overpredicted mortality (intercept -0.79 [95% CI -1.05 to -0.53], slope 1.37 [1.05-1.69]) and acceptably predicted unfavorable outcome (intercept 0.07 [-0.14 to 0.29], slope 1.19 [0.96-1.42]), with good discrimination (c-statistics 0.84 and 0.83, respectively). The CRASH models overpredicted mortality (intercept -1.06 [-1.36 to -0.75], slope 0.96 [0.79-1.14]) and unfavorable outcome (intercept -0.60 [-0.78 to -0.41], slope 1.20 [1.03-1.37]), with good discrimination (c-statistics 0.92 and 0.88, respectively). IMPACT overpredicted mortality and acceptably predicted unfavorable outcome in the severe and moderate TBI subgroups, with good discrimination (c-statistic ≥ 0.81). CRASH overpredicted mortality in the severe and moderate TBI subgroups and acceptably predicted mortality in the mild TBI subgroup, with good discrimination (c-statistic ≥ 0.86); unfavorable outcome was overpredicted in the severe and mild TBI subgroups with adequate discrimination (c-statistic ≥ 0.78), whereas calibration was nonlinear in the moderate TBI subgroup. In subjects ≥ 65 years of age, the models performed variably (IMPACT-mortality, intercept 0.28, slope 0.68, and c-statistic 0.68; CRASH-unfavorable outcome, intercept -0.97, slope 1.32, and c-statistic 0.88; nonlinear calibration for IMPACT-unfavorable outcome and CRASH-mortality). Model performance differences were observed across the top enrolling sites for mortality and unfavorable outcome.

Conclusions: The IMPACT and CRASH models adequately discriminated mortality and unfavorable outcome. Observed overestimations of mortality and unfavorable outcome underscore the need to update prognostic models to incorporate contemporary changes in TBI management and case-mix. Investigations to elucidate the relationships between increased survival, outcome, treatment intensity, and site-specific practices will be relevant to improve models in specific TBI subpopulations (e.g., older adults), which may benefit from the inclusion of blood-based biomarkers, neuroimaging features, and treatment data.

Keywords: Glasgow Outcome Scale; clinical prediction rules; mortality; prognosis; statistical models; traumatic brain injury.

FIG. 1.

CONSORT flow diagram of the included subjects. Figure is available in color online only.

FIG. 2.

Prediction of mortality in the overall cohort, stratified by GCS score and age, using the IMPACT models. Calibration plots for prediction of 6-month mortality in the overall TRACK-TBI validation cohort are shown for the IMPACT Core (n = 441) (A), Extended (n = 441) (B), and Lab (n = 441) (C) models. Stratified analyses using the IMPACT-Lab model are shown for TBI severity (GCS score 3–8 [n = 335] [D] and GCS score 9–12 [n = 106] [E]) and age (17–64 years [n = 398] [F] and ≥ 65 years [n = 43] [G]). The ideal reference line in red represents perfect model calibration with slope = 1 and intercept = 0. Estimated model calibration with LOESS smoothing is shown as the black curved line in each plot. The intercept, slope, and c-statistic of model calibration are shown with 95% CIs in the top left corner of each plot, and 95% CIs are shaded in gray on the plot. Figure is available in color online only.

FIG. 3.

Prediction of unfavorable outcome in the overall cohort, stratified by GCS score and age, using IMPACT models. Calibration plots for prediction of 6-month unfavorable outcome (GOSE score 1–4) in the overall TRACK-TBI validation cohort are shown for the IMPACT Core (A), Extended (B), and Lab (C) models. Stratified analyses using the IMPACT-Lab model are shown for TBI severity (GCS score 3–8 [D] and GCS score 9–12 [E]) and age (17–64 years [F] and ≥ 65 years [G]). The intercept, slope, and c-statistic of model calibration are shown with 95% CIs in the top left corner of each plot, and 95% CIs are shaded in gray on the plot. Cohort sizes (n) for each panel are the same as those reported in Fig. 2. Figure is available in color online only.

FIG. 4.

Prediction of mortality in the overall cohort, stratified by GCS score and age, using CRASH models. Calibration plots for prediction of 2-week mortality in the overall TRACK-TBI validation cohort are shown for the CRASH-Basic (n = 831) (A) and CRASH-CT (n = 831) models (B). Stratified analyses using the CRASH-CT model are shown for TBI severity (GCS score 3–8 [n = 335] (C), GCS score 9–12 [n = 106] [D], and GCS score 13–14 [n = 390] [E]) and age (17–64 years [n = 732] [F] and ≥ 65 years [n = 99] [G]). The intercept, slope, and c-statistic of model calibration are shown with 95% CIs in the top left corner of each plot, and 95% CIs are shaded in gray on the plot. Figure is available in color online only.

FIG. 5.

Prediction of unfavorable outcome in the overall cohort, stratified by GCS score and age cohorts, using CRASH models. Calibration plots for prediction of 6-month unfavorable outcome (GOSE score 1–4) in the overall TRACK-TBI validation cohort are shown for the CRASH-Basic (A) and CRASH-CT (B) models. Stratified analyses using the CRASH-CT model are shown for TBI severity (GCS score 3–8 [C], GCS score 9–12 [D], and GCS 13–14 [E]) and age (17–64 years [F] and ≥ 65 years [G]). The intercept, slope, and c-statistic of model calibration are shown with 95% CIs in the top left corner of each plot, and 95% CIs are shaded in gray on the plot. Cohort sizes (n) for each panel are the same as those reported in Fig. 4. Figure is available in color online only.