Performance of CRASH and IMPACT Prognostic Models for Traumatic Brain Injury at 12 and 24 Months Post-Injury

Abstract

The Corticoid Randomization after Significant Head Injury (CRASH) and International Mission for Prognosis and Analysis of Clinical Trials (IMPACT) prognostic models are the most reported prognostic models for traumatic brain injury (TBI) in the scientific literature. However, these models were developed and validated to predict 6-month unfavorable outcome and mortality, and growing evidence supports continuous improvements in functional outcome after severe TBI up to 2 years post-injury. The purpose of this study was to evaluate CRASH and IMPACT model performance beyond 6 months post-injury to include 12 and 24 months post-injury. Discriminative validity remained consistent over time and comparable to earlier recovery time points (area under the curve = 0.77–0.83). Both models had poor fit for unfavorable outcomes, explaining less than one quarter of the variation in outcomes for severe TBI patients. The CRASH model had significant values for the Hosmer-Lemeshow test at 12 and 24 months, indicating poor model fit past the previous validation point. There is concern in the scientific literature that TBI prognostic models are being used by neurotrauma clinicians to support clinical decision making despite the goal of the models' development being to support research study design. The results of this study indicate that the CRASH and IMPACT models should not be used in routine clinical practice because of poor model fit that worsens over time and the large, unexplained variance in outcomes.

Comparative Analysis of Clinical Severity and Outcomes in Penetrating Versus Blunt Traumatic Brain Injury Propensity Matched Cohorts

“…The IMPACT score, originally developed and validated for intermediate follow-up (at 6 months) following moderate and severe TBI, underscores an overarching concern in the scientific literature that prognostic models for TBI may be utilized by clinicians to inappropriately guide individualized clinical decisions, despite the original purpose of these models being geared toward facilitating research study design. 22 In this case, the model exhibits inadequate discrimination for early outcome prediction, particularly in the context of PBI, further emphasizing that despite comparable clinical severity, the two disease states exhibit notable variations in outcomes. Another illustration of this variability in disease severity is manifested in the elevated mortality rates observed in PBI cases with higher GCS scores when compared with blunt TBI, thereby casting doubts on the applicability of GCS and its associated classifications (mild, moderate, and severe) in the context of PBI.…”

“…Finally, the IMPACT score is validated for assessing intermediate and long-term outcomes in blunt TBI. 8 , 22 Here, we employ it to scrutinize immediate dispositional outcomes, as a first approximation and comparison of its distinctive performance in the context of PBI compared with blunt TBI.…”

Traumatic Brain Injury and Traumatic Spinal Cord Injury

“…Common predictors of poor outcomes in virtually all models include older age and lower GCS scores. Prognostication following TBI is evolving with longitudinal studies demonstrating continued recovery in patients well beyond the 6 months targeted by most models, 81 underscoring the limitations of models such as CRASH and IMPACT and the need for prognostic humility. It is worth noting that the prognostically relevant epidemiology of TBI is dynamic; for example, with the implementation of preventive strategies to reduce road traffic injuries in young individuals, and with an aging population, centers in the United States are seeing an increasing proportion of fall-related TBI 82 …”