Predicting outcome after traumatic brain injury: practical prognostic models based on large cohort of international patients

Abstract

Objective: To develop and validate practical prognostic models for death at 14 days and for death or severe disability six months after traumatic brain injury.

Design: Multivariable logistic regression to select variables that were independently associated with two patient outcomes. Two models designed: "basic" model (demographic and clinical variables only) and "CT" model (basic model plus results of computed tomography). The models were subsequently developed for high and low-middle income countries separately.

Setting: Medical Research Council (MRC) CRASH Trial.

Subjects: 10,008 patients with traumatic brain injury. Models externally validated in a cohort of 8509.

Results: The basic model included four predictors: age, Glasgow coma scale, pupil reactivity, and the presence of major extracranial injury. The CT model also included the presence of petechial haemorrhages, obliteration of the third ventricle or basal cisterns, subarachnoid bleeding, midline shift, and non-evacuated haematoma. In the derivation sample the models showed excellent discrimination (C statistic above 0.80). The models showed good calibration graphically. The Hosmer-Lemeshow test also indicated good calibration, except for the CT model in low-middle income countries. External validation for unfavourable outcome at six months in high income countries showed that basic and CT models had good discrimination (C statistic 0.77 for both models) but poorer calibration.

Conclusion: Simple prognostic models can be used to obtain valid predictions of relevant outcomes in patients with traumatic brain injury.

Conflict of interest statement

Competing interests: None declared.

Figures

Fig 1 Relation between age and mortality at 14 days

Fig 2 Relation between Glasgow coma scale and mortality at 14 days

Fig 3 Calibration of basic models using expected and observed probabilities of mortality at 14 days (top) and death or severe disability at six months (bottom) in patient with traumatic brain injury according to income level of country. P value is for Hosmer-Lemeshow test

Fig 4 Calibration of computed tomography models using expected and observed probabilities of mortality at 14 days (top) and death or severe disability at six months (bottom) in patient with traumatic brain injury according to income level of country. P value is for Hosmer-Lemeshow test

Fig 5 Screenshot of web based calculator available at www.crash2.lshtm.ac.uk/. If CT scan available box is ticked, calculator displays additional CT variables

Fig 6 External validation of basic model for death or severe disability at six months in IMPACT database

Fig 7 External validation of CT model for death or severe disability at six months in IMPACT database