Validation of the GCS-Pupil scale in Traumatic Brain Injury Incremental prognostic performance of pupillary reactivity with GCS in the prospective observational cohorts CENTER-TBI and TRACK-TBI

Objective: To compare the incremental prognostic value of pupillary reactivity as captured in the GCS-Pupils score (GCS-P) or added as separate variable to the Glasgow Coma Scale (GCS) in traumatic brain injury (TBI). Methods: We analyzed patients enrolled between 2014 and 2018 in the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI, n=3521) and the Transforming Research and Clinical Knowledge in Traumatic Brain Injury (TRACK-TBI, n=1439) cohorts. We used logistic regression to quantify the prognostic performances of GCS-P versus GCS according to Nagelkerke R2. Endpoints were mortality and unfavorable outcome (Glasgow Outcome Scale-Extended score 1-4) at 6 months after injury. We estimated 95% confidence intervals with bootstrap resampling to summarize the improvement in prognostic capability. Results: GCS as a linear score had a R2 of 24% (95% confidence interval [CI] 17-30) and 30% (95%CI 17-43) for mortality and 29% (95%CI 25-34) and 38% (95%CI 29-47) for unfavorable outcome in CENTER-TBI and TRACK-TBI respectively. In the meta-analysis, pupillary reactivity as a separate variable improved the R2 by an absolute value of 6% and 2% for mortality and unfavorable outcome (95%CI 4.0-7.7 and 1.2-3.0, respectively), with half the improvement captured in the GCS-P score (3%, 95%CI 2.1-3.3 and 1%, 95%CI 1-1.7, respectively). Conclusions: GCS-P has a stronger association with outcome after TBI than the GCS alone. However, for prognostic models, inclusion of GCS and pupillary reactivity as separate scores is preferable.