Reproducible intubation contrast without evidence of a unique threshold at Glasgow Coma Scale 8: a two-era nationwide retrospective cohort study

Abstract

A Glasgow Coma Scale (GCS) score of 8 or lower is widely used in trauma classification and airway assessment, but a difference across a familiar cutoff does not necessarily mean that risk changes abruptly at that boundary. We tested whether the boundary between GCS 8 and 9 behaved as a unique prognostic or recorded-intubation threshold. We analyzed adults in two Japan Trauma Data Bank eras (2008–2014 and 2019–2023) who were transported directly from scene, had valid hospital-arrival GCS, no recorded prehospital advanced airway or cardiopulmonary support, and predefined arrival physiology. Outcomes were severe head injury, in-hospital death, urgent cranial surgery, and recorded post-arrival intubation. We asked whether GCS 8 and 9 differed, whether that difference was unusual compared with neighboring scores, and whether adding a discrete jump between GCS 8 and 9 improved model fit beyond a graded GCS-outcome relationship. Bayesian information criterion (BIC) was the prespecified criterion for added-step model comparisons; Akaike information criterion (AIC), likelihood-ratio tests, and coefficient-level inference were secondary. Cohorts included 71,988 patients from 190 hospitals and 66,417 from 209 hospitals. Prognostic and cranial-surgery differences between GCS 8 and 9 were imprecisely estimated. Recorded intubation was 9.1 and 10.6 percentage points more frequent at GCS 8 (pooled adjusted odds ratio, 1.61; 95% confidence interval, 1.36–1.91). Other adjacent-score intubation differences were also present. At the GCS 8/9 boundary, BIC favored the graded model in every outcome in both eras, including a GCS 5–12 spline sensitivity; secondary criteria were less consistent. Categorical-model estimates of local exceptionality were imprecise and inconsistent across eras. A recorded-intubation contrast was reproduced temporally within one national registry. Its local exceptionality can neither be established nor excluded. Prespecified BIC comparisons did not favor an added 8/9 step, but this does not establish the absence of a threshold. These observational data do not determine whether maintaining, changing, or abandoning an intubation rule improves outcomes.

The authors' abstract, as published at the source. Scandinavian Journal of Trauma Resuscitation and Emergency Medicine, 2026 · DOI ↗