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A considerable number of patients with mild traumatic brain injury have been known to "talk and die." Serial neurological examinations, however, have been the only method of determining the necessity of repeat computed tomography (CT), and no validated method has been available to predict early deterioration of minor head injury. This study aimed to evaluate the association between hypertension and bradycardia, a classic sign of raised intracranial pressure (Cushing reflex) on hospital arrival and determine the clinical consequences of minor head injury after blunt trauma. We created a new Cushing Index (CI) by dividing the systolic blood pressure by the heart rate (equaling the inverse number of the Shock Index, a score for hemodynamic stability) and hypothesized that a high CI would predict surgical intervention for deterioration and in-hospital death among patients with minor head injury. To test our hypothesis, a retrospective observational study was conducted using a nationwide trauma database. Accordingly, adult blunt trauma with minor head injury (defined as a Glasgow Coma Scale of 13–15 and Abbreviated Injury Scale score of ≥2 in the head) who were transported directly from the scene by ambulances were included. Among the 338,744 trauma patients identified in the database, 38,844 were eligible for inclusion. A restricted cubic spline regression curve for risks of in-hospital death was created using the CI. Thereafter, the thresholds were determined based on inflection points of the curve, and patients were divided into low-, intermediate-, and high-CI groups. Patients with high CI showed significantly higher in-hospital mortality rates compared with those with intermediate CI (351 [3.0%] vs. 373 [2.3%]; odds ratio [OR] = 1.32 [1.14–1.53]; p < 0.001). Patients with high index also had a higher incidence of emergency cranial surgery within 24h after arrival than those with an intermediate CI (746 [6.4%] vs. 879 [5.4%]; OR = 1.20 [1.08–1.33]; p < 0.001). In addition, patients with low CI (equal to high Shock Index, meaning hemodynamically unstable) showed higher in-hospital death compared with those with intermediate CI (360 [3.3%] vs. 373 [2.3%]; p < 0.001). In conclusion, a high CI (high systolic blood pressure and low heart rate) on hospital arrival would be helpful in identifying patients with minor head injury who might experience deterioration and need close observation. [ABSTRACT FROM AUTHOR]