Can the shock index be a reliable predictor of early mortality after trauma in older patients? A retrospective cohort study.

Abstract

AimOlder patients have different physiological characteristics; thus, the reliability of the shock index (SI) to predict mortality could depend on age. We investigated whether the SI is a reliable predictor of early mortality in older patients and evaluated the clinical benefit of age in the interpretation of the SI.MethodsUsing data from the Japan Trauma Data Bank, we identified injured patients aged 20–84 years. Area under the receiver operating characteristic curve (AUC) was used to evaluate the discrimination ability of the SI to predict early mortality. A formula to determine the cut‐off for each age was derived using linear regression analysis. Performance of the new method was compared with that of the traditional SI cut‐off of ≥0.9 AUC.ResultsWe analyzed data from 146,802 patients. Early mortality was observed in 4% of patients. The AUC showed a significant negative correlation with age (Spearman's ρ = –0.97, P < 0.001), and it decreased from 0.788 (95% confidence interval [CI], 0.761–0.815) in the 20–24 years age group to 0.660 (95% CI, 0.643–0.676) in those aged 80–84 years. By adjusting for age in the SI interpretation, AUC significantly improved from 0.681 (95% CI, 0.675–0.688) to 0.695 (95% CI, 0.688–0.701) (P < 0.001).ConclusionsThe performance of the SI to predict mortality after trauma was significantly worse in older patients. Even if the SI cut‐off value was adjusted based on age, the decrease in performance was not sufficiently prevented. Our results indicated that clinicians should be cautious when using the SI in older patients.