Abstract
AIM: Older 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. METHODS: Using 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. RESULTS: We 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). CONCLUSIONS: The 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.