Establishing thresholds for shock index in children to identify major trauma

Background

An abnormal shock index (SI) is associated with greater injury severity among children with trauma. We sought to empirically-derive age-adjusted SI cutpoints associated with major trauma in children, and to compare the accuracy of these cutpoints to existing criteria for pediatric SI.

Methods

We performed a retrospective cohort study using the 2021 National Trauma Data Bank (NTDB) Participant Use File. We included injured children (<18 years), excluding patients with traumatic arrests, mechanical ventilation upon hospital presentation, and inter-facility transfers. Our outcome was major trauma defined by the standardized triage assessment tool (STAT) criteria. Our exposure of interest was the SI. We empirically-derived upper and lower cutpoints for the SI using age-adjusted Z-scores. We compared the performance of these to the SI, pediatric-adjusted (SIPA), and the Pediatric SI (PSI). We validated the performance of the cutpoints in the 2019 NTDB.

Results

We included 64,326 and 64,316 children in the derivation and validation samples, of whom 4.9 % (derivation) and 4.0 % (validation) experienced major trauma. The empirically-derived age-adjusted SI cutpoints had a sensitivity of 43.2 % and a specificity of 79.4 % for major trauma in the validation sample. The sensitivity of the PSI for major trauma was 33.9 %, with a specificity of 90.7 % among children 1–17 years of age. The sensitivity of the SIPA was 37.4 %, with a specificity of 87.8 % among children 4–16 years of age. Evaluated using logistic regression, patients with an elevated age-adjusted SI had 3.97 greater odds (95 % confidence interval [CI] 3.63–4.33) of major trauma compared to those with a normal age-adjusted SI. Patients with a depressed SI had 1.55 greater odds (95 % CI 1.36–1.78) of major trauma. The area under the receiver operator characteristic curve (AUROC) for the empirically-derived model (0.62, 95 % CI 0.61–0.63) was similar to the AUROC for PSI (0.62, 95 % CI 0.61–0.63); both of which were greater than the SIPA model (0.58, 95 % CI 0.57–0.59).

Conclusion

Age-adjusted SI cutpoints demonstrated a mild gain in sensitivity compared to existing measures. However, our findings suggest that the SI alone has a limited role in the identification of major trauma in children.