Objectives: The delta shock index (ΔSI), defined as the change in shock index (SI) over time, is associated with hospital morbidity and mortality, but prehospital studies about ΔSI are limited. We investigate the association of prehospital ΔSI with mortality and resource utilization, hypothesizing that increases in SI among field trauma patients are associated with increased mortality and blood product transfusion.
Methods: We performed a multicenter, retrospective, observational study from the Linking Investigators in Trauma and Emergency Services (LITES) network. We obtained data from January 2017 to June 2021. We fit logistic regression models to evaluate the association between an increase ΔSI > 0.1 and 28-day mortality and blood product transfusion within 4 h of emergency department (ED) arrival. We used negative binomial models to evaluate the association between ΔSI > 0.1 and days in hospital, intensive care unit (ICU), and on ventilator (up to 28 days).
Results: We identified 33,219 prehospital patients. We excluded burn patients and those without documented prehospital or ED heart rate or blood pressure, resulting in 30,511 cases for analysis. In adjusted analysis for the primary outcome of 28-day mortality, patients who had a ΔSI > 0.1 based on initial vital signs were 31% more likely to die (adjusted odds ratio (AOR) of 1.31, 95% CI 1.21-1.41) compared to those patients who had a ΔSI ≤0.1. These patients also spent 16% more days in hospital (adjusted incident rate ratio (AIRR) 1.16, 95% CI 1.14-1.19), 34% more days in ICU (AIRR 1.34, 95% CI 1.28-1.41), and 61% more days on ventilator (ARR 1.61, 95% CI 1.47-1.75). Additionally, patients with a ΔSI > 0.1 had higher odds of receiving blood products (AOR 2.00, 95% CI 1.88-2.12) within 4 h of ED arrival. Models fit excluding hypotensive patients performed similarly.
Conclusions: An increase of greater than 0.1 in the ΔSI was associated with increased 28-day mortality; increased days in hospital, in ICU, and on ventilator; and increased need for blood product transfusion within 4 h of ED arrival. This association held true for initially normotensive patients. Validation and implementation are needed to incorporate ΔSI into prehospital and ED triage.