The clinical utility of shock index to predict the need for blood transfusion and outcomes in trauma

Background: We aimed to evaluate the clinical utility of shock index (SI) to assess the need for blood transfusion and predict the outcomes in trauma. Materials and methods: We conducted a retrospective analysis for trauma patients between 2012 and 2016 in a level-1 trauma center. Data included patient demographics, vital signs, mechanism of injury, Injury Severity Score (ISS), New Injury Severity Score (NISS), Trauma and Injury Severity Score (TRISS), blood transfusion, hospital length of stay (HLOS), and mortality. Patients were classified into group I (SI < 0.8) and group II (SI ≥ 0.8). Results: Out of 8710 admitted patients, 1535 (22%) had SI ≥ 0.8 and 976 (12.5%) received blood transfusion (89 received massive transfusion, following massive blood transfusion protocol [MTP]). In comparison to lower SI, patients with SI ≥ 0.8 were mostly female patients, 8 y younger (43 ± 22 versus 51 ± 23), had greater ISS (15 ± 12 versus 10.5 ± 8), higher NISS (19 ± 15 versus 14 ± 11), lower pulse pressure (43 ± 14 versus 62 ± 18), lower TRISS (0.892 ± 0.20 versus 0.953 ± 0.11), and received more blood transfusion (28.6% versus 9.0%) or MTP (17.7% versus 3%), P = 0.001. Also, they had mostly exploratory laparotomy (13.3% versus 6.6%, P = 0.001), longer HLOS (11.3 versus 7.0 d, P = 0.001), and higher mortality (7.0% versus 3.1%, P = 0.001). SI was correlated with age (r = −0.188), pulse pressure (r = −0.51), HLOS (r = 0.168), ISS (r = 0.251), NISS (r = 0.211), amount of blood transfused (r = 0.27), Glasgow Coma Scale (r = −0.96), and TRISS (r = −0.230). After adjusting for age and sex, ISS, and Glasgow Coma Scale in two multivariable analyses, high SI was found to be an independent predictor for mortality (odd ratio, 2.553; 95% confidence intervals: 1.604-4.062) and blood transfusion (odd ratio, 3.57; 95% confidence intervals: 3.012-4.239). The cutoff point of SI for predicting MTP is 0.81 (sensitivity, 85%; specificity, 64%; positive predictive value, 16%; and negative predictive value, 98%). Conclusions: The SI after injury can be used early to predict the need for MTP and laparotomy and mortality. It correlates with other physiological and anatomical variables. However, its cutoff values for risk stratification and prognostication need further evaluation.