Shock index combined with focused abdominal sonography for trauma examination as a predictor for therapeutic laparotomy in blunt trauma

Abstract

Study objectives: The focused abdominal sonography for trauma (FAST) examination was developed to help rapidly identify those blunt trauma patients who require emergency laparotomy. Since then, the clinical use of the FAST examination has expanded. When applied to hemodynamically stable blunt trauma patients, the FAST examination is less sensitive for any injury and particularly the need for laparotomy. Combining FAST results with a measure of hemodynamic stability might better predict the need for emergency laparotomy as a therapeutic intervention and thus give a more meaningful predictive value to the positive test. We therefore sought to determine whether a first measured shock index of 1 or greater, when combined with a positive FAST examination, better predicts the need for therapeutic laparotomy in blunt trauma patients than FAST alone. Methods: This is a retrospective, case-control study using the institutional trauma database at an American College of Surgeons–verified Level I trauma center during 2003. Patients were included in the study if injured by blunt mechanism and if they required the highest level of trauma team activation by standardized institutional criteria. Patients were excluded if they had previous peritoneal lavage or transfusion or were younger than 14 years. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the test (positive FAST plus shock index ≥1) for therapeutic laparotomy were calculated, along with 95% confidence intervals (CIs). The first emergency department recorded values for heart rate and systolic blood pressure were used to calculate the shock index. Results: Four hundred ninety-one patients were included in the study, 27 of whom underwent emergency laparotomy (rate 5.50%). Two of these laparotomies were classified as nontherapeutic. Of the 464 patients without laparotomy, 303 (65.3%) were men, with a mean age of 37.2 years. Of the patients with laparotomy, 17 (63.0%) were men, with a mean age of 38.4 years. Motor vehicle collisions were the mechanism of injury in 50.4% and 66.7% of those without and with laparotomy, respectively. The mean presenting Glasgow Coma Scale score was 12 versus 8 for those without and with laparotomy, and the mean Injury Severity Score was 16.9 versus 33.7 for those without and with laparotomy. Three hundred forty-four patients had FAST results recorded for analysis. The sensitivity of a positive FAST examination plus shock index of 1 or greater for therapeutic laparotomy was 44.0% (95% CI 26.3 to 62.8%), specificity 99.4% (95% CI 98.0 to 99.9%), and PPV 84.6% (95% CI 60.5 to 97.1), whereas the NPV was 95.7% (95% CI 93.2 to 97.6). Conclusion: Although the sensitivity for a positive FAST examination and a shock index of 1 or greater to predict therapeutic laparotomy is low, the PPV of the test is quite high. The combination of FAST results plus first measured vital signs (even if they later respond to intravenous fluid or transfusion) indicates a high likelihood of the need for therapeutic laparotomy.