Use of abdominal computed tomography in blunt trauma: Do we scan too much?

OBJECTIVES: To determine what proportion of abdominal computed tomography (CT) scans ordered after blunt trauma are positive and the applicability and accuracy of existing clinical prediction rules for obtaining a CT scan of the abdomen in this setting. SETTING: A leading trauma hospital, affiliated with the University of Ottawa. DESIGN: A retrospective cohort study. PATIENTS AND METHODS: All patients with blunt trauma admitted to hospital over a I-year period haring an Injury Severity Score (ISS) greater than 12 who underwent CT of the abdomen during the initial assessment. Recorded data included age, sex, Glasgow Coma Scale (GCS) score, ISS, type of injuries, number of abdominal CT scans ordered, and scan results. Two clinical prediction rules were found in the literature that identify patients likely to have intra-abdominal injuries. These rules were applied retrospectively to the cohort. The predicted proportion of positive CT scans was compared with the observed proportion, and the sensitivity, specificity, and accuracy were estimated. RESULTS: Of the 297 patients entered in the study, 109 underwent abdominal CT. The median age was 32 years, 71% were male and the median ISS was 24. In only 36.7% (40 of 109) of scans were findings suggestive of intra-abdominal injuries. Application of one of the clinical prediction rules gave a sensitivity of 93.8% and specificity of 25.5% but excluded 23% of patients because of a GCS score less than 11. The second prediction rule tested could be applied to all patients and was highly sensitive (92.5%) and specific (100.0%). CONCLUSIONS: The assessment of the abdomen in blunt trauma remains a challenge. Accuracy in predicting positive scans in equivocal cases is poor. Retrospective application of an existing clinical prediction rule was found to be highly accurate in identifying patients with positive CT findings. Prospective use of such a rule could reduce the number of CT scans ordered without missing significant injuries.