Usefulness of free intraperitoneal air detected by CT scan in diagnosing bowel perforation in blunt trauma: Experience from a community-based hospital

Introduction Computed tomography (CT) scan has increasingly become the diagnostic modality of choice for the evaluation of patients with blunt abdominal trauma. CT scan is highly sensitive in the detection of small amounts of free intraperitoneal air (FIA). We aimed to evaluate the usefulness of FIA detected by CT scan in diagnosing bowel perforation in blunt trauma patients. Patients and methods All abdominal CT scans of blunt trauma patients who were treated at Al Rahba Hospital during the period from October 2010 till December 2013 were retrospectively reviewed. The results of abdominal CT scan were compared with the clinical follow up and operative findings to evaluate the sensitivity, specificity, predictive values, and usefulness index of CT-detected FIA in diagnosing bowel perforation. Results Abdominal CT scans were performed for 419 trauma patients. 21 (5%) patients were found to have FIA, two of them were true positive (10%), six (29%) needed mechanical ventilation, and eleven (52%) had a pneumothorax. 15/21 (71%) patients had multiple FIA pockets; the median (range) was 3 (2-10) air pockets. Two patients with multiple air pockets of 10 mm-thick cuts or more had small bowel perforation. Six (29%) patients had a single air pocket of less than 10 mm and none had bowel perforation. 398 patients had negative CT scan for FIA; two of them were false negative. CT-detected FIA scan had a sensitivity of 50% (95% CI: 6.8%-93.2%), specificity of 95.4% (95% CI: 92.9%-97.2%.), a positive predictive value of 9.5% (95% CI: 1.2%-30.4%) and a negative predictive value of 99.5% (95% CI: 98.2%-99.9%) for detecting bowel perforation. The usefulness index for abdominal CT scan FIA for detecting bowel perforation was 0.23 (not useful). Conclusions Our study which stemmed from a community-based hospital showed that free intraperitoneal air found on abdominal CT scan of blunt trauma patients was an unreliable radiological finding for bowel perforation. The decision for laparotomy should be based on combined clinical and radiological findings. Conservative management with active observation may avoid unnecessary laparotomy.