Abdominal CT in Blunt Trauma: Hold the Contrast?

Abstract & Commentary

Source: Allen TL, et al. Computed tomographic scanning without oral contrast solution for blunt bowel and mesenteric injuries in abdominal trauma. J Trauma 2004;56:314-322.

Since the 1980s, computed tomography (CT) scanning has been used to search for traumatic injuries to the abdomen in stable patients. From CT’s inception as an imaging modality, oral contrast agents were employed, as they were thought to aid in the identification of injuries to the bowel wall and mesentery. Blunt bowel and mesenteric injuries (BBMIs) are thought to occur in 1-5% of patients suffering blunt abdominal trauma. Further, morbidity and mortality from missed injuries to these organs is believed to be significantly increased when surgical treatment is delayed by as few as eight hours. There have been a number of smaller studies that have questioned this dogma of oral contrast administration. Only one, however, was prospective: Stafford’s study published in 1999 cast doubt on whether oral contrast added any significant data to the evaluation of this patient population.1

This prospective, non-randomized, cohort study from Salt Lake City included 500 consecutive Trauma I (their highest designation) patients; oral contrast was omitted from the routine trauma abdominal CT scan. CT images were interpreted initially by the attending radiologist, trauma surgeon, and chief surgical resident, and a prospective data sheet was completed. Routine trauma care, including laparotomy if indicated, was provided based on the results of the trauma evaluation. All scans were re-read 24 hours later by a study radiologist who was blinded to the first reading and to the patient’s clinical course. True BBMI was determined to be present if either laparotomy or autopsy identified bowel or mesentery injury, or both the study radiologist and the hospital discharge summary described bowel or mesenteric injury. All patients had three-month phone follow-up to determine if there were any late missed injuries.

Nineteen of 20 BBMIs were identified on the initial non-contrast study, for a sensitivity of 95% (95%; CI: 75-99%). There were two false-positive readings, yielding a specificity of 99.6% (95%; CI: 98-99%). The missed injury was a duodenal tear that became clinically apparent approximately 12 hours after admission. Notably, this injury was identified by the blinded study radiologist the following day. The two false-positive scans were a) a suspected gastric hematoma that was ruled out by adding oral contrast following the non-contrast study; and b) a suspected bowel injury that resulted in a laparotomy where the bowel was uninjured, but a splenic injury was found, resulting in splenectomy. The authors note that their sensitivity and specificity compares favorably with published numbers for contrasted studies.

Commentary by Andrew D. Perron, MD, FACEP, FACSM

In a perfect world, this would have been a prospective, randomized, double-blinded study in which the two groups go head-to-head to show equivalency between the two techniques. Unfortunately, as the authors of this paper point out, with an incidence of 1-5% for BBMI, an equivalency study would need to enroll more than 30,000 patients to have 80% power to reject the null hypothesis…no small feat, even for a multi-center trial. As with most "perfect-world" scenarios, we don’t live in one, and have to make decisions based on what we have. What I do take away from this study is that at a large trauma center, eliminating oral contrast from the CT evaluation of blunt abdominal trauma patients resulted in sensitivities that are as good as, or better than, those cited in contrasted studies. While the attendant risk of oral contrast administration is low (e.g., aspiration, time delay), the risk of not giving it seems lower.

Dr. Perron, Residency Program Director, Department of Emergency Medicine, Maine Medical Center, Portland, ME, is on the Editorial Board of Emergency Medicine Alert.

References

1. Stafford RE, et al. Oral contrast solution and computed tomography for blunt abdominal trauma: A randomized study. Arch Surg 1999;134:622-627.