Trauma/original research
Clinical Prediction Rules for Identifying Adults at Very Low Risk for Intra-abdominal Injuries After Blunt Trauma

Presented at the SAEM annual meeting, Chicago, IL, May 2007.
https://doi.org/10.1016/j.annemergmed.2009.04.007Get rights and content

Study objective

We derive and validate clinical prediction rules to identify adult patients at very low risk for intra-abdominal injuries after blunt torso trauma.

Methods

We prospectively enrolled adult patients (≥18 years old) after blunt torso trauma for whom diagnostic testing for intra-abdominal injury was performed. In the derivation phase, we used binary recursive partitioning to create a rule to identify patients with intra-abdominal injury who were undergoing acute intervention (including therapeutic laparotomy or angiographic embolization) and a separate rule for identifying patients with any intra-abdominal injury present. We considered only clinical variables readily available with acceptable interrater reliability. The prediction rules were then prospectively validated in a separate cohort of patients.

Results

In the derivation phase, we enrolled 3,435 patients, including 311 (9.1%; 95% confidence interval [CI] 8.1% to 10.1%) with intra-abdominal injury and 109 (35.0%; 95% CI 29.7% to 40.6%) with intra-abdominal injury requiring acute intervention. In the validation study, we enrolled 1,595 patients, including 143 (9.0%; 95% CI 7.6% to 10.5%) with intra-abdominal injury. The derived rule for patients with intra-abdominal injuries who were undergoing acute intervention consisted of hypotension, Glasgow Coma Scale (GCS) score less than 14, costal margin tenderness, abdominal tenderness, hematuria level greater than or equal to 25 red blood cells/high powered field, and hematocrit level less than 30% and identified all 44 patients in the validation phase with intra-abdominal injury who were undergoing acute intervention (sensitivity 44/44, 100%; 95% CI 93.4% to 100%). The derived rule for the presence of any intra-abdominal injury consisted of GCS score less than 14, costal margin tenderness, abdominal tenderness, femur fracture, hematuria level greater than or equal to 25 red blood cells/high powered field, hematocrit level less than 30%, and abnormal chest radiograph result (pneumothorax or rib fracture). In the validation phase, the rule for any intra-abdominal injury present had the following test performance: sensitivity 137 of 143 (95.8%; 95% CI 91.1% to 98.4%), specificity 434 of 1,452 (29.9%; 95% CI 27.5% to 32.3%), and negative predictive value 434 of 440 (98.6%; 95% CI 97.1% to 99.5%).

Conclusion

These derived and validated clinical prediction rules can aid physicians in the evaluation of adult patients after blunt torso trauma. Patients without any of these variables are at very low risk for having intra-abdominal injury, particularly intra-abdominal injury requiring acute intervention, and are unlikely to benefit from abdominal computed tomography scanning.

Introduction

Abdominal trauma is a leading cause of morbidity and mortality.1 Identifying patients with intra-abdominal injuries can be difficult because the abdominal examination does not reliably identify all patients with intra-abdominal injuries.2, 3, 4, 5, 6 With improvement in computed tomography (CT) technology, abdominal CT scanning has become the primary method of evaluating hemodynamically stable blunt trauma patients believed to be at risk for intra-abdominal injury at both trauma and nontrauma centers.6, 7, 8, 9, 10, 11, 12, 13 Despite the increase in use of abdominal CT scanning in blunt trauma, the indications for abdominal CT in this setting are not well defined.14 Routine abdominal CT scanning of all blunt trauma patients is expensive and impractical in most busy emergency departments (EDs). Furthermore, there is evidence that overuse of CT scanning exposes patients to unnecessary ionizing radiation, potentially leading to lethal malignancies.15, 16, 17, 18 Thus, appropriate selection of injured patients for abdominal CT scanning would provide more efficient, cost-effective, and safe patient care.

Clinical prediction rules have previously been developed to assist clinicians in determining the need for radiographic evaluation of injured patients after head and cervical spine trauma.19, 20, 21, 22, 23 Previous studies suggest that a clinical prediction rule for abdominal imaging may be feasible because these studies have identified several clinical variables associated with an increased risk of intra-abdominal injury.3, 24, 25 Despite the apparent need for an instrument to assist clinicians with decisionmaking about abdominal CT scanning,14 a clinical prediction rule for identifying adult patients with blunt torso trauma who are at risk for intra-abdominal injury has not yet been developed.

The objective of this study was to derive and validate clinical prediction rules to identify adult patients at very low risk for intra-abdominal injury after blunt torso trauma. We hypothesize that we could derive and validate clinical prediction rules that identify a group of patients at sufficiently low risk for intra-abdominal injury that abdominal CT imaging could be obviated.

Section snippets

Materials and Methods

We conducted a prospective observational cohort study at an urban Level I trauma center. The study was approved by the study site's institutional review board.

We enrolled adult patients, 18 years of age or older, with blunt torso trauma who underwent a definitive diagnostic test to determine the presence or absence of intra-abdominal injury. For study purposes, a definitive diagnostic test was defined as any of the following: abdominal CT scan, diagnostic peritoneal lavage, or

Results

From March 2002 to April 2004, we enrolled 3,435 patients into the derivation phase of the study. Of these 3,435 patients, 311 (9.1%; 95% CI 8.1% to 10.1%) were identified as having an intra-abdominal injury. Of the 311 patients with intra-abdominal injuries, 109 (35.0%; 95% CI 29.7% to 40.6%) underwent an acute intervention (therapeutic laparotomy or angiographic embolization). Interventions included the following (mean intervention/patient=1.6): angiographic embolization 6,

Limitations

We did not evaluate all potentially clinically important variables in this study. For example, we did not assess the utility of liver function tests41 because these are not routinely obtained in the evaluation of adult trauma patients. It is possible that several of the patients with hepatic injuries “missed” by the prediction rules would have been identified by these laboratory tests. We did not enroll all eligible patients. The rate of intra-abdominal injury was similar, but we did not

Discussion

In this study, we derived and validated clinical prediction rules with high sensitivity and negative predictive value for identifying adult patients with and without intra-abdominal injury after blunt torso trauma. The clinical variables in these rules are routinely collected as part of the assessment of patients with blunt torso trauma who present to the ED and are thus readily available when the decision to perform abdominal CT scanning is considered. In addition, these variables have

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      Citation Excerpt :

      It has also been emphasized that CT scanning should be used selectively to minimize these disadvantages. A few studies have assisted clinicians in determining the need for abdominal CT scanning in blunt trauma patients [20–22]. We hypothesized that a nomogram developed to predict the need for abdominal and pelvic CT (APCT) scanning in patients with blunt trauma after the primary survey would predict positive findings on CT scans.

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    Supervising editor: Judd E. Hollander, MD

    Author contributions: JFH was responsible for the study concept and supervision, analyzing and interpreting the data, and drafting the article. JFH, WRM, and NK were responsible for the study design. JFH, DHW, and JPM acquired the data. All authors were responsible for critical revision of the article for important intellectual content. JFH and NK provided statistical expertise and obtained funding. JH takes responsibility for the paper as a whole.

    Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article that might create any potential conflict of interest. See the Manuscript Submission Agreement in this issue for examples of specific conflicts covered by this statement. Funded in part by the Society for Academic Emergency Medicine Research Training Grant.

    Publication date: Available online May 19, 2009.

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