| | Clinical Prediction Rules for Identifying Adults at Very Low Risk for Intra-abdominal Injuries After Blunt TraumaPresented at the SAEM annual meeting, Chicago, IL, May 2007. Received 8 September 2008; received in revised form 8 January 2009 and 28 March 2009; accepted 15 April 2009. published online 20 May 2009. Study objectiveWe derive and validate clinical prediction rules to identify adult patients at very low risk for intra-abdominal injuries after blunt torso trauma. MethodsWe 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. ResultsIn 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%). ConclusionThese 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. Editor's Capsule SummaryWhat is already known on this topic Many trauma patients get abdominal computed tomography (CT) scans but do not have an injury. What question this study addressed Whether a clinical decision rule can be developed and validated to predict patients at low risk of abdominal injury. What this study adds to our knowledge Patients with none of the following are unlikely to have an abdominal injury: Glasgow Coma Scale score less than 14, abdominal or costal margin tenderness, hematuria, low hematocrit level, femur fracture, or abnormal chest radiograph result. How this might change clinical practice These criteria lend credence to those who prefer clinical judgment to very liberal CT scanning, with its radiation exposure. 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. 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 laparoscopy/laparotomy.7, 26, 27 We excluded all patients with penetrating trauma, pregnant patients, those presenting in cardiopulmonary arrest, and those patients with blunt torso trauma who did not undergo a definitive diagnostic test. Data Collection and Processing Historical and physical examination findings for each enrolled patient were recorded onto a standardized data collection form by the treating physician (resident or faculty physician) before knowledge of the results of the diagnostic test. These historical and physical examination findings included the following: mechanism of injury; initial ED systolic blood pressure; Glasgow Coma Scale (GCS) score; thoracic, abdominal, flank, and pelvic bone examinations for tenderness; clinical evidence of alcohol intoxication; and presence of a distracting painful injury (as determined by the treating physician). The results of the initial chest and pelvic radiographs, as well as laboratory tests (hematocrit level and urinalysis), were also collected. Hypotension was considered present if the initial systolic blood pressure was less than 90 mm Hg. Plain chest radiograph results were considered abnormal if either a rib fracture or a pneumothorax was identified. Plain pelvis radiograph results were considered abnormal if a pelvic fracture was identified. Two physicians (at least 1 an ED faculty member) independently evaluated a convenience sample of 720 enrolled patients to assess interobserver agreement, as measured by the κ statistic.28 Outcome Measures The 2 outcome measures were patients with intra-abdominal injury who were undergoing acute intervention and patients with any intra-abdominal injury. Patients were considered to have an intra-abdominal injury if any injury was documented to the following structures: spleen, liver, gallbladder, pancreas, kidney, ureter, urinary bladder, gastrointestinal tract, or an intra-abdominal vascular structure. Patients with intra-abdominal injuries were considered to have undergone an acute intervention for their intra-abdominal injuries if they underwent a therapeutic laparotomy or angiographic embolization of an injured abdominal organ/vessel. Neither a patient with a normal laparotomy result (ie, no intra-abdominal injury identified) nor a patient with an intra-abdominal injury who underwent a laparotomy that did not have a specific therapy for that intra-abdominal injury was considered to have an intra-abdominal injury undergoing acute intervention. Outcome determination was made by an investigator masked to all ED clinical data. Primary Data Analysis We described the study population with simple descriptive statistics and 95% confidence intervals (CIs). We then created 2 clinical prediction rules. One prediction rule was derived to identify patients with intra-abdominal injury who were undergoing acute intervention, and a second prediction rule was derived to identify patients with any intra-abdominal injury. We developed the clinical prediction rules by using binary recursive partitioning with Classification and Regression Trees (CART) software (Salford Systems, San Diego, CA). Binary recursive partitioning is a nonparametric technique that classifies subjects according to clinical variables for the outcome of interest by using a treelike structure with prediction nodes.29 This analytic technique is considered preferable to multiple logistic regression when the goal is to develop a clinical prediction rule with high sensitivity.30 The structure of the tree allows the clinician to determine the risk of the patient according to the presence/absence of the clinical variables in the tree. In building the trees, we used the Ginni splitting function in CART. We set the misclassification costs for missing an intra-abdominal injury undergoing acute intervention at 500:1 (relative cost of 500 for misclassifying 1 patient with intra-abdominal injury who was undergoing acute intervention to that of misclassifying 1 patient without intra-abdominal injury who was undergoing acute intervention). In the second prediction rule, we set the misclassification costs for missing any intra-abdominal injury at 100:1 (relative cost of 100 for misclassifying 1 patient with any intra-abdominal injury to that of misclassifying a patient without an intra-abdominal injury). The cost for intra-abdominal injury undergoing acute intervention (500:1) was set higher than the cost for any intra-abdominal injury (100:1), following clinical sensibility about the greater need to identify those patients undergoing an intervention for their intra-abdominal injury as opposed to patients with intra-abdominal injuries that are simply observed without any specific therapy. In the derivation phase, predictor variables were selected for inclusion according to a priori determined associations with intra-abdominal injury3, 4, 5, 10, 24, 25, 31, 32, 33, 34, 35, 36, 37, 38, 39 and acceptable interrater reliability. The latter was defined as a κ statistic with a lower bound of the 95% CI greater than or equal to 0.40, which indicates at least moderate agreement between observers.28 In addition, we excluded any physical examination variables that were missing from the data collection more than 5% of the time. The variables considered in the prediction rules included the following: hypotension, costal margin tenderness, abdominal tenderness, abdominal “seatbelt sign” (a linear area of ecchymosis/abrasion over the abdomen because of the seatbelt), GCS score less than 14, clinical evidence of alcohol intoxication, distracting painful injury, initial hematocrit level less than 30%, hematuria greater than or equal to 25 red blood cells/high powered field, abnormal chest radiograph result (rib fracture or pneumothorax), femur fracture, and pelvic fracture on initial pelvic radiograph.3, 4, 5, 10, 24, 25, 31, 32, 33, 34, 35, 36, 37, 38, 39 After derivation of the clinical prediction rules, we then validated the rules in a separate cohort of patients (validation phase). Patients in the validation phase were enrolled in the same manner as those in the derivation phase. In addition, we queried the physicians providing care to these patients about their perceived risk of intra-abdominal injury after clinical evaluation and before abdominal CT. Physician-perceived risk of intra-abdominal injury was categorized as less than 1%, 1% to 5%, or greater than 5%. We calculated the sensitivity, specificity, and positive and negative predictive values with 95% CIs of the 2 prediction rules when applied to patients in the validation phase. Relative risk ratios were calculated for individual variables identified in the prediction rules. The a priori sample size for the derivation study was calculated as 299 patients with intra-abdominal injury, assuming a desired sensitivity of the rule for intra-abdominal injury of 100%, with a desired lower bound of the 95% CI of 99.0%. The sample size for the validation study was set at 100 patients with intra-abdominal injury, consistent with previous literature for validation of clinical prediction rules.40 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, splenectomy/splenorrhaphy 40, Avitene/Surgifoam to bleeding livers/spleen 21, liver packing 13, nephrectomy 4, mesentery repair 22, gastrointestinal perforation resection 21, gastrointestinal serosal repair 19, gastrointestinal perforation repair 10, pancreas drainage/resection 9, and other 12. Of the 3,435 patients enrolled, 1,546 (45%) had no abdominal tenderness and a GCS score greater than or equal to 14, including 72 (4.7%) patients with intra-abdominal injury. We enrolled 81% of eligible patients. Of the 806 eligible patients not enrolled, 69 (8.6%; 95% CI 6.7% to 10.7%) had intra-abdominal injuries. From May 2004 to April 2005, 1,595 patients were enrolled into the validation phase of the study. Of these 1,595 patients, 143 (9.0%; 95% CI 7.6% to 10.5%) were identified as having intra-abdominal injuries. Of the 143 patients with intra-abdominal injuries, 44 (31%; 95% CI 23% to 39%) underwent acute interventions. The characteristics of the patients in both the derivation and validation phases of the study are presented in Table 1. | | |  | Clinical Variable | Derivation Phase, n=3,435 | Validation Phase, n=1,595 | |
|---|
| Mean age (±1 SD) | 39.6±16.8 | 40.3±17.5 | | | Age range, y | 18-101 | 18-95 | | | Male sex (%) | 2,138 (65) | 1,038(65) | | | MVC (%) | 1,759(51) | 827(52) | | | Fall (%) | 466(14) | 194(12) | | | Assault (%) | 407(12) | 147(9) | | | Auto vs pedestrian (%) | 286(8) | 136(9) | | | Other mechanism (%) | 517(15) | 291(18) | | | Abdominal CT performed (%) | 3,381(98.4) | 1,566(98.2) | | | Diagnostic peritoneal lavage performed (%) | 57(1.7) | 9(0.6) | | | Laparotomy performed (%) | 130(3.8) | 42(2.6) | | | | |
The results of the interrater reliability for the clinical variables evaluated for possible consideration for entry into the prediction rule are presented in Table 2. Most of these were considered for inclusion into the prediction rules; however, several, including flank tenderness, abdominal distention, and peritoneal irritation, were not considered further because of insufficient interrater reliability. None of the physical examination variables were missing in more than 5% of the cases (all eligible variables missing ≤3%). The derived clinical prediction rule (Figure 1) for intra-abdominal injury undergoing acute intervention consisted of the following 6 variables: hypotension (systolic blood pressure <90 mm Hg), 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%. The derived clinical prediction rule (Figure 2) to identify patients with intra-abdominal injury consisted of the following 7 variables: 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 (rib fracture or pneumothorax). The relative risk ratios for all variables identified in either rule are presented in Table 3. | | | | Clinical Variable | IAI Present | IAI Absent | Relative Risk (95% CI) | |
|---|
| Systolic blood pressure <90 mm Hg | 37/311 | 72/3,124 | 4.1(3.1-5.5) | | | GCS score <14 | 71/311 | 363/3,124 | 2.0(1.6-2.6) | | | Costal margin tenderness | 161/311 | 1,100/3,124 | 1.9(1.5-2.3) | | | Abdominal tenderness | 177/311 | 1,326/3,124 | 1.7(1.4-2.1) | | | Femur fracture | 38/311 | 130/3,124 | 2.7(2.0-3.7) | | | Hematuria level >25 red blood cells/high powered field | 122/300⁎ | 270/2,729⁎ | 5.1(4.1-6.2) | | | Hematocrit level <30% | 36/311 | 95/3,124 | 3.3(2.4-4.5) | | | Abnormal chest radiograph result | 87/311 ⁎ | 224/3,069⁎ | 3.8(3.1-4.8) | | | | |
| ⁎ Diagnostic test not obtained for all subjects. |
The test performance of the clinical prediction rule for identifying patients with intra-abdominal injuries undergoing acute intervention in the validation phase is presented in Table 4. The specificity was such that if the clinical prediction rule was applied and abdominal CT scans were not obtained for those patients with negative prediction rule results, nearly one third of the abdominal CT scans in this study would be avoided. The test performance of the clinical prediction rule for identifying patients with any intra-abdominal injury on the patients in the validation phase is presented in Table 5. Similarly, the prediction rule displayed excellent sensitivity and, if strictly applied, would result in a similar reduction in abdominal CT scanning. In addition, the prediction rules had similar test performance characteristics in the derivation sets. | | | | | Derivation Phase (95% CI) | Valiation Phase (95% CI) | |
|---|
| Sensitivity | 109/109 | 100%(97.2,100%) | 44/44 | 100%(93.4,100%) | | | Specificity | 824/3,326 | 24.8%(23.3,26.3%) | 476/1,551 | 30.7%(28.4,33.1%) | | | Positive predictive value | 109/2,611 | 4.2%(3.4,5.0%) | 44/1,119 | 3.9%(2.9,5.2%) | | | Negative predictive value | 824/824 | 100%(99.6,100%) | 476/476 | 100%(99.4,100%) | | | | |
| | | | | Derivation Phase (95% CI) | Validation Phase (95% CI) | |
|---|
| Sensitivity | 305/311 | 98.1%(95.8,99.3%) | 137/143 | 95.8%(91.1,98.4%) | | | Specificity | 818/3,124 | 26.2%(24.6,27.8%) | 434/1,452 | 29.9%(27.5,32.3%) | | | Positive predictive value | 305/2,611 | 11.7%(10.5,13.0%) | 137/1,115 | 11.9%(10.1,13.9%) | | | Negative predictive value | 818/824 | 99.3%(98.4,99.7%) | 434/440 | 98.6%(97.1,99.5%) | | | | |
The characteristics of the 6 patients with intra-abdominal injury in the derivation phase and the 6 patients with intra-abdominal injury in the validation phase who were not identified by either prediction rule are presented in Table 6. None of the patients who had negative results for both prediction rules underwent acute intervention for their intra-abdominal injury. All were observed in the hospital and then subsequently discharged safely to home. | | | | Age, y | Mechanism | Injury | Hemo⁎ | Other Clinical Findings | Hospital Course | |
|---|
| 20 | High speed MVC | Spleen | Yes | L1 burst fracture | Observation | | | 20 | Assault with club | Kidney | No | Intoxicated, abdominal abrasions | Observation | | | 64 | 9-Foot fall | Liver | No | T12 burst fracture | Observation | | | 35 | 30-Foot fall | Liver | No | L1 burst fracture | Observation | | | 18 | MVC, low speed | Liver | No | Back/flank pain | Observation | | | 54 | MVC | Liver | No | Gluteal hematoma | Observation | | | 35 | MVC, low speed | Liver | No | Tibial fracture | Observation | | | 26 | MVC | Spleen | No | Concussion, GCS score=15 | Observation | | | 30 | MVC, rollover | Liver | Yes | T8 Fx, L1, L2 transverse process Fx | Observation | | | 53 | 8-Foot fall | Spleen/kidney | No | Intracranial hemorrhage, GCS score=15 | Observation | | | 55 | MVC, rollover | Spleen | Yes | Rib fractures, L1 transverse process Fx | Observation | | | 51 | Fall | Kidney | No | L1, L2 transverse process Fx | Observation | | | | |
| ⁎ Hemoperitoneum identified by abdominal CT or at laparotomy. |
In the validation phase, we queried the physicians providing care to these patients about their perceived risk of intra-abdominal injury after clinical evaluation and before CT. Data were available for 1,453 of 1,595 (91%) patients, including 135 of those with intra-abdominal injury. In 8 (5.9%) of 135 patients with intra-abdominal injury, physicians assessed the patient to have a less than 1% risk of intra-abdominal injury, and 31 of 135 (23.0%) were considered to have a 1% to 5% risk of intra-abdominal injury. Assuming a physician-estimated risk of less than 1% as “negative for intra-abdominal injury” and a physician risk estimate greater than or equal to 1% as “positive for intra-abdominal injury,” physician estimation had the following test characteristics: sensitivity 127 of 135 (94%; 95% CI 89% to 97%), specificity 365 of 1,318 (28%; 95% CI 25% to 30%), positive predictive value 127 of 1,080 (12%; 95% CI 9.9% to 13.8%), and negative predictive value 373 of 385 (98%; 95% CI 96% to 99%). One patient considered at less than 1% risk by physician suspicion for intra-abdominal injury underwent a therapeutic laparotomy for a gastrointestinal injury. 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 capture further data on missed eligible patients for comparison. The study was primarily designed to identify a population of adult trauma patients in whom abdominal CT scanning would be of very low utility. Therefore, we studied only patients who underwent a definitive diagnostic study and therefore cannot comment on patients who did not receive definitive diagnostic testing. These prediction rules should be viewed as “assistive” and not “directive” for abdominal CT scanning of all patients who have one of the high-risk variables present.42 The implications and risks associated with the presence of only 1 of the variables in the rules is different from the risk associated with a different variable or combinations of variables in the rule. Furthermore, we excluded variables with unacceptably low κ measurements. Inclusion of these variables may have resulted in a different rule, but inclusion of variables with unacceptable κ measurements violates principles of decision rule development.30 The κ measurements include an assessment by a resident physician and a faculty physician. The reliability of the resident examination may not be equal to that of a faculty emergency physician. The prevalence of intra-abdominal injury in this study was similar to that of previous studies (including multicenter studies), suggesting similar rates of CT utilization among US trauma centers.3, 43 As with previous studies, we considered abdominal CT scanning to be a reference standard test for the identification of intra-abdominal injury, although it is likely that the CT scan is not a perfectly accurate diagnostic test. This may have resulted in some patients without intra-abdominal injury being misclassified as having intra-abdominal injury because of a falsely positive abdominal CT scan result. If the abdominal CT scan has a theoretical specificity of 99%, we would expect 1% of patients in this study (ie, 50 patients) to be misclassified as having an intra-abdominal injury because of false-positive abdominal CT scan results. It is therefore possible that several of the patients categorized with intra-abdominal injury according to CT, but not identified by the prediction rules, did not truly have an intra-abdominal injury. Because the prediction rules do not identify all patients with intra-abdominal injury, strict application would result in some patients with intra-abdominal injury not being identified. These patients “missed” by the decision rules were all observed and none underwent specific therapy. The implications of missing a few injuries that do not require specific therapy is unclear. However, some may argue that counseling patients with minor intra-abdominal injuries about return to sports activity and other contact activity would be important. Finally, we did not include bedside abdominal ultrasonography for consideration in the creation of this prediction rule. Abdominal ultrasonography is used with increasing frequency in the evaluation of patients with blunt trauma. However, its use in the United States has been primarily restricted to trauma centers, and it is not routinely available or used in all EDs.12 Creating a prediction rule in which a technology is not available to all physicians evaluating trauma patients would limit its applicability.42 We did, however, model a prediction rule for patients with intra-abdominal injury when the ultrasonographic result was included as a predictor variable. This analysis resulted in a prediction rule that included the following variables: positive ultrasonographic examination result, hypotension, GCS score less than 14, costal margin tenderness, abdominal tenderness, and hematuria level greater than or equal to 25 red blood cells/high powered field. Thus, the variables included in the models are similar, regardless of the inclusion of abdominal ultrasonographic results in the model. 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 acceptable levels of interobserver agreement and thus can be reliably assessed by emergency physicians. These clinical prediction rules identified nearly all patients with intra-abdominal injuries and, more important, identified all patients in both the derivation and validation phases with intra-abdominal injuries who were undergoing acute intervention. These data provide scientific evidence to assist clinicians in their decisions about CT imaging of the abdomen in patients with blunt torso trauma. Initial identification of patients at risk for intra-abdominal injury may be difficult, and delayed diagnosis is associated with increased morbidity and mortality.44, 45, 46 Most adult patients with blunt torso trauma, however, do not have intra-abdominal injuries; therefore, routine imaging of all patients is not warranted because there are disadvantages to excessive abdominal CT utilization.18 Furthermore, abdominal CT scanning is a source of substantial radiation risk to the trauma patient.47 Reducing abdominal CT use would have several potential benefits, including decreasing patient ED length of stay, patient care costs, and associated risks (radiation-induced malignancy, aspiration of oral contrast, intravenous contrast reactions, and contrast-induced nephropathy).16, 48, 49, 50 If the clinical prediction rules derived and validated in this study were strictly applied to the studied patient population, nearly one third of abdominal CT scans in this study would have been obviated. Previous research studying indications for abdominal CT scanning after blunt torso trauma has identified multiple variables associated with the presence of intra-abdominal injury but has had methodological limitations, including the use of inadequate analytic techniques or retrospective data.3, 24, 25 In the current study, we followed standard and accepted methodological recommendations for deriving and validating clinical prediction rules.30, 51, 52 The single largest prospective study previously conducted to identify those blunt trauma patients not requiring abdominal CT suggested that patients with GCS scores greater than 13, normal abdominal ultrasonographic examination results, normal chest and pelvic radiograph results, and normal laboratory testing results (hematocrit level, WBC count, and lactate, amylase, and serum glutamic oxaloacetic transaminase levels) do not require abdominal CT imaging.3 Application of these findings would have obviated the need for abdominal CT scanning in 12% of their studied population. That study, however, did not collect urine data, relied heavily on laboratory testing, and used logistic regression to identify risk factors associated with intra-abdominal injury, all of which may have impaired the utility and clinical feasibility of applying the final rule in practice.22, 30 A prospective study conducted by Salim et al6 suggested that some adults with blunt torso trauma but without apparent clinical findings of intra-abdominal injury may, in fact, have intra-abdominal injuries. Among the 1,000 patients in that study considered not to have “obvious signs of injury,” 49 (4.9%) nevertheless had intra-abdominal injuries. Twenty-one (2.1%) of these patients, however, had depressed levels of consciousness, making the abdominal examination results unreliable. In the current study, the clinical variable “GCS score less than 14” applied to the Salim et al6 study population would have identified these 21 patients. Of the remaining 28 patients with intra-abdominal injuries but with normal mental status and without “obvious signs of injury” in the study, how many had other findings that the current study would suggest are predictive of intra-abdominal injury (costal margin tenderness, femur fracture, hematuria, abnormal initial chest radiograph result, etc) was not described. Furthermore, had we implemented a definition of “without obvious signs of injury” similar to that in the Salim et al6 study, 4.7% of our patients with intra-abdominal injuries in the derivation phase would be considered to be “without signs of injury.” Several other studies have focused on special populations with specific clinical characteristics in attempts to determine the appropriate use of CT scanning after blunt abdominal trauma. These studies have identified a variety of associations with intra-abdominal injury, including the importance of the abdominal “seatbelt sign,”38, 53 costal margin injury,34, 37 femur fractures,31 and “distracting injuries.”33 In our study, we considered “distracting painful injury” separately from femur fractures and thoracic injuries as candidate variables. Our subsequent recursive partitioning analysis did not find the variable “distracting painful injuries” useful in indentifying patients with intra-abdominal injuries but did find that femur fractures and thoracic injuries were very important predictors. The most important variable in our prediction rule, located at the top of the “prediction tree” (Figure 1, Figure 2) and having the highest relative risk for intra-abdominal injury, however, was the presence of significant hematuria. Although hematuria, including microscopic hematuria, is a recognized independent risk factor for intra-abdominal injury in children,35, 54 this variable is more controversial in the evaluation of adult trauma patients. Many ED clinicians and trauma surgeons simply use the urinalysis as a screen for genitourinary trauma and frequently do not consider the urinalysis as a screen for other intra-abdominal injuries. However, given the close proximity of other intra-abdominal organs to the kidneys, it is not surprising that hematuria is a marker for other intra-abdominal injuries. In fact, one previous study has suggested that microscopic hematuria is a very important predictor of intra-abdominal injury in adults and is useful as a screening tool.10 Another study suggests hematuria is an important predictor of intra-abdominal injury in those adult trauma patients with normal abdominal ultrasonographic examination results.55 We created prediction rules for patients with intra-abdominal injuries undergoing acute intervention and for patients with any intra-abdominal injuries. Not surprisingly, the 2 rules are similar. However, hypotension was identified as a risk factor for patients with intra-abdominal injuries who were undergoing acute intervention but not for patients with any intra-abdominal injuries. This is not surprising because it is intuitive that hypotension after blunt torso trauma would be a marker for high-severity injury. We would advocate considering patients with any of the variables identified by either of these 2 rules to be at nonnegligible risk for intra-abdominal injury and therefore that appropriate evaluation (abdominal CT, ultrasonography, or serial abdominal examinations) be implemented according to the clinical scenario and resources available. To assist with the decision of how aggressively to evaluate for intra-abdominal injury, a patient's particular risk for intra-abdominal injury, as well as intra-abdominal injury undergoing acute intervention, can be determined by reviewing the decision trees. In conclusion, clinical prediction rules consisting of hypotension, 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 (rib fracture or pneumothorax) can aid physicians in the evaluation of adult patients with blunt torso trauma. Patients without any of the high-risk variables are at very low risk of intra-abdominal injury and are unlikely to benefit from abdominal CT scanning. References 1. 1Minino AM, Heron MP, Murphy SL, et al. Deaths: final data for 2004. Natl Vital Stat Rep. 2007;55:1–119. MEDLINE 2. 2Perez FG, O'Malley KF, Ross SE. Evaluation of the abdomen in intoxicated patients: is computed tomography scan or peritoneal lavage always indicated?. Ann Emerg Med. 1991;20:500–502. Abstract |
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7. 7Griffin XL, Pullinger R. Are diagnostic peritoneal lavage or focused abdominal sonography for trauma safe screening investigations for hemodynamically stable patients after blunt abdominal trauma? (A review of the literature). J Trauma. 2007;62:779–784. MEDLINE 8. 8Heilbrun ME, Chew FS, Tansavatdi KR, et al. The role of negative CT of the abdomen and pelvis in the decision to admit adults from the emergency department after blunt trauma. J Am Coll Radiol. 2005;2:889–895. 9. 9Holmes JF, Harris D, Battistella FD. Performance of abdominal ultrasonography in blunt trauma patients with out-of-hospital or emergency department hypotension. Ann Emerg Med. 2004;43:354–361. Abstract | Full Text |
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a Department of Emergency Medicine, UC Davis School of Medicine, Sacramento, CA b Department of Surgery, UC Davis School of Medicine, Sacramento, CA c Department of Radiology, UC Davis School of Medicine, Sacramento, CA d Department of Pediatrics, UC Davis School of Medicine, Sacramento, CA e Division of Emergency Medicine, UCLA School of Medicine, Los Angeles, CA  Address for reprints: James F. Holmes, MD, MPH, UC Davis Medical Center, Department of Emergency Medicine, 2315 Stockton Blvd, PSSB 2100, Sacramento, CA 95817-2282; 916-734-1533, fax 916-734-7950
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. PII: S0196-0644(09)00398-9 doi:10.1016/j.annemergmed.2009.04.007 © 2009 American College of Emergency Physicians. Published by Elsevier Inc. All rights reserved. | |
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