Article, Radiology

Rate of intra-abdominal injury after a normal abdominal computed tomographic scan in adults with blunt trauma

Unlabelled imageAbdominal injury after a n”>American Journal of Emergency Medicine (2012) 30, 574-579

Original Contribution

Rate of intra-abdominal injury after a normal abdominal computed tomographic scan in adults with blunt trauma?

James F. Holmes MD, MPH a,?, John P. McGahan MD b, David H. Wisner MD c

aDepartment of Emergency Medicine, UC Davis School of Medicine, Sacramento, CA, USA bDepartment of Radiology, UC Davis School of Medicine, Sacramento, CA, USA cDepartment of Surgery, UC Davis School of Medicine, Sacramento, CA, USA

Received 29 December 2010; revised 11 February 2011; accepted 17 February 2011

Abstract

Objective: The objective of this study is to determine the rate of intra-abdominal injury (IAI) in adults with blunt abdominal trauma after a normal abdominal computed tomographic (CT) scan. We hypothesize that the risk of subsequent IAI is so low that hospital admission and observation for possible IAI are unnecessary.

Methods: We conducted a prospective, observational cohort study of adults (N18 years) with blunt trauma who underwent abdominal CT scanning in the emergency department. Computed tomographic scans were obtained with intravenous contrast but no oral contrast. Abnormalities on abdominal CT included all visualized IAIs or any finding suggestive of possible IAI. Patients were followed up to determine the presence or absence of IAI and the need for therapeutic intervention if IAI was identified. Results: Of the 3103 patients undergoing abdominal CT, 2734 (88%) had Normal CT scans. The median age was 39 years (interquartile range, 26-51 years); and 2141 (78%) were admitted to the hospital. Eight (0.3%; 95% confidence interval, 0.1%-0.6%) were identified with IAIs after normal Abdominal CT scans including the following injuries: pancreas (5), liver (4), gastrointestinal (2), and spleen (2). Five underwent therapy at laparotomy. Abdominal CT had a likelihood ratio (+) of 20.9 (95% confidence interval, 17.7-24.8) and likelihood ratio (-) of 0.034 (0.017-0.068).

Conclusion: Adult patients with blunt torso trauma and normal abdominal CT scans are at low risk for subsequently identified IAI. Thus, hospitalization for evaluation of possible IAI after a normal abdominal CT scan is unnecessary in most cases.

(C) 2012

Introduction

Trauma is a common problem and the leading cause of death in those younger than 44 years [1-2]. Identification of

? Prior presentation: Society for Academic Emergency Medicine Annual Meeting, Phoenix, AZ, June 2010.

* Corresponding author. Department of Emergency Medicine, UC

Davis Medical Center, Sacramento, CA 95817-2282, USA. Tel.: +1 916 734 1533; fax: +1 916 734 7950.

E-mail address: [email protected] (J.F. Holmes).

Intra-abdominal injuries (IAI) is important as delayed diagnosis leads to potential morbidity and mortality [3-5].

Observation for possible IAI is a frequent indication for hospital admission or short stay (23 hour) observation among adult patients with blunt trauma. Such observation involves serial Abdominal examinations and hematocrit measure- ments. This practice generated from experience before routine availability of computed tomographic (CT) scanners. After the introduction of abdominal CT scanning, it rapidly became the standard for diagnosing many traumatic injuries including IAIs. Older CT scanners, however, failed to

0735-6757/$ – see front matter (C) 2012 doi:10.1016/j.ajem.2011.02.016

adequately identify gastrointestinal or Pancreatic injuries [6-9]. Thus, many centers continued the practice of hospital observation to “rule out” IAI despite normal abdominal CT scans.

A multicenter study of 1809 patients with normal abdominal CT scans suggested that subsequent diagnosis of IAI is rare such that hospitalization and observation have low yield [10]. Eight patients in that study, however, had IAI, including 6 undergoing therapeutic laparotomies. With continued improvement in CT technology, the risk of an IAI after a normal CT has likely further decreased such that hospitalization is probably of even lower use.

The objective of this study is to identify the rate of IAI in adult patients with blunt abdominal trauma after a normal abdominal CT scan on a 16-slice helical CT and to identify the types of IAIs not identified by the emergency department (ED) abdominal CT scan. We hypothesize that the risk of subsequent IAI is so low that hospital admission and observation for possible IAI are unnecessary after a normal ED abdominal CT.

Methods

Study design

We conducted a prospective, observational study evalu- ating the rate of IAI in adult patients with normal ED abdominal CT scans. The study was approved by the study site’s institutional review board.

Study setting and population

The study was conducted at an urban level 1 trauma center. The trauma center admits more than 3000 patients with trauma per year and serves more than 2 million people. Eligible patients included those adult patients (N18 years old) who underwent abdominal CT scanning in the ED after a blunt traumatic mechanism of injury. Eligible patients included those “activated” for care by a trauma team as well as those solely cared for by the ED physicians. Patients were excluded if they were transferred to the study site with prior abdominal CT scanning or if they had a penetrating injury.

Study protocol

The subjects’ history and physical examination findings were documented by the treating physician (resident or faculty) on a structured data collection form once the decision to obtain abdominal CT scanning was made and before the actual abdominal CT scan. Patients underwent abdominal CT scanning on a Lightspeed GE 16-slice CT scanner (GE, Milwaukee, WI). Abdominal CT scans were obtained with intravenous contrast (Omnipaque [Princeton, NJ], 125 mL at 2.5 to 3 mL per second), but no oral contrast was administered.

Images were reconstructed at 5-mm slice thickness with delayed images through the abdomen at 5 minutes. Images were obtained from the dome of the diaphragm to the symphysis pubis and were reviewed in abdominal, bone, liver, and lung windows in transverse, sagittal, and coronal planes. Findings on CT scan considered abnormal for purposes of this study included all visualized IAIs (liver, spleen, adrenal gland, gallbladder, kidney, and pancreas). In addition, abdominal CT scans were considered abnormal for any findings suggestive of possible IAI including any of the following: intraperitoneal fluid, bowel wall edema, mesen- teric edema, mesenteric streaking, mesenteric hematoma, pneumoperitoneum, or extravasation of vascular contrast [11-15]. All abdominal CT scans were interpreted by board- certified/eligible faculty radiologists, and their interpreta-

tions were used for this study.

Hospital admission decisions were made by the trauma surgery team and ED faculty. Hospitalized patients were followed up for at least 24 hours with serial abdominal examinations and hematocrit measurements. These patients were subsequently discharged from the hospital if they had normal hematocrit measurements, abdominal exam- inations, tolerated oral intake, and had no other injuries mandating hospitalization.

All patients’ medical records were reviewed at least 30 days after the day of their ED visit. This review was conducted to determine if any patient who was discharged from the ED or the hospital after their initial admission were subsequently evaluated for or identified with an IAI. Finally, ED, trauma, and hospital continuous quality improvement (CQI) committee records were reviewed to identify any patient discharged from the ED or hospital who was subsequently identified with an IAI at another facility and referred to any of these CQI committees. The criterion for judging the effectiveness for abdominal CT scan in identifying IAI was no identifiable IAI at time of medical record and CQI review.

Outcome measures

The outcome measures included (1) the existence of IAI and (2) the existence of an IAI that underwent a therapeutic intervention. Intra-abdominal injury undergoing a thera- peutic intervention was defined as any IAI undergoing any one of the following events: surgical therapy at laparotomy, angiographic embolization, blood transfusion for anemia secondary to hemorrhage from the IAI, or intravenous fluid administration for more than 48 hours (in those patients with gastrointestinal or pancreatic injuries).

Data analysis

The study’s data are described with descriptive statistics including 95% confidence intervals (CIs). Continuous data are reported as the median with interquartile ranges (IQRs).

We report the negative predictive value (NPV) for abdominal CT scanning for IAI and IAI undergoing therapeutic intervention. We performed a sensitivity analysis for those patients discharged from the ED. Because these patients did not receive direct clinical follow-up, we applied the prevalence rate of IAI in the hospitalized patients to this population. This calculation provides upper bounds for the rate of IAI in the entire population. Data analysis was performed with STATA version 11.0 (2009; College Station, TX).

Results

Study population

We enrolled 3103 patients over 24 months, and 369 (11.9%) patients had abnormal abdominal findings on abdominal CT scans. Intra-abdominal injuries were identi- fied in 237 (64%) of these 369 patients and included injuries to the spleen (118), liver (101), kidney (55), gastrointestinal tract (34), pancreas (15), and adrenal gland (15). The number of patients with abnormal findings on CT was greater than the number with IAI, as some patients with abnormal findings on CT (eg, intraperitoneal fluid, bowel wall edema, and other) were never diagnosed with an IAI.

Thus, the final study population consisted of the 2734 patients with normal abdominal CT scans. The median age was 39 years, IQR 26 to 51 years (range, 18-100 years); and 66% were male. The mechanisms of injury were motor vehicle collision (1378 [51%]), fall (364 [13%]), assault (295 [11%]), auto vs pedestrian/bicycle (292 [11%]), motorcycle

(194 [7%]), fall off bike (37 [1%]), Crush injury (27 [1%]),

and other (147 [5%]).

Two thousand one hundred forty-one patients (78%) were admitted to the hospital, and 593 were discharged from the ED. Table 1 describes differences in those patients hospitalized and discharged from the ED. Patients admitted were more likely to have a decreased mental status and less likely to have assault as their mechanism of injury. Of the 2141 admitted patients, 649 (30%) were admitted for 1 day;

and 511 (24%) were admitted for 2 days. In these 649 patients hospitalized for 1 day, 15 (2%) died of severe traumatic brain injury. Initial findings in the 634 surviving patients included abdominal tenderness, 325 (51%); dis- tracting painful injury, 83 (13%); initial Glasgow Coma Scale (GCS) less than 15, 65 (10%); and underwent

nonabdominal surgery, 32 (5%). The surgeries in the 32 patients included orthopedic (23), complex laceration (4), facial surgery (3), neurosurgery (1), and eye surgery (1).

Rate of IAI

None (0%; 95% CI, 0%-0.5%) of the 592 patients discharged from the ED returned with IAI or were referred to

Admission Discharged from (n = 2141) the ED (n = 593)

Age (y) (median, IQR) Mechanism of injury MVC

Fall

Auto vs pedestrian/bike Assault

Motorcycle Other

GCS score >=14

Initial chest tenderness in ED a

Initial abdominal tenderness in ED a

ethanol intoxication b

39

(26-52)

36

(24-46)

1093

(51%)

285

(48%)

288

(14%)

76

(13%)

232

(11%)

60

(10%)

195

(9%)

100

(17%)

165

(8%)

29

(5%)

168

(7%)

43

(7%)

1876

(88%)

561

(95%)

889

(47%)

258

(46%)

831

(44%)

293

(52%)

456

(21%)

125

(21%)

MVC indicates motor vehicle crash.

a Variables are assessed only in those subjects with GCS scores of 14 or higher.

b Ethanol intoxication as determined by the treating physician and

not based on Laboratory analysis.

the ED, hospital, or trauma CQI committees. Of the 592 discharged patients, 3 had repeat abdominal CT scans (after ED discharge); and 3 were normal. Of the 2141 patients admitted, 8 (0.4%; 95% CI, 0.2%-0.7%) were subsequently identified with IAIs. A detailed description of these 8 patients is presented in Table 2. One patient with IAI (pancreatic laceration) not visualized on the ED abdominal CT was identified by abdominal magnetic resonance imaging (MRI). The remaining 7 patients had IAIs identified at laparotomy. Of the 7 patients with injuries identified at laparotomy, 5 (71%; 95% CI, 29%-96%) underwent specific therapy (see Table 2 for interventions at laparotomy).

Abdominal CT test characteristics

Table 1 Comparison of patients admitted vs those discharged from the ED

For the 3103 patients enrolled, abdominal CT had the following test characteristics: sensitivity, 237 of 245 (96.7%; 95% CI, 93.7%-98.6%) and specificity, 2726 of 2858

(96.6%; 95% CI, 95.9%-97.3%). The likelihood ratio

positive was 20.9 (95% CI, 17.7-24.8), and likelihood ratio negative was 0.034 (0.017-0.068). The NPV of a normal abdominal CT for IAI was 2726 of 2734 (99.7%; 95% CI, 99.4%-99.9%); and for IAI, undergoing acute intervention was 2729 of 2734 (99.8%; 95% CI, 99.6%-99.9%).

Sensitivity analysis

The rate of IAI identified in the hospitalized patients was 8 of 2141 (0.37%). A sensitivity analysis was performed for those patients discharged from the ED, as they did not have direct clinical follow-up. Application of the rate of IAI in hospitalized patients (0.37%) to the 592 patients discharged

Age (y)

Mechanism Initial

GCS

Examination

Injury

Therapy

26

Crush

15

Abdominal

Pancreas

Pancreatic

tenderness

drainage

30

Assault

5

Normal

Liver

None at

(grade 1)

laparotomy

30

MVC

14

Abdominal

Pancreas a

Observation

90 mph

tenderness

32

Auto vs

7

Normal

Liver, GI

None at

pedestrian

(serosal

laparotomy

tear)

42

Motorcycle 15

Abdominal

Spleen,

Pancreas

tenderness/

pancreas

drainage

abrasions

52

Fall from

11

Normal

Liver

Avitene,

horse

liver

packing

54

MVC 50

15

Abdominal

GI

Colon

mph

abrasions

(serosal

serosal

tear)

repair

Pancreas

Pancreatic

drainage

72

MVC

15

Costal

Spleen,

Splenectomy

high

margin

liver,

speed

tenderness

pancreas

Abdominal

seat belt

sign

GI indicates gastrointestinal.

a Identified by MRI and elevated Pancreatic enzymes.

from the ED would suggest 2.2 patients discharged from the ED would be identified with an IAI. Abdominal CT test characteristics after adding 2 patients with IAI would be as follows: sensitivity, 237 of 247 (96.0%; 95% CI 92.7%-

Table 2 Description of the 8 patients with normal initial abdominal CT scans ultimately identified with an IAI

98.0%) and specificity, 2724 of 2856 (95.4%; 95% CI, 94.6%-96.1%). The likelihood ratio positive would be 20.8 (95% CI, 17.5-24.6), and likelihood ratio negative would be

0.042 (95% CI, 0.023-0.078).

Discussion

This study demonstrates that the rate of IAI after a normal abdominal CT scan is very, very low. Thus, hospitalization for abdominal observation for possible IAI is of low yield in those patients with normal abdominal CT scans. A small percentage of patients, however, will ultimately be identified with IAI, despite the normal ED abdominal CT scan. Furthermore, most of the patients with delayed IAI diagnosis will undergo therapy for their injuries.

Our results further previous research on this topic. Surprisingly, most data on the safety of discharging ED patients with normal abdominal CT scans are found in the

pediatric population [16-19]. These studies indicate that pediatric patients are at such low risk for IAI after a normal abdominal CT scan that hospitalization is unwarranted. One multicenter study in adults demonstrated a rate of IAI of 0.4% in those with normal ED abdominal CT scans [10]. That study, however, involved early generation helical CT scanners, included oral contrast, excluded patients dis- charged from the ED, and measured outcomes at the time of discharge. We sought to determine the performance with more advanced CT technology and measured outcomes at 30 days after ED arrival. Increasing the time for outcome assessment to 30 days postTraumatic event would assuredly identify all patients with subsequently identified IAI (3 of the

8 patients had their injuries diagnosed N24 hours after admission). In addition, to generalize this study to all ED patients evaluated with abdominal CT, we also included an assessment of eligible patients who were discharged from the ED. Finally, abdominal CT scans were performed without oral contrast, which is becoming the standard in patients with blunt abdominal trauma.

In this study, liver, spleen, and Renal injuries were exceedingly rare after a normal abdominal CT scan. This finding confirms the reliability of CT scanning for these solid Organ injuries, although 1 recent study has suggested that CT scanning has a sensitivity ranging from 92% to 96% for Solid organ injuries [20]. We would expect only minor solid organ injuries to be “missed” by abdominal CT scanning [10,16]. However, we identified 1 splenic injury and 1 liver injury that underwent acute intervention (splenectomy and liver packing). Thus, in very rare instances, solid organ injuries undergoing operative therapy may occur despite a normal abdominal CT scan.

Not surprising, pancreatic injuries were the most common injury identified after a normal initial abdominal CT. Five patients had pancreatic injuries identified after a completely normal abdominal CT scan. Failure to identify pancreatic injury is a known limitation of abdominal CT, as current generation (including both 16-slice and 64-slice helical CT scanners) fail to identify at least 40% of pan- creatic injuries [21].

Of the 8 patients with IAI after a normal abdominal CT scan, 3 had significantly decreased mental status and would not be discharged from the ED. Of the 5 patients with normal mental status, all had abnormal abdominal examinations, including tenderness and/or abrasions. Thus, the subset of patients with normal mental status, abdominal examinations, and abdominal CT scans is at even low risk for having a subsequent IAI (none identified in this series).

Instead of formal hospitalization, some centers “watch” patients with trauma in observation areas often located within or in areas adjacent to the ED. The period of observation may range from 8 to 23 hours. The practice of 23-hour observation after a normal ED evaluation, however, has previously been questioned because of its low yield [22]. Again, our data fail to support the practice of observation for possible IAI after a normal abdominal CT

scan. More than 600 patients (28%) in this study were hospitalized for 1 day without any other clear indications for hospitalization beyond observation. A substantial cost savings would be recognized if these patients were ultimately discharged from the ED.

As IAI may still occur in a very small number of patients with normal ED abdominal CT scans, a subset of very high risk patients may still require a period of observation or formal hospitalization. These decisions should be handled on a case-by-case basis. More importantly, careful discharge instructions must be given to all patients being discharged from the ED and include information that a small but measurable risk of IAI still exists despite a normal ED abdominal CT. As some patients with undiagnosed IAI will be discharged from the ED after a normal CT, all patients should be educated on the appropriate signs and symptoms of IAI and to return to the ED if such evidence develops.

It should be noted that abdominal CT scanning imparts a large amount of radiation and that a small but measurable risk of Radiation-induced malignancy occurs with abdominal CT scanning [23-25]. A derived and validated clinical decision rule exists for identifying those patients who are at such low risk for IAI that abdominal CT scanning is not indicated [26]. To minimize inappropriate radiation expo- sure, trauma abdominal CT scanning should be used only if indicated. Those patients with normal abdominal CT scans are at such low risk for occult IAI that discharging to home with appropriate precautions is safe.

Limitations

This study has certain limitations. These results are based on findings from a single trauma center. The abdominal CT readings were based on the faculty radiologist interpretations and not on resident or “nighthawk” radiologists’ interpreta- tions as performed at some centers. The radiologists at the study site are experienced in the interpretation of trauma abdominal CT scans, and their results may not be replicable by other radiologists.

The NPV may be falsely elevated because of the inclusion of patients with more Significant injuries relative to suspicion of abdominal injury. The rate of abnormal abdominal CT scanning, however, was 12%, which is similar to prior evidence [10]. Thus, we believe that selection bias has minimal impact on this study. In those patients discharged from the ED, we assessed for IAI by evaluating hospital records for return visits and CQI committee reviews. Obtaining more definitive follow-up (ie, conducting tele- phone follow-up) would potentially increase the certainty of outcome assignment. However, in previous studies, we have not found such telephone follow-up to be significantly additive, as missed injuries were identified by other methods [27-29]. Furthermore, the sensitivity analysis performed indicates that potential missed IAIs in the population discharged from the ED have limited impact on the abdominal CT scan performance. It is likely that some

patients with normal abdominal CT scans had IAIs that were never identified. The importance of identifying these subclinical IAIs is unclear, and ethical considerations prevented us from more aggressive follow-up methods (ie, repeat abdominal CT scanning or MRI).

The abdominal CT scans were performed on a 16-slice helical CT scanner. We anticipate that CT performance would improve with 64-slice helical CT scanners. However, limited data fail to demonstrate improvement in IAI diagnosis with increasing from 16-slice CT to 64-slice CT scanners [21]. Finally, abdominal CT scans were performed without oral contrast. Although evidence indicates that oral contrast is not needed for trauma abdominal CT scans [12,15,30], abdominal CT scan performance may change if oral contrast is administered.

We designed the study to identify the rate of IAI after a normal abdominal CT and included both patients admitted to the hospital and discharged from the ED. Obviously, some patients with trauma have other injuries mandating hospital- ization. Including those patients in this study simply provides the best estimates for the test performance of abdominal CT scanning. The true reduction in hospital admission if those patients who were admitted for abdominal observation were not admitted is unknown.

Conclusion

In conclusion, adult patients with blunt torso trauma and normal abdominal CT scans are at low risk for subsequently identified IAI. Thus, hospitalization or prolonged observa- tion for evaluation of possible IAI after a normal abdominal CT scan, when combined with clinical judgment, is unnecessary in most cases. Careful discharge instructions are warranted in all patients being discharged from the ED, as a very small percentage will be diagnosed with IAI despite a normal CT and some will require therapy.

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