Emergency department ultrasound for hemothorax after blunt traumatic injury

The Journal of Emergency Medicine, Vol. 25, No. 2, pp. 181–184, 2003 Copyright © 2003 Elsevier Inc. Printed in the USA. All rights reserved 0736-4679/03 $–see front matter

doi:10.1016/S0736-4679(03)00168-9

Selected Topics: Emergency Radiology EMERGENCY DEPARTMENT ULTRASOUND FOR HEMOTHORAX AFTER BLUNT TRAUMATIC INJURY Paul-Andre´ C. Abboud,

MD

and John Kendall,

MD

Department of Emergency Medicine, Denver Health Medical Center, Denver, Colorado Reprint Address: John Kendall, MD, Dept. of Emergency Medicine, Denver Health Medical Center, 777 Bannock St., Mailcode 0108, Denver, CO 80204

e Abstract—Diagnosing hemothorax after blunt trauma may be aided by emergency department (ED) ultrasound (US). Various prior studies have evaluated ED US using different gold standards. A prospective study of blunt trauma patients who underwent computed tomography (CT) scan of the chest, abdomen, or both, was performed. Before CT scan, an US examination was performed specifically to identify free fluid in the thorax. The CT scan findings were used as the gold standard for validation of US results. From July 1998 to June 1999, 142 of 155 patients who underwent US and CT scan for evaluation of blunt trauma were included in this study. The CT scan identified 16 cases of hemothorax among these patients. ED US resulted in 2 true-positive, 2 false-positive, 14 false-negative, and 124 true-negative findings. ED US was 12.5% sensitive and 98.4% specific. ED US did not detect small-volume hemothorax identified by CT scan. Future research should focus on further defining the size of hemothorax appreciable with ED US, with increased attention paid to the type of gold standard implemented for its evaluation. © 2003 Elsevier Inc.

standard algorithm for detection of hemoperitoneum (1). Given the widespread acceptance of ED US for blunt trauma patients, many other applications have been considered, including evaluation for hemothorax. The detection of hemothorax presents a diagnostic challenge in the blunt trauma patient who arrives in the ED immobilized on a long spine board. ED US may aid in the rapid diagnosis of hemothorax in such cases where the initial supine chest radiograph may be equivocal (2). Although some European studies have investigated the use of US for diagnosing hemothorax, we are aware of only four investigations published in the English language (2–7). In these investigations, ED US generally was found to be an accurate screening tool for hemothorax. The reported sensitivities range from about 67% to 100%, with specificities of 99% or higher (Table 1). Our study differs from these investigations in its diagnostic gold standard. Rather than using clinical course, chest radiography (CXR), or a combination of either serial chest radiography, computed tomography (CT) scan, or tube thoracostomy, as these studies did, we used CT scan to analyze ED US for the evaluation of hemothorax in blunt trauma (2,6,7).

e Keywords— ultrasound; trauma; hemothorax; diagnosis; Emergency Department

INTRODUCTION MATERIALS AND METHODS

Emergency department ultrasound (ED US) was first promoted by the American College of Surgeons in 1993 as part of the Advanced Trauma Life Support Course’s

A prospective cohort study using a convenience sample of patients was performed in the ED of an urban level 1

Selected Topics: Emergency Radiology is coordinated by Jack Keene, Rhinebeck, New York

RECEIVED: 26 April 2002; FINAL ACCEPTED: 6 January 2003

SUBMISSION RECEIVED:

22 November 2002; 181

MD,

of Emergency Treatment Associates,

182

P.-A. C. Abboud and J. Kendall

Table 1. Prior Published Studies of ED US for Hemothorax Author, year published (Location)

N

HTX rate

72

Unreported

Rothlin, 1993 (Switzerland)

312

18.6%

Ma, 1997 (Wisconsin)

160

5%

Sisley, 1998 (Atlanta)

268

2.6%

Kimura, 1991 (Japan)

Test Characteristics Sens ⬃67% Spec ⬃99% Sens 81% Spec 100% Sens 96% Spec 100% Sens 100% Spec 100%

Gold Standard Unknown Clinical course Serial CXR, CT, or thoracostomy CXR

Sens ⫽ sensitivity; Spec ⫽ specificity; CXR ⫽ chest radiography; CT ⫽ computed tomography; N ⫽ study denominator; HTX ⫽ hemothorax.

trauma center. The investigational review board for this institution approved the study protocol. All patients presenting to the ED after blunt traumatic injury, who subsequently underwent computed tomography (CT) scan of the chest or abdomen during their ED evaluation, were eligible for study. Although the decision to obtain CT scans was at the discretion of the attending Emergency Physician or Trauma Surgeon, guidelines for this decision are regularly utilized within our institution. Indications for chest CT scan for blunt traumatic injury include a high energy mechanism of injury (such as high speed motor vehicle crash with interior compartment damage, especially if the patient was unrestrained, or in the case of a patient driving the motor vehicle, the steering wheel was damaged), evidence of significant chest trauma on physical examination (such as significant chest wall contusions or dyspnea), or CXR findings suggestive of trauma (such as wide mediastinum or rib fracture). Indications for abdominal CT scan for blunt traumatic injury include a high energy mechanism of injury (similar to those listed for chest CT scan), altered mental status (including perseveration, or disorientation to person, place, time, or reason for presence in the ED), evidence of multisystem trauma (for example, long bone or pelvic fractures in addition to altered mental status), or hemodynamic instability resolved without resuscitation. After initial trauma evaluation, which included a portable CXR and 4-view US examination to detect hemoperitoneum or pericardial effusion, eligible patients underwent a secondary US study while awaiting CT scan. Emergency Physicians who performed the secondary US were not blinded to the results of the initial trauma evaluation. The purpose of the secondary US was to specifically identify the presence of hemothorax. The secondary US consisted of long and short axis scans through the liver and spleen followed by views using these organs as acoustic windows for evaluation of the pleural space. Hard copy images of representative views and any

injury were made. All studies were performed with a Toshiba SSH-140A (Toshiba, San Francisco CA) equipped with a 3.75 MHz sector transducer. Patients were excluded from the study if they were transferred from another facility with a known solid organ injury, hemothorax, or pneumothorax, if the CT scan was interrupted or not completed, or if performing the secondary US would delay patient care. Emergency medicine residents (post-graduate year 2 to 4) or attendings performed all secondary US studies. Both residents and attendings had previously completed a standardized 15-h didactic and practical emergency US curriculum at our institution, and utilize US on a daily basis for evaluating trauma in the ED. Additionally, residents and attendings received an orientation on the views to be used for the secondary US, and viewed videotapes and still images demonstrating hemothorax. The training curriculum focused on determining the presence of hemothorax, not on estimating its size. Hemothorax on US was defined as an anechoic region located distal to the hyperechoic line of the diaphragm. Upon completion of the secondary US, the physician performing the US completed a data sheet and prospectively identified the presence or absence of hemothorax. The patient’s mechanism of trauma, as well as the number of prior 4-view trauma US studies completed by the performing physician, were recorded on the data sheet. Data sheets and hard copy images were identified with patient name and hospital number, and stored together. The recorded US findings were later compared to the official CT scan report that had been dictated by an attending radiologist. Confidence intervals for test characteristics were calculated using the Yates-corrected chisquare equation (8). The secondary US was performed either before the patient’s transport to CT or immediately upon the patient’s return. In the rare instances when the US was performed upon the patient’s return from CT, it was always performed before results of the CT scan were

ED US for Hemothorax

183

Table 2. Test Characteristics of ED US Compared to CT Scan for Hemothorax CT scan

US ⫹ US ⫺

⫹

⫺

2 14

2 124

US ⫽ ultrasound, CT ⫽ computed tomography

known. CT scans were considered positive for hemothorax if the attending radiologist documented the presence of either “hemothorax” or “pleural effusion” in the dictated report. Radiologists were blinded to the results of the secondary US. The electronically stored charts of all included patients were reviewed retrospectively for the development of new hemothoraxes or the need for further interventions beyond those performed in the ED.

RESULTS Between July 1998 and June 1999, 155 patients with blunt traumatic injury were enrolled in the study. Of these, 3 patients were transferred from an outside facility after laparotomy with a diagnosis of hemothorax already confirmed, and records were incomplete for 10 patients. Among the remaining 142 patients analyzed, 87 (61.3%) presented after motor vehicle crashes (MVCs), 19 (13.4%) suffered falls, 13 (9.2%) were victims of autopedestrian collisions, 10 (7.0%) were assaulted, 4 (2.8%) were involved in motorcycle crashes, 4 (2.8%) were involved in bicycle crashes, and 5 (3.5%) suffered blunt trauma from other causes, including 2 intoxicated patients who were unable to provide clear histories of their injuries, a snowboarding crash, an attack by a horse, and a victim of an assault followed by an MVC. The mean age was 38 years old (range, 5– 89 years). All but two of the secondary US studies were performed in less than 10 min. The time interval between ED US and CT scan varied from less than 1 h to over 4 h. The self-reported experience level of physicians performing ED US ranged from ⬍ 25 to ⬎ 100 prior 4-view trauma US studies. The CT scan documented hemothorax in 16 cases (Table 2), for a prevalence of 11.3%. All of the hemothoraxes documented on CT scan were qualified as “small” or “tiny.” The objective difference between “small” and “tiny” was not determined. The use of these labels depended on the radiologists’ personal definitions of the qualitative size of the effusion. ED US identified 2 of the 16 hemothoraxes seen on CT scan, for a sensitivity of 12.5% (95% CI, 2.3–22.7%). There were 2 false-

positives on ED US, providing a specificity of 98.4% (95% CI, 97.1–99.7%). The positive predictive value was 50.0% (95% CI, 9.3–90.6%) and the negative predictive value was 89.9% (95% CI, 88.7–91.0%). The median time interval between ED US and CT scan among the false-negative ED US studies was 50 min (range 20 to 191 min). Two of these false-negative ED US studies were performed after the CT scan was completed. The 2 true-positive ED US studies were obtained 25 and 45 min, respectively, before the CT scan was completed. The 2 false-positive ED US studies were obtained 13 and 40 min, respectively, before the CT scan was completed. Only 2 patients in the cohort underwent emergent chest thoracostomy based on the ED CXR findings and clinical status consistent with hemothorax or hemopneumothorax. Of these, only 1 had hemothorax based on 500 cc of blood return immediately upon placement of the chest tube. The ED US image of a left-sided hemothorax in this patient is presented in Figure 1. The other patient was found to have severe pulmonary contusions on CT scan obtained after an adequately placed chest tube failed to drain fluid in the ED. Discharge summaries or daily progress notes were available for all patients included in the study. No new hemothoraxes were noted after patients left the ED. No surgical interventions were undertaken in any of the patients who had been noted to have small or tiny pleural effusions on CT scan.

DISCUSSION This study contrasts with previously published investigations that advocate for ED US to screen for hemothorax in blunt trauma (2–7). There may be several reasons for this difference. We believe that our gold standard, CT scan, is the most sensitive test for hemothorax. However, due to this exceptional sensitivity, CT scan may not be the most clinically relevant standard to use. Indeed, the patients who were noted to have small or tiny effusions on CT scan did not have clinically relevant consequences due to these lesions on chart review. The crux of the matter when evaluating a diagnostic modality is to define what findings are significant. Hemothoraxes found on CT scan and not on US in our cohort were not clinically relevant. According to our chart review, none of the “small” or “tiny” hemothoraxes seen on CT scan developed into clinically significant lesions. The CXR was limited for diagnosis of hemothorax in this cohort. Most trauma patients arrive at our ED immobilized with spine precautions on a backboard. Because the initial CXR is obtained with the patient supine,

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Figure 1. ED ultrasound image of a left hemothorax.

distinguishing between pulmonary contusion and effusion may be impossible, especially in patients who have small lesions. This study has other potential limitations. The low prevalence of larger or otherwise significant hemothorax in our cohort is disappointing. Varying experience levels of ED US users, the difficulty in properly positioning distressed trauma patients, and the wide range of time intervals between CT scan and ED US evaluations may have limited the relevance of our findings. We did not evaluate for inter-rater reliability in the interpretations of ED US or CT scan. Furthermore, because our patient database represents a convenience sample, we cannot be certain that we captured the full spectrum of presentations of hemothorax in blunt trauma. In conclusion, ED US for hemothorax in blunt trauma was not found to be sensitive in this study. Further investigations, certainly with larger sample sizes, are needed to clarify the value of ED US for the diagnosis of hemothorax in blunt trauma. Perhaps more importantly, an easily reproducible and clinically relevant gold stan-

dard must be identified for further evaluation of ED US for diagnosing hemothorax. REFERENCES 1. Advanced trauma life support. Chicago: American College of Surgeons, 1993. 2. Ma OJ, Mateer JR. Trauma ultrasound examination versus chest radiography in the detection of hemothorax. Ann Emerg Med 1997; 29:312– 6. 3. Walz M, Muhr G. Sonographische Diagnostik beim stumpfen Thoraxtrauma. Unfallchirurg 1990;93:959. 4. Borner N, Kelbel C, Lorenz J, et al. Sonographische Volumenbestimmung and Drainage von Pleuraergessen. Ultraschall Klin Prax 1987;2:148. 5. Kimura A, Otsuka T. Emergency center ultrasonography in the evaluation of hemoperitoneum: a prospective study. J Trauma 1991; 31:20 –3. 6. Rothlin MA, Naf R, Amgwerd M, Candinas D, Frick T, Trentz O. Ultrasound in blunt abdominal and thoracic trauma. J Trauma 1993; 34:488 –95. 7. Sisley AC, Rozyycki GS, Ballard RB, Namias N, Salomone JP, Feliciano DV. Rapid detection of traumatic effusion using surgeonperformed ultrasonography. J Trauma 1998;44:291–7. 8. Fleiss JL, ed. Statistical methods for rates and proportions, 2nd edn. New York: John Wiley & Sons, 1981.