Trauma: Abdominal And Thoracic Ultrasound
Trauma: Abdominal And Thoracic Ultrasound
The Focused Assessment with Sonography for Trauma, or the FAST examination, is a well-established diagnostic and resuscitative modality for patients who present with trauma. New-found understanding of pulmonary ultrasound in addition to the FAST scan has allowed for more complete bedside analysis of the acutely injured patient.
Abdominal Ultrasound: Focused Assessment With Sonography In Trauma (FAST)
As early as 1971, the utility of ultrasound scanning for patients with splenic injuries was documented.2 It was not until the early 1990s, however, that ultrasound became widely advocated and studied in patients with blunt abdominal trauma.3-6 Since then, ultrasound has been included in the Advanced Trauma Life Support protocol of the American College of Surgeons6 and in the Eastern Association for the Surgery of Trauma (EAST) guidelines for the management of blunt abdominal trauma.8 The American College of Radiology also recommends the use of ultrasonography — and specifically, the FAST scan — to evaluate for free or localized intra-abdominal fluid collections.9 (See Figures 1 and 2)
Ultrasound evaluation of patients with trauma has numerous benefits. The test can be rapidly performed at the bedside, accurately predicts the presence of hemoperitoneum, is noninvasive, can be repeated, and does not involve ionizing radiation or intravenous contrast media. Unfortunately, the number of RCTs assessing the FAST examination is limited. In 2005, The Cochrane Collaboration reviewed the efficiency and effectiveness of trauma algorithms that include ultrasound in the evaluation of patients suspected of having blunt abdominal trauma. Their initial conclusion, which remains unchanged in 2008 (after correction of their first review), is that there is still insufficient evidence from RCTs to justify promoting ultrasoundbased clinical pathways in the diagnosis of patients with blunt injury to the abdomen.10 Although the mortality data reviewed by The Cochrane Collaboration do not favor the FAST examination, the use of ultrasound in this setting has been shown to decrease the time to recognition of intraabdominal trauma, the time to operative therapy, hospital costs and resource use, and the number of CT scans and diagnostic peritoneal lavages performed.11-13
In a retrospective review of patients with penetrating cardiac injury, Plummer et al found that 2-dimensional echocardiography in the ED decreased the time to diagnosis and improved both survival and neurologic outcomes of survivors.14 Although the value of the FAST examination in hemodynamically unstable trauma patients is accepted, its role in the management of those who are hemodynamically stable is unclear and often questioned.
Moylan et al found that the FAST examination can indeed assist in the risk stratification of normotensive patients with blunt abdominal trauma.15 In a retrospective cohort analysis of consecutive normotensive blunt abdominal trauma patients at 2 different level I trauma centers, they tested the association between a positive result on FAST and the need for therapeutic laparotomy. They found that the odds ratio for an unadjusted association between a positive FAST result and laparotomy was 116 and that this association persisted after adjusting for confounding variables, with an odds ratio of 44. This study showed a strong association between a positive FAST and the need for therapeutic laparotomy and noted that very few normotensive patients with a negative FAST required therapeutic laparotomy. The sensitivity of the FAST examination as a diagnostic test for therapeutic laparotomy, however, was found to be only 75.8%; similarly, its positive predictive value was found to be only 37.3%.15
The traditional FAST examination involves 4-quadrant scanning with views of the hepatorenal space, the perisplenic and splenorenal interface, the pelvis, and the pericardium through a subxiphoid or parasternal approach. Recently, authors have studied an extended version of the FAST examination, referred to as the Extended Focused Assessment with Sonography for Trauma (E-FAST). In addition to the 4-quadrant views of the FAST, the E-FAST includes views of both hemithoraces at the levels of the diaphragm-abdominal interface and over bilateral anterior chest walls. (See Figure 3) It is designed to assess for pneumothorax in the anterior views and for pleural effusion or hemothorax in the supradiaphragmatic views.
Evaluation of the patient with thoracic trauma begins with an examination for external injuries and auscultation of lung sounds, usually followed by radiographic evaluation with a portable supine anteroposterior chest x-ray. Unfortunately, the physical examination is frequently insufficient and carried out in a loud environment where diminished breath sounds are not easily appreciated. In addition, portable chest radiographs are not sensitive enough to rule out lung injury and have been estimated to miss traumatic pneumothoraces up to 50% of the time.16-21
The use of ultrasound to detect pneumothorax has been well established. Lichtenstein and Menu showed that in patients in the intensive care unit (ICU), bedside ultrasound has a sensitivity of 95.3%, a specificity of 91.1%, and a negative predictive value of 100% when compared with CT scanning as the reference standard for the detection of pneumothorax.22 In ICU patients with radio-occult pneumothoraces, the same group showed that ultrasound was superior to plain radiography for the detection of pneumothorax, with a specificity approaching 100%.23 Both of these studies were conducted in ICU patients in whom disease processes such as fibrotic lung disease and acute respiratory distress syndrome may affect the quality of the sonogram, resulting in both false-positive and false-negative studies.
In a prospective study of blunt trauma patients, Blaivas et al found that the sensitivity of ultrasound in detecting pneumothorax was 98.1% and the specificity was 99.2%, while chest radiography had a sensitivity of 75.5% and a specificity of 100%.16 An article by Rowan et al also compared the accuracy of sonography with supine chest radiography for the detection of traumatic pneumothorax. In 27 patients who sustained blunt thoracic injury, the radiographic and ultrasound findings were compared with CT scan results as the gold standard for diagnosis. Eleven of the 27 patients had pneumothoraces on CT and all 11 cases were detected with sonography. There was, however, 1 false-positive with ultrasound, resulting in a sensitivity of 100% and a specificity of 94%. Supine chest radiography had a specificity of 100% but a sensitivity of only 36%.17
Two studies by Soldati and colleagues also found highly superior sensitivity and comparable specificity for ultrasound when compared with chest x-ray, again using CT as the gold standard.18,19 In a prospective study of patients with blunt trauma, Zhang et al found a sensitivity of 86% and a specificity of 97% with sonography, while plain film had a sensitivity of 27.6% and a specificity of 100%. Of note, they found that the mean time needed to diagnose pneumothorax was significantly shorter with ultrasound than with chest x-ray (2.3 ± 2.9 vs 19.9 ± 10.3 min, P < 0.001).20 Kirkpatrick et al compared the value of supine chest radiography versus a handheld ultrasound device in 208 patients with blunt or penetrating trauma to detect pneumothorax during their initial resuscitation. The methods in this study differed slightly from those in previous studies in that they used both a composite standard (which included CT, chest x-ray, and the escape of air with tube thoracostomy) and CT as the gold standard in the comparison with the sonograms and chest radiographs. Ultrasound had a sensitivity of 58.9% and a specificity of 99.1% when compared with the composite standard and a sensitivity of 48.8% and a specificity of 98.7% when compared with CT alone; chest x-ray had a sensitivity of 20.9% and a specificity of 99.6% when compared with CT alone.21 Again, these results demonstrate the superiority of ultrasound over supine chest radiography for the detection of pneumothorax, although the sensitivity reported in this study is much lower than that described previously. As a possible explanation for the decreased sensitivity, the authors cite the technical limitations related to using a hand-held ultrasound device for trauma resuscitations.
The ability of ultrasound to detect hemothorax and pleural effusions has also been well-documented. There are advantages to the use of BUS, as with the E-FAST examination, when compared with traditional methods of assessing for blood or other fluid in the pleural space. Ma et al were among the first to show that emergency clinicians can use BUS to rapidly assess trauma patients with a time-to-completion of approximately 4 minutes for a thoracoabdominal sonographic study.24 In a follow-up retrospective study of the same patient sample, these authors showed that both thoracic ultrasound and chest x-ray were 96.2% sensitive, 100% specific, and 99.6% accurate for the detection of hemothorax, using chest CT and tube thoracostomy as criterion standards.25 Sisley and colleagues showed that the performance time for ultrasound was significantly shorter than that for a portable chest radiograph and had superior sensitivity, with both techniques offering comparable specificity.26 Other authors have confirmed these findings.27,28 In addition, ultrasound has been reported to be able to detect smaller quantities of fluid than chest radiography. Ultrasound can detect as little as 20 mL of pleural fluid,29 while approximately 175 mL is required before findings are noted on supine chest radiography.30
By adding thoracic views to the standard 4 views of the FAST examination, the emergency clinician can rapidly assess the trauma patient for hemothorax and pneumothorax, and this technique is a valuable tool in initial management. Although CT remains the mainstay for detecting parenchymal injuries and other intraperitoneal trauma, the use of clinician-performed ultrasound has many advantages, including lower cost, time-sensitive bedside assessments, ease of repetition for reevaluation, and lack of ionizing radiation. The last advantage is of particular importance, given recent evidence that ionizing radiation from CT does, in fact, increase a patient’s lifetime risk of cancer.31-33 Since many trauma patients are young, the use of a nonionizing diagnostic test is ideal. Repeat assessment is often necessary in trauma patients if there is a change in vital signs or patient status or after interventions are carried out. In these scenarios, repeat evaluation with BUS can be performed rapidly and can guide the clinician in terms of further interventions.
James Q. Hwang; Heidi Harbison Kimberly; Andrew S. Liteplo; Dana Sajed
March 2, 2011