Since the 1980s, ultrasound has been used to detect free fluid such as blood in the pericardial and intraperitoneal spaces in acutely injured patients.24,25 This simple, rapid, and accurate ultrasound technique was adopted in the United States in the 1990s and subsequently named the focused assessment with sonography for trauma (FAST).26 The application of ultrasound has expanded to other areas of the body to identify injuries and help to direct the management in the prehospital setting and in the emergency room.
Technique of FAST—General Principles
The FAST examination is performed by a trauma team member (trauma surgeon, emergency medicine physician, trainee, or advanced practice provider) (Fig. 16-2). Although a designated examiner typically performs the FAST examination, the care provider who conducts the primary and secondary survey may also complete the FAST sequentially. The patient’s chest and abdomen are exposed during the primary survey. Trauma patients are normally placed in the supine position during the primary and secondary survey of the advanced trauma life support algorithm.27 Therefore, dependent portions in the abdominal cavity should be scanned to identify abnormal hypoechoic areas (ie, free fluid). In many institutions, a small size portable ultrasound machine is attached to the bedside tower in the emergency room (Fig. 16-3). For the FAST examination, either a sector- or convex-shaped transducer (low-frequency: 2.5–5.0 MHz) is used to visualize the pericardial space and relatively deep regions in the abdominal cavity. A linear-shaped transducer (high-frequency: ≥7.5 MHz) is not suitable for this reason (Fig. 16-4). Before starting the examination, the image settings including depth or gain should be adjusted. Recording of real-time images is required for review to ensure quality of the FAST examination. The entire examination should not require more than 5 minutes, even in the hands of trainees. The goal of the FAST examination is to detect or exclude fluid in the pericardial space and abdominal cavity.
Transducer positions for the FAST (focused assessment with sonography in trauma) examination: subxiphoid, right upper quadrant, left upper quadrant, and pelvis.
Ultrasound machine used for the FAST (focused assessment with sonography in trauma) examination.
Various types of transducers; from left to right: low-frequency convex, sector, and high-frequency linear.
The FAST examination typically starts with visualizing the heart so that the image settings, such as gain or depth, can be optimized (with a known fluid-filled structure). The intracardiac blood should be anechoic, and the posterior heart should be visualized on the screen. First, a transducer is placed in the subxiphoid region for a sagittal or transverse view of the heart. The transducer should be directed toward the head of the patient under the xiphoid process. In this position, the heart will be visualized beneath the left lobe of the liver. This sagittal view enables the examiner to view simultaneously the inferior vena cava and was prescribed in the original description of the FAST examination. A transverse view allows the provider to visualize more pericardial surface area, although more pressure is applied with consequent pain. A pericardial effusion is seen as an anechoic area around the heart (Fig. 16-5). Both the anterior and posterior wall of the heart should be visualized as a small effusion can otherwise be missed. For patients with severe injury to the chest and/or abdominal wall, subcutaneous emphysema, a narrow costal angle or a thick thoracoabdominal wall, appropriate views may not be obtainable through this window. Alternate views include the apical view or parasternal view in which the transducer is placed adjacent to the left nipple or along the sternum in the second intercostal space.
Normal (A) and abnormal (B) views of pericardial examination. *pericardial effusion
There are three dependent spaces that are scanned in the abdominal portion of the FAST examination as follows: the hepatorenal recess (Morison’s pouch), the splenorenal recess and the pelvis around the bladder. To obtain a longitudinal view in the hepatorenal recess, the transducer is placed in the right upper quadrant (RUQ) of the abdomen. Although this view is often called the “RUQ view,” optimal views typically are obtained in the right mid-to-posterior axillary line at the level of the 9th to 12th ribs. The right lobe of the liver and the right kidney should be visualized in the same view (Fig. 16-6). Fanning the transducer to visualize the right kidney from one side to the other is the key to preventing a false-negative examination, and free fluid can be identified between the liver and kidney. For patients with a significant amount of intraperitoneal fluid, this fluid may also be visualized above the anterior surface of liver. The longitudinal view of the splenorenal recess is obtained next in the left upper quadrant (LUQ). The transducer should be oriented more superiorly and posteriorly than the RUQ to visualize (Fig. 16-7). Trauma patients often present with a full stomach that can be misread as free fluid. Thus, it is imperative to visualize the spleen and the left kidney in the same image (Fig. 16-8). Finally, sagittal and transverse views are obtained in the pelvis. The transducer is placed a few centimeters above the pubic symphysis. The FAST examination is ideally performed before an indwelling urinary catheter is placed. Fluid inside (urine) and outside (blood) of the bladder is visualized as an anechoic area separated by the bladder wall (Fig. 16-9).
Normal (A) and abnormal (B) views of Morison’s pouch. *intraperitoneal free fluid.
Coronal and axial view of the abdominal cavity. Note that the splenorenal recess is located more superiorly and posteriorly (arrows) than the hepatorenal recess.
Normal (A) and abnormal (B) views of the splenorenal recess. Free fluid is seen around the spleen (arrows).
Normal (A: transverse view, B: longitudinal view) and abnormal views (C) of the pelvic region. *intraperitoneal free fluid.
Data in Blunt Trauma Using the FAST Examination
The utility of the FAST examination has been examined most extensively in patients with blunt torso injury.2,7,28,29,30,31,32,33,34,35 Since the 1990s, many prospective and retrospective studies have been conducted in various patient populations. A significant disparity in data regarding the FAST examination is due to different inclusion criteria and outcomes of interest (intraperitoneal fluid vs any intra-abdominal injury). Accuracy of the FAST examination can be affected by several factors including hemodynamic stability (a likely surrogate for amount of fluid) or associated injuries.36,37 Currently, the most appropriate indication for the use of the FAST examination is for hypotensive patients with blunt torso injuries. A large prospective study conducted by Rozycki et al. demonstrated that surgeon-performed FAST was 100% sensitive and 100% specific for detecting hemoperitoneum in hypotensive patients with blunt abdominal trauma.38 Patients with a positive FAST examination (showing intra-abdominal free fluid) should be taken to the operating room emergently for exploratory laparotomy. In contrast, a negative FAST examination should not be used to rule out a serious intra-abdominal injury in patients with unstable vital signs. The patient should not be transported to the CT scanner, unless a repeat FAST is negative 15 minutes later. Another option is to perform a bedside diagnostic peritoneal aspiration (DPA) as a more sensitive test to determine the presence of intraperitoneal bleeding than the FAST examination. Further, it is known that the FAST examination may not be sensitive for intraperitoneal fluid in patients with pelvic fractures. Friese et al. reported that the sensitivity of the FAST examination performed by surgical residents for high-risk patients with pelvic fracture (age >55, systolic blood pressure [SBP] <100 mm Hg or unstable pattern fracture) was only 26.1% to detect intraperitoneal fluid.36 Even for patients with a SBP < 100 mm Hg, the FAST examination was not reliable to rule out a hemoperitoneum (sensitivity 36.4%). Although several studies have been reported showing the utility of the FAST examination in detection of intraparenchymal injuries involving solid organs, the FAST examination has a low sensitivity to detect intra-abdominal injuries that are not associated with intra-abdominal fluid.8,39,40 In the series by Chiu et al., 29% of patients with blunt abdominal injury had no hemoperitoneum.8 In these patients, the FAST examination was interpreted as negative, although CT imaging identified grade 2–3 splenic and hepatic injuries.
Pericardial fluid secondary to a cardiac injury is rarely seen in patients with blunt trauma. Therefore, there are scarce data regarding the accuracy of the FAST examination to detect this fluid in such patients. A series early in the 1990s had no patients with pericardial fluid after blunt trauma.38 Press et al. focused on the cardiac component of the FAST examination in blunt trauma using institutional databases.41 Out of 29,236 patients with blunt trauma evaluated over 7 years, only 14 patients were identified with a hemopericardium and 3 patients with cardiac rupture, respectively. Further, the incidence of hemopericardium confirmed in the emergency cardiac ultrasound was 0.13%.
Data in Penetrating Trauma Using the FAST Examination
Patients with penetrating injury to the anterior chest can potentially sustain life-threatening injuries. A cardiac injury with an associated hemopericardium should be identified rapidly and accurately regardless of a patient’s hemodynamic stability, as early detection of these injuries improves the prognosis. Thus, using ultrasound for patients with penetrating wounds in the so-called “cardiac box” is another appropriate indication for the FAST examination. A prospective multicenter study by Rozycki et al. examining patients with a precordial or transthoracic wound at five Level 1 trauma centers suggested that a hemopericardium could be identified in all patients without any false-negative examinations (sensitivity 100%).42 Therefore, patients with a positive pericardial view should have an emergent sternotomy or thoracotomy based on the very high specificity (96.9%). These data were consistent with results from other series of the precordial FAST examination. A pitfall in interpreting the pericardial FAST examination for patients with a suspected penetrating cardiac injury is that pericardial blood can decompress into the thoracic cavity if there is an associated laceration of the pericardial sac.43 In these cases, a patient could present with a hemothorax without evidence of hemopericardium on the FAST examination.
The utility of the FAST examination is limited in patients with penetrating abdominal trauma as compared to blunt trauma. Hemodynamically unstable patients with a penetrating injury require operative intervention regardless of the result of the FAST examination. Similarly, patients with peritonitis should be explored no matter what the FAST examination shows. Therefore, ultrasound examination is not included in the algorithm suggested by the Western Trauma Association based on a multicenter study to guide the management of patients with anterior abdominal stab wounds.44 This is supported by multiple studies showing a low sensitivity of the FAST examination for intra-abdominal injuries.45,46 While Rozycki et al. showed comparable sensitivity and specificity for the FAST examination in patients with penetrating wounds (sensitivity: 83.8%, specificity: 97.4%), subsequent studies consistently failed to replicate this accuracy.7 In the aforementioned multicenter study, the FAST examination was performed in half of hemodynamically stable and asymptomatic patients with abdominal stab wounds.44 Of these, only 21% of patients who required therapeutic laparotomy had a positive FAST examination. Similarly, Soffer et al. conducted a prospective cohort study to include patients with both stab and gunshot wounds.47 A majority of the FAST examinations were performed by trauma surgeons or surgical trainees. Sensitivities of the FAST examination for therapeutic laparotomy in patients with stab and gunshot wound were 47% and 49%, respectively. Approximately 40% of injuries to a hollow viscus, the most common injury identified at exploratory laparotomy, were missed by the FAST examination. Furthermore, authors have indicated that initial FAST findings rarely alter the management (3/177 cases). To date, there are no studies to report the role of the FAST examination in hemodynamically unstable patients with penetrating injury. For unstable patients with multicavitary penetrating injury (eg, thoracoabdominal injury), the FAST examination can be a useful tool to guide the surgeon to decide which cavity needs to be explored first.
Technique of E-FAST (Extended FAST)
Thoracic injuries are fairly common in multisystem blunt or penetrating trauma to the torso.48 The ATLS protocol emphasizes the importance of identifying life-threatening thoracic injuries including pneumothorax and hemothorax during the primary and secondary survey.27 Frequently, these injuries are missed on a physical examination as patients do not present with classic signs. Although a chest x-ray (CXR) is considered the gold standard to screen for these serious thoracic injuries, equipment or personnel may not be readily available in certain circumstances. Further, because of the patient’s position (supine) and other factors such as a backboard, foreign bodies, and/or associated injuries, the quality of the CXR may not be adequate for use as a screening tool. The application of thoracic ultrasound in trauma patients was reported as a part of ultrasound examination in the 1990s.49 Initially, the thoracic component was not incorporated into the FAST examination; however, recent enthusiasm exists for this application of ultrasound in trauma patients. Thus, an extended FAST (E-FAST) examination is often performed in the trauma bay to detect thoracic injuries.
The E-FAST is normally performed as a continuation of the FAST examination. It is not necessary to change the position of the patient (supine) or the type of transducer (low-frequency sector or convex type). The primary goal in the thoracic part of the E-FAST examination is to detect air (pneumothorax) and/or fluid (hemothorax) in the thoracic cavity. After the pericardial and abdominal examination, the transducer is placed longitudinally in the mid-axillary line, a few costal spaces more cephalad than the area for the RUQ FAST examination. This view should include the right lobe of the liver and diaphragm which has respiratory excursion. A hemothorax is seen above the diaphragm as an anechoic area (Fig. 16-10). In patients with a moderate to large hemothorax, passively collapsed lung parenchyma is detected as a hypoechoic structure. This maneuver is repeated on the left side to scan the entire thoracic cavity. The transducer should be placed more posteriorly and cephalad to visualize the left hemidiaphragm. The reminder of the E-FAST examination can be performed with either the same low-frequency transducer or a high-frequency (7.5–10 MHz) linear transducer. When a low-frequency transducer is used, the depth of image needs to be adjusted to focus on more superficial structures of the anterior thoracic wall. Patients should be maintained in the supine position as the goal of this maneuver is to identify a pneumothorax located anteriorly. The transducer is placed in the midclavicular line longitudinally. In order to obtain an optimal view, the transducer should be placed in the intercostal spaces (superior, mid, and lower levels). In normal individuals, a “lung sliding” sign can be observed. This is the finding whereby the parietal and visceral pleurae (both hyperechoic linear structures) are moving in relation to each other. Similarly, “comet tails” are visualized in normal individuals due to artifacts generated by reverberation of the ultrasound waves. This sign is named for vertical, hyperechoic lines arising from the pleural line (Fig. 16-11). These two signs (sliding and comet tails) are not observed in patients with a pneumothorax, who have air between the parietal and visceral pleurae. If an ultrasound machine with an M-mode (motion mode) function is used, the cursor is placed perpendicular to the pleural line. While linear and granular patterns are seen above and below the pleural line, respectively, in normal lung (“seashore sign”), a linear pattern both above and below the pleural line, the so-called “barcode sign,” is appreciated in those with a pneumothorax (Fig. 16-12). An even more specific ultrasonographic sign for a pneumothorax is called the “lung point.” The transition zone between normal lung and the pneumothorax is apparent by the seashore (normal) and barcode signs (abnormal) aligning on M mode or the sliding lung (normal) adjacent to the nonsliding lung (abnormal) in B mode imaging (Fig. 16-13).
Hemothorax (*) is seen above the right diaphragm.
The “lung sliding” artifact is seen about the pleural line (vertical arrow) in dynamic imaging of the normal lung. Comet-tail artifacts (horizontal arrows) can be observed in the normal lung as well.
M-mode images show a “seashore” sign in the normal lung (A) and “barcode sign” in that with a pneumothorax (B) (see text).
The lung point is best visualized on M mode imaging representing the transition between normal lung and a pneumothorax.
Data in Trauma Patients using the E-FAST
Application of thoracic ultrasound in the trauma setting has been described since the 1990s.49,50 In an early series reported by Ma et al., thoracic ultrasound performed by emergency medicine physicians on 240 patients with both blunt and penetrating trauma had a sensitivity of 96.2%, a specificity of 100%, a positive predictive value of 100%, a negative predictive value of 99.5%, and an accuracy of 99.6% to detect a hemothorax confirmed by either tube thoracostomy or computed tomography.50 Surgeon-performed ultrasound to detect a hemothorax had similar results (sensitivity: 97.5%, specificity: 99.7%) to that of the CXR, but with a significantly shorter examination time (1.30 ± 0.08 vs 14.18 ± 0.91 minutes, p < 0.0001).51 Other early studies that examined the sensitivity and specificity of the ultrasound for a hemothorax also showed promising results comparable to the CXR. The utility of ultrasound to detect a pneumothorax was demonstrated in the 1990s for patients in the ICU.52 Bedside ultrasound can be helpful to expedite care in patients with unstable vital signs. In trauma patients, Knudson et al. conducted a prospective study to evaluate surgeon-performed ultrasound to detect a pneumothorax.53 As previously noted, the diagnosis of a pneumothorax was made based on the absence of the lung-sliding sign and/or the comet-tail artifact. Of note, a low-frequency (2.5–4 MHz) transducer was used in this study. In comparison with the CXR, ultrasound had a sensitivity of 92.3%, a specificity of 99.6%, a positive predictive value of 92.3%, a negative predictive value of 99.7%, and an accuracy of 99.3%.
Ultrasound-guided Resuscitation in the Emergency Department
The resuscitation of severely injured patients should be initiated immediately in the trauma bay. While damage-control resuscitation has been proposed for a decade, invasive hemodynamic monitoring devices to guide the resuscitation are not always available until the patient is transferred to the ICU. Two components of information that should be obtained using ultrasound are the intravascular volume status (preload) and contractility of the heart. The assessment of intravascular volume status can be estimated by measuring the diameter and collapsibility of the inferior vena cava (IVC) using ultrasound (Fig. 16-14).54 In one study, non-cardiologists successfully visualized the IVC to measure the diameter in 89% of trauma and surgical patients.55 The assessment of the intravascular volume depletion by a small IVC diameter (<1 cm) with significant collapsibility (>50% with respiration) was comparable to the central venous pressure measured with an intravenous catheter with regards to the examination of cardiac function. Murthi et al. compared the cardiac index (CI) obtained by the focused rapid echocardiography evaluation (FREE) to other relevant invasive hemodynamic monitoring methods (pulmonary artery catheter and arterial pressure waveform-based device).56 Their data suggested that patient management was frequently changed based on the data derived from FREE. Further, there was good agreement between the CIs obtained in FREE and a pulmonary artery catheter. Of interest, the role of point-of-care bedside ultrasound for unstable trauma patients has been evaluated in a randomized control trial.57 In this study, the limited transthoracic echocardiogram (LTTE) was performed by trained non-cardiologists (trauma surgeon, emergency medicine physician, surgical, and emergency medicine residents) in the trauma bay. In the LTTE, fluid status, contractility, and pericardial effusion were reported. The use of the LTTE was associated with significantly less volume of intravenous fluid administered, less time to the operating room, and a higher rate of admission to the ICU. In a subgroup of patients with a traumatic brain injury, a significantly lower mortality rate was noted in the LTTE group (14.7% vs 39.5%, p = 0.03).
The inferior vena cava is measured within a few centimeters of entry into the right atrium.
Ultrasound in Prehospital, Mass Casualty, and Military Settings
With recent advances in technology, currently used ultrasound machines are often portable. In special environments such as prehospital settings, mass casualty incidents, or with military care, a smaller size, hand-carried ultrasound machine can be used to make rapid diagnoses in trauma patients.58,59,60,61,62 One of the goals of ultrasound examination in the out-of-hospital setting is to help triage patients. Although a smaller machine is used, the quality of images should be equivalent to those obtained in the conventional FAST/E-FAST examination in the emergency department. This will facilitate detection of free fluid in the pericardial and intra-abdominal spaces and a hemothorax and pneumothorax. In addition, ultrasound has been used for the evaluation of other types of injuries to the eye and extremities.63,64
The impact of the prehospital FAST (PFAST) examination on the management of patients with blunt abdominal trauma was evaluated in a multicenter prospective study from Germany.65 In 95% of patients, the prehospital time was not prolonged because of the PFAST examination (mean time was 2.4 minutes) and good or acceptable quality images could be obtained to establish a diagnosis in 93% of patients. Compared with the FAST examination or CT performed in the emergency room, the PFAST examination had a sensitivity of 93%, a specificity of 99%, and an accuracy of 99%. A mass casualty incident is another unique situation that requires rapid and accurate triage of a large number of trauma victims. The use of ultrasound in a mass casualty incident was initially reported by Sarkisian et al. in the early 1990s.59 Following the Armenian earthquake in 1988, ultrasound examinations identified trauma-related pathology in 51 of 400 patients screened. The average study time was 4 minutes with no false positive and four false negative cases. Zhou et al. reported a sensitivity of 91.9%, a specificity of 96.9%, and an accuracy of 96.6% in detecting any intra-abdominal injury from a more recent experience of surgeon-performed ultrasound in a Chinese earthquake.62
Similarly, there are a few studies to show the feasibility of ultrasound use for the triage of wounded soldiers and civilians in the combat setting.66,67 The FAST examination was performed in 281 patients during the 1-month period of the Second Lebanese War.67 Sensitivity, specificity, and accuracy of the FAST examination to detect intraperitoneal free fluid were 76.5%, 98.4%, and 94.0% in soldiers and 67.6%, 95.2%, and 91.6% in civilians, respectively. As further developments in telemedicine are expected to improve the accuracy of the ultrasound examination in the field, images obtained there can be reviewed by physicians at a support hospital.68