Introduction

Ultrasound for the evaluation of trauma patients was one of the first applications of bedside ultrasound used by emergency physicians (EPs). The FAST examination (originally, focused abdominal sonography for trauma; currently, focused evaluation with sonography for trauma) was developed initially as a noninvasive modality for the initial triage of patients with hypotensive blunt abdominal or thoracic trauma. Its purpose was to rapidly identify patients with free intraperitoneal fluid or with pericardial effusion. However, over the past 20 years, FAST has evolved considerably to include the evaluation of patients after normotensive blunt trauma and penetrating trauma. Implementation of other bedside ultrasound advances has led to the development of E-FAST (or extended FAST). E-FAST involves evaluation of the inferior vena cava (IVC) for overall intravascular fluid status and assessment of the chest for pneumothorax and pleural effusion.

For more information on E-FAST, see www.expertconsult.com

Comparison of Imaging Modalities for Trauma

Before the development of FAST, either computed tomography or diagnostic peritoneal lavage was the standard method for evaluating patients with abdominal trauma. Each of these modalities has distinct advantages and drawbacks.

FAST allows the EP to rapidly evaluate trauma patients at the bedside, frequently while other interventions are ongoing. It requires a minimum of training, is noninvasive, and can be repeated. In addition to evaluating the abdomen, ultrasound can be used to evaluate the pericardium and pleura. Another important advantage of this technique is that intravenous contrast material or ionizing radiation is not required, which allows safe use in a broad spectrum of patients, including pregnant women. FAST is not without limitations, however. Although it can be learned quickly by most, it is operator dependent. Achievement of the highest sensitivity relies on the sonographer obtaining adequate views, which can be hampered by patient habitus, bowel gas, or the presence of subcutaneous air. FAST is not as reliable for pinpointing the site of hemorrhage or for discerning solid organ injury. The retroperitoneum is also typically poorly visualized, and hemorrhage in this area may be missed.

What We Are Looking For

Following trauma, particularly blunt trauma, patients may be hemodynamically unstable because of bleeding from multiple sites. It can frequently be difficult to ascertain where the patient’s injuries lie based on the history and physical examination alone. FAST was designed to identify possible sources of bleeding that result in instability. It relies on the premise that free fluid (blood) within the peritoneum will accumulate within the most gravity-dependent areas. These areas are the right upper quadrant between the liver and kidney (pouch of Morison), the right paracolic gutter, the left upper quadrant between the spleen and kidney, the potential space between the spleen and diaphragm, the left paracolic gutter, and the pelvis. FAST seeks to evaluate these areas quickly for the presence of free fluid. It also seeks to evaluate the pericardial sac for the presence of pericardial effusion and possible cardiac tamponade. The presence of cardiac activity or the status of overall cardiac function can also be assessed.

Literature Review

Multiple studies have demonstrated the utility of FAST for the evaluation of patients after blunt abdominal trauma. One of the first studies to highlight FAST by EPs was performed by Ma and Mateer in 1995. This study evaluated ultrasound for detection of free fluid not only in the peritoneum but also in the pericardium, the retroperitoneal space, and the pleural cavity. The authors evaluated a total of 975 cavities and calculated a sensitivity of 90%, a specificity of 99%, and an accuracy of 99%.¹ This study demonstrated that with training, EPs are capable of identifying free fluid with high sensitivity and specificity.

Subsequent studies focusing on FAST have found variable results ranging from sensitivities of 79% to 100% and specificities of 95.6% to 100%.^2–5 Although calculated sensitivities and specificities have been variable across studies, one finding that seems consistent is that both sensitivity and specificity appear to increase in hypotensive patients.⁶

Conversely, a Cochran review published in 2005 found “insufficient evidence from RCTs [randomized controlled trials] to justify promotion of ultrasound-based clinical pathways in diagnosing patients with suspected blunt abdominal trauma.”⁷ These findings have been controversial, and a similar literature review by Melniker found “the FAST examination, adequately completed, is a nearly perfect test for predicting a ‘Need for OR’ in patients with blunt torso trauma.”⁸

One finding that has appeared consistently in most studies is that although FAST is sensitive and specific for the detection of intraperitoneal free fluid, it has poor results when used in attempts to localize solid organ injury.^9,10

Ultrasound has been shown to be a reliable study for the evaluation of traumatic pericardial effusions. Mandavia et al. found that EPs with training in echocardiography had a sensitivity of 96%, a specificity of 98%, and an overall accuracy of 97.5% for this indication.¹¹

How to Perform a FAST Examination

FAST consists of ultrasound views of four primary areas, the right and left upper quadrants of the abdomen, the pelvis, and a view of the pericardium from the subxiphoid area.

A low-frequency transducer is typically used to ensure proper depth of penetration.

Subxiphoid View

To evaluate the subxiphoid view of the heart, the transducer is placed just below the subxiphoid process and aimed toward the patient’s left shoulder (Fig. 9.1). It is frequently necessary to apply some pressure to the upper part of the patient’s abdomen to enable the sonographer to look “up” into the patient’s chest. It is also helpful to think of the transducer as a flashlight and imagine shining it toward the left side of the patient’s chest. Another helpful tip for beginning sonographers is to increase the depth if at first the heart is not seen in full. A four-chamber view of the heart should be sought (Fig. 9.2). Specifically, the bright white (or hyperechoic) outline of the pericardium should be sought to evaluate for the presence of pericardial effusion.

Fig. 9.1 Proper placement of the transducer for a subxiphoid view of the heart.

Note that the sonographer is holding the transducer overhand and pushing downward into the subxiphoid space while pointing the transducer toward the left side of the chest.

Fig. 9.2 Subxiphoid view of the heart.

A four-chamber view of the heart surrounded by the hyperechoic (white) border of the pericardium is seen. At the top of the screen, the left lobe of the liver is adjacent to the right ventricle.

Right Upper Quadrant

The right upper quadrant should be evaluated in both the coronal and transverse planes. To begin, the transducer is placed on the patient’s midaxillary line between the 8th and 11th ribs (Fig. 9.3). This position should be adjusted as needed to overcome rib shadowing and to obtain the best image possible. Aiming the indicator toward the patient’s head will yield a coronal image. The interface between the liver and kidney (pouch of Morison) and the potential spaces around this area should be thoroughly evaluated for the presence of free fluid (Fig. 9.4). This can be done by sweeping the transducer anteriorly and posteriorly. Moving the transducer superiorly a rib space or two will usually allow a view of the echogenic diaphragm curving over the dome of the liver. The area superior to the diaphragm, the costophrenic recess, can be evaluated for the presence of pleural fluid as well. Once a coronal image has been obtained, the transducer should be rotated so that the indicator points toward the patient’s right to obtain a transverse view. Although such placement frequently provides an adequate view, it is often helpful to angle the transducer on a slightly oblique plane so that it fits into the intercostal space and thus limits rib shadowing. Once the liver and kidney are seen, sweeping the transducer superiorly and inferiorly offers a full evaluation of areas in which free fluid may collect.

Fig. 9.3 Placement of the transducer for evaluation of the right upper quadrant.

Note that the indicator on the transducer is pointing toward the patient’s head. This will yield a coronal image. The transducer should be placed along the anterior midaxillary line between the 8th and 11th rib spaces.

Fig. 9.4 Normal right upper quadrant as viewed in a coronal orientation.

The liver is seen on the left of the image, with the kidney seen to the right and slightly inferior to the liver. The diaphragm is seen as a brightly echogenic arc on the far left of the image.