Evaluation of blunt trauma patients with ultrasound (US) has been described for over 30 years.1,2 Its use in the United States in the early assessment of blunt abdominal trauma patients rapidly increased in the 1990s.1 It is currently taught as an adjunct to the secondary survey in the Advanced Trauma Life Support (ATLS) course.1,3 US evaluation of the trauma patients decreases the time to operative care, resource utilization, and the costs of blunt trauma patients.4,5 The focused assessment with sonography in trauma exam, also known as the FAST exam, can be completed within 5 minutes.1 It has essentially replaced the need for a diagnostic peritoneal lavage in the initial assessment of all but a few trauma patients.6,7 This chapter reviews the technique and interpretation of the FAST exam.
The FAST exam evaluates four anatomical areas or potential spaces for the presence or absence of intraperitoneal fluid. These include the hepatorenal recess (Morrison's pouch), the splenorenal recess, the rectovesical or rectouterine space, and the pericardial space. The assumption is that fluid represents blood in the setting of trauma. The presence of ascites, urine, and bowel fluid can appear similar. These spaces represent the most dependent areas in the supine patient (Figure 5-1). The volume of fluid accumulation required for visualization by US ranges from 250 to 620 mL.8,9 More experienced sonographers are able to visualize volumes closer to 250 mL.8
The posterior reflection of the peritoneum is where blood initially layers in the supine patient. The hepatorenal (A) and splenorenal (B) recesses represent the posterior peritoneal reflections between the inferior pole of the kidney and the liver or spleen, respectively.
The FAST exam is performed after the primary survey. It can be performed in conjunction with ongoing resuscitative efforts. It is indicated when evaluating for the presence of intraperitoneal or pericardial blood in the setting of acute thoracoabdominal trauma. It is useful in determining resource allocation in the setting of multipatient trauma scenarios.1
Blunt Thoracoabdominal Trauma
The most studied use of the FAST exam has been in adult patients with blunt abdominal trauma. The early diagnosis of hemoperitoneum and/or hemopericardium in the setting of blunt trauma is critical in the management of these patients. The sensitivity and specificity for the presence of hemoperitoneum varies depending on the comparison “gold standard,” and is generally reported between 78% to 90% and 98% to 100%, respectively.7,10–14 It has been reported to approach 100% sensitivity and 100% specificity in hypotensive patients.6,10 One study by Miller et al. reported a sensitivity of 42% and a specificity of 98%.15 The ...