Focussed Assessment with Sonography for Trauma (FAST):
Ultrasound provides an important initial screening examination in the adult trauma patient. However, ultrasound is not a replacement for the more sensitive imaging studies often needed to identify specific injuries in patients with concerning abdominal or thoracic symptoms or signs. Most such patients, if hemodynamically stable, undergo computed tomography (CT). Unstable patients with intraperitoneal hemorrhage identified by ultrasound generally proceed directly to laparotomy.
For unstable patients without an obvious source of bleeding and in whom the initial ultrasound examination is negative (ie, without intraperitoneal fluid), a diagnostic peritoneal tap, or angiography, may be needed depending upon the clinical scenario. As an example, ultrasound generally plays a more limited role in the evaluation of patients with significant pelvic fractures because it is less sensitive for detecting pelvic bleeding, cannot detect retroperitoneal bleeding, and cannot differentiate between blood and urine. The management of such patients is discussed separately.
Ultrasound evaluation performed as part of the initial examination and resuscitation of the trauma patient is known as the Focused Assessment with Sonography for Trauma (FAST). The extended FAST examination (E-FAST) is used when views are added to evaluate for pneumothorax.
The primary purpose of the FAST examination is to determine the presence of pathologic pericardial or intraperitoneal free fluid, which appears as a hypoechoic or anechoic (ie, dark grey or black) collection. The sole contraindication to the FAST examination is the need for immediate surgery.
The major interrogations that comprise the FAST examination use established views (or windows) to evaluate the pericardial, peritoneal, and pleural cavities. The standard order of evaluation is as follows:
— Right flank (hepatorenal view or “Morison’s pouch”)
— Left flank (perisplenic view)
— Pelvic (retrovesical views)
— Thoracic (pneumothorax evaluations)