FAST exam is specific but not sensitive

Blunt abdominal trauma is common in motor vehicle collisions, as shearing forces created by sudden deceleration can cause laceration to both solid and hollow intraabdominal organs and injury to vascular or retroperitoneal structures. Although the ultrasonographic videos (Video 1, Video 2, Video 3, and Video 4) do not demonstrate free intraabdominal fluid, current guidelines would recommend abdominal CT scanning in this clinical setting (choice B is correct; choices A, C, and D are incorrect).

The focused assessment with sonography for trauma (FAST) examination is a bedside ultrasonographic protocol developed to identify hemoperitoneum and hemopericardium rapidly in trauma patients. The FAST examination includes rapid imaging of the right upper quadrant, subcostal cardiac window, left upper quadrant, and pelvis, typically performed with a curvilinear (abdominal) or phased array (cardiac) probe. Areas of anechoic free fluid in the hepatorenal recess (Morison pouch), around the caudal tip of the liver, pericardial space, splenorenal recess, or retrovesicular (male patients) or rectouterine and vesicouterine pouches (female patients) strongly suggest hemoperitoneum or intraabdominal injury in this setting. The right upper quadrant view is generally considered the most sensitive of these views to identify free intraabdominal fluid (Figure 1). The extended FAST protocol includes imaging of the lower thorax and diaphragm to identify pleural fluid or hemothorax, and additional sonographic assessment of the anterior chest wall is often performed to exclude pneumothorax.

Although a positive FAST examination is very specific for free fluid or organ injury, which might prompt urgent operative intervention, its sensitivity varies widely, and therefore its negative predictive value alone is insufficient when there is a high pretest probability of intraabdominal injury. In patients who are stable with a clinically significant mechanism of injury, abdominal pain, abdominal wall bruising, unexplained transient hypotension, or equivocal or unreliable physical examination results, abdominal CT scanning remains the recommended diagnostic modality of choice to identify most likely intraabdominal injuries, although identification of blunt hollow viscus trauma can be challenging even with this study. Serial ultrasonography evaluation is commonly used to reassess patients at high risk with normal CT scans or patients at lower risk to exclude delayed bleeding or occult injury when clinical changes occur. Although diagnostic peritoneal lavage (DPL) was once considered the diagnostic gold standard in this setting, it is less sensitive than CT scanning to detect solid organ and retroperitoneal injury and does not offer the same advantages for preoperative planning. As a result, DPL is usually relegated to situations in which uncertainty persists after initial ultrasonography and CT scanning or when these diagnostic modalities are not readily available. Exploratory laparotomy is appropriate in patients who are unstable with a positive FAST examination or DPL or when CT scanning identifies injuries that require acute surgical intervention.123456

Footnotes

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