The FAST exam is a rapid ultrasonography examination that is routinely performed in the setting of blunt or penetrating torso trauma. It is designed to evaluate for free fluid (blood until proven otherwise) in the peritoneum, pleural space, and around the heart. Four areas are interrogated with ultrasound: the subxiphoid, right upper quadrant, left upper quadrant, and pelvis/suprapubic areas. The most dependent space (most likely to collect fluid) in supine adult patients is the hepatorenal space (Morison pouch) which is therefore usually the first space to be assessed; however, the order of the FAST exam can be changed depending on the mechanism of injury.

A downside to the FAST exam is the fact that usually 200 to 250 mL of fluid needs to accumulate before it can be visualized sonographically. Furthermore, it cannot evaluate the retroperitoneum and misses solid organ injuries. The utility of FAST resides in the bedside examination of the hemodynamically unstable patient with trauma, determining operative management versus considering other potential sources of shock. It has largely replaced deep peritoneal lavage as the initial screening tool for intra-abdominal injury. An extended version of the FAST exam (E-FAST) incorporates the thoracic window to allow detection of pneumothorax as a potential cause of hemodynamic instability.

References

• Austin S, Haase D, Hamera J. Advances in trauma ultrasound. Emerg Med Clin North Am. 2023;41:131-142.
• Hoff WS, Holevar M, Nagy KK, et al. Practice management guidelines for the evaluation of blunt abdominal trauma: the East Practice Management Guidelines Work Group. J Trauma. 2002;53:602-615.
• Richards JR, McGahan JP. Focused assessment with sonography in trauma (FAST) in 2017: what radiologist can learn. Radiology. 2017;283:30-48.
• Rozycki GS, Root HD. The diagnosis of intraabdominal visceral injury. J Trauma. 2010;68:1019-1023.