Focused assessment with sonography for trauma
Focused Assessment with Sonography for Trauma (commonly abbreviated as FAST) is a rapid bedside ultrasound examination performed by surgeons and emergency physicians as a screening test for blood around the heart (pericardial tamponade) or abdominal organs (hemoperitoneum) after trauma.
The four areas that are examined for free fluid are the perihepatic space (also called Morrison's pouch or the hepatorenal recess), perisplenic space, pericardium, and the pelvis. With this technique it is possible to identify the presence of intraperitoneal or pericardial free fluid. In the context of traumatic injury, this fluid will usually be due to bleeding.
Extended FAST
The extended FAST (EFAST) allows for the examination of both lungs by adding bilateral anterior thoracic sonography to the FAST exam. This allows for the detection of a pneumothorax with the absence of normal ‘lung-sliding’ and ‘comet-tail’ artifact (seen on the ultrasound screen). Compared with supine chest radiography, with CT or clinical course as the gold standard, bedside sonography has superior sensitivity (49–99 versus 27–75%), similar specificity (95–100%), and can be performed in under a minute. Several recent prospective studies have validated its use in the setting of trauma resuscitation, and have also shown that ultrasound can provide an accurate estimation of pneumothorax size. Although radiography or CT scanning is generally feasible, immediate bedside detection of a pneumothorax confirms what are often ambiguous physical findings in unstable patients, and guides immediate chest decompression. In addition, in the patient undergoing positive-pressure ventilation, the detection of an otherwise ‘occult’ pneumothorax prior to CT scanning may hasten treatment and subsequently prevent development of a tension pneumothorax, a deadly complication if not treated immediately, and deterioration in the radiology suite (in the CT scanner).
Advantages
FAST is less invasive than diagnostic peritoneal lavage, involves no exposure to radiation and is cheaper compared to computed tomography, but achieves a similar accuracy.
Numerous studies have shown FAST is useful in evaluating trauma patients. It also appears to make emergency department care faster and better. However, some authorities still have not accepted its use.
Interpretation
FAST is most useful in trauma patients who are hemodynamically unstable. A positive FAST result is defined as the appearance of a dark ("anechoic") strip in the dependent areas of the peritoneum. In the right upper quadrant this typically appears in (between the liver and kidney). In the left upper quadrant, blood may collect anywhere around the spleen (perisplenic space). In the pelvis, blood generally pools behind the bladder (in the rectovesicular space or Pouch of Douglas). A positive results suggests hemoperitoneum; often CT scan will be performed if the patient is stable or a laparotomy if unstable. In those with a negative FAST result, a search for extra-abdominal sources of bleeding may still need to be performed.
References
External links
- eMedicine: Blunt abdominal trauma
- FAST exam tutorial
- The FAST examination from Trauma.org, includes tutorial videos.
Retrieved from : http://en.wikipedia.org/wiki/Focused_assessment_with_sonography_for_trauma
