Scanning
The phased-array transducer is placed systematically in four locations known to provide easy and accessible windows into the torso. However, the precise location of these windows will vary from patient to patient based on body habitus and normal anatomic variation. Therefore physicians planning on performing FAST exams in trauma situations should be practiced in finding these locations in different individuals.
As the transducer is placed over a certain window, it is tilted, rocked and rotated to provide real-time imaging and evaluation. If possible, images or video loops should be recorded for the purposes of documentation, quality assurance or teaching. Remember, a dynamic record such as a video loop provides much more information at a later time than does a static image.
Technique
Most physicians will choose to scan in a particular order as much out of habit as not to miss an important area in the chaos of the trauma bay. The order, however, may be influenced by the clinical picture of the patient. The single most likely site for free fluid to accumulate in the abdomen is the right upper quadrant. Therefore most FAST exams begin with a view of the hepatorenal interface and continue in a clockwise fashion to include the subcostal or subxyphoid view of the pericardium, the splenorenal interface and the paracolic gutters of the pelvis. Each scan should not be limited to a single plane or view, but should involve views in at least two orthogonal directions. This will reduce the chances of fluid being overlooked.
Right Flank (Perihepatic) View
From this view, four areas of interest may be scanned: the pleural space, subphrenic space, hepatorenal interface (Morrison’s Pouch) and the inferior pole of the kidney. Because of its density, the liver provides a wonderful window for scanning in this region. In some patients the liver reaches low enough that the probe may be positioned subcostally; however, an intercostal approach will be necessary for most patients.
With the probe indicator directed toward the vertebral end of the rib and angles superiorly, the pleural space may be visualized. Abnormal fluid collections will be seen as anechoic or hypoechoic collections in the costophrenic angles. Obviously gravity makes this more difficult in a supine patient, so repositioning the patient may be necessary to effectively view this area if such collections are strongly suspected.
Morrison’s pouch is scanned by angling inferiorly until the hepatorenal interface is seen. Anechoic blood may be seen at any point between the liver and kidney, and clotted blood, which may appear hypoechoic, should not be confused with perinephric fat.
Scanning more inferiorly still, the inferior pole of the kidney may be visualized. Occasionally bowel gas may be found between the liver and the inferior pole, so a more posterior angle may facilitate visualization.
Normal Morrison's Pouch (RUQ) View
Onto Additional Views!
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