Focused Assessment with Sonography for Trauma: Methods, Accuracy, and Indications

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Anatomic review

Intra-abdominal views on FAST are based on 3 dependent areas within the peritoneal cavity in which free fluid is most likely to accumulate when the patient is in the supine position: (1) perihepatic, subphrenic and hepatorenal recess/Morrison pouch; (2) perisplenic, splenorenal fossa/subphrenic; and (3) pelvis. The minimum volume of free intraperitoneal fluid required for detection by FAST has been reported to range from 100 to 620 mL (Table 1).4, 5, 6, 7, 8 Volumes at the lower end of the

Patient Position

The patient is preferably examined in the supine position. Other positions (Trendelenburg, reverse Trendelenburg, and decubitus) may facilitate pooling of fluid in dependent regions, thereby potentially increasing detection yield, and should be considered if the clinical scenario permits.

Transducer

Transducer selection depends on the size of the patient. For a typical adult, sound wave penetration must be at least 20 cm. Therefore, a lower-frequency transducer is selected, such as 3.5 to 5 MHz curved

FAST examination views

A typical FAST examination incorporates a minimum of 4, but up to 6, views (Fig. 1).13 When imaging a patient, the left side of the display screen should always be the patient’s right side (Fig. 2). The screen should reflect cranial to caudal going from left to right when displaying a longitudinal view (Fig. 3).

Image optimization

Image quality and overall sensitivity of the examination may be optimized by manipulation of factors influencing signal strength and image acquisition.

Gain

Gain refers to the amplification of receiver signals from deeper tissues to compensate for increased attenuation compared with near-field structures. Gain can be adjusted to brighten or darken the whole image. The time gain compensation (TGC) curve can also be adjusted to brighten or darken segments of the image. The TGC curve requires frequent adjustments because different structures attenuate sound differently.

Focal Zone

The focal zone is the depth at which the sound waves have narrowed, resulting in

Clinical applicability

Two decades after the incorporation of ultrasonography in trauma, its precise role remains unclear. Much of this can be attributed to the comparative reference standards (DPL, computed tomography [CT], laparotomy, clinical observation) and end points (fluid detection, intervention), by which its effectiveness has been judged. In addition, advances in skills and technology have confounded the simple initial intent “detection of free fluid” and use as an “adjunct, not substitute” for preexisting

Pediatric trauma

Few studies on the efficacy of ultrasonography in children with abdominal injury have been reported. Scaife and colleagues32 conducted an electronic survey of the use of FAST at American College of Surgeons (ACS) level 1 trauma centers, National Association of Children’s Hospitals, and freestanding children’s hospitals. FAST examinations were used in 96% adult-only institutions, 85% combined adult and pediatric centers, and 15% children’s hospitals. The largest impediment to the use of FAST in

Accreditation

After an initial 8-hour course that included didactic and hands-on training with FAST, Thomas and colleagues37 reported a sensitivity of 81%, specificity of 91%, and overall accuracy of 98%.

At The International Consensus Conference in 1999,22 the majority viewpoint supported an 8-hour (4 theoretical, 4 practical) minimum training period to learn the FAST procedure, with a minimum of 200 supervised patient examinations. A minority viewpoint was that as few as 50 examinations were sufficient. The

Future directions

Recent technological advancements in sonography can improve and expand the FAST examination in appropriate clinical settings. Three-dimensional sonography allows for multiplanar imaging, enabling acquisition of a plane through a desired point of interest that may not be accessible with conventional sonography because of size or location of the acoustic window. It also provides a new display of the images that can improve the ability to determine spatial relationships between normal and abnormal

Summary

FAST has had a significant effect in the management of abdominal trauma, with its ease of rapid performance, portability, and noninvasive nature, resulting in a significant increase in its use over the past 2 decades. Extending its use from the original intent as a diagnostic adjunct for detection of free intraperitoneal fluid and pericardial effusion to a stand-alone diagnostic modality has raised questions regarding its validity and optimal role. FAST remains an invaluable adjunct in the

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