The focused assessment with sonography for trauma (FAST) examination is a safe, portable, noninvasive diagnostic tool to investigate for hemoperitoneum, hemopericardium, and hemothorax in trauma victims. The FAST exam can help detect free fluid (ie, hemoperitoneum in the hypotensive patient); however, the FAST exam cannot exclude solid organ injury. Hemoperitoneum in the pediatric trauma patient is usually a result of hepatic or splenic injury and will appear as an anechoic (dark) collection on ultrasound (US). The primary indications for use of the FAST exam are blunt or penetrating thoracic or abdominal trauma.
Use a low-frequency (1–5 MHz) curvilinear abdominal or phased-array probe or higher-frequency (6–12 MHz) linear transducers. The latter will provide better resolution as pediatric patients have thinner abdominal walls and less subcutaneous fat. Perform the scan with the patient in the supine position. Direct probe indicator toward the patient’s head or the patient’s right side. When imaging the right upper quadrant (RUQ) and the left upper quadrant (LUQ), rotate the probe counterclockwise during scanning to allow for successful imaging between intercostal rib spaces.
Obtain the following four views:
Subxiphoid view of the heart
Hepatorenal space (Morison pouch) in the right upper quadrant (RUQ)
Splenorenal recess, as well as the subphrenic space, in the left upper quadrant (LUQ)
Rectovesicular pouch (males)
Pouch of Douglas (females)
RUQ and pelvic views are routinely performed first in the pediatric trauma patient as these are most sensitive in detecting intraperitoneal free fluid
Figure 21.1 ▪ FAST Exam Ultrasound Windows.
(A) The 4 US windows of the FAST exam: (1) The right upper quadrant view of the hepatorenal recess; (2) the left upper quadrant view of the splenorenal recess; (3) the subxiphoid cardiac view; and (4) the suprapubic view. (B) Probes Used for Ultrasound. Few probes that one may use in their clinical practice are shown. A. Low-frequency curved array or convex probe. B. Low-frequency phased array or sector probe. C. High-frequency linear array probe. D. High-frequency endocavitary probe. (Reproduced with permission from Ma OJ, Mateer JR, Blaivas M: Emergency Ultrasound, 2nd ed. McGraw-Hill, New York, 2008 [A].) (Photo contributor: Dimitrios Papanagnou, MD [B].)
Figure 21.2 ▪ A Positive Right Upper Quadrant FAST View.
The liver (L) is visualized on the left side of the image with the right kidney (K) on the right side of the image; between the 2 organs, an anechoic stripe is visualized, representing free fluid (FF or hemoperitoneum) in a patient sustaining blunt trauma. (Photo contributor: James Tsung, MD.)
Figure 21.3 ▪ A Positive Left Upper Quadrant FAST View.