Authors: Allison Lee, MD and Nicole Anthony, MD
Out of the several right upper quadrant (RUQ) FAST views obtained over the past month at KCHC, which RUQ view was positive for free fluid?
#2. As the sonographer fans through the area, a small stripe of free fluid (FF) can be visualized beneath the caudal edge of the liver. This patient presented with a GSW to the abdomen; FF was identified in both the RUQ and pelvis. He was immediately and directly taken to the operating room.
An adequate RUQ view includes:
1. The hepatorenal interface
2. Cephalad subphrenic and pleural space
3. Inferior pole of the kidney
Review your FAST views at 5 minute sono here.
Indication:
The FAST may be used as initial evaluation in stable trauma patients presenting with blunt and/or penetrating abdominal injuries. Because the sensitivity of FAST is much lower in hemodynamically stable patients (as low as 22% when compared to CT as the reference standard), stable patients with a negative FAST should be followed up with a CT scan, serial FAST, or observation.[1] FAST should only be used to rule IN, not rule OUT intra-abdominal injury.
Figure 1. An algorithm for FAST in blunt abdominal trauma.[1]
Likelihood Ratios
Figure 2. Sensitivity, specificity, and likelihood ratios of FAST in adults.[2,3]
Figure 3. Sensitivity, specificity, and likelihood ratios of FAST in the pediatric population.[2,3]
Pitfalls – False Positives
Perinephric Fat:
Figure 4. Peri-nephric fat can be differentiated from FF on FAST by the hyperechoic appearance of fascia on the ultrasound, termed the “double line sign.”[5]
Gallbladder:
Figure 5. Note that the gallbladder will appear well-circumscribed and would not typically have the appearance of free fluid.[6]
IVC:
Figure 6. If you are unsure whether you are visualizing free fluid or a vessel, turn on your color flow.[6]
Ascites:
Unfortunately, there is no way to differentiate ascites from acute hemorrhage on ultrasound.
Pitfalls – False Negatives
The FAST exam is not as reliable in detecting subcapsular hemorrhage and cannot be used to evaluate the retroperitoneal space. Further, in order to have a positive pelvic view on the FAST, there must actually be at least 100cc of fluid present, and at least 400cc to 700cc in the hepatorenal and splenorenal views. Placing the patient in the Trendelenburg position may improve the sensitivity.[7]
Sources
1. Richards JR, McGahan JP. Focused Assessment with Sonography in Trauma (FAST) in 2017: What Radiologists Can Learn. Radiology. 2017;283(1):30-48. doi:10.1148/radiol.2017160107
2. The Evidence Atlas: Trauma. The POCUS Atlas. https://www.thepocusatlas.com/ea-trauma. Published May 25, 2018. Accessed on June 1, 2022.
3. Nishijima DK, Simel DL, Wisner DH, Holmes JF. Does this adult patient have a blunt intra-abdominal injury?. JAMA. 2012;307(14):1517-1527. doi:10.1001/jama.2012.422
4. Lobo V, Hunter-Behrend M, Cullnan E, et al. Caudal Edge of the Liver in the Right Upper Quadrant (RUQ) View Is the Most Sensitive Area for Free Fluid on the FAST Exam. West J Emerg Med. 2017;18(2):270-280. doi:10.5811/westjem.2016.11.30435
5. SonoTutorial: The FAST Part 1: The right upper quadrant– the right way to do it. SonoSpot: Topics in Bedside Ultrasound. https://sonospot.wordpress.com/2012/09/04/sonotutorial-the-fast-part-1-the-right-upper-quadrant-the-right-way-to-do-it/. Published September 4, 2012. Accessed June 1, 2022.
6. Teismann N. UCSF ED Liver and Gallbladder/Biliary Ultrasound Protocol. UCSF Emergency Medicine Ultrasound. https://edus.ucsf.edu/sites/edus.ucsf.edu/files/wysiwyg/UCSF%20ED%20US%20Protocol%20Biliary_Final.pdf. Published May 15, 2015. Accessed June 1, 2022.
7. Abrams BJ, Sukumvanich P, Seibel R, Moscati R, Jehle D. Ultrasound for the detection of intraperitoneal fluid: the role of Trendelenburg positioning. Am J Emerg Med. 1999;17(2):117-120. doi:10.1016/s0735-6757(99)90040-2
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