Ultrasound for All Blunt Abdominal Trauma? Not so FAST…
Patient JD presents via EMS, brought in following a motor vehicle collision.
Patient was the restrained driver struck head-on by another vehicle at an unknown speed. The front airbags were deployed.
Airway patent, breath sounds are auscultated bilaterally, 2+ dorsalis pedis and radial pulses bilaterally.
GCS 15, patient responding to questions appropriately, moving all extremities.
Exam notable for a seatbelt sign.
Vitals: T 36.9°, BP 139/80, HR 98, RR 24, SpO2 99% on room air
As I hustle over to the trauma bay, the ultrasound machine is already being prepped. I watch and try to interpret the pixels in my mind - I don’t think I see any pockets of fluid. The surveys are completed, IV access is acquired and the patient is then wheeled to CT. As I walk alongside the stretcher, I find myself thinking…
In a resource-rich setting, what is the role of the FAST exam in evaluating patients with blunt abdominal trauma (BAT)?
Summary of Evidence
Since the FAST exam was coined in 1995,(3) it has been incorporated into the ATLS guidelines and is now used in 96% of level 1 trauma centers.(4) Despite this, the lack of strong, blinded supporting trials has also led to it being described as both “near perfect” and as there being “insufficient justification” for its use at all, in competing reviews.(5,6)
Hemodynamically Stable Patients: When time is not a constraint of assessment, the focus of initial evaluation is on the ability to rule out any pathological changes. The data studying the FAST has not shown it capable of consistently doing this, with reported sensitivities of detecting injury ranging from 43 – 98%.(7,8) Possible explanation for this heterogeneity could be explained by limitations including:
Operator Dependent: twice as sensitive when used by an “expert” (9)
Patient Dependent: limited by obesity, bowel gas (10)
Average detectable fluid level in Morrison’s pouch: between 440 – 620 mL (11,12)
Inability to differentiate between urine and blood: decreased detection rate (55% sensitivity) of urological injury (13)
Hemodynamically Unstable Patients:
When time and patient mobility are restricting factors in initial evaluation, the FAST exam has the potential to facilitate rapid diagnosis. FAST has consistently demonstrated high specificity in determining injury after BAT (14) - meaning that a positive exam virtually always represents true hemoperitoneum. A negative exam, however, has little meaning – in fact, patients with more severe injury after BAT may even have a lower detection rate than those with less severe injury.(15) Data regarding the value of FAST in trauma assessment is mixed:
Mortality and laparotomy rates: no difference when ultrasound was used(6)
Use of CT: reduced by 30% when ultrasound was used(16)
To some the value of this reduction in CT have been seen as beneficial in reducing patient exposure to excessive radiation and cost.(17) Others who argue against the use of the FAST exam in BAT disagree, stating that a reduction in CT is potentially harmful to patients by increasing the risk of missing significant injury. This belief partly stems from data suggesting that whole body CT may be safe and beneficial in unstable patients.(18)
New technology such as the Butterfly iQ – a single probe chip-based ultrasound device that attaches to the IPhone – is likely to open the door to ultrasound, to more non-physician healthcare workers as well as health curious lay people.(19,20) This makes it timely for providers to critically review and assess the role of the FAST exam at their institutions. Even with increased mobile availability, the limitations of ultrasound suggest that it will continue to face pressure to justify its role in BAT assessment.
In the hemodynamically stable patient there is insufficient evidence to support the FAST exam. At best, it represents an additional cost of time and resources. At worst, a false negative exam may inappropriately reassure the health care team, preventing further imaging and resulting in missed injury.
In the hemodynamically unstable patient, a positive FAST exam may reduce unnecessary CT imaging. A negative exam should not be used to rule out injury.
1. Von Kuenssberg Jehle, D., Stiller, G. & Wagner, D. Sensitivity in detecting free intraperitoneal fluid with the pelvic views of the FAST exam. Am. J. Emerg. Med. 21, 476–8 (2003).
2. Meet Butterfly iQ - Whole body imaging, under $2k. Available at: https://www.butterflynetwork.com/. (Accessed: 20th June 2018)
3. Rose, J. S. Ultrasonography and Outcomes Research: One Small Step for Mankind or Another Drop in the Bucket? Ann. Emerg. Med. 48, 237–239 (2006).
4. Bloom, B. A. & Gibbons, R. C. Trauma, Focused Assessment with Sonography for Trauma (FAST). StatPearls (StatPearls Publishing, 2018).
5. Melniker, L. A. The value of focused assessment with sonography in trauma examination for the need for operative intervention in blunt torso trauma: a rebuttal to ‘emergency ultrasound-based algorithms for diagnosing blunt abdominal trauma (review)’, from the Cochrane Collaboration. Crit. Ultrasound J. 1, 73–84 (2009).
6. Stengel, D., Rademacher, G., Ekkernkamp, A., Güthoff, C. & Mutze, S. Emergency ultrasound-based algorithms for diagnosing blunt abdominal trauma. Cochrane Database Syst. Rev. (2015). doi:10.1002/14651858.CD004446.pub4
7. Richards, J. R. & McGahan, J. P. Focused Assessment with Sonography in Trauma (FAST) in 2017: What Radiologists Can Learn. Radiology 283, 30–48 (2017).
8. Natarajan, B. et al. FAST scan: is it worth doing in hemodynamically stable blunt trauma patients? Surgery 148, 695-700–1 (2010).
9. Sato, M. & Yoshii, H. Reevaluation of Ultrasonography for Solid-Organ Injury in Blunt Abdominal Trauma. J. Ultrasound Med. 23, 1583–1596 (2004).
10. Kornezos, I. et al. Findings and limitations of focused ultrasound as a possible screening test in stable adult patients with blunt abdominal trauma: a Greek study. Eur. Radiol. 20, 234–238 (2010).
11. Branney, S. W. et al. Quantitative sensitivity of ultrasound in detecting free intraperitoneal fluid. J. Trauma 39, 375–80 (1995).
12. Abrams, B. J., Sukumvanich, P., Seibel, R., Moscati, R. & Jehle, D. Ultrasound for the detection of intraperitoneal fluid: The role of Trendelenburg positioning. Am. J. Emerg. Med. 17, 117–120 (1999).
13. McGahan, P. J., Richards, J. R., Bair, A. E. & Rose, J. S. Ultrasound detection of blunt urological trauma: a 6-year study. Injury 36, 762–70 (2005).
14. Savatmongkorngul, S., Wongwaisayawan, S. & Kaewlai, R. Focused assessment with sonography for trauma: current perspectives. Open Access Emerg. Med. 9, 57–62 (2017).
15. Becker, A., Lin, G., McKenney, M. G., Marttos, A. & Schulman, C. I. Is the FAST exam reliable in severely injured patients? Injury 41, 479–83 (2010).
16. Rose, J. S. et al. Does the presence of ultrasound really affect computed tomographic scan use? A prospective randomized trial of ultrasound in trauma. J. Trauma 51, 545–50 (2001).
17. Arrillaga, A., Graham, R., York, J. W. & Miller, R. S. Increased efficiency and cost-effectiveness in the evaluation of the blunt abdominal trauma patient with the use of ultrasound. Am. Surg. 65, 31–5 (1999).
18. Huber-Wagner, S. et al. Whole-body CT in haemodynamically unstable severely injured patients--a retrospective, multicentre study. PLoS One 8, e68880 (2013).
19. Stolz, L. A. et al. Point-of-care ultrasound education for non-physician clinicians in a resource-limited emergency department. Trop. Med. Int. Heal. 20, 1067–1072 (2015).
20. Bowra, J., Forrest-Horder, S., Caldwell, E., Cox, M. & D’Amours, S. K. Validation of nurse-performed FAST ultrasound. Injury 41, 484–487 (2010).