Jul 29, 2022, 01:00 AM by Austin Sargent, MD, Stephen C. Haskins, MD, and Melissa Byrne, DO, MPH

Cite as: Sargent A, Haskins SC, Byrne M. POCUS spotlight: focused assessment with sonography in trauma (FAST) exam. ASRA Pain Medicine News 2022;47. https://doi.org/10.52211/asra080122.037 

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Across surgical and emergency medicine literature, the focused assessment with sonography in trauma (FAST) exam has been well-established and extensively studied. Since its description by trauma surgeon Grace Rozycki more than 25 years ago, the FAST exam remains an integral component of advanced trauma life support and the standard of care in major trauma centers.^1-7 However, as point-of-care ultrasound (POCUS) has become more commonly practiced in anesthesiology, the FAST exam also is emerging as a meaningful tool in the perioperative setting.

 

 

The Indication, Acquisition, Interpretation, and Medical Decision-Making (I-AIM) framework was first described by Bahner et al. in 2012 as a novel teaching model to learn the FAST exam. Since its description, the I-AIM framework remains a standardized and invaluable tool for learning new ultrasound skills.⁸

I - Indication

Perioperative FAST exam adoption is increasing across the globe, allowing for the evaluation of free fluid within the peritoneal and pericardial cavities. As a result, it has become an essential diagnostic tool in the perioperative setting and a monitoring tool for serial evaluation.

Three clinical questions should be addressed during a FAST performance:

1. Is there free fluid in the pericardial cavity?
2. Is there free fluid in the peritoneal cavity?
3. Is there free fluid in the thoracic cavity?

A list of indications for perioperative FAST exam performance is provided in Figure 1. Preoperatively, the FAST exam may prove beneficial in evaluating patients with long-standing heart, renal, or liver failure requiring information to guide further clinical management. Intraoperatively, the critically ill or trauma patient presenting for emergency surgery may warrant FAST exam performance. The FAST exam also can evaluate ongoing hypotension or diagnose intra-abdominal fluid extravasation following hip arthroscopy, causing increased postoperative pain.⁹

 

As a Diagnostic Tool	As a Monitoring Tool
Hemodynamic instability (in the OR or PACU) Evaluation of the initial trauma patient Identification of pericardial effusion yielding tamponade physiology Identification of a pleural effusion Narrowing the DDx of a critically ill patient Evaluation of acute, chronic or decompensated heart, renal or liver failure Nausea or abdominal pain following hip arthroscopy	Serial evaluation of hemodynamic instability (in the OR or PACU) Serial evaluation of trauma patients

Figure 1. Clinical Indications for FAST Exam Performance in the Perioperative Setting

Abbreviations: OR – operating room; PACU – Post-Anesthesia Care Unit; DDx – differential diagnosis; adapted from Manson et al.¹⁰

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A – Acquisition

Traditionally, the low-frequency (2-5 MHz) curvilinear transducer is used given its wide field of view and depth of penetration to assess for free fluid in the abdomen or thorax. A phased array probe is also a viable alternative.

For abdominal ultrasound imaging, aim the probe orientation marker cephalad for the right upper quadrant (RUQ), left upper quadrant (LUQ), and longitudinal pelvic views. Aim the probe orientation marker to the patient’s right side for transverse pelvic and cardiac views. The on-screen orientation indicator should be located on the left side of the screen.

To scan, place the patient supine with arms abducted or raised over the head. As the FAST exam seeks to detect free fluid, optimizing the positioning can improve sensitivity; note that Trendelenburg positioning increases the sensitivity of the RUQ view while reverse Trendelenburg increases the sensitivity of the pelvic views (Table 1).

 

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Table 1. FAST Exam Views and Evaluation

 

View	Evaluate
Right upper quadrant	Morison’s pouch – a potential space between the liver and right kidney Caudal edge of the liver (liver tip) Space between the liver and the diaphragm (sub-diaphragmatic space)
Left upper quadrant	Perisplenic space, including the space between the spleen and the diaphragm as well as the splenorenal recess – a potential space between the spleen and left kidney
Pelvic (transverse & longitudinal)	Rectovesicular space (male) Vesicouterine pouch and rectouterine pouch (Pouch of Douglas) (female)
Subcostal cardiac view	Pericardial space

 

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I - Interpretation

 

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Figure 2. FAST images and potential spaces for expected free fluid (red arrow). Potential sites for pleural fluid noted by star. Black dot on ultrasound denotes the orientation marker (OM).

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Figure 2 demonstrates imaging obtained for each of the FAST exam views. The red arrow in each image highlights potential spaces to assess for free fluid.

Right Upper Quadrant

Traditional FAST exam performance starts with the RUQ view: the liver, diaphragm, and right kidney are visualized with free fluid in the hepatorenal recess (ie, Morison’s pouch). This view is considered “high-yield” and the most sensitive view for detecting free fluid as it is the most-dependent point of the upper peritoneum when supine.

Left Upper Quadrant

By contrast, the LUQ view is often much more challenging to obtain and yields images of the spleen, left kidney, and diaphragm with fluid expected in the perisplenic space (including the splenorenal recess). Posterior placement of the ultrasound probe as well as fanning anteriorly and posteriorly is imperative to obtain this view accurately.

Cardiac View

Pericardial effusions can be identified using the subcostal or subxiphoid cardiac view. This image is improved with patient inspiration, which increases venous return and contracts the diaphragm to move the heart caudad towards the ultrasound probe.

Pelvic Views

The pelvic views allow for visualization of fluid accumulation in the most dependent part of the peritoneum. For males, fluid is found in the rectovesicular space posterior to the bladder wall. The rectouterine pouch, or pouch of Douglas, is the most dependent location in females; however, fluid can also be seen in the vesicouterine pouch posterior to the bladder. The suprapubic views require an image in both transverse and longitudinal planes. A full bladder can improve acoustic windows significantly, while an empty bladder can result in false negatives. Fluids can be administered when necessary to aid visualization. Although not discussed in this article, bladder catheter placement also can be assessed using the suprapubic view.

 

M – Medical Decision-Making

FAST Management Algorithm

The following figure provides an algorithm for managing patients in whom the FAST exam may be warranted. The greatest concern is for the hemodynamically unstable patient with positive FAST exam findings that likely warrants urgent or emergent surgical exploration. Further imaging, serial FAST examinations, or observation may be reasonable for patients as other causes of hemodynamic instability are investigated.

 

 

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Figure 3. FAST management algorithm

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Pitfalls and Limitations

It is imperative to understand that the FAST exam has excellent specificity (as high as 99%) but only moderate sensitivity (60-80%), and, therefore, the FAST exam cannot be used for ruling out free fluid.^11-14 Therefore, in a clinically unstable patient, a positive FAST exam reliably predicts the need for an exploratory laparotomy; however, the FAST exam has been demonstrated to be less capable of ruling out free fluid in the abdomen.¹⁵ Therefore, the FAST exam has been deemed the best initial imaging modality in trauma, recognizing that patient evaluation, repeat ultrasound, or CT imaging are often necessary when a FAST exam is a negative and clinical suspicion for free fluid remains.

Figure 4 lists several well-documented normal findings that novice FAST exam learners can mistake as free fluid.

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• Pleural effusions
• Pre-existing peritoneal fluid
  • Ascites
  • Peritoneal dialysate
  • Ventriculoperitoneal shunt overflow
• Perinephric or pericardial fat
• Edge artifact (interface of liver and kidney)
• A full stomach – gastric contents can mimic a perisplenic fluid collection
• Massive volume resuscitation --> intravascular to intraperitoneal fluid transudation
• Injury-related free fluid (not hemoperitoneum)
  • Urine
  • Bile
  • Bowel contents
• Ovarian cyst rupture or polycystic ovarian disease
• Seminal vesicles
• Atypical vasculature
• Gall bladder, hepatic veins, or biliary ducts

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Figure 4. Common false-positive findings with the FAST exam

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eFAST Exam

The eFAST, or extended Focused Assessment with Sonography in Trauma, adds bilateral pleural views through the perihepatic and perisplenic windows to the standard FAST exam. The addition of the pleural views allows for the evaluation of potential pneumothorax, pleural effusion, and diaphragm dysfunction.

Special Populations

Pregnancy

Abdominal and pelvic ultrasound may be helpful in the evaluation of hemodynamically unstable pregnant patients when there is a high index of suspicion for pathologies involving peritoneal free fluid, such as uterine rupture. However, this is not well-validated, and there is an increased risk of both false-positive and false-negative results given the wide variability of normal abdominal ultrasound findings in this patient population. Therefore, abdominal ultrasound of the parturient should only be performed by anesthesiologists in emergencies when an obstetrician trained in abdominal ultrasound is unavailable.

Pediatrics

The use of abdominal ultrasound in pediatric trauma patients has very low sensitivity and specificity for the detection of free fluid and, as such, is not widely used. Therefore, the pediatric FAST exam should only be performed by expert practitioners.¹⁵

Intra-abdominal Fluid Extravasation (IAFE) After Hip Arthroscopy

The FAST exam can be a useful diagnostic tool in hip arthroscopy patients with symptoms concerning for peritoneal fluid. The incidence of IAFE may be as high as 16%.⁹ While usually presenting as postoperative abdominal pain and nausea that responds to conservative treatment, this is a potentially devastating complication that can lead to abdominal compartment syndrome necessitating transfer to a higher acuity setting, inpatient admission, or, in severe cases, surgical decompression.

Clinical Pearls

The following suggestions can improve image acquisition.

• Depth and gain may need to be adjusted when transitioning between views.
• Position can increase the sensitivity of the exam, particularly with Trendelenburg aiding the RUQ and LUQ views and reverse Trendelenburg improving the pelvic views.
• Avoid bladder catheterization before obtaining the pelvic views when clinically appropriate.
• If a single view is challenging (eg, LUQ view), move on to another location.
• Fluid accumulation is a dynamic process; serial examinations can decrease the risk of false-negative exams.

Conclusion

This “POCUS Spotlight” article describes how to perform the FAST exam using the I-AIM framework. The FAST exam is becoming an essential skill in the perioperative setting to evaluate and guide management in patients with hemodynamic instability, trauma, or significant pain following hip arthroscopy. Furthermore, it is imperative to recognize the exam’s strengths and weaknesses, highlighting the importance of serial assessment and integration with clinical context to provide appropriate care to patients.^15,16

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Austin Sargent, MD, is a clinical instructor in the department of Anesthesiology at Michigan Medicine in Ann Arbor.

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Stephen C. Haskins, MD, is an associate attending anesthesiologist in the department of Anesthesiology, Critical Care and Pain Management at the Hospital for Special Surgery and a clinical associate professor in the department of Anesthesiology at Weill-Cornell Medical College, in New York, NY.

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Melissa Byrne, DO, MPH, is a clinical assistant professor in the department of Anesthesiology at Michigan Medicine in Ann Arbor.

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References

1. Rozycki GS, Ochsner MG, Feliciano DV, et al. Early detection of hemoperitoneum by ultrasound examination of the right upper quadrant: a multicenter study. J Trauma 1998;45:878-83. https://doi.org/10.1097/00005373-199811000-00006
2. Plummer D, Brunette D, Asinger R, et al. Emergency department echocardiography improves outcome in penetrating cardiac injury. Ann Emerg Med 1992;21:709-12. https://doi.org/10.1016/s0196-0644(05)82784-2
3. Rozycki GS, Ochsner MG, Jaffin JH, et al. Prospective evaluation of surgeons’ use of ultrasound in the evaluation of trauma patients. J Trauma 1993;34:516-27. https://doi.org/10.1097/00005373-199304000-00008
4. Rozycki GS, Ochsner MG, Schmidt JA, et al. A prospective study of surgeon-performed ultrasound as the primary adjuvant modality for injured patient assessment. J Trauma 1995;39:492-500. https://doi.org/10.1097/00005373-199509000-00016
5. Rozycki GS, Ballard RB, Feliciano DV, et al. Surgeon-performed ultrasound for the assessment of truncal injuries: lessons learned from 1540 patients. Ann Surg 1998;228:557-67:10. https://doi.org/10.1097/00000658-199810000-00012
6. Rozycki GS, Feliciano DV, Schmidt JA, et al. The role of surgeon-performed ultrasound in patients with possible cardiac wounds. Ann Surg 1996;223:737-46. https://doi.org/10.1097/00000658-199606000-00012 
7. Rozycki GS. Surgeon-performed ultrasound: its use in clinical practice. Ann Surg 1998;228:16-28. https://doi.org/10.1097/00000658-199807000-00004
8. Miller MT, Pasquale MD, Bromberg WJ, et al. Not so fast. J Trauma 2003;54:52-60. http://dx.doi.org/10.1097/00005373-200301000-00007
9. Bahner DP, Hughes D, Royall NA. I-AIM: a novel model for teaching and performing focused sonography. J Ultrasound Med 2012;31:295-300. https://doi.org/10.7863/jum.2012.31.2.295
10. Haskins SC, Desai NA, Fields KG, et al. Diagnosis of intra-abdominal fluid extravasation after hip arthroscopy with point-of-care ultrasonography can identify patients at an increased risk for postoperative pain. Anesth Analg 2017;124:791-9. https://doi.org/10.1213/ANE.0000000000001435
11. Manson WC, Kirskey M, Boublik J, et al. Focused assessment with sonography in trauma (FAST) for the regional anesthesiologist and pain specialist. Reg Anesth Pain Med 2019;44:540-548. https://doi.org/10.1136/rapm-2018-100312
12. Boulanger BR, McLellan BA, Brenneman FD, et al. Prospective evidence of the superiority of a sonography-based algorithm in the assessment of blunt abdominal injury. J Trauma 1999;47:632-7. https://doi.org/10.1097/00005373-199910000-00005
13. Brenchley J, Walker A, Sloan JP, et al. Evaluation of focused assessment with sonography in trauma (fast) by UK emergency physicians. Emerg Med J 2006;23:446-8. https://doi.org/10.1136/emj.2005.026864
14. Gaarder C, Kroepelien CF, Loekke R, et al. Ultrasound performed by radiologists - confirming the truth about FAST in trauma. J Trauma 2009;67:323-9. https://doi.org/10.1097/TA.0b013e3181a4ed27
15. Tayal VS, Nielsen A, Jones AE, et al. Accuracy of trauma ultrasound in major pelvic injury. J Trauma 2006;61:1453-7). https://doi.org/10.1097/01.ta.0000197434.58433.88  
16. Miller MT, Pasquale MD, Bromberg WJ, et al. Not so fast. J Trauma 2003;54:52-60. https://doi.org/10.1097/00005373-200301000-00007  
17. Holmes JF, Kelley KM, Wootton-Gorges SL, et al. Effect of abdominal ultrasound on clinical care, outcomes, and resource use among children with blunt torso trauma: a randomized clinical trial. JAMA 2017;317(22):2290-6. https://doi.org/10.1001/jama.2017.6322