Focused Assessment with Sonography for Trauma (FAST)

Focused assessment with sonography for trauma is a point-of-care ultrasound examination protocol for the abdominal and thoracic cavities performed in the emergency room as part of the secondary survey in advanced trauma life support. The main goal of the FAST exam is to identify free intraperitoneal fluid (blood) and pericardial effusion from trauma. As FAST requires only an ultrasound machine at the bedside and an experienced sonographer, it is widely available, quicker, and less invasive than other image modalities. Focused assessment with sonography for trauma has largely replaced diagnostic peritoneal lavage.

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Introduction

Definition

Focused assessment with sonography for trauma (FAST) is a point-of-care ultrasound (POCUS) examination protocol of the abdominal and thoracic cavities performed with the goal of identifying free intraperitoneal fluid and/or pericardial effusion.

Background

  • History and physical exams often lack the necessary sensitivity and specificity to diagnose acute traumatic pathology of the abdomen accurately.
  • Free fluid within the peritoneal cavity settles into dependent areas within the peritoneum when the individual is supine and can be detected using ultrasound imaging.
  • Sensitivity of 42% and specificity ≥ 98% for free peritoneal fluid
  • 100 mL of free fluid can be seen, though > 500 mL is needed for the common user.
  • Pulmonary ultrasound (in the extended FAST (E-FAST)) has a sensitivity of 95%, specificity of 91%, and a negative predictive value of 100%.
  • Diagnostic peritoneal lavage (DPL) was previously used as the standard test to help physicians decide which individuals with trauma needed an emergent exploratory laparotomy.
  • FAST has replaced DPL and is often beneficial over CT for many reasons.
Table: Advantages and disadvantages of the FAST exam
AdvantagesDisadvantages
  • Can be performed on any individual
  • Early operative determination
  • ↓ Time to diagnosis for acute abdominal injury
  • Accurately diagnoses hemoperitoneum
  • Noninvasive
  • Integrated into the primary or secondary survey
  • Can be performed quickly
  • Available at the bedside
  • Ease of use for serial examinations
  • Safe for use in pregnant individuals and children
  • ↓ Radiation than CT
  • Leads to ↓ DPL
  • Can lead to ↓ CT scans
  • Operator-dependent method
  • Only evaluates for the presence of blood within the peritoneal cavity and not its source
  • Distortion of images due to obesity, bowel gas, and subcutaneous air
  • Can miss diaphragm, bowel, and pancreatic injuries
  • Does not assess retroperitoneal structures
  • Does not visualize extraluminal air
DPL: diagnostic peritoneal lavage

Indications

  • Blunt abdominal trauma
  • Penetrating abdominal trauma without other indications for immediate laparotomy

Contraindications

  • No absolute contraindications 
  • Should not delay resuscitation efforts

Findings

  • + FAST will have 1 of the following:
    • Anechoic area (blood) within the pericardial space
    • Anechoic area (blood) between the liver and kidney
    • Anechoic area (blood) between the diaphragm and spleen
    • Anechoic area (blood) between the spleen and kidney
    • Anechoic area (blood) between superior and posterior to the posterior wall of the bladder
  • + E-FAST can have 1 of the added findings:
    • Anechoic area (blood) above the diaphragm between the diaphragm and lung
    • Absent lung sliding
  • – FAST should be repeated if there is a change in the condition of the individual.
Decision making pathway for use of the FAST

Decision-making pathway for use of the FAST exam in a trauma setting

Image by Lecturio. License: CC BY-NC-SA 4.0

Basics of Ultrasonography

Imaging

  • Sonography is an imaging technique based on ultrasound (high-frequency, inaudible sound waves). 
  • Sound waves having a frequency of 2–18 MHz are used in medical imaging.
  • The equipment utilizes a transducer acting as the emitter and receptor of sound waves, and a central computer processes the electrical signals to generate the image.

Terminology

  • Hyperechoic (e.g., surface of bone, urinary tract calculi, fat-containing lesions): a structure that produces high-amplitude echo (lighter grays and white)
  • Hypoechoic (e.g., abscesses without gas, solid tumors without calcifications or fat): a structure that produces low-amplitude echo (darker grays)
  • Anechoic (e.g., simple cysts): a structure that produces no echo at all (looks completely black)
  • Isoechoic: a structure that produces an echo with an amplitude very similar to that of its environment, which is very difficult to distinguish
Imaging concepts of ultrasound

Imaging concepts of ultrasound

Image by Lecturio. License: CC BY-NC-SA 4.0

Probes

  • Curvilinear or convex probe:
    • “Abdominal probe”
    • 2–5 MHz (low frequency)
    • High penetration
    • Big footprint
    • Bad for movement
    • Used for most internal organs, the aorta, abdomen, lung, pleura, gynecology, FAST, E-FAST
  • Phased array probe:
    • “Cardiac probe”
    • 1–5 MHz (low frequency)
    • High penetration
    • Small footprint
    • Great for movement
    • Uses: cardiac, pleura, FAST, E-FAST
  • Linear probe:
    • “Vascular probe”
    • 6–13 MHz probe (high frequency)
    • Low penetration
    • Big footprint
    • Uses: vascular, pleural (in E-FAST), optic nerve, venous access

Exam

Select probe:

  • Curvilinear probe is ideal for all parts of FAST.
  • Cardiac probe can be used for cardiac window.
  • If E-FAST is performed, linear probe is used for pleura.

Location:

  • Sequence traditionally varies based on the mechanism.
  • Blunt trauma starts with RUQ view.
  • Most sensitive view for free peritoneal fluid
  • Penetrating trauma starts with cardiac view.
  • Rule out pericardial effusion and (impending) tamponade.
  • Include cardiac, RUQ, pelvic, LUQ, and pulmonary views.

RUQ view (Morison’s pouch or hepatorenal fossa)

  • Probe placement:
    • Coronal view over the right flank
    • Right 8th to 11th ribs on the mid- or anterior axillary line
    • Probe must be held parallel to avoid rib shadows.
  • Landmarks:
    • Visualize the hepatorenal interface.
    • Space between the right lobe of the liver and the right kidney = Morison’s pouch
  • Scan anterior to posterior and the superior and inferior poles of the kidney.
  • Liver tip is a common location for missed free fluid.
  • Intraperitoneal fluid + hemodynamic instability → exploratory laparotomy
  • Anechoic image above the diaphragm = pleural effusion

Cardiac view (subxiphoid view)

  • Probe placement:
    • Subxiphoid process: The right and left ventricles should be visualized in a long axis.
    • Parasternal long, if abdomen is distended or subxiphoid view difficult to obtain
  • Landmarks:
    • Visualize the heart and pericardium.
    • Scan anterior to posterior through the heart.
    • Note: An anterior fat pad can give the impression of pericardial effusion but should not be seen on posterior views.
    • An anechoic (black) stripe around the ventricles indicates pericardial effusion. 
Ultrasound after chest injury showing pericardial tamponade

Resuscitative ultrasound image following a penetrating chest injury illustrating the presence of a pericardial tamponade from a hemopericardium (*):
Arrowheads illustrate the wall of the right ventricle.
RA: right atrium
LA: left atrium
LV: left ventricle

Image: “Ultrasound after chest injury showing pericardial tamponade” by Regional Trauma Services, Calgary Heath Region and Foothills Medical Centre, Calgary, Alberta, Canada. License: CC BY 2.0

Left upper quadrant view (splenorenal view or splenorenal fossa)

  • Probe placement:
    • Similar to that for Morison’s pouch on the contralateral (left) side
    • Coronal view over the left flank
  • Landmarks:
    • Appears similar to Morison’s pouch view
    • Identify the space between the spleen and diaphragm and the splenorenal interface.
  • Fluid collects cephalad to the spleen, beneath the diaphragm.
  • Anechoic image above the diaphragm = pleural effusion

Bladder view (pelvic)

  • Probe placement:
    • On the midline, immediately superior to the pubic bone
    • Sagittal view, just superior to the pubic symphysis
  • Landmarks:
    • Identify the bladder.
    • Scan medial to lateral to identify the fluid posterior and superior to the bladder.
    • This view will be limited if the bladder is empty.
    • Free fluid appears as anechoic, posterior to the bladder.
    • In women, fluid collects in the space called the pouch of Douglas (rectouterine pouch).
Ultrasound of the bladder

Normal ultrasound scan of the bladder:
Blood/fluid can be seen above or below the bladder.

Image by Lecturio.

Extended FAST pulmonary view

  • Probe placement:
    • Coronal view over the right and left diaphragm (curvilinear probe)
    • Sagittal view over the midclavicular line between the 2nd and 3rd intercostal space (linear probe)
  • Landmarks:
    • Identify the interface between the diaphragm and lung on the right and left (curvilinear probe).
    • Identify lung sliding between 2 ribs over the anterior thorax (linear probe).
  • Visualization of both hemithorax is included in the protocol to assess the presence of:
    • Hemothorax
    • Pneumothorax
Placement of linear ultrasound

Placement of linear ultrasound probe for view of lung pleura and lung sliding in the evaluation for pneumothorax

Image by Lecturio.

Clinical Relevance

  • Sonography: an imaging technique based on ultrasound (high-frequency, inaudible sound waves). Sound waves having a frequency of 2–18 MHz are used in medical imaging. The equipment utilizes a transducer acting as the emitter and receptor of sound waves, and a central computer processes the electrical signals to generate the image. The general advantages of this type of imaging are its low cost, availability, and safety.
  • Hemopericardium (tamponade): the accumulation of excess fluid in the pericardial space around the heart, which increases pressure, restricts cardiac filling, and results in decreased cardiac output. Symptoms include dyspnea, hypotension, muffled heart sounds, jugular venous distension, and pulsus paradoxus. Diagnosis is confirmed with echocardiography. Management is emergent pericardiocentesis or pericardiotomy.
  • Hemothorax: collection of blood in the pleural cavity that most commonly occurs due to damage to the intercostal arteries. Affected individuals present with shortness of breath, chest pain, hypotension, tachycardia, decreased lung sounds, and dullness on percussion of the chest. Diagnosis is by chest X-ray. Management is with tube thoracostomy drainage, video-assisted thoracoscopic surgery (VATS), or thoracotomy.
  • Pneumothorax: a life-threatening condition in which air collects in the pleural space, leading to lung collapse. Individuals present with chest pain, dyspnea, and diminished breath sounds. A diagnosis is made with imaging, though tension pneumothorax is a clinical diagnosis. Management is based on the size and stability of the affected individual and can include needle decompression and chest tube (thoracostomy) placement. 
  • Pleural effusion: fluid accumulation between the layers of the parietal and visceral pleura. Common causes of pleural effusion include infection, malignancy, autoimmune disorders, or volume overload. Clinical manifestations include chest pain, cough, and dyspnea. Management is dependent on the underlying condition and whether the effusion is causing respiratory distress.

References

  1. Roberts, J., Custalow, C., Thomsen, T. (2019). Roberts and Hedges’ Clinical Procedures in Emergency Medicine and Acute Care. Philadelphia, PA: Elsevier.
  2. Bloom, B.A., Gibbons, R.C. (2021). Focused assessment with sonography for trauma. StatPearls. Treasure Island (FL): StatPearls Publishing. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK470479/
  3. American College of Surgeons. (2018). Advanced trauma life support: Student course manual. Chicago, IL: American College of Surgeons.
  4. Natarajan, B., Gupta, P.K., Cemaj S, et al. (2010). FAST scan: Is it worth doing in hemodynamically stable blunt trauma patients? Surgery. 148, 695-700.
  5. Miller, M.T., Pasquale, M.D., Bromberg, W.J., et al. (2003). Not so FAST. J Trauma. 54, 52–59.
  6. Von Kuenssberg, J.D., Stiller, G., Wagner, D. (2003). Sensitivity in detecting free intraperitoneal fluid with the pelvic views of the FAST exam. Am J Emerg Med. 21, 476-478.
  7. McKenney, K.L., McKenney, M.G., Cohn, S.M., et al. (2001). Hemoperitoneum score helps determine need for therapeutic laparotomy. J Trauma. 50, 650–654.
  8. Lichtenstein, D.A., Menu, Y. (1995). A bedside ultrasound sign ruling out pneumothorax in the critically ill. Lung sliding. Chest. 108, 1345–1348.
  9. Chen, M.M., Whitlow, C.T. (2011). Chapter 1. scope of diagnostic imaging. Chen, M.M., & Pope, T.L., & Ott D.J.(Eds.). Basic Radiology, 2e. McGraw-Hill. https://accessmedicine-mhmedical-com.ezproxy.unbosque.edu.co/content.aspx?bookid=360&sectionid=39669007
  10. Zaer, N.F., Amini B, Elsayes, K.M. (2014). Overview of diagnostic modalities and contrast agents. Elsayes, K.M., Oldham, S.A.(Eds.). Introduction to Diagnostic Radiology. McGraw-Hill. https://accessmedicine-mhmedical-com.ezproxy.unbosque.edu.co/content.aspx?bookid=1562&sectionid=95875179

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