Around 4.4 million deaths are annually recorded in India due to trauma or accidents. Traumatic brain injury (TBI) and hemorrhage are accounted for > 91% of all deaths that occur. Proper initial assessment and a post-trauma patient-centric plan should be adopted to prevent such deaths. Focused Assessment with Sonography in Trauma (FAST) is an ultrasound scan performed in the emergency department to assess patients admitted with trauma.
Image Credits: Bromley Emergency Courses
The primary goal of FAST is to identify internal bleeding in the heart (hemopericardium), chest (hemothorax), and abdomen (hemoperitoneum) due to trauma, and a detailed evaluation of the heart, lungs, or other abdominal organs is not possible. The ultrasound is done by trained emergency physicians to identify the presence of free fluid, which may represent hemoperitoneum or internal bleed.
What is FAST?
Focused Assessment with Sonography in Trauma (FAST) is an emergency ultrasound protocol developed to assess hemoperitoneum (blood accumulation between the abdominal wall and organs) and hemopericardium (blood accumulation in the heart cavity) in post-trauma patients. Experienced providers perform the FAST exam in less than 5 minutes which helps reduce the time for surgical intervention, patient hospitalization, and rates of CT and DPL (diagnostic peritoneal lavage). As a part of the Advanced Trauma Life Support (ATLS) algorithm, more trauma centers are incorporating the FAST protocol. The implementation of point-of-care ultrasound that uses no radiation has significantly impacted the evaluation and treatment of patients.
Since the adoption of FAST, trauma patients with multiple injuries are increasingly managed by non-surgical means if they are hemodynamically stable, and the presence of intraperitoneal fluid does not influence the treatment.
How does FAST help?
FAST is indicated in the evaluation of the unstable, multi-trauma patient with an unidentified cause of hypotension. In a scenario where CT is contraindicated, FAST provides a rapid screening test without moving the patient from the resuscitation area. FAST being a small portable and handheld machine improves its accessibility and its benefits are frequently recognized as an established and essential part of the emergency department services. The most useful application is to identify intra-abdominal hemorrhage in unstable patients, especially in the presence of other bleeding sources (i.e., pelvic fracture). Furthermore, it is non-invasive, has no radiation or contrast agents use, and is inexpensive.
How does FAST work?
Bedside sonographic assessment of the post-trauma victim is considered a standard of care and can be used as an adjunct. A low-frequency transducer or abdominal probe (3.5 MHz to 5 MHz) is used for the FAST exam to eliminate delays when switching between transducers.
Quadrants of abdomen assessed in FAST:
The abdomen is theoretically divided into 9 quadrants by clinicians which helps to identify the affected organs depending on which quadrant is involved.
For quick diagnosis, 4 Quadrants are examined in FAST
Epigastric: To look for bleeding around the heart
Right Hypochondrium: To look for liver injury
Left Hypochobdirum: To look for Spleen injury
Pelvis: To look for bleed in the abdomen
Image source: SONOSIF
How to proceed for FAST?
Let the patient rest in a supine position, at the level of the examiner’s waist. Initiate the scans from the patient’s right. This will give more grip to the provider’s right hand to manipulate the probe while the left hand is used to adjust gain and depth for optimizing image acquisition. For transverse images, the probe is positioned with an indicator toward the patient’s right.
Image source: Nemours Kids Health
Perform the pelvic examination before inserting the Foley catheter or after instilling 200 - 250 mL of saline to increase sensitivity and accuracy. Check if the patient is placed in the left or right lateral decubitus position as smaller amounts of fluid may be detected.
Interpretation of FAST
A black stripe on the ultrasound indicates free fluid and denotes a positive FAST. A positive FAST points out abdominal exploration in hemodynamically unstable patients. Identification of free fluid indicates a potential injury and necessitates further evaluation.
Limitations to FAST
The management of post-trauma patients is usually under an inter-professional team including trauma nurses.
Ultrasound image acquisition and interpretation are limited by the provider’s experience; the patient’s body habitus; and the presence of bowel gas, the presence of air, or gas in the abdominal cavity.
Prior knowledge and training required to strictly adhere to the protocol will maximize the probability of detecting free fluid, hemorrhage, and other abnormal fluids (urine and bile).
Not possible to detect every abnormality or injury
While the sensitivity for detecting >250 mL of fluid is excellent, the source of the bleeding or severity of the injury is not reliably determined.
Preexisting conditions such as ascites and pericarditis/effusion may render the assessment and may be ineffective.
Summary
All trauma patients who have injuries that cannot be cleared by physical examination should have an initial FAST. In unstable, multi-trauma patients, FAST should be used to rule out hemoperitoneum. FAST may also help direct operative strategy to the correct body cavity in patients with penetrating trauma. A secondary FAST should be performed on hemodynamically unstable patients with an initial negative FAST and ongoing instability despite adequate resuscitation. Continuous developments in multi-detector CT and the contrast-enhanced ultrasound have broadened the management options for post-trauma patients with a faster diagnostic pathway than was previously possible.
References
Bickle, I., Botz, B. Focused Assessment with Sonography for Trauma (FAST) scan. Reference article, Radiopaedia.org DOI: 10.53347/rID-26339
Timothy Jang, MD. Focused Assessment with Sonography in Trauma (FAST). Medscape. [Link]
Jane Smith, Focused assessment with sonography in trauma (FAST): should its role be reconsidered, Postgraduate Medical Journal, 2010, DOI: 10.1136/pgmj.2008.076711
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