Focused Assessment With Sonography in Trauma (FAST)

Updated: Nov 07, 2022
  • Author: Timothy Jang, MD; Chief Editor: Mahan Mathur, MD  more...
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Practice Essentials

Focused Assessment With Sonography in Trauma (FAST) is an ultrasound protocol developed to assess for hemoperitoneum and hemopericardium. The sensitivity of FAST has been measured between 85 and 96%, and specificity greater than 98%. In hypotensive trauma patients, sensitivity has approached 100%. FAST can be performed by experienced personnel in less than 5 minutes, and its use has been shown to decrease the time to surgical intervention, the patient length of stay, and the need for computed tomography (CT) and diagnostic peritoneal lavage (DPL). It is estimated that over 96% of level 1 trauma centers incorporate FAST into their trauma algorithms. [1]

Blunt abdominal trauma (BAT) is a common reason for presentation to the emergency department (ED). Unfortunately, patient history and physical examination often lack the necessary sensitivity and specificity for accurate diagnosis of acute traumatic pathology. Diagnostic peritoneal lavage was historically used to determine which patients needed exploratory laparotomy, but DPL is difficult to perform in pregnant patients, it cannot be used for serial assessment, and it is overly sensitive, which leads to a high negative laparotomy rate. [2]  Abdominal CT has better specificity than DPL for intra-abdominal injury in BAT, but it can be difficult to perform in hemodynamically unstable patients, it is expensive, it requires removing patients from the clinical arena, and it may be relatively contraindicated in pregnant patients. [3]  FAST is an important and valuable diagnostic alternative to DPL and CT that can often facilitate timely diagnosis for patients with BAT. [4, 5, 6, 7, 8, 9]

Guidelines for FAST examination have been published by the American Institute of Ultrasound in Medicine (AIUM) and the American College of Emergency Physicians (ACEP). [10]  The primary FAST examination classically includes the subxiphoid window of the heart to denote pericardial fluid. Indications for FAST include evaluation of the torso for free fluid suggesting injury to the peritoneal, pericardial, and pleural cavities, particularly in cases of trauma. FAST examination may be used to evaluate the lungs for pneumothorax. [10, 11, 12]

Benefits of the FAST examination include the following:

  • Decreases time to diagnosis for acute abdominal injury in BAT

  • Helps accurately diagnose hemoperitoneum

  • Helps assess the degree of hemoperitoneum in BAT

  • Is noninvasive

  • Can be integrated into the primary or secondary survey and can be performed quickly, without removing patients from the clinical arena

  • Can be repeated for serial examinations

  • Is safe in pregnant patients and children, as it requires less radiation than CT [13]

  • Leads to fewer DPLs; in the proper clinical setting, can lead to fewer CT scans (patients admitted to the trauma service and to receive serial abdominal examinations) [14]

An extended version of the standard FAST examination (E-FAST) has been established and offers additional information. Along with images of the abdomen, the E-FAST examination includes views of bilateral hemithoraces to assess for hemothorax and views of bilateral upper anterior chest walls to assess for pneumothorax. [15, 16, 17, 18, 19, 20] For the remainder of this monograph, the FAST examination is referred to as the E-FAST examination, as appropriate.

The wide variation in the accuracy and reliability of FAST and E-FAST for children after blunt abdominal trauma reflects user expertise. FAST and E-FAST that are performed by expert personnel tend to be more accurate and reliable. [21]

Several accepted indications have been identified for the FAST examination, including the following:

When emergency treatments such as intravenous (IV) fluids or blood transfusions are indicated, performance of a FAST examination should not delay initiation of these treatments.

The E-FAST allows clinicians to rapidly diagnose traumatic thoracoabdominal injuries at the bedside without use of ionizing radiation. It has high specificity and is extremely useful as an initial test to rule in dangerous diagnoses such as hemoperitoneum, pericardial effusion, hemothorax, and pneumothorax. Its moderate sensitivity means that it should not be used alone as a tool to rule out dangerous thoracoabdominal injuries. In patients with a mechanism or presentation of concern, additional imaging should be obtained despite a negative FAST examination. [23]

Although ongoing resuscitation and a patient in extremis are not contraindications, the FAST examination can be difficult to perform in such situations.

Next:

Technique

Anesthesia generally is not necessary for sonographic evaluation. Analgesics may be required for pain control secondary to the particular trauma. Patients should be evaluated in the supine position but may be moved to the Trendelenburg or lateral decubitus position for improved visualization of particular views if there are no contraindications (eg, spinal precautions). Male patients should have the entire abdomen exposed for the examination. Take care with female patients to minimize exposure of sensitive areas. Typically, no complications are associated with this procedure, and no special efforts at complication prevention are required.

Focused assessment with sonography for trauma (FAST) should include views of (1) the hepatorenal recess (Morison pouch), (2) the perisplenic area, (3) the subxiphoid pericardial window, and (4) the suprapubic window (Douglas pouch). If an extended FAST (E-FAST) examination is performed, views of (1) bilateral hemithoraces and (2) the upper anterior chest wall should also be obtained.

(The videos below show demonstrations of FAST and E-FAST.)

Demonstration of focused assessment with sonography for trauma (FAST). Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
Focused assessment with sonography for trauma (FAST) cardiac extension for E-FAST. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.

Blood tends to pool in dependent areas. The hepatorenal recess (Morison pouch) is the most dependent space in the supramesocolic region. The suprapubic view allows assessment of fluid in the most dependent area in the inframesocolic region. In women, this space (the rectouterine space) is known as the pouch of Douglas.

To visualize the Morison pouch, the transducer-probe should be placed in the right upper quadrant or laterally along the thoracoabdominal junction (see the images and videos below). This placement uses the liver as an acoustic window and avoids interference from air-filled bowel. The probe should be moved toward the inferior margin of the liver to obtain improved images of the right kidney.

Probe placement for right upper quadrant laterally Probe placement for right upper quadrant laterally.
Right upper quadrant view. Right upper quadrant view.
Focused assessment with sonography for trauma (FAST) that depicts fluid in the Morison pouch. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
Focused assessment with sonography for trauma (FAST) depicting normal right upper quadrant findings. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.

In cases of acute hemoperitoneum, blood appears as an anechoic stripe in the recess (see the image below).

Free fluid in Morison pouch. Free fluid in Morison pouch.

To obtain the perisplenic view, the transducer-probe should be placed over the left flank, lateral to the spleen along the posterior axillary line (see the images below). When it is placed in this position, the handle of the probe should nearly touch the gurney. This placement allows the spleen to be used as an acoustic window and avoids interference from air-filled bowel. The probe should then be moved superiorly (toward the thoracoabdominal junction) and inferiorly to assess for the presence of free fluid above the spleen and along the spleen tip.

Probe placement for left upper quadrant laterally. Probe placement for left upper quadrant laterally.
Left upper quadrant view. Left upper quadrant view.

Be sure to assess the hepatodiaphragmatic and splenodiaphragmatic spaces (see the image and videos below); blood often accumulates in these areas. A common pitfall is to scan only through the hepatorenal and splenorenal spaces.

Blood in the splenodiaphragmatic recess. Blood in the splenodiaphragmatic recess.
Focused assessment with sonography for trauma (FAST) depicting fluid in the splenorenal space. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
Focused assessment with sonography for trauma (FAST) depicting a normal splenorenal space. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.

To obtain the suprapubic view, place the probe just above the pubic symphysis and direct it inferiorly into the pelvis (see the images and video below). This view is easier to obtain when the bladder is full and before a Foley catheter is placed. Be sure to obtain both sagittal and transverse suprapubic views.

Suprapubic probe placement. Suprapubic probe placement.
Suprapubic view. Suprapubic view.
Focused assessment with sonography for trauma (FAST) depicting fluid in the pelvis, sagittal view. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.

For the subxiphoid view, the transducer-probe should be placed in the subxiphoid area and directed into the chest toward the left shoulder to provide a view of the diaphragm and the heart (see the images below). This view can be difficult to obtain if the patient is experiencing significant abdominal pain. It often requires pressing the probe into the abdomen and angling the probe so that it is nearly parallel to the skin. In such cases, it is helpful to place the palm over the top of the probe with the thumb on the indicator.

Subxiphoid probe placement. Subxiphoid probe placement.
Subxiphoid view that demonstrates traumatic tampon Subxiphoid view that demonstrates traumatic tamponade.

If the patient is experiencing significant abdominal pain or is obese, consider switching to a parasternal long-axis view. The subxiphoid long-axis view is another view that can be used to assess for pericardial effusions. This view also allows the examiner to assess the size and collapsibility of the inferior vena cava (IVC).

If an E-FAST examination is being performed to rule out pneumothorax, place a high-frequency linear probe (8-12 MHz) with the indicator toward the patient’s head in a long-axis orientation. Place the probe high on the patient’s chest, just below the clavicles in the midclavicular line. Look for the pleural line sitting at the back of the ribs. The presence of sliding between the visceral and parietal pleura indicates absence of a pneumothorax in the area being scanned. The absence of sliding implies the presence of a pneumothorax.

(See the videos below.)

Extended focused assessment with sonography for trauma (E-FAST) that shows no pneumothorax. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
Extended focused assessment with sonography for trauma (E-FAST) that shows pneumothorax. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.

If an E-FAST examination is being performed to rule out hemothorax, place the transducer probe laterally on the lower thorax just above the diaphragm. This can be visualized by sliding the probe superiorly from the standard right and left upper quadrant views. Blood appears as an anechoic stripe in the thorax.

Additional Considerations

If rib shadowing is an obstacle, rotate the transducer probe by 30° to fit between the ribs. Consider switching to a probe with a smaller footprint (eg, a phased array probe) if such a device is available.

If the desired recesses are difficult to visualize, ask the patient to take a slow, deep breath and, if possible, to hold it. This may move the recess into view.

Be sure to fully interrogate each region by scanning through it in its entirety. A single negative view in each region does not constitute a negative E-FAST examination.

Intraperitoneal free fluid may not be hemoperitoneum. Consider ascites, urine, peritoneal dialysate, and other sources of intraperitoneal fluid. Be aware of false positives from fatty tissue, and attempt to determine precisely where the visualized fluid is located. In pregnant patients, the presence of free fluid after BAT may not be physiologic, especially if there is >2 mm to 4 mm and if the patient has no history of ovarian hyperstimulation syndrome. [24]

Hemoperitoneum may take time to accumulate. Maintain a low threshold for repeating the E-FAST examination, especially if the patient’s vital signs or examination findings change. Serial E-FAST examinations increase the sensitivity with which intraperitoneal free fluid secondary to blunt abdominal trauma can be detected.

The E-FAST examination is an excellent initial imaging modality for identifying the presence of hemothorax or pneumothorax in the setting of trauma. Although it is quite specific, it is not sensitive enough to rule out all significant pathology.

Peer teaching can be applied to teach practical skills such as E-FAST without loss of clinical application skills. This relieves the burden of removing doctors from patient care situations while maintaining teaching standards. [25]

Miniaturization of ultrasound has enabled helicopter emergency medical services (HEMS) to use point-of-care ultrasound to care for trauma patients on scene, allowing HEMS to detect life-threatening, time-sensitive conditions such as pneumothorax, pericardial effusion, and intraperitoneal hemorrhage. HEMS E-FAST has the potential to triage certain trauma patients directly to the operating room, bypassing the emergency department and saving crucial time. [26]

Evaluation of the lung during E-FAST cannot be used in the trauma setting to identify patients with active COVID-19 infection or to stratify patients as having high or low risk of infection. This is likely due to differences in lung imaging techniques and the presence of concomitant thoracic injury. [27]

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