Focused Assessment with Sonography in Trauma (FAST)
- Author: Timothy Jang, MD; Chief Editor: Gowthaman Gunabushanam, MD, FRCR more...
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 to diagnose acute traumatic pathology accurately.
Diagnostic peritoneal lavage (DPL) was historically used to determine which patients needed exploratory laparotomy, but DPL is difficult to perform in pregnant patients, cannot be used for serial assessment, and is overly sensitive, which leads to a high negative laparotomy rate.
Abdominal computed tomography (CT) has better specificity than DPL for intra-abdominal injury in BAT but can be difficult to perform in hemodynamically unstable patients, is expensive, requires removing patients from the clinical arena, and may be relatively contraindicated in pregnant patients.
Focused assessment with sonography for trauma (FAST), on the other hand, is an important and valuable diagnostic alternative to DPL and CT that can often facilitate a timely diagnosis for patients with BAT.[3, 4, 5]
Guidelines for FAST examination have been published by the American Institute of Ultrasound in Medicine (AIUM) and the American College of Emergency Physicians (ACEP). 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.[6, 7, 8]
The benefits of the FAST examination include the following:
Decreases the time to diagnosis for acute abdominal injury in BAT
Helps accurately diagnose hemoperitoneum
Helps assess the degree of hemoperitoneum in BAT
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
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) 
An extended version of the standard FAST examination (E-FAST) has been established and offers additional information. In addition to imaging 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.[10, 11, 12, 13, 14, 15] For the remainder of this article, the FAST examination is referred to as the E-FAST examination, as appropriate.
There are several accepted indications for the FAST examination. They include the following:
Assessment of the degree of intraperitoneal free fluid
When emergency treatments such as intravenous (IV) fluids or transfusion of blood are indicated, performance of a FAST examination should not delay the initiation of these treatments.
Although ongoing resuscitation and a patient in extremis are not contraindications, the FAST examination can be difficult to perform in such situations.
Focused assessment with sonography for trauma (FAST) should include views of (1) the hepatorenal recess (Morison pouch), (2) the perisplenic view, (3) the subxiphoid pericardial window, and (4) the suprapubic window (Douglas pouch). If an extended FAST (E-FAST) examination is performed, views of (1) the bilateral hemithoraces and (2) the upper anterior chest wall should also be obtained. The videos below depict demonstrations of FAST and E-FAST, respectively.
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 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.
In cases of acute hemoperitoneum, blood appears as an anechoic stripe in the recess (see the image below).
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 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.
Be sure to assess the hepatodiaphragmatic and splenodiaphragmatic spaces (see the images below); blood often accumulates in these areas. A common pitfall is to scan only through the hepatorenal and splenorenal spaces.
To obtain the suprapubic view, the probe should be placed just above the pubic symphysis and directed inferiorly into the pelvis (see the images below). This view is easier to obtain when the bladder is full and before the placement of a Foley catheter. Be sure to obtain both sagittal and transverse suprapubic views.
For the subxiphoid view, the transducer-probe should be placed in the subxiphoid area and directed into the chest toward the left shoulder so as to view the diaphragm and 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.
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 the absence of a pneumothorax in the area being scanned. The absence of sliding implies the presence of a pneumothorax. See the videos below.
If an E-FAST examination is being performed to rule out hemothorax, the transducer probe should be placed 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.
If rib shadowing is an obstacle, rotate the transducer-probe 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 visualized fluid is located. In pregnant patients, the presence of free fluid after BAT may not be physiologic, especially if there is >2mm to 4mm, and the patient has no history of ovarian hyperstimulation syndrome.
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 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.
Anesthesia is generally not necessary for sonographic evaluation. Analgesics may be required for pain control secondary to the particular trauma.
Equipment requirements are modest. The examiner will need an ultrasound machine and ultrasound-conducting gel.
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 the exposure of sensitive areas.
Typically, no complications are associated with this procedure. No special efforts at complication prevention are required.
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