What is the purpose of a Focused Assessment with Sonography for Trauma (FAST) exam ultrasound?

From the Guidelines

Fast exam ultrasound, also known as Focused Assessment with Sonography for Trauma (FAST), is a rapid bedside ultrasound examination used to detect free fluid in trauma patients, and it is recommended as a basic skill for intensivists in the general and neuro intensive care unit population 1.

Key Components of FAST Exam

• The standard FAST exam evaluates four specific areas: the perihepatic space (right upper quadrant), perisplenic space (left upper quadrant), pericardium, and pelvis.
• To perform a FAST exam, use a low-frequency (3-5 MHz) curvilinear or phased array transducer.
• Begin with the patient supine, scanning the right upper quadrant to visualize the hepatorenal recess (Morison's pouch), then move to the left upper quadrant to examine the splenorenal recess.
• Next, obtain a subxiphoid or parasternal long axis view of the heart to assess for pericardial fluid.
• Finally, scan the pelvis transversely and longitudinally to evaluate for free fluid in the pouch of Douglas or rectovesical space.

Benefits and Limitations of FAST Exam

• The FAST exam takes approximately 3-5 minutes to complete and can detect as little as 100-200 mL of free fluid, making it valuable for quickly identifying potentially life-threatening internal bleeding in trauma patients.
• However, the FAST exam may not differentiate between different types of pathological fluid, such as urine and blood, and may not identify certain important traumatic conditions, such as hollow viscus injury, mesenteric vascular injury, and diaphragmatic rupture, which can cause minimal hemorrhage 1.

Clinical Application of FAST Exam

• The FAST exam is an integral component of trauma resuscitation and should be performed as soon as possible after the decision to evaluate the patient with sonography 1.
• The integration of clinical assessment with the evaluation of the presence or absence of free peritoneal fluid in traumatic acute abdomen is a basic skill for intensivists 1.
• The FAST exam can be used to rapidly triage multiple victims in mass casualty situations and can be performed on patients with spinal immobilization and with portable equipment, allowing it to be used in remote or difficult clinical situations 1.

From the Research

Fast Exam Ultrasound

• The Focused Assessment with Sonography for Trauma (FAST) exam is a rapid, reproducible, portable, and noninvasive method for detecting hemopericardium, hemoperitoneum, and hemopneumothorax in trauma patients 2.
• The FAST protocol is indicated for hemodynamically unstable patients with blunt abdominal trauma, penetrating trauma of the thoracoabdominal transition, and for any patient with an unknown cause of instability 2.
• The traditional FAST protocol examines four regions: pericardium, right upper abdominal quadrant, left upper abdominal quadrant, and pelvis 2.
• The extended FAST (e-FAST) protocol also searches the pleural spaces for hemothorax and pneumothorax 2.

Image Acquisition and Limitations

• The FAST exam image acquisition involves patient positioning, transducer selection, image optimization, and exam limitations 3.
• The exam is designed to provide a simple "yes or no" answer regarding the presence of bleeding, but it is not intended to quantify the bleeding nor evaluate organ lesions due to its limited accuracy for these purposes 2.
• The amount of bleeding and/or the identification of organ lesions will not change patient management, as hemodynamically unstable patients with positive FAST must go to the operating room without delay 2.

Accuracy and Current Perspectives

• The accuracy of FAST in disaster settings has been evaluated in a meta-analysis, which found a sensitivity of 92.1%, specificity of 98.7%, positive predictive value of 90.7%, and negative predictive value of 98.8% for the detection of intra-abdominal injury 4.
• FAST is a part of resuscitation of trauma patients recommended by international panel consensus, and its purpose is to identify free fluid, which necessarily means blood in acute trauma patients 5.
• The role of FAST and CT scan in the diagnosis of blunt abdominal trauma has been defined, with FAST being useful as the initial diagnostic tool and CT scan being the diagnostic modality of choice in hemodynamically stable patients 6.