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.
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.
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.
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.