Overview
Definition:
The Focused Assessment with Sonography for Trauma (FAST) exam is a rapid, bedside ultrasound protocol used to screen for occult or life-threatening hemoperitoneum, hemopericardium, or pneumothorax in trauma patients
It is a non-invasive diagnostic tool that can be performed quickly at the point of care, guiding immediate management decisions.
Epidemiology:
Trauma remains a leading cause of death globally, especially in younger populations
The FAST exam has become a cornerstone in the initial evaluation of blunt and penetrating abdominal trauma, significantly improving the diagnostic accuracy and reducing the time to definitive care
Its utility extends to detecting other critical injuries like tension pneumothorax.
Clinical Significance:
The FAST exam is crucial for identifying internal bleeding and other life-threatening conditions in hemodynamically unstable trauma patients, facilitating timely surgical intervention and improving outcomes
Its rapid application can differentiate between patients requiring immediate laparotomy and those who can be managed non-operatively
It is a fundamental skill for surgeons, emergency physicians, and critical care providers.
Acquisition Technique
Probe Selection:
A low-frequency curvilinear transducer (2-5 MHz) is generally preferred for abdominal and pelvic views due to its better penetration
A high-frequency linear transducer (5-12 MHz) is used for thoracic views to better visualize pleural surfaces.
Patient Positioning:
The patient should be positioned supine
The ultrasound equipment should be readily accessible
The operator should be positioned to comfortably manipulate the probe and view the screen.
Scanning Protocol:
The standard FAST exam involves four views: 1
Pericardial View (subxiphoid): Probe placed just below the xiphoid process, angled cephalad to visualize the pericardial sac and effusion
2
Perihepatic View (Morison's Pouch): Probe placed in the right anterior axillary line, between the ribs, to visualize the potential space between the liver and the right kidney
3
Perisplenic View: Probe placed in the left anterior or mid-axillary line, between the ribs, to visualize the potential space between the spleen and the left kidney
4
Pelvic View: Probe placed in the midline of the lower abdomen or suprapubically, to visualize the pouch of Douglas (rectovesical or rectouterine pouch)
Extended FAST (eFAST) includes bilateral anterior thoracic views to detect pneumothorax.
Thoracic Views For EFAST:
For eFAST, anterior chest views are obtained bilaterally in the 2nd or 3rd intercostal space in the midclavicular line to assess for lung sliding (absence suggests pneumothorax) and lung point (specific sign of pneumothorax).
Interpretation
Normal Findings:
In a normal FAST exam, no anechoic (black) fluid is seen in the peritoneal cavity (Morison's pouch, perisplenic space, pelvis) or pericardial sac
Lung sliding is present bilaterally on thoracic views.
Abnormal Findings Abdominal:
The presence of anechoic fluid in the perihepatic, perisplenic, or pelvic views suggests hemoperitoneum
The amount of fluid can be graded as small, moderate, or large
Fluid is typically seen in dependent areas and can layer between organs.
Abnormal Findings Pericardial:
Anechoic fluid in the pericardial sac indicates a pericardial effusion, which can be circumferential or loculated
Significant pericardial effusion, especially if rapidly accumulating, can lead to cardiac tamponade.
Abnormal Findings Thoracic EFAST:
Absence of lung sliding on thoracic views, presence of B-lines (suggesting pulmonary edema), or the visualization of a "lung point" (where lung lung sliding is seen in one area but absent in another) are indicative of pneumothorax
Pericardial effusion is also assessed in eFAST.
Pitfalls And Artifacts:
Common pitfalls include inadequate probe contact, incorrect angulation, patient movement, overlying bowel gas, and mistaking normal physiological fluid (e.g., ascites, urine in bladder) for hemoperitoneum
Fascial planes can also mimic small fluid collections.
Indications And Contraindications
Indications:
The FAST exam is indicated in hemodynamically unstable patients with blunt or penetrating abdominal trauma
patients with significant abdominal pain or distension
suspected diaphragmatic rupture
and for serial reassessment of trauma patients
It is also used in the evaluation of cardiac tamponade.
Contraindications:
Absolute contraindications are rare
Relative contraindications include severe patient instability preventing proper examination, severe burns or open wounds preventing probe placement, and significant overlying dressings or casts
In urgent surgical situations, the need for FAST may be bypassed if the clinical indication for laparotomy is overwhelming.
Role In Trauma Management
Hemodynamic Instability:
In unstable patients, a positive FAST exam (fluid in the abdomen or pericardium) is a strong indication for immediate surgical exploration (laparotomy or thoracotomy/cardiac surgery)
A negative FAST exam in an unstable patient warrants further investigation, such as diagnostic peritoneal lavage (DPL) or CT scan.
Hemodynamic Stability:
In stable patients, a positive FAST exam may prompt closer observation or contrast-enhanced CT scan for definitive diagnosis and localization of injury
A negative FAST exam in a stable patient often allows for non-operative management and outpatient follow-up, though CT may still be indicated for specific injuries.
Serial Assessment:
Repeat FAST exams are crucial in trauma patients, especially if their clinical status changes
A new or increasing amount of fluid detected on serial FAST can indicate ongoing bleeding and necessitate intervention.
Extended Fast And Beyond
Enhanced FAST EFAST:
eFAST expands the FAST protocol to include bilateral anterior thoracic views, allowing for the rapid diagnosis of pneumothorax and hemothorax, making it a more comprehensive resuscitation tool for trauma patients.
Further Ultrasound Applications:
Beyond FAST, ultrasound can be used for identifying fluid in other potential spaces like the splenorenal recess, as well as for guiding resuscitation with vascular access (e.g., ultrasound-guided central venous catheter insertion) and assessing for solid organ injury on CT.
Limitations:
The FAST exam has limitations, including sensitivity for small volumes of fluid, retroperitoneal injuries, and hollow viscus injuries
It is operator-dependent, and interpretation requires adequate training and experience.
Key Points
Exam Focus:
Understand the standard FAST views and their order
Differentiate anechoic fluid from normal physiological structures
Recognize the signs of cardiac tamponade
Crucially, know the interpretation of lung sliding and lung point for eFAST.
Clinical Pearls:
Always correlate ultrasound findings with the patient's clinical status and vital signs
Use a systematic approach
Don't be afraid to repeat the exam if the patient's condition changes
Consider FAST as a dynamic tool that guides management, not a definitive diagnosis alone.
Common Mistakes:
Mistaking ascites or urine in the bladder for hemoperitoneum
Failing to identify small fluid collections due to poor technique or probe selection
Not performing serial exams when indicated
Over-reliance on a negative FAST in a deteriorating patient.