What are the steps to perform a bedside Focused Assessment with Sonography for Trauma (FAST) in a hemodynamically unstable trauma patient?

FAST Exam: Step-by-Step Procedure

In a hemodynamically unstable trauma patient, perform bedside ultrasound (FAST exam) immediately as the initial diagnostic modality to identify free fluid and determine the need for emergent laparotomy 1.

Indications for FAST Exam

Perform FAST when:

• Hemodynamically unstable (systolic BP <90 mmHg) with blunt abdominal trauma 1
• Penetrating trauma of thoracoabdominal transition with unclear abdominal cavity penetration 2
• Any trauma patient with unstable vital signs and unknown cause 2

Equipment Setup

• Use a low-frequency curvilinear transducer (2-5 MHz) for optimal depth penetration 3
• Position the ultrasound machine directly across from you with the screen at eye level
• Apply adequate ultrasound gel to ensure good acoustic contact

Four Standard FAST Views (Perform in Sequence)

1. Perihepatic/Right Upper Quadrant (RUQ) View

• Place transducer in right midaxillary line between 8th-11th intercostal spaces
• Orient marker toward patient's head (longitudinal plane)
• Visualize: liver, right kidney, Morrison's pouch (hepatorenal recess), right hemidiaphragm
• Look for: Anechoic (black) fluid in Morrison's pouch or subdiaphragmatic space

2. Perisplenic/Left Upper Quadrant (LUQ) View

• Place transducer in left posterior axillary line between 6th-9th intercostal spaces
• Orient marker toward patient's head (longitudinal plane)
• Visualize: spleen, left kidney, splenorenal recess, left hemidiaphragm
• Look for: Anechoic fluid in splenorenal recess or subdiaphragmatic space
• Pitfall: This is the most technically difficult view; fluid accumulates here last

3. Pelvic View

• Place transducer suprapubically in transverse orientation (marker to patient's right)
• Angle probe caudally into pelvis
• Visualize: bladder (should appear anechoic when full), rectouterine pouch (females) or rectovesical pouch (males)
• Look for: Anechoic fluid posterior to bladder or surrounding bladder
• Pitfall: Empty bladder reduces sensitivity; consider Foley catheter clamping if time permits

4. Subxiphoid/Pericardial View

• Place transducer just below xiphoid process
• Orient marker toward patient's right
• Angle probe toward left shoulder with significant pressure
• Visualize: heart chambers, pericardial sac
• Look for: Anechoic fluid stripe around heart (pericardial effusion/hemopericardium)
• Alternative: If subxiphoid view inadequate, use parasternal long axis view

Extended FAST (eFAST) - Add These Views

5. Right Thoracic View

• Place transducer in right midaxillary line, 4th-5th intercostal space
• Look for: Hemothorax (anechoic fluid above diaphragm) or pneumothorax (absent lung sliding, absent comet-tail artifacts)

6. Left Thoracic View

• Place transducer in left midaxillary line, 4th-5th intercostal space
• Look for: Same findings as right thoracic view

Image Optimization

• Adjust depth to visualize entire organ and potential fluid spaces (typically 15-20 cm)
• Adjust gain to optimize contrast between fluid and solid structures
• Use fan/sweep technique: slowly fan through each window to avoid missing fluid in adjacent spaces
• Obtain images in two planes (longitudinal and transverse) when possible

Interpretation

POSITIVE FAST:

• Any anechoic (black) fluid collection in peritoneal, pericardial, or pleural spaces
• Action: Proceed directly to operating room for emergent laparotomy if hemodynamically unstable 1
• Sensitivity: 69.8-90%, Specificity: 92.1-100% 1, 4, 5

NEGATIVE FAST:

• No free fluid visualized in any window
• Critical caveat: Does NOT rule out injury 1, 4
• Action: Serial FAST exams, continued clinical monitoring, or CT scan if patient stabilizes 5
• Negative predictive value: 0.98 5

Key Limitations and Pitfalls

• Cannot detect: Solid organ injuries without bleeding, bowel injuries, retroperitoneal bleeding, diaphragmatic injuries 1, 2
• False negatives occur with: Small volume bleeding (<400-500 mL), early examination before fluid accumulation, obesity, subcutaneous emphysema 2, 4
• False positives: Ascites, peritoneal dialysis fluid, physiologic pelvic fluid in females 2
• Operator-dependent: Requires adequate training and experience 5

Clinical Integration

The FAST exam takes 2-5 minutes to complete and should be performed during the primary survey without interrupting resuscitation efforts 1, 6. The exam provides a simple "yes or no" answer regarding free fluid presence—it is not designed to quantify bleeding volume or identify specific organ injuries 2. For hemodynamically stable patients with negative FAST, proceed to CT scan for definitive evaluation 1, 2.