How reliable is Focused Assessment with Sonography for Trauma (FAST) in pediatric trauma?

FAST in Pediatric Trauma: Limited Reliability Requiring Supplemental Imaging

FAST examination has limited reliability in pediatric trauma with low sensitivity (42-55%) despite high specificity (96-100%), and should not be used as the sole diagnostic tool for detecting intra-abdominal injuries in children. 1

Diagnostic Performance of FAST in Pediatric Trauma

FAST examination demonstrates significant limitations in pediatric trauma patients:

• Sensitivity: Only 42-55% for detecting intra-abdominal injuries 1, 2
• Specificity: High at 96-100% 1, 3
• Negative Predictive Value: 76-97% depending on study methodology 3, 4
• Positive Predictive Value: 56-100% 3, 4

These statistics reveal a critical weakness: FAST misses approximately half of intra-abdominal injuries in children, making it unreliable as a standalone screening tool.

Clinical Application Algorithm

1. Initial Assessment:

   • Perform FAST as part of the initial trauma evaluation for rapid detection of free fluid 1
   • Recognize that a negative FAST does NOT exclude significant injury 1, 2

2. Hemodynamically Unstable Patients:

   • Positive FAST + hemodynamic instability → immediate surgical intervention 1
   • Negative FAST + persistent instability → consider other sources of bleeding and additional imaging if patient can be temporarily stabilized

3. Hemodynamically Stable Patients:

   • Positive FAST → proceed to CT scan for injury characterization 1
   • Negative FAST + concerning mechanism/exam → proceed to CT scan 1, 4
   • Negative FAST + minimal symptoms + minimal clinical findings + hematuria <50 RBCs/HPF → consider ultrasound/contrast-enhanced US for follow-up 1

Key Limitations in Pediatric Patients

• Children have less intra-abdominal fat, making free fluid detection more difficult 5
• Solid organ injuries in children may not produce significant free fluid 2
• In one study, 10 patients had solid organ injuries without free fluid, making detection by FAST impossible 2
• False negative FAST examinations have led to missed injuries requiring intervention 4

Improving Diagnostic Accuracy

• Combine FAST with thorough physical examination (increases sensitivity to 90%) 6
• Consider contrast-enhanced ultrasound in stable patients when available 1
• Use complete abdominal ultrasound rather than limited FAST views when possible 1
• Recognize that CT scan remains the gold standard for definitive diagnosis 1

Practice Variation and Institutional Considerations

• Significant practice variation exists, with FAST utilization ranging from 0.84% to 94.1% across pediatric trauma centers 4
• Higher frequency of FAST use at an institution does not correlate with improved accuracy 4
• CT utilization remains high (41%) even after negative FAST examinations 4

Conclusion

FAST examination should be viewed as a rapid screening tool with significant limitations in pediatric trauma. Its high specificity makes positive findings valuable, but its poor sensitivity means negative examinations cannot reliably exclude injury. CT scan remains necessary for definitive diagnosis in most cases of significant pediatric trauma.