Ultrasound (FAST) is the Most Informative Initial Investigation in Abdominal Injuries
The most informative initial investigation in abdominal injuries is ultrasound (FAST - Focused Assessment with Sonography for Trauma). 1
Rationale for FAST as Initial Investigation
Advantages of FAST:
- Rapid and non-invasive diagnostic approach for detection of intra-abdominal free fluid 1
- High specificity (96-100%) and accuracy (92-99%) for detecting hemoperitoneum 1, 2
- Can be performed during the primary survey in the resuscitation area
- Does not delay resuscitation efforts
- Can be repeated as needed during patient assessment
- Helps identify patients requiring immediate surgical intervention
FAST Performance Characteristics:
- Sensitivity: 74-76% for detecting intraperitoneal free fluid 1, 2
- Specificity: 84-96% for detecting intraperitoneal free fluid 1, 2
- Can rule out significant hemoperitoneum (>500ml) when negative 1
Clinical Algorithm for Abdominal Trauma Assessment
Initial FAST examination for all patients with suspected abdominal trauma 1
- Positive FAST + hemodynamic instability → immediate surgery 1
- Positive FAST + hemodynamic stability → CT scan for further evaluation
- Negative FAST + hemodynamic stability → CT scan if mechanism concerning
- Negative FAST + hemodynamic instability → repeat FAST or consider DPL
CT scan as secondary investigation (not initial) for:
- Hemodynamically stable patients with positive FAST
- Patients with negative FAST but concerning mechanism or exam
- Characterization of specific organ injuries
Limitations of Other Modalities as Initial Investigations
CT Scan (Option A):
- Time-consuming and requires patient transport from resuscitation area
- Inappropriate for hemodynamically unstable patients
- Better suited as a secondary investigation after initial FAST 3
- Superior for detailed injury assessment but not as initial screening tool
Diagnostic Peritoneal Lavage (DPL) (Option B):
- Invasive procedure with potential complications
- Has largely been replaced by FAST in modern trauma protocols 3
- Only indicated when ultrasound is unavailable or results are equivocal 3
X-ray (Option D):
- Limited sensitivity for abdominal injuries
- Cannot reliably detect free fluid or solid organ injuries
- Not recommended as primary investigation for abdominal trauma
Important Caveats and Pitfalls
- FAST has limitations in detecting specific organ injuries - negative FAST does not rule out all abdominal injuries 1, 4
- Up to 29% of abdominal injuries may be missed if FAST is used as the sole diagnostic tool 4
- FAST may miss:
- Retroperitoneal injuries
- Hollow viscus injuries without significant free fluid
- Low-grade solid organ injuries 2
- Serial examinations and additional imaging are often necessary
Conclusion
While each modality has its role in trauma assessment, ultrasound (FAST) provides the most valuable initial information in the critical first minutes of trauma care, balancing speed, accessibility, and diagnostic utility. It allows for rapid triage of patients requiring immediate surgical intervention while identifying those who can safely undergo more detailed imaging studies.