In abdominal injuries, what is the most informative initial investigation?

Most Informative Initial Investigation in Abdominal Trauma

Ultrasound (FAST - Focused Assessment with Sonography for Trauma) is the most informative initial investigation in abdominal injuries. 1

Rationale for FAST as Initial Investigation

• FAST is rapid and non-invasive, allowing for immediate assessment during the primary survey without delaying resuscitation efforts 1
• High specificity (96-100%) and accuracy (92-99%) for detecting hemoperitoneum 1
• Can be performed in the resuscitation area while other stabilization measures are ongoing 1
• Helps guide immediate decision-making, particularly for hemodynamically unstable patients 1, 2

Diagnostic Performance of FAST

• Sensitivity: 74-76% for detecting intraperitoneal free fluid 1, 3
• Specificity: 84-96% 1, 3
• Accuracy: 79-99% 1, 3
• Negative FAST can reliably rule out significant hemoperitoneum (>500ml) 1

Limitations of FAST

• Limited sensitivity for specific organ injuries 1
• Up to 29% of abdominal injuries may be missed if FAST is used as the sole diagnostic tool 4
• Less reliable for detecting low-grade solid organ injuries 3

Comparison with Other Modalities

CT Scan

• Superior for detailed assessment but inappropriate as initial investigation for unstable patients 1
• Recommended as secondary investigation for:
  • Hemodynamically stable patients with positive FAST
  • Patients with negative FAST but concerning mechanism or exam
  • Characterization of specific organ injuries 1, 2
• Time-consuming and requires patient transport from resuscitation area 1

Diagnostic Peritoneal Lavage (DPL)

• Invasive procedure with potential complications 1
• Largely replaced by FAST in modern trauma protocols 1
• Only indicated when ultrasound is unavailable or results are equivocal in unstable patients 2

X-Ray

• Limited sensitivity for abdominal injuries 1
• Cannot reliably detect free fluid or solid organ injuries 1

Clinical Decision Algorithm

1. Perform FAST as initial investigation for all patients with suspected abdominal trauma
2. If FAST is positive + patient is hemodynamically unstable → immediate surgery
3. If FAST is positive + patient is hemodynamically stable → proceed to CT scan
4. If FAST is negative but high clinical suspicion remains → proceed to CT scan in stable patients
5. Consider risk factors associated with abdominal injury despite negative FAST:
   • Abrasions/contusions in lower chest or upper abdomen
   • Pulmonary contusion
   • Lower rib fractures
   • Hemo/pneumothorax
   • Hematuria
   • Pelvic or thoracolumbar spine fractures 4

The answer is C. US (Ultrasound).