Recommended Diagnostic Evaluation
This patient requires an abdominal CT scan with intravenous contrast immediately. 1
Clinical Reasoning
This hemodynamically stable patient (BP 128/74, though tachycardic at 114) presents with concerning peritoneal signs (diffuse abdominal pain with rebound tenderness and guarding) following significant blunt trauma. Despite the negative FAST exam, a negative FAST does not exclude significant intra-abdominal injury and should not be relied upon as the sole diagnostic test in this clinical scenario. 1
Why CT is the Definitive Answer
- CT has superior sensitivity (97%) and specificity (95%) for detecting intra-abdominal injuries requiring intervention in blunt abdominal trauma 1
- FAST has significant limitations with a sensitivity of only 79% and misses injuries in 17% of patients requiring therapeutic laparotomy 1
- CT is particularly critical for detecting bowel injuries, which FAST frequently misses - the sensitivity for small bowel perforation by CT is 92-94% 1
- Physical examination findings of rebound tenderness and guarding indicate peritoneal irritation, which mandates definitive imaging regardless of FAST results 1
Why Other Options Are Inadequate
Repeating the FAST exam (Option C) is inappropriate because:
- Fluid takes time to accumulate, but this patient already has peritoneal signs requiring immediate definitive evaluation 1
- Serial FAST may be helpful in some scenarios, but not when peritoneal signs are already present 1
Serial physical exams alone (Option D) are dangerous because:
- Physical examination is unreliable in trauma patients, with 19% of patients with intra-abdominal injuries having no abdominal tenderness 1
- This patient already has concerning exam findings that warrant immediate imaging 1
- Delayed recognition of injury occurs in 4% of cases when imaging is inappropriately deferred 2
Diagnostic peritoneal lavage (Option B) is outdated because:
- DPL has been almost entirely replaced by CT in modern trauma evaluation 1
- While DPL has 100% sensitivity for hemoperitoneum, it is invasive and cannot identify specific organ injuries or retroperitoneal trauma 1
- CT provides comprehensive evaluation of all abdominal organs in a single examination 1
CT Protocol Specifications
Use IV contrast-enhanced CT of the abdomen and pelvis 1:
- Oral contrast is NOT required and delays diagnosis 1
- IV contrast increases detection of solid organ injuries, vascular injuries, and active bleeding 1
- Single-phase IV contrast-enhanced examination is typically sufficient 3
Critical Pitfall to Avoid
Never assume a negative FAST exam rules out significant intra-abdominal injury in a patient with peritoneal signs. 1 FAST identifies free fluid but cannot determine the source of injury, and requires a minimum volume of fluid to be detectable. In hemodynamically stable patients with concerning physical exam findings, CT remains the gold standard regardless of FAST results. 1