Belted blunt trauma with free fluid and an equivocal bowel scan — seat-belt reading, FAST/CT limits, scores, child rules and antibiotic stop

Model answer

(A) Bruise, FAST and free fluid — 4 marks

• Bruise above the iliac spines carries a positive likelihood ratio of 4.2 for belt-related injury against 1.5 at or below — admit and image the above-spine mark; the low mark alone does not earn routine imaging.^[12]
• eFAST detects free fluid at 74% sensitivity and 98% specificity (74/95 hypotensive, 76/98 normotensive adults) — a rule-in triage tool whose negative result never excludes visceral injury; Cochrane concurs: high specificity, low sensitivity.^[4][5]
• In 754 belted patients the hollow viscus prevalence was 9.2% with only one injured patient showing a truly negative CT; free fluid raised hollow viscus odds more than 40-fold and classified best at AUC 0.87 — free fluid means hollow viscus until proven otherwise.^[11]
• A careful negative CT in the stable belted patient predicts absence of hollow viscus injury well (one miss in 754; a separate 425-patient series read 100% sensitive) — consider discharge only for the stable with explicit return precautions, never for the equivocal scan in front of you.^[11][13]

(B) Equivocal bowel scan — score, watch, re-image — 3 marks

• Prospective CT reporting reaches only 63.6% sensitivity (specificity 79.6, PPV 53.9, NPV 85.5), with barely half of blunt bowel injuries diagnosed preoperatively and mostly indirect signs in the missed — the equivocal scan stays admitted.^[10]
• No single CT feature predicts bowel injury; commonest findings are free fluid 71.3%, free air 43.6% and mesenteric infiltration 23.4%.^[7]
• Apply the Bowel Injury Prediction Score (white-cell count, abdominal tenderness, CT mesenteric grade) to select for early diagnosis; head-to-head AUCs run Faget 95.3, Raharimanantsoa 89.2 and BIPS 87.6, with significant injury in ~3% and delay beyond 24 hours in roughly a fifth.^[9][8]
• Observe with strict monitoring and follow-up imaging for high-risk injuries per the reviewed strategy; peritonitis, deterioration or score progression triggers operation without further delay.^[2]

(C) Child, elder, antibiotics — 3 marks

• Child: gate CT by the PECARN abdominal rule, derived to cut inappropriate scanning; acute intervention means therapeutic operation, embolisation, transfusion for abdominal bleeding, or 2+ nights of fluids for pancreatic/gut injury — external validation 99% sensitive with clinically important injury in 2.3%.^[37][38][39]
• Older adult: hollow viscus rate matches the young (5.5 vs 9.8%) but mortality runs fivefold higher (5.5 vs 1.1%) with longer stay — admit, observe and re-examine rather than trusting reassurance.^[15]
• Colon injury found: 24 hours of intravenous cover equals five days (300-patient cefoxitin trial, no influence of duration); Cochrane compares regimens only, never treatment against nothing.^[34][33]