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A 70-year-old male heavy smoker presents to the emergency department with sudden onset severe lower abdominal and back pain. BP 85/50, HR 120. On examination, a pulsatile mass is palpable in the epigastrium.
Questions
a) What is the diagnosis and what is the immediate management priority? (3 marks)
Diagnosis: Ruptured abdominal aortic aneurysm (classic triad: pain + hypotension + pulsatile mass).
Immediate management:
- Straight to theatre — do NOT delay for CT in an unstable patient.
- Two large-bore IV cannulae; activate massive transfusion protocol; crossmatch 6 to 10 units.
- Permissive hypotension (SBP 70 to 80 mmHg) — do NOT over-resuscitate (may dislodge retroperitoneal tamponade).
b) What is the approximate mortality rate for this condition, and what proportion die before reaching hospital? (2 marks)
Overall mortality: 80 to 90%. Approximately 50% die before reaching hospital (free intraperitoneal rupture with rapid exsanguination). Of those who reach hospital alive, 40 to 50% die despite emergency surgery.
c) Laplace law explains the vicious cycle of aneurysm growth. State the law and explain its relevance. (2 marks)
Laplace law: Wall Tension (T) = Pressure (P) x Radius (r) / Wall Thickness.
As the aneurysm grows (radius increases), wall tension increases proportionally. Higher tension causes further dilation, increasing tension further — a vicious cycle. This explains why rupture risk increases dramatically with size: under 1% per year at 5 cm, 5 to 10% at 5.5 to 6 cm, over 20% at 7 cm.
d) Six months earlier, this patient had an ultrasound showing a 5.8 cm AAA but declined surgery. At what size threshold is elective repair recommended, and why was this patient at high risk of rupture? (3 marks)
Elective repair threshold: 5.5 cm. This patient's AAA was 5.8 cm (above threshold) and he was a smoker — both increase rupture risk. The UK Small Aneurysm Trial showed that for AAA under 5.5 cm, surveillance is safe. Above 5.5 cm, rupture risk exceeds operative mortality (2 to 5%), justifying elective repair. Screening (ultrasound for men 65 to 75 who smoked) aims to detect AAA before it reaches this threshold.