Bashir Agim, a 75-year-old male, presents to A+E with sudden onset left sided back pain and collapse at home.

• His past medical history includes MI, CVA, HTN and he is a life-long smoker.
• He has no known drug allergies and medications include Aspirin 75mg OD, Atorvastatin 80mg OD, bisoprolol 5mg OD and furosemide 40mg OD.
• On examination the patient looks pale and clammy.
• He has a tachycardia P105, BP 70/40, Oxygen Saturation of 92% on air. An arterial blood gas identifies a pH 7.2, pO2 8kPa, PCO2 4kPa, Lac 5mmol/L, Hb9g/L, HCO3 18mmol/L, BE -2mmol/L.
• A FAST scan in A+E reveals an 8cm abdominal aortic aneurysm.

Discuss differential diagnoses, investigations and management for this patient.