Ruptured Abdominal Aortic Aneurysm

Ruptured abdominal aortic aneurysm is full thickness rupture of an abdominal aortic aneurysm (diameter 3.0 cm or more), with haemorrhage into the retroperitoneum or peritoneum. It is a surgical emergency with overall mortality of about 80% including patients who die before reaching hospital.

Epidemiology. Prevalence of aneurysm is about 1 to 2% in men over 65 years. Rupture risk rises steeply with diameter: about 1 to 3% each year at 5.0 cm and 10 to 20% each year at 6 to 7 cm. Hospital mortality is 30 to 50% after repair.

Risk factors. Male sex, age over 65, smoking, hypertension, family history, connective tissue disease, rapid expansion (over 1 cm in a year), female sex at smaller diameters, and fluoroquinolone exposure.

Pathophysiology. Wall stress exceeds strength and the aorta ruptures, usually posterolaterally into the retroperitoneum, where tamponade may limit blood loss briefly. Free intraperitoneal rupture is rapidly fatal. Rare forms are aortocaval and aortoenteric fistulas.

Presentation is sudden abdominal, back or flank pain, hypotension and a pulsatile abdominal mass (the full triad is present in a minority). Syncope, groin pain, leg ischaemia, pale mottled skin and renal colic like pain occur. Aortocaval fistula causes heart failure and a machinery murmur.

Red flags.

• Known aneurysm with pain, or pain with unexplained hypotension in a man over 60 years.
• Syncope, shock or a pulsatile mass.
• Recent abdominal pain misdiagnosed as renal colic.

In the unstable patient with a known aneurysm, do not delay transfer to theatre for imaging. Bedside ultrasound shows aneurysm and free fluid. CT angiography of the aorta in stable patients defines rupture, anatomy and suitability for endovascular repair. Send group and crossmatch (10 units available), full blood count, coagulation, creatinine, lactate and ECG.

Differential diagnosis. Acute aortic dissection, mesenteric ischaemia, renal colic, perforated viscus, pancreatitis, myocardial infarction and diverticulitis.

Resuscitation.

• Two large bore IV cannulae and an arterial line (do not delay surgery to place them).
• Permissive hypotension: systolic pressure 70 to 90 mmHg (mean arterial 50 to 70 mmHg) while the patient is conscious, because normotension can dislodge clot and increase bleeding.
• Limit crystalloid. Transfuse red cells, plasma and platelets in a ratio near 1 to 1 to 1, with warming and calcium (calcium gluconate 10% 20 mL for each 4 units).
• Oxygen, analgesia in small doses (fentanyl 25 microgram IV) and avoid sedation until the patient is in theatre.
• Hold anticoagulants and reverse if relevant.

Repair.

• Endovascular repair if anatomy is suitable and the patient stable enough, usually under local anaesthesia with sedation. Open repair if anatomy is unsuitable or the patient cannot wait.
• Induce anaesthesia only after the surgical team is scrubbed and the abdomen prepared, because loss of muscle tone removes tamponade.
• Aortic balloon occlusion proximal to the renal arteries via the femoral artery can control bleeding in extremis (resuscitative endovascular balloon occlusion of the aorta, zone 1).
• Heparin 5000 units IV before clamping if time allows.
• Antibiotic prophylaxis: cefazolin 2 g IV (3 g if weight is over 120 kg).

Postoperative care. Intensive care. Look for abdominal compartment syndrome (measure bladder pressure, decompress at over 20 mmHg with organ dysfunction), colonic ischaemia (sigmoidoscopy), renal failure, limb ischaemia, spinal cord ischaemia, respiratory failure and coagulopathy. Treat acidosis and hypothermia.

Monitoring. Arterial pressure, lactate, haemoglobin, urine output, bladder pressure, distal pulses and coagulation.

Referral and escalation. Vascular surgery, anaesthesia, interventional radiology and blood bank at once. Transfer to a vascular centre without waiting for imaging if the patient is stable enough to travel.

Special groups. In frail older patients with poor prospects, early discussion of goals of care. In suspected aortoenteric fistula, endoscopy is not delayed to stabilise.