AAA

• An abdominal aortic aneurysm (AAA) refers to dilation of the abdominal aorta, with a diameter of more than 3cm. This is usually asymptomatic, however, it has the potential to rupture, leading to haemorrhage and rapid death.
• Although the exact aetiology is unknown, it is largely believed to be due to atherosclerosis. Atherosclerotic plaques are thought to compress the aortic media, leading to ischaemia and wall weakening.
• Anatomy:

  • Abdominal aorta is a continuation of the descending thoracic aorta
  • Supplies all of the abdominal organs and its terminal branches supply the pelvis and lower limbs
  • Also supplies the undersurface of the diaphragm and parts of the abdominal wall
  • The abdominal aorta begins at T12 and ends at L4 - where it bifurcates into the right and left common iliac arteries
  • The normal diameter of the abdominal aorta is <2cm
• Pathophysiology:

  • Atherosclerosis causes inflammation, which leads to infiltration by macrophages and deposition of immune complexes in the aortic wall - elastic depletion and smooth muscle loss = dilatation of aortic wall
  • Aneurysm can be juxta-renal (within 1cm of renal arteries), supra-renal (above renal arteries), and intra-renal (below renal arteries)
  • Can be saccular (spherical outpouching)
  • Most commonly fulsiform - diffuse and circumferential dilation
• Risk factors:

  • Male sex (but women have a greater risk of rupture)
  • Smoking - most important risk factors
  • Family history
  • Increasing age
  • Hyperlipidaemia
  • History of atherosclerosis (PAD and coronary artery disease)
  • History of other aneurysm
  • Hypertension - also increases risk of rupture
  • COPD - elastin degradation
  • Connective tissue disorders
• Diabetes appears to be a protective factor against the development of AAA.
• Symptoms:

  • Usually asymptomatic and clinically well - most diagnosed due to screening programme or when AAA ruptures
  • If AAA ruptures - rapid onset abdominal, flank or back pain, shock and rapid loss of consciousness (usually with cardiac arrest)
• Clinical exam:

  • Peripheral vascular exam
  • Expansible pulsatile central abdominal mass superior to the umbilicus (absence does not rule out AAA)
  • Signs of hyperlipidaemia - xanthelasma, corneal arcus
  • Abdominal scars
  • Features of Marfan syndrome - high arched palate, tall
  • Previous cardiac or vascular surgical scars
  • Abdominal/renal bruits
  • Abdominal distension - sign of rupture
  • Grey turner's sign - retroperitoneal haemorrhage indicating rupture
  • Signs of hypovolaemic shock
• AAA screening:

  • All men 65 and over
  • No aneurysm found (less than 3 cm) - no further scans are required
  • Small AAA (3-4.4 cm) - placed under surveillance and repeat scan in 12 months
  • Medium AAA (4.5-5.4 cm) - placed under surveillance and repeat scan in 3 months
  • Large AAA (5.5 cm or more) - to be seen by vascular surgeon within 2 weeks
  • Also urgent referral if >4cm and rapidly growing (>1cm a year)
• Conservative management of asymptomatic AAA:

  • If less than 5.5cm
  • Lifestyle advice - smoking cessation
  • Antiplatelet therapy - aspirin 75mg OD
  • Statins
  • Anti-hypertensives if BP >140mmHg
  • Surveillance (annually if 3-4.4cm, every 3 months if 4.5-5.4cm)
• Surgical management:

  • If the aneurysm is ≥5.5cm in diameter or >4cm and rapidly growing (>1cm per year), the patient will need an elective surgical repair.
  • Antibiotic prophylaxis
  • VTE prophylaxis
  • Open aortic repair or endovascular aortic repair (EVAR)
  • Require 2 units of RBC cross-matched and cell salvage
• EVAR:

  • For patients with more co-morbidities, women of any age and men >70 years
  • Lower perioperative mortality and decreased length of hospital stay
  • More prone to more longer-term complications than open repair so needs long term post surgical surveillance
  • Inserting a stent graft through the femoral arteries under radiological guidance - blood diverted through the graft instead of the aneurysm
  • Endoleaks is a common complication - blood flows outside the stent-graft
  • one, six, and 12 month post operative ultrasounds
  • Annual ultrasound following this
• Open aortic repair:

  • Preferred in healthier patients and men <70 years
  • Grafting in open surgery lasts longer and has more up-front risks than EVAR
  • Done via laparotomy incision - aorta is clamped proximally and iliac arteries clamped distally. Removal of affected segment and replace with prosthetic graft.
• Assessment and investigation of ruptured AAA:

  • Surgical emergency
  • Must be considered for anyone with abdominal/back pain and signs of shock
  • ABCDE assessment and urgent senior clinical review
  • Bedside aortic ultrasound
  • Bloods: G+S and cross match, coagulation, FBC
  • CT angiography is the definitive imaging modality - retroperitoneal haematoma and contrast extravasation
  • A stable patient with ruptured AAA has a better chance of survival with local anaesthetic EVAR compared to open surgery
  • CT angiography should not delay treatment of unstable patients - assess, scan and theatre within 30 minutes
• Management of ruptured AAA:

  • IV access (and limited fluid resuscitation)
  • Analgesia
  • Antibiotic prophylaxis
  • Major haemorrhage protocol activation
  • Blood transfusion if Hb <100 g/L with intraoperative bleeding
  • Do not over correct the BP as this could exacerbate the rupture
  • Definitive treatment is an urgent surgical repair by either EVAR or open aortic repair
• Ruptured AAA complications:

  • 80% mortality rate
  • Abdominal compartment syndrome
• Early postoperative complications:

  • Postoperative ileus - common
  • AKI - EVAR uses iodine contrast, clamping of renal arteries in open repair
  • Bowel ischaemia - blood diarrhoea, worsening lactate
  • Spinal cord ischaemia
  • Pseudoaneurysms - more common in EVAR following femoral artery puncture
  • Distal embolism resulting in acute limb ischaemia
  • Retrograde ejaculation - semen enters the bladder during ejaculation
  • Open surgery also has risks of chest infection, respiratory failure and MI
• Late postoperative complications:

  • Aortic neck dilation
  • Graft infection - can lead to aortic fistula
  • Graft occlusion
  • Endoleak - following EVAR
  • Incisional hernia
  • Abdominal adhesions
• Most AAA usually grow at a rate of 0.2-0.3cm per year. The risk of AAA rupture for aneurysms >5.5 cm is approximately 5% per year. However, the rupture risk depends on the size.
• Do not give too many fluids if patient has ruptured AAA

  will bleeding into retroperitoneal space but too much fluid can cause them to perforate and bleed into the peritoneal space - larger space for blood to collect
• Aortoenteric fistula:

  • connection between the aorta and a loop of bowel
  • Primary - chronic, untreated aortic aneurysm erodes into adjacent bowel tissue
  • Secondary (most common) - inflammation from previous aortic graft
  • Surgical emergency - signs of upper and lower GI haemorrhage e.g. haematemesis and melaena leading to shock
  • Abdominal pain
• DVLA rules:

  • Car and motorcycle drivers must tell the DVLA if AAA measures more than 6cm and stop driving if it reaches 6.5cm
  • Bus, coach and lorry drivers must tell the DVLA if they have an AAA of any size and stop driving if it reaches 5.5cm