Infra-Renal Abdominal Aortic Aneurysm repair (IRAAA) - open surgery
Introduction
What is it?
The aorta is the main pipe which conveys blood from the heart to the rest of the body. It is normally 1-1.5 cm in diameter. All other major arteries to the limbs and the organs branch off it.
The aorta leaves the heart and travels upwards, it then arches backwards and runs along the back of the chest in from of the spine. It continues downwards in front of the spine and passes into the abdomen (belly) by piercing the diaphragm. In the abdomen it splits into two iliac arteries for the legs.
An Abdominal Aortic Aneurysm (AAA) is an abnormal swelling of the aorta (major artery/ blood vessel conveying blood from the heart to the systemic circulation). The swelling is considered an aneurysm when it is over 1.5 times its normal diameter (1).
Risk factors for AAA development are smoking, advanced age, hypertension, hypercholesterolemia, peripheral vascular disease, coronary artery disease, white race, positive family history and male gender (2, 3).
Classification according to involvement of Branch arteries
AAAs can be described relative to the involvement of the renal (kidney) or visceral arteries (arteries to the guts, called the Coeliac axis and Superior Mesenteric artery). From these relationships, they can be categorised as:
Infra-renal aneurysm – the aneurysm originates below the level of the renal arteries and there is a segment of non-diseased aorta to allow repair to be done below the renal arteries (4).
This is the most common type of AAA. Only approximately 5% affect the aorta higher up and involve the renal (kidney) arteries or visceral (guts) artery segment of aorta.
Up to 40% of patients with AAAs also have iliac artery aneurysms (5).
There are a number of terms which are used to describe how high up the aneurysm
Suprarenal aneurysm – involves the origins of one or more visceral vessels, but does not extend to the chest.
Para-renal aneurysm – renal/ kidney arteries arise from the aneurysmal (swollen) aorta, but the aorta at the level of the superior mesenteric artery is not aneurysmal;
Juxta-renal aneurysm – the aneurysm originates just below the origin of the renal arteries and there is no segment of non-aneurysmal aorta distal to the renal arteries, but the aorta at the level of renal arteries is not aneurysmal.
Why is it done?
Aneurysms, generally, do not cause symptoms and are diagnosed during abdominal imaging for unrelated conditions. Occasionally, patients may feel a ‘’pulse’’ in their abdomen or palpate (feel) a pulsating mass in the belly. Large aneurysms may give chronic back pain or abdominal pain, which is vague and difficult to locate. Rarely, large aneurysms can cause symptoms from local compression on structured inside the belly, including the duodenum, ureter and iliac veins.
Acute symptoms of aneurysms are related to either emboli from the aortic thrombus, which may cause acute limb ischaemia or thrombosis of aneurysm and combined rate of occurrence is 2 – 5% (3).
Abdominal aortic aneurysm can become symptomatic due to the rupture or acute (sudden) expansion.
Aneurysm size predicts risk of rupture
AAA size remains widely accepted clinical predictor of rupture. Historically reported annual risk of rupture of a AAA is:
5% - for size of 5 cm
10% - for a size of 6 cm
20% - for the size of 7 cm (1).
What is the role of growth rate?
Growth rate of AAA is a marker for rupture as well and surgery is indicated if size increases 10mm/year (6).
Diameter of the aorta exceeding 3 cm defines the presence of the aneurysm and predicts clinical events for men. However, for women, although the aorta is still considered aneurysmal when diameter exceeds 3 cm, the diameter is less predictive of clinical events.
An aortic scaling index (ASI), calculated as diameter (cm)/body surface area (m2), is more predictive of clinical events than absolute aortic diameter in women (7).
Elective (planned) repair of the aneurysm is recommended when the risk of rupture exceeds the risk associated with repair and is indicated when the aneurysm size is 5.5 cm and above. Two randomised control studies carried out in UK (UKSAT – UK Small Aneurysm Trial) and USA (ADAM – The Aneurysm Detection and Management) showed lack of benefit of early surgery for abdominal aortic aneurysms with size 4cm to 5.5 cm (3). Aneurysm repair can be accomplished using open surgical or endovascular techniques.
Will I need to do any preparation?
Prior to undertaking surgery, it is common these days to undergo clinical assessment and a battery of tests designed to assess how well your body is able to withstand the stress of the surgery. It is on the basis of these tests and your teams assessment that you should do well from surgery that the operation will be considered.
You will need to fast before the operation (Six hours for food and two hours for clear liquids).
Your recovery after surgery will be greatly enhanced by your state of health before the procedure. The stronger and fitter you are able to get before the procedure, the better the likely outcome and recovery. This approach is sometimes called pre-habilitation as opposed to rehabilitation (which happens afterwards).
Technique
Anaesthesia
Anaesthesia for Open repair of AAA will be General Anaesthetic and you will be asleep for the operation. Often the anaesthetist will add a Spinal or Epidural Anaesthetic (needle in the back to number your lower half) to help with pain relief during the surgery and also for the first few days after the operation.
What does it involve?
The most common incision (cut) which is used to enter the abdomen or belly is a vertical one. The incision extends almost the entire length of the abdomen from breast bone above to the pubic bone below.
An alternative approach which may be feasible is a horisontal or transverse incision.from side to side. This can be better in terms of post-operative discomfort and pain.
Technically, the abdominal aorta can be exposed through a transperitoneal or retroperitoneal approach. This is a technical issue with regards to how the surgeon approaches the aorta - whether to go between the guts or to rotate them full out of the way.
Once the abdomen is entered the whole of the abdominal contents are checked. Next, Infra-renal aorta is exposed from the surrounding tissues. This exposure is needed so that a clamp can be applied to prevent blood from escaping from the circulation when the aneurysm is being repaired.
The Common iliac arteries are dissected and exposed from the surrounding tissues also. This allows the far end of the aorta to be clamped - again to isolate the segment of aorta to be repaired.
The medicine Heparin is given to prevent the blood clotting when the circulation in the area to be operated on is clamped off. Without heparin clot would form in the artery above and below which would prevent circulation being restored at the end of the operation.
The aneurysmal is then cut open and any thrombus or clot inside it removed. Lumbar arteries are small arteries which feed off the aorta in this section to supply the spine. They tend to bleed back through their branch points and need to be closed with stitches..
Next a tube shaped graft is stitched to the aortic neck below the renal arteries and to the aortic bifurcation. If needed an upside down Y shaped graft can be used and separate anastomoses (joins) are performed with the iliac arteries separately.
Before the far anastomosis (join) is finished, blood is allowed to escape from above and below so that any clot which has developed is flushed out.
After any bleeding points have been secured, the remnant aneurysmal sac is closed over the graft to protect it. The retroperitoneal lining is closed as well.
Sometimes additional procedures may be needed:
- Embolectomy if acute limb ischaemia noted
- Reimplantation of inferior mesenteric artery if visceral collateral flow is not sufficient
- Aorto-iliac or bifemoral graft if iliacs are also aneurysmal
- Axillo-bifemoral if infrarenal aorta not suitable for grafting
Alternative procedures:
1. EVAR
2. Non-operative management in high risk patients or those not expected to survive at least 2 years (8).
How long does it take?
The operation usually takes from two to four hours, however there will be time taken to prepare for anaesthesia as well as time in recover afterwards.
Post procedure course (follow-up)
Usually a patient will spend at least one night in a 'Critical Care' setting either in the High Dependancy or Intensive Care Unit (HDU/ ICU).
It may be that a number of tubes are attached to you to help you over the first few days. These may include a tube through your nose into your stomach to prevent nausea and vomiting. This can happen as the bowels often do not start working immediately after abdominal surgery.
There may be a tube in your back providing pain relief. There may be a tube in your bladder to allow free drainage of urine.
Once the immediate post operative course is done then the open repair is very durable and is very unlikely to need further intervention or surveillance.
How long will I stay in hospital?
A fit patient without any significant complications should expect to be home within a week or so of the surgery.
What care will I need at home?
You will not feel one hundred percent of your usual self for a number of weeks or months from the time of surgery. However you will not be discharged from hospital without being assessed as being able to look after yourself. Having said that individual cases are unique and a tailored approach is best according to your needs.
Will I need someone to stay with me?
It may be helpful to have someone to help you at home for the first couple of weeks. This may well allow you to go home earlier than you otherwise would be able to do do.
Will I need any special equipment when I go home?
Occupational Therapists and Physiotherapists assess your individual needs before being discharged and advice on what if anything is required.
What follow up care is needed?
You may be followed up annually in a clinic and perhaps have the entire aorta checked four to five years later in case any further swelling up of the aorta occurs above the repair.
