Keywords: abdominal aortic aneurysm, aorto-iliac aneurysms, inflammatory and ruptured abdominal aneurysms

INTRODUCTION

Abdominal aortic aneurysm repair is a commonly performed vascular procedure. This article describes how we repair abdominal aortic aneurysms with the emphasis on the routine rather than the exception. We shall describe in some detail how we deal with the large aorto-iliac, the inflammatory and the ruptured aneurysm. It is not the purpose of this article to deal with the rarer forms of aneurysms which involve the intra-abdominal branches of the supra-renal abdominal aorta.

PATIENT SELECTION AND PRE-OPERATIVE PREPARATIONS

All patients who have abdominal aortic aneurysms, with an antero-posterior diameter on ultrasound of 5.5 cm or greater, are considered for repair. (1)  Any patient with a known aneurysm who complains of abdominal or back pain, in the absence of any other established pathology, is regarded as having a symptomatic aortic aneurysm until proven otherwise and is also considered for repair. This latter criteria is justified on the basis that national figures show a peri-operative mortality of 7.5% from elective repair, whilst population studies have shown at least an 80% mortality if aneurysms rupture.( 2)   Patients with athero-emboli to the legs resulting in tissue damage, where no cause is found other than the presence of an aortic aneurysm, are also regarded as symptomatic and are offered repair.

Fitness for operation is decided in conjunction with the consultant vascular anaesthetist. All patients have baseline blood tests, a chest radiograph and ECG carried out. Special cardiac and respiratory investigations are done in patients with known cardiac or lung disease. We do not routinely perform either computerised tomography (CT) or angiography in these patients. All patients are given subcutaneous heparin (5000 i.u.bd) for thrombo-embolic prophylaxis which is omitted on the morning of surgery and they receive Picolax for bowel preparation the day before. Bowel preparation eases the access at operation, as well as intra-operative bowel palpation, and we believe makes the post-operative period more comfortable for the patient.

ANAESTHESIA

Most patients undergoing consideration for aortic aneurysm repair have significant co-morbidity and in our practice treatment of these patients is a team effort by the vascular surgeon and the vascular anaesthetist. We never perform elective aneurysm repair without the presence of both consultants. All patients have invasive monitoring including a central venous pressure line, arterial line and urinary catheter. Swan-Ganz catheters are rarely used but if the patient is at high risk or has a rupture a Swan-Ganz introducer is placed in the internal jugular vein; the central line is inserted through this and later, if required, a Swan-Ganz catheter can be inserted. Unless contra-indicated all patients have an epidural catheter inserted for postoperative analgesia. The upper torso is covered in a body warming system and the theatre table is covered by a silastic mattress to reduce the risk of pressure damage, particularly over the sacrum and buttocks. Prophylactic antibiotic, in the form of Cefuroxime 1.5 gm, is given. If the patient is allergic or is at risk of methicillin-resistant staphylococcus aureus, Teicoplanin 400 mg is administered at induction. A second dose of Cefuroxime is given, if the operation lasts more than 3 hours, and a second dose of Teicoplanin is given the following morning to patients at risk from infection with methicillin resistant staphylococcus aureus.

THEATRE PREPARATION

In the operating theatre the patient is shaved from the xiphisternum to mid-thigh. We find a small, hand-held, battery operated vacuum cleaner of great use in clearing the shaved hair. The patient lies supine on the operating table, preferably with both arms by the side. If the anaesthetist wishes to have an arm out, this is the left arm. The shaved area is then prepared using Chlorhexidine spirit. Draping of the large area is easily achieved by the use of four laparotomy sheets applied to the legs and torso on both sides. The groin is covered using an abdominal pack. Four towel clips are used to hold the sheets in place and a large Ioban (3M) drape is then used to cover the exposed area. This holds the sides and groin towels in place with no gaps and we believe helps to prevent contamination of the graft and wound (Figure 1).

Figure 1 Towels, groin pack and Ioban in place

LAPAROTOMY

A midline xiphisternum to pubis incision is made with a scalpel. Bleeding points are controlled with diathermy and a full laparotomy carried out. The finding of co-morbid pathology is not unusual in this group of patients. The presence of previously undiagnosed cancer may lead to delay in the aneurysm repair. When an aneurysm is large, however, the risk of rupture in the postoperative period justifies the synchronous procedure of bowel resection after the aneurysm is dealt with and the graft well covered. The laparotomy will also define whether the abdominal aortic aneurysm is aortic or aorto-iliac. Once the laparotomy is completed a ring wound drape is inserted (Figure 2).

Figure 2 Abdominal midline incision with wound drape positioned

This is usually used in abdominal surgery to prevent wound contamination by bowel organisms but we use it prevent potential contamination of the graft from the wound edges. It has been shown that most infections come from the patient's own skin. In vascular operations which tend to be prolonged we feel it is our duty to reduce the risk of contamination of the graft from the skin is reduced by the use of both Ioban skin cover and a wound drape. (3)  Thereafter, the retro-peritoneum is exposed by withdrawing the small bowel onto the right of the wound and protecting it with an abdominal pack. A second abdominal pack is placed in the abdomen on the left side to hold the transverse, descending and sigmoid colon out of the field. The base of the small bowel mesentery is retracted towards the right by the assistant and the surgeon's left hand and with Lloyd Davis scissors the peritoneum over the aorta is divided to the right of the inferior mesenteric artery up to the level of the crossing inferior mesenteric vein. This vein is divided if it low and obviously obstructing access to the neck of the aneurysm to avoid tearing it during retraction later in the procedure. The assistant needs to actively assist by picking up the peritoneum with forceps and diathermy any bleeding points. Packs are then rearranged in order to allow placement of retractors for both the dissection of the neck and the distal dissection.

Figure 3 Dyball and Dever retractors in place held by assistants to expose aortic aneurysm after retroperitoneum opened

We either use Dyball and Dever retractors held by two further assistants to hold the wound edges apart (Figure 3) or, alternatively, the Omnitract (Figure 4).

Figure 4 Omnitract retractor system positioned showing aneurysm exposed. The aortic bifurcation is to the right

PROCEDURE FOR AORTIC ANEURYSMS

The proximal part of the aneurysm is next approached by dividing the areolar tissue on the front of the aneurysm. Small blood vessels and lymphatics are diathermied or ligated. The left renal vein is usually exposed but occasionally the neck is so low that this is not required. Whenever there is any difficulty identifying the top end of the aneurysm the left renal vein should be looked for. The neck of the aneurysm is usually covered antero-laterally by a venous arch consisting of the left gonadal vein, the left renal vein and the cava and knowing where these structures are makes damage to these less likely during dissection and clamping of the neck of the aneurysm.

The right side of the neck is dissected close to the arterial wall pushing the cava to the right. This is usually done by a combination of sharp and blunt dissection using Lloyd Davis scissors as a dissector rather than as a cutting instrument and continued until the front of the vertebra is felt and adequate space is created for insertion of a Fogarty straight aortic clamp. The same procedure is then carried out on the left side where the chances of haemorrhage is higher both from damage to the gonadal vein, as well as from transverse lumbar veins. A retro-aortic renal vein is an occasional problem and should clearly be borne in mind, particularly if the main left renal vein in front of the aorta cannot be found or if it is small. The purpose of dissecting the neck is to obtain satisfactory side to side clamp position and by sticking close to the arterial wall trouble is avoided.

When venous bleeding is caused accidentally, patience with packing and waiting before exposing and repairing it is usually adequate to achieve haemostasis. Actively securing the bleeding site, when necessary, can be difficult.

Occasionally, when the neck of the aneurysm is high the left renal vein may need to be divided. This is achieved by clamping the vein with small Debakey vascular clamps, dividing it near the vena cava (to preserve the left kidney's collateral venous drainage through the suprarenal and gonadal veins) and then securing both ends with a running 5/0 Prolene suture. A satisfactory proximal clamp position having been obtained, the retractors are placed distally and the lower end dissected. Once the peritoneum has been divided the 'broad spade' of the closed Lloyd Davis scissors is invaluable in gently pushing the peri-aortic tissue away. Clamp positions are thereby easily obtained either on the aorta just above the bifurcation, when the aneurysm is strictly involving the aorta alone, or on the common iliac arteries, when the aneurysm extends fully to the bifurcation and into the proximal part of the common iliac arteries. If the iliac arteries are dilated a decision needs to be made on the type of repair. Two factors determine our willingness to repair concomitant iliac disease, the condition of the patient and the appearance of the artery. If the patient is elderly and the aneurysm ruptured then speed is important and dilatation (up to 2.5 cm) of the iliacs is accepted. When the distal clamp position has been determined Heparin (3000-5000 units), depending upon the patient's size, is given and allowed to circulate for 3 minutes. After agreement from the anaesthetist, clamps are applied; firstly an aortic straight Fogarty clamp, followed by an angled Fogarty clamp to the distal aorta or to both proximal common iliac arteries (Figure 5).

Figure 5 Straight Fogarty clamp applied to aorta proximal to aneurysm (left in this picture) and angled Fogarty clamp on the common iliac arteries

The aorta is then incised to the right of the inferior mesenteric artery with an arteriotomy knife. Scissors are used to extend the incision superiorly and inferiorly. Time is taken to remove the laminated thrombus, when present, and to endarterectomise the sac, when calcified atheroma is present. This aids the oversewing of any lumbar vessels using 2/0 Nurolon.

We do not favour leaving the graft surrounded by a potentially infected sac contents. We, therefore, usually clean the inside of the aneurysmal sac and believe that we get better healing of the inlay graft into the aneurysmal sac. The inferior mesenteric artery is inspected and if there is brisk back bleeding it is oversewn at this stage. If there is not much back bleeding it is controlled with a micro clip until the end of the procedure to make sure that the colonic circulation is adequate. If not, a patch of aortic wall with the inferior mesenteric artery can then be reimplanted into the graft. The upper and lower end of the arteriotomy is "T-ed" by making transverse incisions near the top and bottom of the aneurysm with scissors. Care should be taken to leave an adequate section of the aortic wall below the proximal clamp for the anastomosis. A Cohen's self-retaining retractor is put into the opened aneurysmal sac to ease the construction of the proximal anastomosis (Figure 6).

Figure 6 Aneurysm opened and Cones retractor in place. Proximal and distal extent of the aneurysm is easily seen

The graft is then selected which is usually between 14 and 20 mm in diameter. We currently use a knitted polyester gelatin sealed prosthesis (Gelsoft, Vascutek, Scotland). If we are concerned with regard to infection, for instance in a patient who is documented to be an MRSA carrier, has a stoma or in a patient who has other abdominal surgery synchronously (e.g. cholecystectomy or bowel resection), the graft is soaked in Rifampicin. The top anastomosis is performed using a continuous 3/0 Prolene suture mounted on a curved needle holder, commencing in the midline posteriorly and suturing from inside the artery proximally and out distally. Having anchored the graft securely in the midline posteriorly traction can be firmly applied by the assistant to ease the construction of the anastomosis (Figure 7). 

Figure 7 Proximal midline posterior Prolene stitch in place with traction on graft and suture

Strong deep bites are taken into the aorta, particularly posteriorly, with the sutures are radiating from inside outwards as the anastomosis is made in the funnel of the aneurysm. Where possible, the aneurysmal sac antero-laterally is incorporated to help buttress the repair. The suture line finishes with a knot in the midline anteriorly (Figure 8).

Figure 8 Top anastomosis finished in midline anteriorly. Graft filled with Heparinised saline and clamped. Proximal aortic clamp is released

An 'active' first assistant is essential and needs to follow the suture with one hand and use the other to keep the field dry with a sucker, and display the area. After informing the anaesthetist, the suture line is tested by releasing the aortic clamp. 'Salvage sutures' are occasionally necessary and it is often a good idea to use a pledget of graft to buttress these sutures. Once the surgeon is satisfied with the top anastomosis, the aortic clamp is removed and placed on the graft just below the anastomosis. This allows the top anastomosis to seal and also relieves any pressure on the renal arteries by the proximity of the clamp to the renal ostea. The graft is next filled with Heparinised saline (10 international units/ml) above the new clamp position and the straight graft is cut to length. A 3/0 Prolene suture is again used for the distal anastomosis. It is our practice again to start the suture line posteriorly, stitching from inside out, starting distally on the aorta or iliac vessels to avoid raising a flap (Figure 9). 

Figure 9 Posterior midline suture in place at distal anastomosis just above aortic bifurcation

Either a 3/0 Prolene suture is used or, if the artery is healthy, a 5/0 with a 16 mm needle may be used. Prior to completion of the distal anastomosis back bleeding is checked and, as a rule, a No 5 Fogarty balloon catheter is passed distally. It is surprising how often some clot or atheromatous debris is retrieved from the distal arterial tree. Thereafter, a baby feeding catheter is used to fill the distal arterial tree with Heparinised saline before reclamping. The graft is also flushed from above to make sure there is no clot prior to completing the anastomosis. After informing the anaesthetist and getting their agreement the distal clamps are removed and any major defect in the distal anastomosis will be obvious with back bleeding and this can be repaired prior to removal of the proximal clamp. When the anaesthetist is satisfied with the condition of the patient the proximal clamp is removed (Figure 10).

Figure 10 Graft functioning after all clamps removed. Proximal and distal anastomoses easily seen

Digital compression of the graft can be easily applied to reduce blood flow down the graft until the anaesthetist is satisfied with the post-clamp release blood pressure. After final restoration of flow the femoral pulses are felt. While the suture line bleeding is settling the sigmoid colon is inspected. If healthy, the inferior mesenteric artery is ligated usually from within the sac or as close as possible to the aortic wall, to avoid compromising the collateral colonic circulation. A final check on haemostasis can be made and only if there is excessive bleeding is the APTT (activated partial thromboplastin time) checked on a portable coagulation meter and, if greater than 150 seconds, Protamine is administered in an appropriate dose.

The aneurysmal sac is then closed in a double breasted fashion over the graft using 2/0 Vicryl. The right leaf of the aneurysmal wall is sutured to the inner aspect of the left leaf postero-laterally so that the peri-graft space is abolished (Figure 11).

Figure 11 Right leaf of aneurysmal sac sutured to inner aspect of the left leaf postero-laterally to obliterate space around the graft

The left leaf is then sutured to the adventitia of the right leaf antero-laterally. This invariably covers both anastomoses. The peritoneum is closed over the sac with 2/0 Vicryl. Towards the proximal end of the aortic wall covering the graft, the peritoneum from the left side is sutured to the peri-aortic tissue on the right in an attempt to extra-peritonealise the duodenum. Often this layer is very weak and little traction should be applied to the suture to avoid it tearing out.

PROCEDURE FOR AORTO-ILIAC ANEURYSMS

Patients with aorto-iliac aneurysms are more awkward to deal with because of the presence often of a very large concurrent iliac aneurysm. The distal dissection, control and anastomosis are usually difficult and time consuming. The first decision to be made is whether it is possible to make the distal anastomosis to the distal common iliac artery, the external iliac or, if it is necessary, to make the anastomosis to the common femoral arteries.

The iliac aneurysms should be handled with great care to avoid dislodging aneurysm content into the distal arterial tree (trash syndrome) which may lead to loss of limb or even life. It is our practice, therefore, to expose the external iliac arteries to check that they are patent and normal enough to allow an anastomosis and then double sloop them. In our experience it is very unusual to have to extend the graft limbs beyond the external iliac arteries. The aortic part of the aneurysm is attended to but the iliac aneurysms are not dealt with in any significant way until the proximal aorta is clamped, the aneurysm opened and the content of the aneurysm evacuated. At this stage, the iliac aneurysms are clamped with Fogarty right angle hydragrip clamps and the proximal surgery completed as for ordinary infra-renal aneurysms. Thereafter, the surgeon and assistants' attention can be focused on the right and left iliac aneurysms in turn. Whenever possible, the distal anastomosis of the bifurcation graft is to the distal common iliac artery providing flow to the internal and external iliac arteries. This is usually a very oblique end-to-end anastomosis and because of the thickness of the artery a 3/0 Prolene suture with a 25 mm needle is usually required. The iliac aneurysms frequently extend into the internal iliac arteries but rarely into the external. In this situation, we usually close the internal iliac artery from within the internal iliac aneurysm as close to its distal end as possible with a 3/0 Prolene suture. The graft is anastomosed to the external iliac artery proximally, if this is of good quality, or further distally where the artery is already slooped. This is usually done end to end obliquely using a 5/0 Prolene suture with a 16 mm needle. Although we attempt to preserve flow into the internal iliac artery, at least on one side, we have no hesitation in ligating both when they are both significantly aneurysmal and have never been aware of any problems with ischaemic nerve or pelvic injury as a result.

PROCEDURE FOR INFLAMMATORY AORTIC ANEURYSMS

Approximately 15% of all abdominal aortic aneurysms are of this type and its aetiology is not known. These aneurysms have a thick fibrous anterior and lateral wall which may be up to 3 cm in maximum thickness. They are usually very adherent to surrounding structures such as the duodenum, the vena cava, the left renal vein and, occasionally, the ureters. The wall can be as rigid as the outer shell of a coconut and difficult to open. After incising it, the duodenum is usually very adherent and has to be dissected off the aneurysm with a thick layer of aneurysmal wall to avoid damaging the duodenum itself. The aneurysm wall can usually be easily split to allow this procedure. The aorta may need to be clamped above the renal vessels to get control but the graft can, in our experience, always be anastomosed below the renal arteries. Distally, the clamp position should be well down the iliac arteries as the fibrous thickening often extends into the upper part of the common iliac arteries. It is hazardous to try and free the iliac arteries here from the iliac veins, the ureters and the inferior mesenteric vessels which are incorporated into the fibrous reaction. Sometimes it is better to get control of the external iliac arteries, as for aorto-iliac aneurysms, and control the internal iliac by the use of a Fogarty balloon catheter with a 3-way tap using it as an occlusion catheter while opening the aneurysm down into healthy vessel wall more distally in the common iliac arteries. Care must always be taken to avoid damage to the ureters, which often are incorporated in this fibrous peri-aortic tissue, particularly distally over the common iliac artery. The graft used and the anastomoses performed are as for the more common atherosclerotic aneurysms. It is often necessary, however, to excise part of the aneurysm wall anteriorly to help the insertion of the inlay graft and the aneurysm wall can only be closed by approximation in front of the graft.

PROCEDURE FOR RUPTURED ANEURYSMS

These patients commonly present with severe backache, abdominal pain and hypovolaemic shock and it is one of the most challenging emergency procedures that surgeons face. Urgency is essential and the diagnosis in most cases should be made from the history and clinical findings alone. Rarely is ultrasound examination or CT scans required to confirm the diagnosis. These patients should be taken to the operating theatre immediately on admission and resuscitation only started as the patient is anaesthetised and the surgical team is ready to start the operation. Ten units of blood and 4 units of fresh frozen plasma is always asked for from the Transfusion Service, urgently.

The procedure itself is basically identical to that used for aortic and aorto-iliac aneurysms but because of the large retro-peritoneal haematoma the anatomy is more difficult to define. The left renal vein may be the only landmark which is easy to find to guide the operator towards the neck of the aneurysm. It is often necessary to do the dissection with a sucker to be able to see anything at all and, once the left renal vein is found, finger dissection along the sides of the aorta is usually fairly safe and allows rapid application of a straight Fogarty Hydragrip clamp. Once the proximal clamp is in position the aneurysm is opened and a finger inserted into the aorta down towards the bifurcation. This usually helps to locate the site and size of the iliac arteries in the grossly haemorrhagic tissue surrounding them. The front of the aneurysmal wall can then usually be identified down into the iliac arteries and Hydragrip angled clamps applied. Mild iliac aneurysmal dilatation is ignored if it is possible to get a straight graft anastomosed to the distal aorta above the common iliac ostea. The procedure is now identical to that described above. Occasionally, when the aneurysm has ruptured on the right side the tear may have caused a fistula into the vena cava. Dark venous blood filling the aneurysm after the aortic clamps have been applied should make the operator rapidly aware of the presence of a fistula. This is easily attended to by using a 3/0 or 5/0 Prolene suture to close the rupture in the aortic wall by a continuous suture. The caval wall is usually adherent to the aorta and this repair, therefore, will also repair the tear in the caval wall.

Prior to completing the anastomosis distally a size 5 Fogarty catheter balloon is passed distally to extract clot and debris. Heparinised saline is again instilled distally. Heparinised saline is also instilled into the proximal part of the graft prior to completing the distal anastomosis. Systemic Heparin is not used in patients with ruptured aneurysms

ABDOMINAL CLOSURE

The abdomen is closed with a mass closure using a blunt needle and 1 PDS. As these patients have been shown to have a high instance of incisional hernia care is taken to use an adequate length of suture material and take appropriate size bites. If necessary, a few interrupted 2/0 Vicryl sutures are placed in the subcutaneous fat and staples are usually used for the skin. Prior to waking the patients up the circulation to the feet is always checked. Patients with ruptured aneurysms are always ventilated for a period and, therefore, are transferred to the Intensive Care Unit.

POSTOPERATIVE CARE

The elective patients after spending time in the recovery ward are returned to the High Dependency Unit for intensive monitoring of the ECG, arterial pressure, central venous pressure, oxygen saturation and hourly urine volume; monitoring is gradually reduced over the next 4 days. Chest physiotherapy is very important and all patients are seen pre and post-operatively. On the first postoperative day, the arterial line is removed and the patient allowed sips of water. On the second day, the nasogastric tube is removed and the patient allowed half cups of tea. When tolerated, the patient is allowed to drink freely and then diet is introduced as the patient feels like it. The epidural is removed on the morning of the fourth postoperative day and the patient returned to the main ward. Full blood counts, urea and electrolytes are measured on the first three postoperative days and only repeated after this if there are any problems with the patient's recovery. The patient is usually discharged home or to convalescence 7-10 days post-operatively.

ACKNOWLEDGEMENTS

The authors are indebted to Miss P Wiseman for secretarial help and the Department of Medical Illustration, Grampian University Hospitals NHS Trust for production of the photographs.