Perioperative management - EVAR – Endovascular Repair of an Abdominal Aortic Aneurysm (Bifurcated Graft)

• Abdominal aortic aneurysm (AAA) > 5 cm
• Smaller aneurysms in cases of eccentric AAA or ulcerations with contained perforation (PAU, primary aortic ulcer)
• Symptomatic aneurysms of any size

Special indications and treatment options in Behçet's disease, Marfan syndrome, mycotic aneurysms such as Salmonella infections, and AAA with peripheral embolisation.

The indication for invasive treatment of an abdominal aortic aneurysm (AAA) is fundamentally derived from weighing the individual risk of rupture in the natural course against the operative risk. If the risk of rupture in the natural course exceeds the individual operative risk, the indication for invasive treatment is generally established.

Classification of rupture risk

Factors	Low risk	Intermediate risk	High risk
Aneurysm diameter	< 5 cm	5-6 cm	> 6 cm
Growth rate per year	< 0.3 cm	0.3-0.5 cm	> 0.5 cm
Smoking/COPD	mild	moderate	heavy
Family history	none	isolated	frequent
Arterial hypertension	none	well controlled	unstable despite therapy
Morphology	fusiform	saccular	protrusions
Sex		male	female

Surgical indication

Classification	Size	Wall	Clinical presentation	Surgical indication
asymptomatic infrarenal	> 5 cm ♂ > 4.5 cm ♀	intact	none	elective
asymptomatic supra-aortic	> 6 cm	intact	none	elective
symptomatic	independent	intact	spontaneous pain, tenderness of the abdomen, back or flank	urgent, within 24 hrs
ruptured	independent	contained or free rupture	diffuse severe spontaneous/palpation pain of the tense abdomen, with/without haemorrhagic shock	emergency
		aortoduodenal fistula	intermittent vomiting, melaena	emergency
		aortocaval fistula	right heart failure, fistula murmurs, central cyanosis, simultaneous contrast enhancement of the aorta & inferior vena cava	emergency

Two procedures are available for the surgical treatment of AAA:

• open replacement of the abdominal aorta with a tube or bifurcated graft (OAR, open aortic repair)
• endovascular implantation of a stent graft (EVAR, endovascular aortic repair)

Laparoscopic aneurysm surgery, usually in combination with a mini-laparotomy, is of rather minor importance.

The following recommendations exist for the selection of the procedure - OAR or EVAR:

OAR (trans-, retroperitoneal)

• normal life expectancy
• low operative risk ('fitness')
• anatomy unsuitable for EVAR: landing zone, aneurysm neck (angle, length), iliac vessels (stenoses, elongation, kinking), thrombi, calcification
• Marfan and other connective tissue disorders

EVAR (standard graft, custom-made)

• previous abdominal operations
• limited life expectancy
• high operative risk
• anatomy suitable for EVAR (see above)

EVAR requires adequate iliac vessels for access, as the stent graft systems are often of large calibre. Atherosclerotically narrowed, tortuous and kinked, as well as aneurysmatically dilated iliac vessels are problematic.

In the long-term course, the endovascular aortic graft is associated with a higher complication rate than open aortic surgery.

The mortality risk for EVAR or OAR of an individual patient can be rapidly calculated using the so-called BAR Score Calculator → www.britishaneurysmrepairscore.com, which can be usefully employed for counselling patients on the risk of an elective procedure with EVAR or OAR.

The video example shows an infrarenal, intact AAA with a diameter of > 5 cm:

Since interventional procedures may require conversion to open surgery due to unexpected technical problems, preoperative risk assessment and definition of contraindications are important:

• Heart failure (ejection fraction < 25-30%)
• COPD (FEV1 < 0.8)
• Uncorrectable severe coronary heart disease
• Incurable cancer

Relative contraindication:

• Compensated renal failure (due to intraoperative contrast agent exposure)

If the operation is to proceed in borderline cases despite contraindications, this must be discussed in detail with the patients and their relatives.

Technical contraindications to endovascular repair: see Preoperative diagnostic work-up/planning.

Thorough vascular surgery examination:

• Pulse status
• Doppler study of both legs
• Possibly a walk test in case of concomitant PAOD and poorly palpable foot pulses
• Abdominal ultrasonography
• Carotid colour duplex study
• Echocardiography
• Exercise ECG
• Laboratory panels (electrolytes, coagulation, renal function, blood count, blood lipids)
• Chest X-ray
• Spiral CT
• In case of concomitant PAOD or critical visceral artery morphology, possibly i.a. DSA of the abdominal aorta and the pelvic and leg arteries

Preoperative angiographic clarification of the access pathology is especially important:

• Stenoses of the femoral and pelvic arteries
• Aneurysms of the access arteries
• Local infections such as, e.g., erythrasma
• Previous operations in the surgical field

The presence of a horseshoe kidney in AAA is a special case requiring special planning in both planned open surgery and endoluminal procedures; this planning must take into account the preservation of the multiple renal arteries in the region of the abdominal aortic aneurysm.

In summary, the preoperative diagnostic work-up must therefore address the following parameters:

1. Aortic pathology

2. Risk factors (multimorbidity)

3. Access pathology

Planning

Here, obtaining the exact dimensions of the aneurysm and taking account of any calcification and stenosis is of crucial importance in order to verify local feasibility.

One possible contraindication to endoluminal repair is severe kinking of the aneurysm neck. Furthermore, coiling, compression, and elongation have to be taken into account, because the graft - depending on the centerline - may deviate from the aneurysm configuration and consequently be malpositioned.

After analysing the morphology, it should also be decided from which side to introduce the main body of the graft, or whether to primarily aim for a so-called ballerina configuration in order to facilitate probing of the contralateral leg.

 

Examples of particular aneurysm configurations and access pathologies

• Identify blood group, provide packed RBCs if needed
• Remove the hair in the surgical field
• Place urinary catheter, if needed
• Prophylactic antibiotics are usually administered as recommended by the German Society for Vascular Surgery (single-shot cefuroxime 30 minutes before skin incision), but the benefit is currently subject to debate because of issues around antibiotic resistance (Robert Koch Institute).

General surgical risks

• Major bleeding, blood transfusions, transmission of hepatitis/HIV through allogeneic blood transfusions
• Allergy/intolerance
• Wound infection
• Thrombosis/embolism
• Skin, vascular, and nerve damage, e.g., due to patient positioning
• Keloids (in open surgery)

Specific procedural risks

• Vascular injuries, e.g., during graft delivery: surgical haemostasis, blood transfusions, in case of severe bleeding or aortic rupture, immediate conversion to open surgery
• Pseudoaneurysm of the punctured vessels, arteriovenous fistula, seroma
• Primary aortoenteric fistula: surgical intervention, possibly with removal of the vascular graft
• Inadequate graft fixation or leakage: corrective procedures, possibly open surgery
• Graft infection: possible after days, months, or even years; endocarditis, sepsis, leg ischaemia, amputation; surgical removal of the vascular graft
• Injury of adjacent organs; intestinal ischaemia → resection, stoma
• Nerve lesions → dysaesthesia, pain, paralysis of the abdominal wall and thigh muscles
• Lymph fistula
• Lymphoedema of the legs; temporary or permanent; compression stockings, lymphatic drainage
• Secondary bleeding
• Impotence
• Deterioration of renal function induced by intraoperative angiography, chronic dialysis

Risks due to impaired perfusion

• Thrombosis/embolism: pulmonary embolism, apoplexy, myocardial infarction; prophylaxis: heparin → HIT II risk
• Legs: thrombosis of the graft and possibly adjacent vascular segments, possibly leg ischaemia, amputation (e.g., toes)
• Kidneys: due to thrombosis or graft delivery; despite immediate surgical repair, kidney damage may be permanent → dialysis
• Bowel: impaired perfusion due to thrombosis/embolism and possibly graft delivery; vascular surgery required, possibly bowel resection, chronic stoma
• Spinal cord: depending on the size of the aneurysm, impaired perfusion due to graft delivery; temporary sensory disturbances/paresis, possibly also permanent paraplegia if the artery of Adamkiewicz originates low in the aorta
• Gluteal muscles: due to overstenting of the iliac arteries, in particular bilaterally; claudication during walking, possibly gluteal necrosis
• Liver: impaired function due to hypoperfusion, especially in pre-existing liver disease