Abdominal Aortic Aneurysms

The following types of procedures are used to treat Abdominal Aortic Aneurysm (AAA): 

• Endovascular repair: Abdominal Endovascular Aneurysm Repair (EVAR), Iliac branch devices, chimney endovascular aortic repair (ChEVAR), and Fenestrated Endovascular aneurysm repair (FEVAR).  
• Open AAA repair: infrarenal, juxtarenal, and paravisceral aneurysm repair (Type IV  thoracoabdominal aortic repair).

The steps are mostly similar for endovascular and open AAA repair.  

Patient History 

The evaluation of a patient with AAA involves a thorough medical, family, and social history to determine the risk factors for expansion and rupture. Careful review of the surgical history is also essential for accurate and timely recognition of AAA disease. Cholecystitis, appendicitis, or pancreatitis may mimic the presentation of a symptomatic aneurysm. In addition, the nature and extent of previous abdominal surgery may influence the operative approach.  

The association between cigarette smoking and AAA disease deserves special emphasis. More than 90% of patients with AAA have smoked cigarettes at some point in their lifetime, and AAA  is second only to lung cancer in epidemiologic association to cigarette smoking—more closely associated than either cerebrovascular or coronary artery disease. A history of smoking can also potentially impact outcomes post repair.¹

Physical Examination 

Physical examination has only a moderate sensitivity for detecting AAA, depending on the extent of abdominal girth and aneurysm size. The common iliac arteries may also become aneurysmal and palpable in the lower abdominal quadrants. Palpation does not precipitate rupture, and the concern for a symptomatic aneurysm should not preclude thorough examination. An abdominal aneurysm is common (37 - 40%) in patients with popliteal artery aneurysms, as are concurrent distal arterial aneurysms in patients with an AAA.² In patients with a suspected or known AAA,  the SVS’ AAA guidelines recommend the performance of a physical examination that includes an assessment of femoral and popliteal arteries.³ 

Imaging 

The diagnosis of AAA is based on imaging and the choice of imaging modality should be based on the patient’s condition and optimal institutional protocols.  

Computerized tomography (CT) scan imaging is recommended when repair is contemplated based on aneurysm size, rate of growth, or patient symptoms.^{3, 4}

CTA offers a detailed visualization of the entire aorta and its surrounding structures. It can distinguish different aortic pathologies and is quick and widely available. CTA is the current “gold standard” for aortic imaging.  

Important disadvantages of CTA include the use of nephrotoxic contrast agents and the exposure of patients to ionizing radiation. In patients at increased risk of contrast-induced nephropathy,  circulating volume expansion with either isotonic sodium chloride or sodium bicarbonate solutions is recommended.  

Alternative imaging modalities such as Magnetic Resonance Imaging/Magnetic Resonance  Angiography (MRI/MRA) and rarely intravascular ultrasound (IVUS) can be considered prior to  EVAR based on the patient’s comorbidities, anatomy, and urgency.  

The SVS’ AAA guidelines recommend using ultrasound, when feasible, as the preferred imaging modality for aneurysm screening and surveillance.³ 

Medical Management and Lifestyle Changes  

During AAA surveillance, the SVS guidelines recommend smoking cessation to reduce the risk of  AAA growth and rupture. Hypertension should be treated but the guidelines suggest not administering beta blockers, statins, doxycycline, roxithromycin, angiotensin converting enzyme inhibitors, or angiotensin receptor blockers for the sole purpose of reducing the risk of AAA  expansion and rupture.³ 

Risk Stratification for Surgery (both cardiac and pulmonary) 

Cardiovascular and pulmonary disease remain the leading causes of early and late death after open surgical repair (OSR) or EVAR. Given the risk associated with either OSR or EVAR, it is essential to evaluate the overall operative risk associated with either method of repair. The first step should be to determine whether an active cardiovascular condition exists, which would mandate further assessment and management before planned aneurysm repair. In the absence of an active cardiovascular condition, further testing, as dictated by functional capacity and cardiovascular risk factors, is indicated only if the results will change the planned treatment approach. 

The SVS AAA guidelines state that, in patients with active cardiac conditions, including unstable angina, decompensated heart failure, severe valvular disease, and significant arrhythmia, cardiology consultation is recommended before EVAR or OSR. In patients with significant clinical risk factors, such as coronary artery disease, congestive heart failure, cerebrovascular disease, diabetes mellitus, chronic renal insufficiency, and unknown or poor functional capacity  (MET < 4), who are to undergo OSR or EVAR, the guidelines suggest noninvasive stress testing and echocardiography. In addition, the guidelines recommend a preoperative resting 12-lead  electrocardiography (ECG) in all patients undergoing EVAR or OSR within 30 days of planned treatment.³

Risk Assessment 

A multidisciplinary approach to care can improve outcomes. Medical specialists and team members can assist patients with risk factor modification, such as smoking cessation, maintaining glycemic control, normalizing blood pressure and lipid levels, maintaining antiplatelet therapy and fostering participation in exercise programs, thereby promoting a positive patient experience.  Discharge planning should be considered at time of surgical planning.^5-9 

a. Cardiac 

The SVS AAA guidelines suggest coronary revascularization before aneurysm repair in patients with acute ST-segment or non-ST-segment elevation myocardial infarction (MI), unstable angina,  or stable angina with left main coronary artery or three-vessel disease.³ The same applies in patients with stable angina and two-vessel disease that includes the proximal left descending artery and either ischemia on noninvasive stress testing or reduced left ventricular function  (ejection fraction < 50%). In patients who may need aneurysm repair in the subsequent 12 months and in whom percutaneous coronary intervention is indicated, the guidelines suggest a strategy of balloon angioplasty or bare-metal stent placement, followed by 4 to 6 weeks of dual antiplatelet therapy.⁷ In summary, a recommendation for percutaneous or surgical intervention for coronary artery disease should follow established clinical practice guidelines, regardless of the need for aneurysm repair. In order to minimize the risk of perioperative coronary stent thrombosis for both bare-metal stents and drug-eluting stents, surgery should be delayed for 14  days after coronary angioplasty and 30 days after a bare-metal stent if dual antiplatelet therapy cannot be continued through the perioperative period. Likewise, open repair should not be  performed within 6 months after implantation of a drug-eluting stent if the cessation of dual  antiplatelet therapy is required.¹⁰ 

The guidelines also recommend perioperative transfusion of packed red blood cells if the hemoglobin level is <7 g/dL.³ 

b. Pulmonary 

EVAR is better tolerated than OSR, particularly if EVAR is performed under local anesthesia (LA). However, patients with severe chronic obstructive lung disease (COPD) exhibit increased in-hospital mortality, pulmonary complications, major adverse events, and decreased five-year survival whether they are treated with open repair or EVAR.¹¹ 

Smoking cessation is recommended for at least two weeks prior to aneurysm repair. In addition,  preoperative pulmonary function studies, including room air arterial blood gas determinations,  are suggested in patients with a history of symptomatic COPD, long-standing tobacco use, or inability to climb one flight of stairs.  

Administration of pulmonary bronchodilators for at least two weeks before aneurysm repair is suggested in patients with a history of COPD or abnormal results of pulmonary function testing. 

c. Renal 

Preoperative renal insufficiency is an established risk factor for poor outcome after aneurysm repair. Among patients with moderate renal dysfunction (eGFR of 30-60 mL/min), mortality and cardiovascular events are more likely for patients treated by OSR than by EVAR.¹² However,  outcomes are uniformly poor in the presence of severe renal dysfunction (eGFR < 30 mL/min),  regardless of the type of repair. Outcomes are equally poor after EVAR or OSR for the patient requiring dialysis, with a 30-day mortality of 11%.  

Several strategies have been recommended to minimize renal injury after EVAR or open repair.  Current guidelines recommend pre-procedure and post procedure hydration with normal saline or  5% dextrose for patients at increased risk of contrast induced nephropathy undergoing EVAR,  and preoperative hydration in all non-dialysis-dependent patients with renal insufficiency before  aneurysm repair.^{13, 14} 

d. Diabetes Mellitus 

Diabetic patients have increased operative mortality after AAA repair, with reduced survival two to five years after surgery, consistent with an increased burden of cardiovascular disease. Whether diabetes is a distinct risk factor for major adverse events or death after OSR or EVAR is not well defined, however.¹⁵ 

Preoperative Labs 

Standard complete blood count (CBC), chemistry profile, and coagulation profile are recommended preoperatively. See above for additional recommendations related to renal abnormalities. From a completion standpoint, obtaining a hemoglobin A1C (HgA1c) measure is a  good indicator of how controlled the patient’s diabetes is. 

Genetic Counseling and Screening 

Genetic influences in AAA disease have been demonstrated by twin studies and by formal segregation analyses. Genetic predisposition likely represents small contributions from a large number of risk alleles, with the effect dependent on the population under consideration as well as relevant environmental considerations, such as cigarette smoking.¹⁶ 

There are no specific genetic testing guidelines for patients with AAA, but the SVS AAA  guidelines suggest ultrasound screening for AAA in first-degree relatives of patients who present with an AAA.³ Screening should be performed in first-degree relatives who are between 65 and  75 years of age or in those older than 75 years and in good health. 

Nutrition Evaluation and Optimization 

The SVS AAA guidelines recommend optimization of preoperative nutritional status before elective open aneurysm repair if repair will not be unduly delayed. In addition, parenteral nutrition is recommended if a patient is unable to tolerate enteral support seven days after aneurysm repair. 

Recommended Preoperative Consultations  

The SVS AAA guidelines recommend multimodality treatment for pain management, including epidural analgesia, for postoperative pain control after OSR of an AAA.

Preoperative Medication Adjustment  

The SVS AAA guidelines recommend intravenous administration of a first-generation cephalosporin or, in the event of penicillin allergy, vancomycin within 30 minutes before OSR or  EVAR. Prophylactic antibiotics should be continued for no more than 24 hours. 

In addition, thromboprophylaxis with unfractionated or low-molecular-weight heparin is suggested for patients undergoing aneurysm repair at moderate to high risk for venous thromboembolism and low risk for bleeding. 

• ACE Inhibitors: given the association of ACE inhibitors and angiotensin receptor antagonists with hypotension on induction of anesthesia, these medications should be held the morning of surgery and restarted after the patient is euvolemic. The SVS AAA  guidelines suggest holding angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor antagonists on the morning of surgery and restarting these agents after the procedure, once euvolemia has been achieved. 
• Beta Blockers. The SVS AAA guidelines suggest continuation of beta blocker therapy during the perioperative period if it is part of an established medical regimen. If a decision is made to start beta blocker therapy (because of the presence of multiple risk factors, such as hypertension, coronary artery disease, renal insufficiency, and diabetes), initiation should be well in advance (weeks to months) of surgery to allow sufficient time to assess safety and tolerability. 
• Anticoagulation and its reversal: oral anticoagulation should be discontinued preoperatively to minimize bleeding complication. Direct oral anticoagulants  (DOACs) should be held for 48-72 hours before procedure. Warfarin should be discontinued 3-5 days in advance. Consider bridging with parenteral anticoagulation  (unfractionated heparin [UFH] or LMWH) in appropriate patients with high thrombosis risk.¹⁷ 
• Diabetes: The SVS guidelines recommend holding metformin at the time of administration of contrast material among patients with an Estimated Glomerular  Filtration Rate (eGFR) of <60 mL/min or up to 48 hours before administration of contrast material if the eGFR is <45 mL/min and restarting no sooner than 48 hours after administration of contrast material as long as renal function has remained stable. This is recommended to prevent metformin-associated lactic acidosis (MALA). Diabetic patients who receive intermediate or long-acting insulin should receive half the scheduled dose when nil per os (NPO) in preparation for surgery. Glycemic control should be considered per the current guidelines of the American Diabetes Association (ADA).¹⁸

Anesthesia Management 

a. Optimization and Risk Assessment  

Patients presenting with abdominal aortic aneurysm often have multiple significant comorbidities such as poorly controlled hypertension, coronary artery disease (CAD) or chronic obstructive lung disease (COPD) due to long standing smoking. These comorbidities may significantly impact the anesthesia plan.  

Patients with significant CAD and congestive heart failure may benefit from intraoperative transesophageal echocardiogram (TEE) to evaluate for regional wall motion abnormalities and left heart strain during cross clamping. 

Acute blood loss may precipitate intraoperative myocardial ischemia (MI) in patients with significant CAD. Moderate to severe COPD predisposes patients to postoperative respiratory complications after open AAA repair.  

b. Anesthesia Management for Open AAA Repair 

i) Anesthesia Techniques for Open AAA Repair  

Open aortic aneurysm repair is performed under general endotracheal anesthesia. 

Preoperative placement of an epidural catheter allows for intraoperative sparing of opioids as well as postoperative pain control and may help improve outcome.^19-21 

Maintenance of anesthesia can be accomplished using volatile anesthetics such as sevoflurane and desflurane or with a propofol drip. Opioids like fentanyl or sufentanil can be used for intraoperative pain control. Non-steroidal drugs such as ketorolac or ibuprofen may need to be  avoided depending on the risk of kidney injury and bleeding 

Most patients can be extubated in the operating room (OR) after open AAA repair.  

If an epidural catheter could not have been placed preoperatively, bilateral transversus abdominal plane blocks (TAP blocks) can be placed in the operating room prior to emerging from anesthesia to facilitate postoperative pain management. 

ii) Monitoring and Access 

Standard monitoring of oxygen saturation (SaO2), EKG, non-invasive blood pressure (BP), and temperature. 

• Invasive Arterial Blood Pressure Monitoring: Placement of an arterial catheter pre-induction allows for tight blood pressure and impulse control in particular during induction of anesthesia and endotracheal intubation. Arterial access also allows for intraoperative blood draws for Activated Clotting Time (ACT) measurements.
• Central Venous Catheter (CVL): The use of vasoactive drugs for tight blood pressure control may require the placement of a CVL after induction of anesthesia. 
• Large Bore Intravenous (IV) Access: the possibility of acute intraoperative blood loss requires large bore intravenous access for volume resuscitation. 

iii) Intraoperative Concerns 

Renal protection during suprarenal aortic cross-clamping remains a controversial topic and thus no recommendations have been included in recent guidelines.^{3, 21} Renal cooling techniques or the use of fenoldopam or mannitol have been considered nephroprotective to some degree in smaller studies.^{22, 23} 

Prior to release of the cross clamp, the administration of an intravenous fluid bolus (500ml  crystalloid or colloid infusion) can mitigate the effects of central hypovolemia caused by aortic cross clamping and the subsequent release of the clamp. Close communication between the surgery and anesthesia teams is crucial to avoid wide fluctuations in blood pressure during reperfusion. The surgeon may have to manually clamp the aorta and slowly release pressure if the patient develops profound hypotension to allow the anesthesiologist to catch up with resuscitation.  

c. Anesthesia Management for Endovascular AAA Repair 

i) Anesthesia Techniques for Endovascular AAA Repair 

The endovascular approach to AAA can be performed under a variety of anesthesia techniques.  General endotracheal anesthesia may be best suited to better control respiration and improve imaging quality. 

Maintenance of anesthesia can be accomplished using volatile anesthetics, such as sevoflurane and desflurane, or with a propofol drip. Opioids like fentanyl or sufentanil can be used for intraoperative pain control. Non-steroidal drugs, such as ketorolac or ibuprofen, may need to be avoided depending on the risk of kidney injury and bleeding. 

Depending on the femoral access approach (percutaneous or cut down), EVAR can be performed under local anesthesia, regional anesthesia (RA) with a nerve plexus block such as ilioinguinal plexus block, or neuraxial anesthesia in the form of epidural or spinal anesthesia. In patients with  contained ruptured AAA, the use of regional or local anesthesia may improve outcomes  (IMPROVE trial).^{24, 25} 

The ilioinguinal nerve plexus block can be performed by the surgeon in the sterile field.²⁶ 

Both the iliohypogastric and the ilioinguinal nerves originate from the nerve root of L1 and perforate the transverse abdominis muscle near the anterior part of the iliac crest. In the anterior abdominal wall, the nerves travel between the transverse abdominis and the internal oblique muscles. The nerve bundle can be visualized using ultrasounds and the injection of 10-20 ml of local anesthetic (e.g., mepivacaine, ropivacaine or bupivacaine) will anesthetize the groin area, as well as the lower portion of the abdominal wall and the upper thigh.

Local anesthesia or regional anesthesia technique can be supplemented with mild to moderate sedation with a propofol or dexmedetomidine drip for patient comfort. 

ii) Monitoring and Access 

Invasive arterial blood pressure monitoring pressure is performed by placing an arterial catheter pre-induction allows for tight blood pressure and hemodynamic impulse control, especially during induction of anesthesia and endotracheal intubation. 

The need for vasoactive drugs as well as significant blood loss is rare during EVAR, hence the placement of central venous catheters is rarely needed. Large bore intravenous access should be adequate to the anticipated blood loss. 

iii) Intraoperative Concerns 

The need for holding respiration during intraprocedural imaging may make neuromuscular blockade necessary. 

d. General and Procedure-Specific Concerns 

General intra-operative concerns: Skin preparation (Chlorhexidine [CHG] wipe timeout for three minutes to dry), Foley placed by trained staff, shaving performed with clippers, maintenance of normothermia. 

Techniques to minimize contrast nephropathy for endovascular procedures in patients with chronic kidney disease (CKD) include perioperative hydration, the use of carbon dioxide (CO2) imaging as needed, minimizing the use of contrast agent, and the possible use of intravascular ultrasound for imaging.  

Techniques to minimize paralysis following endovascular repair include lumbar drain insertion  for high risk thoracoabdominal aneurysm repair, as well as  

Electroencephalography/somatosensory-evoked potentials (EEK/SSEP) monitoring in patients who are at-risk for spinal cord ischemia.

  Steps Prior to Discharge 

General steps include: 

• Foley removal as soon as possible (ASAP) 
• Pulmonary toilet 
• Perioperative glycemic control as indicated 
• Ambulation instruction, physical therapy as needed 
• Wound Care: If applicable (e.g., incisional negative pressure dressing, dry dressing, steps  to prevent wound breakdown)
• Medication: Resumption of home medications and antithrombotic medications, as indicated.

Steps After Discharge 

• Follow-up: Follow-up call within the first week after surgery.  
• Office / Telehealth Visit: Follow-up within one month postoperative, unless indicated sooner. 
• Medication: The use of long-term medications and smoking cessation efforts can be coordinated with the patient’s primary care provider and can include the use of statins or a  proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor in order to achieve optimal low-density lipoprotein (LDL) control. In addition, anti-platelet agents, anti hypertensive agents, and agents for glycemic control should be prescribed, as indicated.  
• Imaging: Most patients especially after endovascular repair receive a CT angiogram and or duplex ultrasound to assess for endoleak at one month after surgery.

References