Open Abdominal Aortic Aneurysm

What the Anesthesiologist Should Know before the Operative Procedure

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

Abdominal aortic aneurysm (AAA) surgery can be emergent, urgent or elective.

Emergent: Ruptured AAA is the 13th-leading cause of death in the United States with an estimated 15,000 deaths per year (in 2004). The patient who presents with abdominal, flank or back pain with an expanding abdominal mass needs to have emergent surgery. There can be distal hypoperfusion that is exacerbated by aggressive blood pressure control in an attempt to limit further rupture. The inferior mesenteric artery is often involved and there can be distal GI tract ischemia. Proximal extension can make the kidneys ischemic. Further proximal extension will put the superior mesenteric artery at risk and this will be associated with significant GI ischemia. There is little time for formal cardiac evaluation. Along with a brief history and physical examination, an assessment of cardiopulmonary reserve (i.e., ability to walk two flights of stairs) will aid in predicting outcome. Preparation for transfusion and invasive hemodynamic monitoring needs to be made. The epidural can be placed only if the patient is hemodynamically stable and risk of epidural hematoma (INR, Plavix, etc.) is normal. ICU postoperative care needs to be arranged.

Urgent: A large aneurysm (>6 to 6.5 cm) or a rapidly expanding aneurysm. A balance between speed and thoroughness will allow preoperative issues to be more fully fleshed out than in an emergent case as there should be time for such tests as a bedside transthoracic cardiac echo. There may not be time for a stress test (if it would be considered under the ACC/AHA guidelines). All preoperative labs can be done. Preparation for transfusion and invasive hemodynamic monitoring needs to be made. The epidural can be placed only if the patient is hemodynamically stable and risk of epidural hematoma (INR, Plavix, etc.) is normal.

Elective: Aneurysm >4.5 cm without any acute pain or organ hypoperfusion. As for any operation, preoperative work-up is guided by the patient’s history. As this is a high-risk surgery, invasive cardiac testing is considered under the appropriate part of the ACC/AHA guidelines. All preoperative labs can be done. Preparation for transfusion and invasive hemodynamic monitoring needs to be made. The epidural can be placed only if risk of epidural hematoma (INR, Plavix, etc.) is normal.

2. Preoperative evaluation

AAA is mostly commonly the result of atherosclerotic disease. Patients need to be evaluated for coronary, carotid/cerebral, and renal ischemia. Many patients will also have smoking-related diseases, so COPD and reactive airways disease need to be considered.

AAA from connective tissue disease (Marfan syndrome and Ehlers-Danlos syndrome type IV – vascular type) usually presents in a younger cohort. Mitral valve disease needs to be considered as a possible concomitant disease in Marfan and Ehlers-Danlos syndrome type IV. Patients with Ehlers-Danlos syndrome type IV can suffer intestinal rupture so NG tubes, Foley catheters, etc. need to placed with care.

Medically unstable conditions warranting further evaluation include coronary and carotic atherosclerotic disease, COPD, renal insufficiency.

Delaying surgery may be indicated if: coronary or carotid disease requires intervention. Delay to allow renal recovery if creatinine is increased after preoperative diagnostic dye load.

3. What are the implications of co-existing disease on perioperative care?

Perioperative risk reduction strategies – AHA/ACC guidelines (http://circ.ahajournals.org/cgi/content/full/116/17/e418) for perioperative cardiac disease risk reduction. Treatment of any pulmonary infection and optimization of COPD care should reduce perioperative pulmonary morbidity, but studies of intensive preoperative pulmonary rehabilitation have not shown consistent improvements in perioperative outcome. Renal outcomes may be improved if 2 weeks elapse between the dye load from preoperative testing and the renal ischemia from aortic cross clamp.

b. Cardiovascular system

Acute/unstable conditions: AHA/ACC guidelines (http://circ.ahajournals.org/cgi/content/full/116/17/e418) for perioperative cardiac disease risk reduction.

Baseline coronary artery disease or cardiac dysfunction: An evaluation of cardiopulmonary reserve (estimation of exercise tolerance) is a reasonable starting point. Antihypertensives should be continued. It is unclear if angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) should be dicontinued prior to surgery. Beta-blockers, calcium channel blockers, and aspirin should be continued. The continuation of Plavix should be individualized and continuation through the perioperative period should be considered if the patient has a drug eluting coronary stent (obviously this makes placement of an epidural too dangerous).

c. Pulmonary

COPD: All usual medications should be continued. Aggressive pulmonary toilet may help, but there is no real proof.

Reactive airways disease (asthma): Continue usual medication.

d. Renal-GI:

The preoperative dye load for diagnosis of the AAA can raise creatinine and potentially cause renal failure, especially if the aneurysm involves the renal arteries. A rise in creatinine should be allowed to normalize prior to elective surgery..

e. Neurologic:

Signs and symptoms of TIA, stroke, and cerebral ischemia/embolism need to be sought due to concomitant carotid disease.

Acute issues: Acute CNS disease warrents concern for a thoracic / aortic arch aneurysm that is disrupting carotid or vertebral arterial flow

f. Endocrine:

Diabetes can be difficult to control given the stress response to an enlarging or ruptured AAA.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

N/A

4. What are the patient's medications and how should they be managed in the perioperative period?

Herbals, vitamins, and relevant OTC drugs should be discontinued.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Vascular surgery patients are often on antihypertensive medications, antiplatelet medications, and HMG CoA reductase (statins) and are sometimes diabetics. The platelet inhibitors need to be handled on a patient-specific basis (see below).

i. What should be recommended with regard to continuation of medications taken chronically?

Cardiac: Antihypertensives should be continued. It is unclear if angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) should be dicontinued prior to surgery. Beta-blockers, calcium channel blockers, and aspirin should be continued. The continuation of Plavix should be individualized and continuation through the perioperative period should be considered if the patient has a drug eluting coronary stent (obviously, this makes placement of an epidural too dangerous).

Pulmonary: Continue all medications.

Renal: Can consider holding AM diuretic.

Neurologic: Continue all medications.

Antiplatelet: Aspirin should be continued. The continuation of Plavix should be individualized and continuation through the perioperative period should be considered if the patient has a drug eluting coronary stent (obviously this makes placement of an epidural too dangerous).

Psychiatric: Stop monoamine oxidase inhibitors.

j. How To modify care for patients with known allergies –

Care for drug allergies is standard: substitution of appropriate drugs with similar function from a different class than the allergen.

k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

Standard measures for latex-allergic patients.

l. Does the patient have any antibiotic allergies- [Tier 2- Common antibiotic allergies and alternative antibiotics]

Antibiotics should cover skin flora. First-generation cephalosporins can be replaced with clindamycin or vancomycin if there is a true allergy. Specific hospital sensitivities should be consulted.

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia (MH)

Documented: Avoid all trigger agents such as succinylcholine and inhalational agents:

Proposed general anesthetic plan: Combine epidural and TIVA can easily avoid MH triggers or any specific medication allergy
Ensure MH cart available [- MH protocol]
Family history or risk factors for MH:

Local anesthetics/ muscle relaxants

5. What laboratory tests should be obtained and has everything been reviewed?

Hemoglobin levels: Due to potential for massive blood loss, both preoperative and intraoperative hemoglobin monitoring is required.

Electrolytes: Due to potential for massive blood loss, both preoperative and intraoperative potassium levels need to be monitored. Due to the risk of perioperative perturbations in renal function, evidence of preoperative renal dysfunction should prompt consideration of a consultation with nephrology to develop a plan for postoperative dialysis. Also, preoperative renal dysfunction from dye studies should prompt a delay of surgery to allow for renal recovery.

Coagulation panel: Due to potential for massive blood loss, both preoperative and intraoperative coagulation monitoring is required.

Imaging: Cardiac stress testing ( MIBI or stress ECHO) is done based upon history and symptomotology.

Room set-up

Prior to the patient’s arrival in the room, preparation for massive resusitations and hemodynamic monitoring needs to be made. It is always easiest to have all the blood (typically 6 units packed red blood cells, 6 units of fresh frozen plasma, and 1 dose [4 units] of platelets) checked and ready for immediate use prior to starting patient care. Similarly, all lab slips for arterial blood gas analysis and/or clotting test should also be filled out ahead of time.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

The major intraoperative challenge in AAA repair is the hemodynamic management for the placement and removal of the aortic cross clamps. This can be accomplished through several complementary routes. An epidural can provide significant afterload reduction. Beta-blockade (typically esmolol) can then be used to control cardiac inotropy and chronotropy. Further vasodilatation/afterload reduction can be achieved with nicardipine, sodium nitroprusside, or nitrogylcerin. Preparation and management of clamp removal are discussed below. Central venous access and arterial blood pressure monitoring are required for tight hemodynamic control. The use of a central venous catheter versus a pulmonary arterial catheter is based more on personal/institutional preference than clear scientific proof of an advantage in perioperative outcome. Regardless, the ability to deliver vasoactive drugs via bolus and infusion needs to be guaranteed.

The aortic clamping is applied as a distal clamp first. Often the iliac arteries are clamped seperately. This allows a staged and progressive increase in afterload. Only after the anesthesiologist has compensated for the increased afterload will the proximal aortic clamp be applied. The placement of the proximal aortic clamp should be discussed ahead of time. Even if the AAA is infrarenal, there may not be sufficient space for the clamp to be applied infrarenally. This is typically the case now as the vast majority of true infrarenal AAAs are repaired endovascularly. The clamp may therefore be placed between the renal arteries or between the renal and celiac axes. The higher the clamp on the aorta, the greater is the afterload reduction. Once the aortic cross clamp is on, the aorta will be transsected. There will be an obligate blood loss from back bleeding. Cell Saver is typically used.

After the proximal anastomosis is complete, the proximal aortic clamp will be moved from native aorta to the graft. As the time between the placement and movement of the clamp should be brief, there is typically not a dramatic reperfusion event. However, if the proximal clamp was supraceliac, then a large area will have been briefly ischemic (liver, spleen, proximal small bowel, some of the stomach) and hypotension can ensue. Typically, vasoconstrictors such as phenylepherine, norepinepherine, or vasopressin are sufficient to offset the afterload reduction (assuming sufficient intravascular volume). If the clamp was supraceliac and on for greater than 10 to 15 minutes, then ½ to 1 g of calcium (chloride or gluconate) will both support afterload, increase inotropy, and stabilze the cardiac membrane if there is potassium washout. Often the proximal clamp will need to be reapplied immediately as there will be leaks identified in the proximal anastomosis; thus, afterload agents need to be used judiciously to prevent wide swings in blood pressure.

During the distal anastomosis (or anastomoses if it is an aortobiliac or bifemoral anastomosis), obligate blood loss from back bleeding will continue. In preparation for removal of the distal aortic cross clamp(s), the patient should be volume loaded. The CVP should be raised to being 2 to 3 cm H2O higher than prior to aortic cross clamping. If a pulmonary arterial catheter is being used, then the pulmonary arterial diastolic should be raised to 2 to 3 cm H2O higher than prior to aortic cross clamping. Essentially this volume loading allows for a redistribution of increased central volume into the increased vascular capacitance of the ischemic legs. Otherwise, there will be pooling of volume into the lower extremities. PRBCs and Cell Saver should be used if the hemoglobin is below 8 to 10 mg/dL. There are no good data to suggest if balanced salt solution vs hetastarch vs albumin imparts any advantage. If blood loss is greater than ~20 mL/kg of ideal body weight, then coagulation testing should be done (if point of care testing or immediate results are available) to determine if FFP, platelets, and/or cryoprecipitate is needed.

For removal of the distal clamp(s), intravenous agents will be necessary. With the washout of the distal GI tract and the lower extremities, there will be an abrupt fall in afterload accompanied by an acid load. If the patient has a near normal cardiac ejection fraction, then ½ to 1 g of calcium (chloride or gluconate) will support afterload, increase inotropy, and stabilze the cardiac membrane. Vasoconstrictors such as phenylephrine, norepinephrine, or vasopressin can also be used to offset the abrupt decrease in afterload. If the patient has a compromised left and/or right ventricle, the inotropic support, typically epinephrine 2 to 8 mcg/min as an infusion, should be considered.

a. Regional anesthesia

Epidural analgesia with a low thoracic catheter (~T10) is strongly recommended. Intraoperative use of the catheter with local anesthetic will provide significant afterload reduction that will decrease the perturbation from the aortic clamp. Postoperative comfort and recovery are improved with the use of dilute local anesthetic and opioid infusion.

Neuraxial

Benefits: As an alternative to epidural analgesia, neuraxial morphine (100 to 300 mcg) can be used for pain relief over the first 18 to 24 hours.
Drawbacks: The patient will be fully anticoagulated, so a traumatic spinal may warrant a delay of the case.

Peripheral nerve block

It is possible that bilateral TAP blocks could be used for postoperative analgesia.

b. General Anesthesia

General anesthesia is required for open AAA repair.

Benefits:General anesthesia is required for open AAA repair. Inhalational anesthetics in combination with epidural analgesia are appropriate. Propofol infusion can also be used. If no epidural is placed, then sufentanil infusion may be appropriate but may have little discernible advantage over bolus opioid.

Drawbacks: The induction and maintenance need to avoid profound hypertension to decrease the risk of AAA rupture. Profound tachycardia and hypotension would need to be avoided due to the high rate of concomitant cardiac disease.

c. Monitored anesthesia care

MAC is not appropriate for open AAA repair.

6. What is the author's preferred method of anesthesia technique and why?

What prophylactic antibiotics should be administered?

Skin flora need to be covered. Cefazolin is appropriate. Clidamycin or vancomycin can be used if there is an allergy to cephalosporins.

What do I need to know about the surgical technique to optimize my anesthetic care?

AAA repair can be done transabdominally (i.e., patient supine) or from a retroperitoneal approach (patient in the right lateral decubitus – need to prepare a soft contour “bean bag” and overhead [Allen] arm support). As discussed above, the surgeon’s placement of proximal and distal aortic clamps needs to be discussed as this will alter the afterload increase with clamp placement (infrarenal < suprarenal < supraceliac) and the drop in afterload when the proximal aortic clamp is moved from native aorta to the graft after the proximal anastomosis is complete. Similarly, bilateral iliac or femoral arterial clamps (distal aortic occlusion) allows for a more staged reperfusion.

What can I do intraoperatively to assist the surgeon and optimize patient care?

Cell Saver should be used routinely. Blood products should be in the room and checked prior to surgical incision. Preparations for arterial blood gas and coagulation studies should be done (forms filled out and syringes/tubes readied) prior to surgical incision.

What are the most common intraoperative complications and how can they be avoided/treated?

Hemodynamic alterations with placement and removal of the aortic cross clamps is discussed in Intraoperative Management. Blood loss can be profound and massive transfusion needs to planned for. Cardiac ischemia from afterload increase from aortic clamp is possble with wall mtion abnormalities reported on TEE.

Complications

Cardiac: Cardiac ischemia from abrupt afterload changes is a significant risk during AAA surgery. While there are no data comparing methods, typical approaches of combined epidural and general anesthesia versus general anesthesia both require active blood pressure management. Initial use of beta-blockade (typically esmolol) to control inotropy and chronotropy (aim for a heart rate below 70) with additional direct vasodilator (nicardipine, sodium nitroprusside, nitrogylcerine, etc) to maintain mean arterial pressure within 20% of baseline. Monitoring of ischemia is more difficult in the lateral decubitus position (retroperitoneal approach) due to the rotation of the heart in the lateral decubitus and the inability to place a V5 lead. Cardiac ischemia can also come from insufficient oxygen delivery either from low oxygen carrying capacity or low mean arterial pressure. Intensive monitoring should reduce this risk. Cardiac arrythmia is possible with pH changes, CO2 changes, release of ischemic mediators and possible embolic phenomena from the reperfusion of the distal extremities. Support of cardiac inotropy with calcium (chloride or gluconate) at the time of intial reperfusion and subsequent support of cardiac performance and blood pressure with vasoactive drugs is typically sufficient. If the patient has a history of pulmonary hypertension or right heart failure then inotropic support of the right heart with epinephrine, isoproterenol, dobutamine and or noreepinephrine need to be considered. Milrinone is not commonly used due to the increased risk of hypotension.

Pulmonary:The vast majority of pulmonary complications are postoperative. They include pneumonia, prolonged intubation/reintubation, pulmonary edema, and acute lung injury. Massive transfusion and resuscitation makes the patient at risk for acute lung injury and pulmonary edema which will often necessitate prolonged intubation. While any general anesthetic will decrease postoperative FRC (functional residual capacity) and thus make hypoxemia and pneumonia more likely, the high abdominal incision and longer duration of the operation increases the risk of pulmonary complication from AAA surgery.

Neurologic: Stroke risk is not different from any major surgery where the patients have significant atherosclerotic disease burden.

a. Neurologic:

N/A

b. If the patient is intubated, are there any special criteria for extubation?

Many patients remain intubated in an ICU for the night after AAA repair. Extubation proceeds when swelling after massive resuscitation subsides; the patient is euthermic, hemodynamically stable, and awake; has their pain properly controlled; and is breathing well.

c. Postoperative management

What analgesic modalities can I implement?

Patient-controlled epidural analgesia via a low to mid thoracic epidural utilizing dilute local anesthetic and opioid probably provides optimal analgesia and improved recovery. For those patients who cannot get or who refuse epidural analgesia, then intravenous patient-controlled opioids combined with nonsteroidal anti-inflammatory drugs and acetaminophen can provide significant pain relief to enable an active pulmonary toilet and early ambulation. Spinal morphine 100 to 300 mcg can provide profound analgesia for up to 24 hours, with the patient then being transitioned to IV PCA opioid.

What level bed acuity is appropriate?

All AAA patients should go to a very high acuity bed for the first 24 hours. The nursing staff should know how to do pulse checks and be able to continue blood replacement.

What are common postoperative complications, and ways to prevent and treat them?

Bleeding from acquired coagulaopathy (blood loss combined with crystaloid replacement), cold, and lack of complete heparin reversal is a concern for all patients. Bleeding from a failure of one of the graft sutures is very rare and often catastrophic. Patients are at high rsk for pulmonary complications (atelectasis, pneumonia), especially because vascular disease is associated with smoking disease. Aggressive postoperative pulmonary toilet combined with excellent analgesia probably reduces this risk.

What's the Evidence?

Davis, CA. “Computed tomography for the diagnosis and management of abdominal aortic aneurysms”. Surg Clin North Am. vol. 91. 2011. pp. 185-93. (This reference is an excellent review of imaging of AAA and how anatomical variation will impact management.)

Moll, FL, Powell, JT, Fraedrich, G, Verzini, F, Haulon, S, Waltham, M, van Herwaarden, JA, Holt, PJ, van Keulen, JW, Rantner, B, Schlosser, FJ, Setacci, F, Ricco, JB. “Management of abdominal aortic aneurysms: clinical practice guidelines of the European Society for Vascular Surgery”. Eur J Vasc Endovasc Surg. vol. 41. 2011. pp. S1-58. (This reference is an excellent review of perioperative care of the patient with AAA.)

Sachs, T, Schermerhorn, M. “Ruptured abdominal aortic aneurysm”. Minerva Chir. vol. 65. 2010. pp. 303-17. (This reference is an excellent review of the emergent presentation and care of a patient with ruptured AAA.)

Toomtong, P, Suksompong, S. “Intravenous fluids for abdominal aortic surgery”. Cochrane Database Syst Rev. 2000. pp. CD000991(A typically thorough review presenting evidence for fluid management during AAA repair.)

“Pathophysiology of abdominal aortic aneurysm relevant to improvements in patients' management”. Curr Opin Cardiol. vol. 24. 2009. pp. 532-8. (This reference is an excellent review of anatomy with focus on echo and catheterization and its impact on management.)

Chaikof, EL, Brewster, DC, Dalman, RL, Makaroun, MS, Illig, KA, Sicard, GA, Timaran, CH, Upchurch, GR, Veith, FJ. “Society for Vascular Surgery. The care of patients with an abdominal aortic aneurysm: the Society for Vascular Surgery practice guidelines”. J Vasc Surg. vol. 50. 2009. pp. S2-49. (This reference is an excellent review of the challenges AAA presents to surgeons and their orientation toward management.)

Monge, M, Eskandari, MK. “Strategies for ruptured abdominal aortic aneurysms”. J Vasc Interv Radiol. vol. 19. 2008. pp. S44-50. (This reference is an excellent review of the emergent presentation and care of a patient with ruptured AAA.)

Wozniak, MF, LaMuraglia, GM, Musch, G. “Anesthesia for open abdominal aortic surgery”. Int Anesthesiol Clin. vol. 43. 2005. pp. 61-78. (A very thorough review of intraoperative strategies and interventions for AAA care.)

Brimacombe, J, Berry, A. “A review of anaesthesia for ruptured abdominal aortic aneurysm with special emphasis on preclamping fluid resuscitation”. Anaesth Intensive Care. vol. 21. 1993. pp. 311-23. (A primer on immediate urgent care of the unstable patient presenting with ruptured AAA.)

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