N. Martin Giesecke, M.D.

Every year in the United States, there are roughly 15,000 deaths directly attributable to abdominal aortic aneurysms (AAA).¹ Of those patients whose aneurysms rupture outside a hospital, 62 percent die at the scene and the overall mortality is 90 percent.² In 1984, for those patients with ruptured aneurysms, hospital losses per patient were in excess of $24,000.³ Elective repair of AAA saved roughly 2,000 lives per year and cost $50 million annually in 1984.⁴ Elective surgical repair, indicated when aneurysms become larger than 5 cm in diameter, carries up to a 20 percent mortality if a comorbid illness is present.^5,6

Endovascular stent repair of AAA was first described in 1991.⁷ In the United States, the first successful endovascular AAA repair was reported in 1995.⁸ In this procedure, a stent-equipped balloon catheter is passed via a femoral arteriotomy to the level of the AAA. Much like a coronary artery stent, the AAA stent is deployed by inflation of the catheter balloon. Exclusion of the aneurysm occurs as the stent expands against the normal aortic intima proximal and distal to the aneurysm. The blood remaining in the aneurysmal sac thromboses around the stent. The stent may be simple, with a constant bore for short aneurysms limited to the abdominal aorta. Aneurysms extending into the iliac bifurcation require more complicated stents with a large bore portion for the abdominal aorta and a smaller diameter extension for placement in one of the iliac arteries. In this circumstance, a second small stent is generally deployed in the contralateral iliac artery, mating with an orifice in the wall of the larger stent. Because the stents are made of a fabric mesh supported by a semi-rigid metal alloy framework (after deployment), they are currently limited to infrarenal aneurysms of a non-tortuous nature.

Complications of stent repair include failure of the device to properly seat itself against the aorta; thus, blood may continue to leak around the stent into the aneurysm. Embolization of atheromatous or thrombotic debris is possible. Migration of the device may present problems of arterial occlusion. Tortuous iliac arteries may preclude passage into the aorta of the stent-equipped balloon catheter. Finally, acute dissection or rupture of the aneurysm can occur.

Advantages of endovascular stent repair of AAA are obvious. There is no abdominal incision to cause postoperative pain and/or pulmonary dysfunction. There is no aortic cross clamp placement and no retroperitoneal dissection required. Typically, these patients receive little or no transfusion of homologous blood products. Not only do these factors make endovascular stent repair of AAA less stressful than surgical repair for high risk patients, they also allow the anesthesiologist a bit more choice in anesthetic technique. Patients may be given monitored anesthesia care, regional anesthesia or general anesthesia. Regional anesthesia techniques have included epidural only⁹ and combined spinal/epidural.¹⁰ Less pulmonary insult makes general anesthesia a viable option in most patients.¹¹ The final choice of anesthetic technique probably is not so important as is the smooth application of that technique.

The anesthesiologist must remain aware of certain aspects of endovascular repair that will affect the overall plan. These procedures typically require significant patient exposure during the surgical prep and drape. Heat loss may be profound; thus, temperature conservation methods should be maximized. Stent deployment takes place during patient apnea (so the fluoroscopic image does not move, allowing precise placement of the device). Awake and sedated patients must therefore have the ability to hold their breath. In addition, a lower heart rate allows for less movement interference of the image caused by beat to beat aortic distension. Use of fluoroscopy requires an understanding of radiation safety procedures and use appropriate measures to protect oneself against undue exposure.

There is always the possibility of the need to convert to open repair of the aneurysm. Aortic dissection may occur and if undetected by fluoroscopy, retroperitoneal or intra-abdominal bleeding can lead to rapid hypotension. Should this occur, the chosen anesthesia plan may have to be altered. Assuring adequate intravascular access for rapid volume resuscitation and arterial access for continuous blood pressure monitoring are understandably important. The anesthesiologist may also find it wise to have blood available in the room for immediate transfusion. The patient's status may preclude transfer to a standard operating room, so all personnel must be ready to deal with operative repair wherever the endovascular procedure is performed (e.g., radiology suite or cardiac catheterization lab).

Since endovascular exclusion of AAA is being used in patients who are considered poor surgical candidates because of coexisting medical problems, the anesthesiologist must take into account the impact of concurrent disease. Most of these patients are at risk of having coronary artery disease. Monitoring ECG leads II and V₅ will maximize the anesthesiologist's ability to recognize myocardial ischemia. Though not reported in these patients, transesophageal echocardiography could provide the observer with a more timely diagnosis of ischemic myocardial dysfunction. Those patients with poor left ventricular function, congestive heart failure, or significant pulmonary dysfunction may not be able to remain supine for the duration of the procedure without receiving general anesthesia. Likewise, a general anesthetic may be necessary for patients with chronic low back pain who may not tolerate lying still for the entire procedure.

At Texas Heart Institute, endovascular stent repairs of abdominal aortic aneurysms are currently performed by cardiologists in the cardiac catheterization laboratory. Though femoral artery access is often accomplished percutaneously using Seldinger's technique, the arteriotomy size (at least 12 Fr) always requires surgical repair at the close of the procedure. All patients receive general anesthesia. Routine monitoring is augmented by two lead ECG (II, V₅) and intra-arterial blood pressure measurement. Patients receive a large bore central venous catheter. At least two units of homologous packed red blood cells are available in the room. Heat conservation is employed. Appropriate lead garments and leaded glass shielding is utilized to protect all personnel from radiation exposure. Despite a high percentage of patients with significant pulmonary disease, most patients are successfully extubated at the completion of the procedure, prior to transport out of the catheterization lab.

The long term risks of stent failure have yet to be seen, as current stent technology is still rapidly evolving. Just as endoscopic surgical procedures have proliferated, so have endovascular stent repairs. Coronary stents now accompany nearly every percutaneous transluminal coronary angioplasty. Stents are used to repair the various obstructions of peripheral vascular disease in femoral, subclavian and carotid arteries. Early studies of cerebral arterial stents are underway. At Texas Heart Institute, a study of stent repair of aneurysms of the descending thoracic aorta will begin soon. Endovascular stent repair of abdominal aortic aneurysms is a new technique with the potential to benefit many patients who were previously considered high-risk candidates for surgical repair.

References:

1. National Center for Health Statistics. Vital Statistics of the United States, 1988: Mortality. Part A. Washington, DC: US Dept. of Health and Human Services, DHHS Publication (PHS 91-1101); 1991.
2. Ingoldby CJ, Wujanto R, Mitchell JE. Impact of vascular surgery on community mortality from ruptured aortic aneurysms. Br J Surg. 1986; 73:551.
3. Breckwoldt WL, Mackey WC, O'Donnell TF Jr. The economic implications of high-risk abdominal aortic aneurysms. J Vasc Surg. 1991; 13:798.
4. Pasch AR, Ricotta JJ, May AG, et al. Abdominal aortic aneurysm: The case for elective resection. Circulation. 1984; 70 (suppl 1):I-1.
5. McCombs PR, Roberts B. Acute renal failure following resection of abdominal aortic aneurysm. Surg Gynecol Obstet. 1979; 148:175.
6. Gardner RJ, Gardner NL, Tarnay TJ, et al. The surgical experience and a one to sixteen year follow-up of 277 abdominal aortic aneurysms. Am J Surg. 1978; 135:226.
7. Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg. 1991; 5:491.
8. Parodi JC, Marin ML, Veith FJ. Transfemoral, endovascular stented graft repair of an abdominal aortic aneurysm. Arch Surg. 1995; 130:549.
9. Chuter TAM, Reilly LM. Surgical reconstruction of the iliac arteries prior to endovascular aortic aneurysm repair. J Endovasc Surg. 1997; 4:307.
10. Aadahl P, Lundbom J, Hatlinghus S, et al. Regional anesthesia for endovascular treatment of abdominal aortic aneurysms. J Endovasc Surg. 1997; 4:56.
11. Boyle JR, Thompson JP, Thompson MM, et al. Improved respiratory function and analgesia control after endovascular AAA repair. J Endovasc Surg. 1997; 4:62.

N. Martin Giesecke, M.D., is an attending anesthesiologist at Texas Heart Institute/St. Luke's Episcopal Hospital, and Clinical Assistant Professor, Department of Anesthesiology, University of Texas Health Sciences Center, Houston, Texas.

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