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The use of an aortoiliac side-arm conduit to maintain distal perfusion during thoracoabdominal aortic aneurysm repair
TECHNICAL NOTES
The use of an aortoiliac side-arm conduit to maintain distal perfusion during thoracoabdominal aortic aneurysm repair Kenneth Ouriel, MD, Cleveland, Ohio Thoracoabdominal aneurysm repair continues to be associated with a significant risk of operative complications, many of which are related to the prolonged period of aortic cross clamping inherent in the procedure. A variety of adjuvant techniques have been used in attempts to decrease morbidity, including atriofemoral extracorporal bypass, subarachnoid drainage, epidural cooling, and preliminary axillofemoral bypass. Herein is described a method to maintain distal perfusion with a side-arm conduit, originating from the most proximal aspect of the aortic graft and terminating on the left iliac artery. The technique has the potential to minimize hemodynamic instability while decreasing the period of pelvic and lower extremity ischemia and simplifying reattachment of aortic branch vessels. This method provides another option that can be considered in these technically demanding operative procedures. (J Vasc Surg 2003;37:214-8.)
The repair of thoracoabdominal aneurysms is associated with a high rate of perioperative complications, including paraplegia, renal failure, intestinal ischemia, and hepatic insufficiency with coagulopathy.1-3 Despite the complexity of the operative procedure, each of these complications shares a single common pathophysiologic mechanism, endorgan hypoperfusion. In some instances, the hypoperfusion occurs as a result of embolization of debris from the aneurysm sac, in some cases, from in situ thrombosis of a major artery supplying the organ, and in still others, from the failure to reimplant a critical vessel. Oftentimes, however, the event develops during the aortic cross-clamp period, when the performance of the anastomoses is associated with an obligatory period of ischemia to the spinal cord, kidneys, and intestines. Further, protracted periods of hepatic ischemia may produce coagulopathy, and lower extremity ischemia generates cardiodepressants and other toxic byproducts.4 These byproducts compound the cardiac instability associated with proximal aortic occlusion, increasing cardiac workload to levels beyond those in which compensation is possible.5,6 Extracorporal circulatory assistance is a commonly used adjuvant employed to minimize the aforementioned complications.7,8 In the most common application, atrial-femoral bypass is used, with insertion of a cannula through the
inferior pulmonary vein to draw blood from the left atrium and return blood through a femoral arterial cannula. Although this technique of “left heart bypass” does provide a margin of safety during the requisite cross-clamp period, the use of moderate doses of anticoagulation and the frequent occurrence of some degree of platelet dysfunction even with centrifugal pumps represent limitations.9-11 Although infrequent, cannulation of the atrium and femoral artery can be associated with injury to these structures. Lastly, the technique is rarely available to the peripheral vascular surgeons who perform thoracoabdominal aneurysm repair. In an effort to decrease the frequency of perioperative ischemic complications while avoiding the use of extracorporal perfusion techniques, a side-branch conduit originating from the proximal aspect of the large diameter thorocoabdominal graft has been constructed and used to limit the distal ischemic period to that period of time necessary to perform the proximal anastomosis. This technique provides the opportunity to revascularize the intercostal arteries while maintaining perfusion to the viscera, kidneys, and lower extremities. Further, cardiac afterload is minimized throughout the procedure, and hemodynamic changes are minimized during the period immediately after clamp release.
From the Department of Vascular Surgery, The Cleveland Clinic Foundation. Competition of interest: nil. Reprint requests: Kenneth Ouriel, MD, Chairman, Department of Vascular Surgery, The Cleveland Clinic Foundation, Desk S40, 9500 Euclid Ave, Cleveland, OH 44195 (e-mail: [email protected]). Copyright © 2003 by The Society for Vascular Surgery and The American Association for Vascular Surgery. 0741-5214/2003/$30.00 ⫹ 0 doi:10.1067/mva.2003.72
OPERATIVE TECHNIQUE
214
The procedure is begun in a manner not dissimilar from traditional thoracoabdominal aneurysm repair. The patient is placed in a lateral decubitus position, with the left arm supported above the neck and the pelvis flattened to provide access to both the left and right groins. The aorta is exposed through a thoracoretroperitoneal approach. The
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Fig 1. Anastomosis of distal aspect of side-arm conduit to left common iliac artery is performed first. When this vessel is heavily diseased, external iliac artery provides second outflow option.
incision is placed over the sixth intercostal space, running in a curvilinear fashion to a point just below the umbilicus. In the case of some type I and II thoracoabdominal aneurysms, an additional intercostal incision may be necessary in the third or fourth interspace, with resection of the fourth rib to obtain adequate proximal exposure. This more proximal incision facilitates exposure of the distal aortic arch, the left subclavian artery origin, and the most proximal descending thoracic aorta. The retroperitoneum is entered first, with division of the oblique muscles of the flank and the anterior fascia of the rectus abdominus muscle. The posterior rectus fascia is left intact until, after careful separation of the fibers of the transversus abdominus muscle laterally, the retroperitoneal space is entered. At this point, the fascial layer immediately overlying the peritoneum can be separated by gently wiping the peritoneal sac away from it; thereafter, the fascia can be safely incised without invasion of the peritoneal cavity. When possible, the peritoneal sac is separated from the dome of the diaphragm with the digits and palm of the operator’s hand. Oftentimes, however, sharp dissection must be used as a result of adhesions to the muscle fibers of the diaphragm. At this point, the chest is entered through the sixth or seventh interspace, and the costal margin is crossed as anterior as is possible to avoid transection of multiple ribs at a point prior to their confluence. Finally, the diaphragm is incised in a circumferential
Fig 2. Proximal aortic anastomosis is constructed, and clamp is moved to point just distal to side arm.
fashion, leaving a 3-cm margin laterally to facilitate subsequent repair. Division of the diaphragm is terminated at the crus, where the splayed muscle fibers overlie the aneurysm. The neck of the aorta proximal to the aneurysm is exposed and prepared for clamp placement. Dissection of the aneurysm commences at the level of the ascending lumbar vein, which must be divided to allow the left renal vein to be released anteriomedially. The origin of the left renal artery is exposed next; when not immediately visualized, this vessel can be palpated as a nodular structure on the lateral aspect of the aorta. The celiac trunk and the superior mesenteric artery are exposed as they originate from the anterior aspect of the aorta. The distal aorta is cleared of surrounding tissue over its anterior and leftlateral aspects at the location of the distal anastomosis. Finally, the left common or external iliac artery is exposed over a length suitable for the distal anastomosis of the bypass conduit. The patient undergoes systemic heparinization, but the dose is limited to 30 to 50 U/kg (2500 to 5000 U) and an activated clotting time of 1.5 times baseline (200 seconds). The left iliac vessels are clamped, and the side branch of the conduit (Hemashield-Gold 1, Boston Scientific, Natick,
216 Ouriel
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Fig 4. Left renal anastomosis is constructed to side of main graft. Fig 3. Visceral patch anastomosis is sewn, including celiac, superior mesenteric, and right renal ostia.
Mass) is sewn end to side to the common or external iliac artery, whichever is less diseased (Fig 1). Next, the aorta is clamped just beyond the left subclavian origin or, occasionally, on the arch between the left common carotid and the left subclavian vessels. In some patients, a segment of thoracic aorta may be found to be free of thrombus or heavy calcification just above the celiac axis. In these cases, a second clamp is positioned at this level to allow retrograde perfusion of the renal and visceral vessels during reimplantation of intercostal vessels immediately after the completion of the proximal aortic anastomosis. In most cases, however, the second clamp is placed at the aortic bifurcation to allow perfusion of both iliac arteries or on the left common iliac artery to allow perfusion of the left pelvis and left leg. The aorta is opened longitudinally, and the proximal anastomosis is constructed in an expeditious manner (Fig 2). On completion of this anastomosis, the aortic clamp is repositioned on the graft just beyond the side branch. Distal perfusion is to the pelvis and limbs, and the short period of total aortic clamping is limited to approximately 15 minutes, resulting in an attenuation of the hemodynamic problems normally associated with aortic unclamping.
The visceral patch is tailored, usually including the celiac, superior mesenteric, and right renal orifices. The patch is anastomosed after excision of an elliptic button off the prosthesis (Fig 3). The left renal artery is excised off the aneurysm wall with a button of aortic wall to allow easy anastomosis to a site just inferolateral to the visceral patch (Fig 4). When, for anatomic reasons, such a configuration is not possible, the side-branch conduit itself can be used as inflow for the left kidney, with construction of an end of artery to side of conduit anastomosis. Finally, the distal anastomosis to the aortic terminus is performed. The use of the side-branch graft configuration provides a level of flexibility for intercostal reattachment (Fig 5). It is our practice to reimplant large intercostals arteries without visible truly pulsatile back bleeding. Further, other investigators have advocated the use of motor-evoked potentials to guide the timing of reimplantation and to identify those vessels that provide spinal cord perfusion.12 Although this approach remains somewhat controversial, maintenance of near normal lower extremity perfusion is a prerequisite because ischemia of the legs limits peripheral nerve conduction irrespective of spinal cord hypoperfusion. Thus, the use of evoked potentials is not feasible with a simple “clamp and sew” technique. When early reattachment is deemed necessary, the main body of the conduit is anastomosed to the back wall of the aorta prior to the visceral patch.
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Fig 5. Side arm facilitates construction of intercostal anastomoses. Anastomosis of two patches of intercostal pairs has been depicted in this case. Fig 6. Completed procedure.
Alternatively, reattachment of intercostal arteries can be more easily performed as the last step, with the side arm as the inflow site. The bypass conduit is always left in place, without detaching the iliac anastomosis (Fig 6). Despite competitive flow, the conduit is almost always observed to be patent on late follow-up computed tomographic scan. The diaphragm is closed, leaving the conduit in the aortic hiatus parallel to the main graft. Finally, the aneurysm sac is approximated over the grafts, and the wound is closed in layers over one or two chest tubes. We have used this technique in more than 40 patients undergoing thoracoabdominal aneurysm repair. Our experience is too preliminary to draw concrete conclusions with respect to morbidity or mortality advantages. In particular, our small numbers have precluded the ability to show reductions in the rate of paraplegia or perioperative mortality. Subjectively, however, an enhanced degree of hemodynamic stability has been obvious, without the dramatic hypotension and acidosis that sometimes accompany aortic unclamping when a nonbypass technique has been used. DISCUSSION A variety of intraoperative tactics have been used to diminish the rate of complications associated with the
repair of thoracoabdominal aortic aneurysms.7,13-18 Distal perfusion with left heart bypass or other partial cardiopulmonary extracorporal bypass methods can be used to maintain perfusion during the period of aortic occlusion. Cannulation of the femoral artery and left atrium directly or through the inferior pulmonary vein is not without risk, however, and a high level of anticoagulation must be maintained with many of the available extracorporal devices. Further, the vigorous jet of retrograde bloodflow associated with these methods may dislodge luminal debris into the renal and mesenteric circulation. Subarachnoid drainage and epidural cooling have been used to prevent spinal cord ischemia, but these techniques do not directly address the myriad complications related to other organs.19,20 Branches have been sewn to the main graft to allow perfusion of the visceral and renal vessels during performance of the proximal anastomosis, but lower extremity perfusion is not addressed with these techniques.21 Axillofemoral bypass grafts can be placed before commencement of the thoracoabdominal aneurysm repair.22 Although cumbersome and rarely used, axillofemoral bypass does provide a means of maintaining distal perfusion without the need for high dose heparinization. Competitive flow phenomena compounded by the long,
218 Ouriel
relatively high-resistance axillofemoral conduit may occasionally result in occlusion of the graft, such that it is nonfunctional at the time of aortic clamping. As a modification of the axillofemoral bypass technique and one that is less unwieldy, we have used an internal side-arm bypass conduit originating from the proximal main aortic graft. This configuration sustains distal perfusion during the period of aortic occlusion, at least to the pelvis and legs and, in some cases, to the viscera as well. Maintenance of antegrade bloodflow into the hypogastric arteries may provide some degree of protection against spinal cord ischemia during the aortic cross-clamp period.23 From the standpoint of diagnosis, the sustenance of lower extremity perfusion prevents limb ischemia and allows the use of motor-evoked potentials as a means of identifying spinal cord ischemia at a time when it can be corrected.24,25 Further, the side-branch limb provides flexibility for reattachment of important intercostal arteries, which, when arising at the lower thoracic level, may be directly opposite the visceral patch, and reattachment to the main graft is technically challenging. Left renal artery reconstruction can be facilitated in a similar manner. Lastly, if the intercostal patch undergoes late aneurysmal change, the side branch may be occluded proximally and distally via percutaneous means, thereby excluding systemic inflow to the degenerated segment. In summary, the technique of using an internal bypass graft to provide flow to the visceral, renal, and distal vasculature offers another option to facilitate the repair of proximal thoracoabdominal aortic aneurysms. Although the method should be considered in patients with type I, II, and III aneurysms where the risk of end-organ ischemic complications remains great, objective comparative studies will be necessary to document clinical benefit. REFERENCES 1. Svensson LG, Crawford ES, Hess KR, Coselli JS, Safi HJ. Experience with 1509 patients undergoing thoracoabdominal aortic operations. J Vasc Surg 1993;17:357-68. 2. Crawford ES, Crawford JL, Safi HJ, Coselli JS, Hess KR, Brooks B, et al. Thoracoabdominal aortic aneurysms: preoperative and intraoperative factors determining immediate and long-term results of operations in 605 patients. J Vasc Surg 1986;3:389-404. 3. Derrow AE, Seeger JM, Dame DA, Carter RL, Ozaki CK, Flynn TC, et al. The outcome in the United States after thoracoabdominal aortic aneurysm repair, renal artery bypass, and mesenteric revascularization. J Vasc Surg 2001;34:54-61. 4. Galt SW, Bech FR, McDaniel MD, Dain BJ, Yeager MP, Schneider JR, et al. The effect of ibuprofen on cardiac performance during abdominal aortic cross-clamping. J Vasc Surg 1991;13:876-83. 5. Fiore WM, Ouriel K, Green R, Geary JE. High-risk aortic aneurysm repair with partial cardiopulmonary bypass. J Vasc Surg 1987;6:563-5. 6. Hafez HM, Berwanger CS, McColl A, Richmond W, Wolfe JH, Mansfield AO, et al. Myocardial injury in major aortic surgery. J Vasc Surg 2000;31:742-50. 7. Frank SM, Parker SD, Rock P, Gorman RB, Kelly S, Beattie C, et al. Moderate hypothermia, with partial bypass and segmental sequential repair for thoracoabdominal aortic aneurysm. J Vasc Surg 1994;19:68797.
JOURNAL OF VASCULAR SURGERY January 2003
8. Safi HJ, Miller CC III, Subramaniam MH, Campbell MP, Iliopoulos DC, O’Donnell JJ, et al. Thoracic and thoracoabdominal aortic aneurysm repair using cardiopulmonary bypass, profound hypothermia, and circulatory arrest via left side of the chest incision. J Vasc Surg 1998;28: 591-8. 9. Wahba A, Rothe G, Lodes H, Barlage S, Schmitz G. The influence of the duration of cardiopulmonary bypass on coagulation, fibrinolysis and platelet function. Thorac Cardiovasc Surg 2001;49):153-6. 10. Kawahito K, Mohara J, Misawa Y, Fuse K. Platelet damage caused by the centrifugal pump: in vitro evaluation by measuring the release of alpha-granule packing proteins. Artif Organs 1997;21:1105-9. 11. Belcher PR, Muriithi EW, Milne EM, Wanikiat P, Wheatley DJ, Armstrong RA. Heparin, platelet aggregation, neutrophils, and cardiopulmonary bypass. Thromb Res 2000;98:249-56. 12. van Dongen EP, Schepens MA, Morshuis WJ, ter Beek HT, Aarts LP, de Boer A, et al. Thoracic and thoracoabdominal aortic aneurysm repair: use of evoked potential monitoring in 118 patients. J Vasc Surg 2001; 34:1035-40. 13. Davison JK, Cambria RP, Vierra DJ, Columbia MA, Koustas G. Epidural cooling for regional spinal cord hypothermia during thoracoabdominal aneurysm repair. J Vasc Surg 1994;20:304-10. 14. Jacobs MJ, Meylaerts SA, de Haan P, de Mol BA, Kalkman CJ. Strategies to prevent neurologic deficit based on motor-evoked potentials in type I and II thoracoabdominal aortic aneurysm repair. J Vasc Surg 1999;29:48-57. 15. McCullough JL, Hollier LH, Nugent M. Paraplegia after thoracic aortic occlusion: influence of cerebrospinal fluid drainage. Experimental and early clinical results. J Vasc Surg 1988;7:153-60. 16. Safi HJ, Hess KR, Randel M, Iliopoulos DC, Baldwin JC, Mootha RK, et al. Cerebrospinal fluid drainage and distal aortic perfusion: reducing neurologic complications in repair of thoracoabdominal aortic aneurysm types I and II. J Vasc Surg 1996;23:223-8. 17. Safi HJ, Miller CC III, Carr C, Iliopoulos DC, Dorsay DA, Baldwin JC. Importance of intercostal artery reattachment during thoracoabdominal aortic aneurysm repair [comments]. J Vasc Surg 1998;27:58-66. 18. Shiiya N, Yasuda K, Matsui Y, Sakuma M, Sasaki S. Spinal cord protection during thoracoabdominal aortic aneurysm repair: results of selective reconstruction of the critical segmental arteries guided by evoked spinal cord potential monitoring. J Vasc Surg 1995;21:970-5. 19. Cambria RP, Davison JK, Carter C, Brewster DC, Chang Y, Clark KA, et al. Epidural cooling for spinal cord protection during thoracoabdominal aneurysm repair: a five-year experience. J Vasc Surg 2000;31: 1093-102. 20. Cambria RP, Davison JK, Zannetti S, L’Italien G, Brewster DC, Gertler JP, et al. Clinical experience with epidural cooling for spinal cord protection during thoracic and thoracoabdominal aneurysm repair. J Vasc Surg 1997;25:234-41. 21. Cambria RP, Davison JK, Giglia JS, Gertler JP. Mesenteric shunting decreases visceral ischemia during thoracoabdominal aneurysm repair. J Vasc Surg 1998;27:745-9. 22. Comerota AJ, White JV. Reducing morbidity of thoracoabdominal aneurysm repair by preliminary axillofemoral bypass. Am J Surg 1995; 170:218-22. 23. Picone AL, Green RM, Ricotta JR, May AG, DeWeese JA. Spinal cord ischemia following operations on the abdominal aorta. J Vasc Surg 1986;3:94-103. 24. Laschinger JC, Owen J, Rosenbloom M, Cox JL, Kouchoukos NT. Direct noninvasive monitoring of spinal cord motor function during thoracic aortic occlusion: use of motor evoked potentials. J Vasc Surg 1988;7:161-71. 25. Svensson LG, Patel V, Robinson MF, Ueda T, Roehm JO Jr, Crawford ES. Influence of preservation or perfusion of intraoperatively identified spinal cord blood supply on spinal motor evoked potentials and paraplegia after aortic surgery. J Vasc Surg 1991;13:355-65. Submitted Jun 21, 2002; accepted Aug 13, 2002.
The use of an aortoiliac side-arm conduit to maintain distal perfusion during thoracoabdominal aortic aneurysm repair Kenneth Ouriel, MD, Cleveland, Ohio Thoracoabdominal aneurysm repair continues to be associated with a significant risk of operative complications, many of which are related to the prolonged period of aortic cross clamping inherent in the procedure. A variety of adjuvant techniques have been used in attempts to decrease morbidity, including atriofemoral extracorporal bypass, subarachnoid drainage, epidural cooling, and preliminary axillofemoral bypass. Herein is described a method to maintain distal perfusion with a side-arm conduit, originating from the most proximal aspect of the aortic graft and terminating on the left iliac artery. The technique has the potential to minimize hemodynamic instability while decreasing the period of pelvic and lower extremity ischemia and simplifying reattachment of aortic branch vessels. This method provides another option that can be considered in these technically demanding operative procedures. (J Vasc Surg 2003;37:214-8.)
The repair of thoracoabdominal aneurysms is associated with a high rate of perioperative complications, including paraplegia, renal failure, intestinal ischemia, and hepatic insufficiency with coagulopathy.1-3 Despite the complexity of the operative procedure, each of these complications shares a single common pathophysiologic mechanism, endorgan hypoperfusion. In some instances, the hypoperfusion occurs as a result of embolization of debris from the aneurysm sac, in some cases, from in situ thrombosis of a major artery supplying the organ, and in still others, from the failure to reimplant a critical vessel. Oftentimes, however, the event develops during the aortic cross-clamp period, when the performance of the anastomoses is associated with an obligatory period of ischemia to the spinal cord, kidneys, and intestines. Further, protracted periods of hepatic ischemia may produce coagulopathy, and lower extremity ischemia generates cardiodepressants and other toxic byproducts.4 These byproducts compound the cardiac instability associated with proximal aortic occlusion, increasing cardiac workload to levels beyond those in which compensation is possible.5,6 Extracorporal circulatory assistance is a commonly used adjuvant employed to minimize the aforementioned complications.7,8 In the most common application, atrial-femoral bypass is used, with insertion of a cannula through the
inferior pulmonary vein to draw blood from the left atrium and return blood through a femoral arterial cannula. Although this technique of “left heart bypass” does provide a margin of safety during the requisite cross-clamp period, the use of moderate doses of anticoagulation and the frequent occurrence of some degree of platelet dysfunction even with centrifugal pumps represent limitations.9-11 Although infrequent, cannulation of the atrium and femoral artery can be associated with injury to these structures. Lastly, the technique is rarely available to the peripheral vascular surgeons who perform thoracoabdominal aneurysm repair. In an effort to decrease the frequency of perioperative ischemic complications while avoiding the use of extracorporal perfusion techniques, a side-branch conduit originating from the proximal aspect of the large diameter thorocoabdominal graft has been constructed and used to limit the distal ischemic period to that period of time necessary to perform the proximal anastomosis. This technique provides the opportunity to revascularize the intercostal arteries while maintaining perfusion to the viscera, kidneys, and lower extremities. Further, cardiac afterload is minimized throughout the procedure, and hemodynamic changes are minimized during the period immediately after clamp release.
From the Department of Vascular Surgery, The Cleveland Clinic Foundation. Competition of interest: nil. Reprint requests: Kenneth Ouriel, MD, Chairman, Department of Vascular Surgery, The Cleveland Clinic Foundation, Desk S40, 9500 Euclid Ave, Cleveland, OH 44195 (e-mail: [email protected]). Copyright © 2003 by The Society for Vascular Surgery and The American Association for Vascular Surgery. 0741-5214/2003/$30.00 ⫹ 0 doi:10.1067/mva.2003.72
OPERATIVE TECHNIQUE
214
The procedure is begun in a manner not dissimilar from traditional thoracoabdominal aneurysm repair. The patient is placed in a lateral decubitus position, with the left arm supported above the neck and the pelvis flattened to provide access to both the left and right groins. The aorta is exposed through a thoracoretroperitoneal approach. The
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Ouriel 215
Fig 1. Anastomosis of distal aspect of side-arm conduit to left common iliac artery is performed first. When this vessel is heavily diseased, external iliac artery provides second outflow option.
incision is placed over the sixth intercostal space, running in a curvilinear fashion to a point just below the umbilicus. In the case of some type I and II thoracoabdominal aneurysms, an additional intercostal incision may be necessary in the third or fourth interspace, with resection of the fourth rib to obtain adequate proximal exposure. This more proximal incision facilitates exposure of the distal aortic arch, the left subclavian artery origin, and the most proximal descending thoracic aorta. The retroperitoneum is entered first, with division of the oblique muscles of the flank and the anterior fascia of the rectus abdominus muscle. The posterior rectus fascia is left intact until, after careful separation of the fibers of the transversus abdominus muscle laterally, the retroperitoneal space is entered. At this point, the fascial layer immediately overlying the peritoneum can be separated by gently wiping the peritoneal sac away from it; thereafter, the fascia can be safely incised without invasion of the peritoneal cavity. When possible, the peritoneal sac is separated from the dome of the diaphragm with the digits and palm of the operator’s hand. Oftentimes, however, sharp dissection must be used as a result of adhesions to the muscle fibers of the diaphragm. At this point, the chest is entered through the sixth or seventh interspace, and the costal margin is crossed as anterior as is possible to avoid transection of multiple ribs at a point prior to their confluence. Finally, the diaphragm is incised in a circumferential
Fig 2. Proximal aortic anastomosis is constructed, and clamp is moved to point just distal to side arm.
fashion, leaving a 3-cm margin laterally to facilitate subsequent repair. Division of the diaphragm is terminated at the crus, where the splayed muscle fibers overlie the aneurysm. The neck of the aorta proximal to the aneurysm is exposed and prepared for clamp placement. Dissection of the aneurysm commences at the level of the ascending lumbar vein, which must be divided to allow the left renal vein to be released anteriomedially. The origin of the left renal artery is exposed next; when not immediately visualized, this vessel can be palpated as a nodular structure on the lateral aspect of the aorta. The celiac trunk and the superior mesenteric artery are exposed as they originate from the anterior aspect of the aorta. The distal aorta is cleared of surrounding tissue over its anterior and leftlateral aspects at the location of the distal anastomosis. Finally, the left common or external iliac artery is exposed over a length suitable for the distal anastomosis of the bypass conduit. The patient undergoes systemic heparinization, but the dose is limited to 30 to 50 U/kg (2500 to 5000 U) and an activated clotting time of 1.5 times baseline (200 seconds). The left iliac vessels are clamped, and the side branch of the conduit (Hemashield-Gold 1, Boston Scientific, Natick,
216 Ouriel
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Fig 4. Left renal anastomosis is constructed to side of main graft. Fig 3. Visceral patch anastomosis is sewn, including celiac, superior mesenteric, and right renal ostia.
Mass) is sewn end to side to the common or external iliac artery, whichever is less diseased (Fig 1). Next, the aorta is clamped just beyond the left subclavian origin or, occasionally, on the arch between the left common carotid and the left subclavian vessels. In some patients, a segment of thoracic aorta may be found to be free of thrombus or heavy calcification just above the celiac axis. In these cases, a second clamp is positioned at this level to allow retrograde perfusion of the renal and visceral vessels during reimplantation of intercostal vessels immediately after the completion of the proximal aortic anastomosis. In most cases, however, the second clamp is placed at the aortic bifurcation to allow perfusion of both iliac arteries or on the left common iliac artery to allow perfusion of the left pelvis and left leg. The aorta is opened longitudinally, and the proximal anastomosis is constructed in an expeditious manner (Fig 2). On completion of this anastomosis, the aortic clamp is repositioned on the graft just beyond the side branch. Distal perfusion is to the pelvis and limbs, and the short period of total aortic clamping is limited to approximately 15 minutes, resulting in an attenuation of the hemodynamic problems normally associated with aortic unclamping.
The visceral patch is tailored, usually including the celiac, superior mesenteric, and right renal orifices. The patch is anastomosed after excision of an elliptic button off the prosthesis (Fig 3). The left renal artery is excised off the aneurysm wall with a button of aortic wall to allow easy anastomosis to a site just inferolateral to the visceral patch (Fig 4). When, for anatomic reasons, such a configuration is not possible, the side-branch conduit itself can be used as inflow for the left kidney, with construction of an end of artery to side of conduit anastomosis. Finally, the distal anastomosis to the aortic terminus is performed. The use of the side-branch graft configuration provides a level of flexibility for intercostal reattachment (Fig 5). It is our practice to reimplant large intercostals arteries without visible truly pulsatile back bleeding. Further, other investigators have advocated the use of motor-evoked potentials to guide the timing of reimplantation and to identify those vessels that provide spinal cord perfusion.12 Although this approach remains somewhat controversial, maintenance of near normal lower extremity perfusion is a prerequisite because ischemia of the legs limits peripheral nerve conduction irrespective of spinal cord hypoperfusion. Thus, the use of evoked potentials is not feasible with a simple “clamp and sew” technique. When early reattachment is deemed necessary, the main body of the conduit is anastomosed to the back wall of the aorta prior to the visceral patch.
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Fig 5. Side arm facilitates construction of intercostal anastomoses. Anastomosis of two patches of intercostal pairs has been depicted in this case. Fig 6. Completed procedure.
Alternatively, reattachment of intercostal arteries can be more easily performed as the last step, with the side arm as the inflow site. The bypass conduit is always left in place, without detaching the iliac anastomosis (Fig 6). Despite competitive flow, the conduit is almost always observed to be patent on late follow-up computed tomographic scan. The diaphragm is closed, leaving the conduit in the aortic hiatus parallel to the main graft. Finally, the aneurysm sac is approximated over the grafts, and the wound is closed in layers over one or two chest tubes. We have used this technique in more than 40 patients undergoing thoracoabdominal aneurysm repair. Our experience is too preliminary to draw concrete conclusions with respect to morbidity or mortality advantages. In particular, our small numbers have precluded the ability to show reductions in the rate of paraplegia or perioperative mortality. Subjectively, however, an enhanced degree of hemodynamic stability has been obvious, without the dramatic hypotension and acidosis that sometimes accompany aortic unclamping when a nonbypass technique has been used. DISCUSSION A variety of intraoperative tactics have been used to diminish the rate of complications associated with the
repair of thoracoabdominal aortic aneurysms.7,13-18 Distal perfusion with left heart bypass or other partial cardiopulmonary extracorporal bypass methods can be used to maintain perfusion during the period of aortic occlusion. Cannulation of the femoral artery and left atrium directly or through the inferior pulmonary vein is not without risk, however, and a high level of anticoagulation must be maintained with many of the available extracorporal devices. Further, the vigorous jet of retrograde bloodflow associated with these methods may dislodge luminal debris into the renal and mesenteric circulation. Subarachnoid drainage and epidural cooling have been used to prevent spinal cord ischemia, but these techniques do not directly address the myriad complications related to other organs.19,20 Branches have been sewn to the main graft to allow perfusion of the visceral and renal vessels during performance of the proximal anastomosis, but lower extremity perfusion is not addressed with these techniques.21 Axillofemoral bypass grafts can be placed before commencement of the thoracoabdominal aneurysm repair.22 Although cumbersome and rarely used, axillofemoral bypass does provide a means of maintaining distal perfusion without the need for high dose heparinization. Competitive flow phenomena compounded by the long,
218 Ouriel
relatively high-resistance axillofemoral conduit may occasionally result in occlusion of the graft, such that it is nonfunctional at the time of aortic clamping. As a modification of the axillofemoral bypass technique and one that is less unwieldy, we have used an internal side-arm bypass conduit originating from the proximal main aortic graft. This configuration sustains distal perfusion during the period of aortic occlusion, at least to the pelvis and legs and, in some cases, to the viscera as well. Maintenance of antegrade bloodflow into the hypogastric arteries may provide some degree of protection against spinal cord ischemia during the aortic cross-clamp period.23 From the standpoint of diagnosis, the sustenance of lower extremity perfusion prevents limb ischemia and allows the use of motor-evoked potentials as a means of identifying spinal cord ischemia at a time when it can be corrected.24,25 Further, the side-branch limb provides flexibility for reattachment of important intercostal arteries, which, when arising at the lower thoracic level, may be directly opposite the visceral patch, and reattachment to the main graft is technically challenging. Left renal artery reconstruction can be facilitated in a similar manner. Lastly, if the intercostal patch undergoes late aneurysmal change, the side branch may be occluded proximally and distally via percutaneous means, thereby excluding systemic inflow to the degenerated segment. In summary, the technique of using an internal bypass graft to provide flow to the visceral, renal, and distal vasculature offers another option to facilitate the repair of proximal thoracoabdominal aortic aneurysms. Although the method should be considered in patients with type I, II, and III aneurysms where the risk of end-organ ischemic complications remains great, objective comparative studies will be necessary to document clinical benefit. REFERENCES 1. Svensson LG, Crawford ES, Hess KR, Coselli JS, Safi HJ. Experience with 1509 patients undergoing thoracoabdominal aortic operations. J Vasc Surg 1993;17:357-68. 2. Crawford ES, Crawford JL, Safi HJ, Coselli JS, Hess KR, Brooks B, et al. Thoracoabdominal aortic aneurysms: preoperative and intraoperative factors determining immediate and long-term results of operations in 605 patients. J Vasc Surg 1986;3:389-404. 3. Derrow AE, Seeger JM, Dame DA, Carter RL, Ozaki CK, Flynn TC, et al. The outcome in the United States after thoracoabdominal aortic aneurysm repair, renal artery bypass, and mesenteric revascularization. J Vasc Surg 2001;34:54-61. 4. Galt SW, Bech FR, McDaniel MD, Dain BJ, Yeager MP, Schneider JR, et al. The effect of ibuprofen on cardiac performance during abdominal aortic cross-clamping. J Vasc Surg 1991;13:876-83. 5. Fiore WM, Ouriel K, Green R, Geary JE. High-risk aortic aneurysm repair with partial cardiopulmonary bypass. J Vasc Surg 1987;6:563-5. 6. Hafez HM, Berwanger CS, McColl A, Richmond W, Wolfe JH, Mansfield AO, et al. Myocardial injury in major aortic surgery. J Vasc Surg 2000;31:742-50. 7. Frank SM, Parker SD, Rock P, Gorman RB, Kelly S, Beattie C, et al. Moderate hypothermia, with partial bypass and segmental sequential repair for thoracoabdominal aortic aneurysm. J Vasc Surg 1994;19:68797.
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8. Safi HJ, Miller CC III, Subramaniam MH, Campbell MP, Iliopoulos DC, O’Donnell JJ, et al. Thoracic and thoracoabdominal aortic aneurysm repair using cardiopulmonary bypass, profound hypothermia, and circulatory arrest via left side of the chest incision. J Vasc Surg 1998;28: 591-8. 9. Wahba A, Rothe G, Lodes H, Barlage S, Schmitz G. The influence of the duration of cardiopulmonary bypass on coagulation, fibrinolysis and platelet function. Thorac Cardiovasc Surg 2001;49):153-6. 10. Kawahito K, Mohara J, Misawa Y, Fuse K. Platelet damage caused by the centrifugal pump: in vitro evaluation by measuring the release of alpha-granule packing proteins. Artif Organs 1997;21:1105-9. 11. Belcher PR, Muriithi EW, Milne EM, Wanikiat P, Wheatley DJ, Armstrong RA. Heparin, platelet aggregation, neutrophils, and cardiopulmonary bypass. Thromb Res 2000;98:249-56. 12. van Dongen EP, Schepens MA, Morshuis WJ, ter Beek HT, Aarts LP, de Boer A, et al. Thoracic and thoracoabdominal aortic aneurysm repair: use of evoked potential monitoring in 118 patients. J Vasc Surg 2001; 34:1035-40. 13. Davison JK, Cambria RP, Vierra DJ, Columbia MA, Koustas G. Epidural cooling for regional spinal cord hypothermia during thoracoabdominal aneurysm repair. J Vasc Surg 1994;20:304-10. 14. Jacobs MJ, Meylaerts SA, de Haan P, de Mol BA, Kalkman CJ. Strategies to prevent neurologic deficit based on motor-evoked potentials in type I and II thoracoabdominal aortic aneurysm repair. J Vasc Surg 1999;29:48-57. 15. McCullough JL, Hollier LH, Nugent M. Paraplegia after thoracic aortic occlusion: influence of cerebrospinal fluid drainage. Experimental and early clinical results. J Vasc Surg 1988;7:153-60. 16. Safi HJ, Hess KR, Randel M, Iliopoulos DC, Baldwin JC, Mootha RK, et al. Cerebrospinal fluid drainage and distal aortic perfusion: reducing neurologic complications in repair of thoracoabdominal aortic aneurysm types I and II. J Vasc Surg 1996;23:223-8. 17. Safi HJ, Miller CC III, Carr C, Iliopoulos DC, Dorsay DA, Baldwin JC. Importance of intercostal artery reattachment during thoracoabdominal aortic aneurysm repair [comments]. J Vasc Surg 1998;27:58-66. 18. Shiiya N, Yasuda K, Matsui Y, Sakuma M, Sasaki S. Spinal cord protection during thoracoabdominal aortic aneurysm repair: results of selective reconstruction of the critical segmental arteries guided by evoked spinal cord potential monitoring. J Vasc Surg 1995;21:970-5. 19. Cambria RP, Davison JK, Carter C, Brewster DC, Chang Y, Clark KA, et al. Epidural cooling for spinal cord protection during thoracoabdominal aneurysm repair: a five-year experience. J Vasc Surg 2000;31: 1093-102. 20. Cambria RP, Davison JK, Zannetti S, L’Italien G, Brewster DC, Gertler JP, et al. Clinical experience with epidural cooling for spinal cord protection during thoracic and thoracoabdominal aneurysm repair. J Vasc Surg 1997;25:234-41. 21. Cambria RP, Davison JK, Giglia JS, Gertler JP. Mesenteric shunting decreases visceral ischemia during thoracoabdominal aneurysm repair. J Vasc Surg 1998;27:745-9. 22. Comerota AJ, White JV. Reducing morbidity of thoracoabdominal aneurysm repair by preliminary axillofemoral bypass. Am J Surg 1995; 170:218-22. 23. Picone AL, Green RM, Ricotta JR, May AG, DeWeese JA. Spinal cord ischemia following operations on the abdominal aorta. J Vasc Surg 1986;3:94-103. 24. Laschinger JC, Owen J, Rosenbloom M, Cox JL, Kouchoukos NT. Direct noninvasive monitoring of spinal cord motor function during thoracic aortic occlusion: use of motor evoked potentials. J Vasc Surg 1988;7:161-71. 25. Svensson LG, Patel V, Robinson MF, Ueda T, Roehm JO Jr, Crawford ES. Influence of preservation or perfusion of intraoperatively identified spinal cord blood supply on spinal motor evoked potentials and paraplegia after aortic surgery. J Vasc Surg 1991;13:355-65. Submitted Jun 21, 2002; accepted Aug 13, 2002.