Technique of open distal anastomosis for repair of descending thoracic aortic aneurysms

Technique of Open Distal Anastomosis for Repair of Descending Thoracic Aortic Aneurysms Denton A. Cooley, MD, and Robert T. Raldwin, MD Department of Cardiovascular Surgery, Texas Heart Institute, Houston, Texas

Ischemic injury to the spinal cord and kidneys continues to be the major complication after resection of aneurysms involving the descending and proximal abdominal aorta. Our recent surgical experience with use of only a proximal clamp on the aorta to perform an ”open” distal anastomosis has proved this technique to be safe and expeditious. We therefore compared our results using the technique of open distal anastomosis for aneurysm repair with those of the conventional two-clamp technique. Since January 1989, we have used the conventional two-clamp technique in 31 patients (group 1) and the technique of open distal anastomosis in 24 patients (group 2). No significant differences were noted between the two groups in terms of age, sex, cause of aneurysm, extent of aneurysm, or site of proximal cross-clamp. The average distal ischemic time was 31 minutes in group 1

patients and 26 minutes in group 2 patients. Renal insufficiency occurred in 8 of 31 patients in group 1and in 0 of 24 patients in group 2 ( p = 0.01). Neurologic complications occurred in 4 patients in group 1 and in 1 patient in group 2. Early mortality rates were similar for both groups (4of 31 [13%1, group 1; 4 of 24 [17%1, group 2). Deaths were attributed to multiorgan failure and sepsis in 6 patients and coexisting coronary artery disease in 2 patients. Based on these results, we believe the technique of open distal anastomosis is safe and may improve the outcome in patients undergoing operation for descending thoracic aneurysms. Maintaining the distal circulation during aortic cross-clamping does not appear to be necessary in this experience.

T

Encouraged by the absence of neurologic complications associated with this technique, we increased its application. This review was undertaken to compare our results using the technique of open anastomosis with those of the conventional two-clamp technique for distal aneurysm repair.

he results obtained with resection and repair of aneurysms involving the descending thoracic aorta have improved during the past four decades; however, the ischemic complications related to aortic cross-clamping continue to result in devastating postoperative morbidity. Renal failure and paraplegia were noted in the earliest series of patients undergoing descending thoracic aortic aneurysm resection [l-31, and they remain the two most frequent major complications [4-81. Since these initial reports, hundreds of investigators have attempted to explain the mechanism of ischemic injury to the spinal cord and to develop methods to prevent the occurrence of postoperative paraplegia and paraparesis. The conventional belief has been that by keeping an increased abdominal aortic pressure capable of maintaining the distal circulation during aneurysm resection, the incidence of paraplegia would be decreased. Because of our recent experience, however, we are now reevaluating this concept. During a difficult technical operation to repair a descending thoracic aortic aneurysm, we found it impossible to place a distal clamp across the aorta below an aneurysm that had extended to the level of the aortic hiatus. To avoid repositioning for a thoracoabdominal incision, an ”open,” unclamped distal anastomosis was performed to the supraceliac aorta without the need for further surgical exposure. Accepted for publication March 12, 1992 Address reprint requests to Dr Cooley, Texas Heart Institute, PO Box 20345, Houston, TX 77225.

0 1992 by The Society of Thoracic Surgeons

(Ann Thorac Surg 1992;54:932-6)

Patients a n d Methods From January 1989 to June 1991, 55 consecutive patients underwent resection and graft replacement of aneurysms involving either the descending thoracic aorta or thoracoabdominal aorta at the Texas Heart Institute in Houston. Of those patients, 31 underwent aneurysm repair with the conventional two-clamp technique (group 1) and 24 underwent repair with the open distal anastomosis technique (group 2). A retrospective review of the patients’ postoperative outcomes was undertaken by using their hospital records and clinic files. Data were recorded for patient information (demographics, past medical history), aneurysmal characteristics (extent, location, cause, presence of aortic rupture), intraoperative details (aortic cross-clamp time, level of proximal aortic cross-clamp, intercostal vessel reattachment), and postoperative outcome (neurologic changes after operation, renal failure requiring dialysis, postoperative hemorrhage requiring reexploration, and 30-day mortality). The surgical technique was standardized for each group and differed only in the method of managing the distal anastomosis. The same surgeon (D.A.C.) performed all 0003-4975/92/$5.00

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A

Fig 1 . The distal anastomosis is performed without an aortic clamp. Continuous aspiration of blood to the autotransfusion reservoir maintains a clear operative field.

operations, and the intraoperative anesthetic care was standardized. Thiopental sodium was intravenously administered for induction of anesthesia, and a narcotic with inhaled isoflurane was used for maintenance. A sodium nitroprusside infusion was used as needed during proximal aortic cross-clamping for blood pressure control and was tapered before release of the clamp. Hypotension during operation or in the postoperative period was treated aggressively in all cases. The outcome of patients who underwent aneurysmal repair by way of the conventional technique (group 1)was compared with those who underwent resection by use of the open distal anastomosis (group 2). The choice of surgical technique was that of the surgeon and was not influenced by patient or aneurysmal characteristics. The surgical technique, however, did reflect the time during which the operation was performed. Early in 1989, for example, most patients underwent resection by the conventional technique, whereas by 1991, almost all patients underwent repair by the open technique of distal anastomosis.

Statis tical Analysis Univariate tests were performed to compare the two groups by use of Student’s t test, Fisher’s exact test, or analysis as appropriate. A p value of less than 0.05 was considered significant for all statistical calculations. Continuous data are presented as the mean ? the standard deviation.

2

Technique of “Open” Distal Anastomosis Generally, an endotracheal tube is used to administer anesthesia; however, in cases involving extensive lesions, an endobronchial tube is substituted to provide selective right lung ventilation. A standard left posterolateral skin incision is made, and the chest is entered through the fourth intercostal space to establish access to the proximal portion of the descending aorta. For extensive aneurysms,

the seventh intercostal space may be entered as well to expose the distal extent of the aneurysm. Thoracoabdominal and suprarenal aortic aneurysms require a formal thoracoabdominal incision. The aorta is dissected at the site of the proximal clamp, and heparin (1mg/kg body weight) is given systemically. The clamp is then applied, and the aneurysm is incised longitudinally. The intraluminal thrombus is quickly removed and any atheromatous debris removed from the sites of anastomosis. Blood is aspirated continuously through the autotransfusion device and returned to the patient. No attempt is made to control bleeding from the distal aorta or from the segmental vessels exposed within the aneurysmal lumen (Fig 1). A woven Dacron tube graft of the appropriate size is then anastomosed to the distal aorta by using 2-0 polypropylene sutures. To expedite the anastomosis, a large MH double-armed needle (No. 8853H; Ethicon, Somerville, NJ) is used (Fig 2). Whenever possible, an oblique suture line is fashioned to incorporate any back-bleeding segmental vessels into the new lumen. This allows for preservation of intercostal flow and alleviates the need to reattach vessels individually. When the distal anastomosis is complete, the graft is attached to the proximal aorta by use of 2-0 or 3-0 polypropylene suture. The proximal clamp is released gradually while appropriate pharmacologic agents are administered to provide a stable proximal blood pressure. Finally, the segmental vessels are oversewn as circulatory stability is restored. The remaining aneurysm is tailored and sewn over the Dacron graft. The effect of heparin is reversed with protamine sulfate. The left lung is reexpanded, and the incision is closed. Conventional chest tube drainage is used. All of the aspirated blood is autotransfused after processing. The open technique described here is also used to repair thoracoabdominal aneurysms. A single patch containing the superior mesenteric, celiac, and both renal arteries is

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COOLEY AND BALDWIN OPEN DISTAL AORTIC ANASTOMOSIS

Table 2. Site of A n e u w s m s DTA

Patient Group

Proximal

Distal

Entire

TAA ~~

Group 1 Group 2 DTA

Fig 2. Large M H needle adjacent to the standard SH needle. The M H needle is preferred for a more expeditious anastomosis.

reattached after the open distal anastomosis is completed. The proximal anastomosis is then completed, and flow is restored to the distal circulation. Control of the segmental vessels, tailoring of the aneurysmal wall, and closing of the incision are done in a fashion similar to that described for descending aneurysms.

Results The patient demographics and past medical history were similar in both groups. The mean age of the group 1 patients (57 years) was not statistically different from that of the group 2 patients (61 years). The predominance of males of 3.4:l in group 1 (24 of 31 patients, 77%) was similar to that of 2.4:l in group 2 (17 of 24 patients, 71%). Concomitant hypertension, chronic obstructive pulmonary disease, a history of previous cardiac operation, and a history of previous aneurysm operation were frequent in both groups (Table 1). There were no sizable differences between the two groups in terms of the characteristics of the aneurysms. In both groups, atherosclerosis was the most frequent underlying cause of the aneurysms (19 in group 1; 17 in group 2). Chronic dissection was the second most frequent cause (9 in group 1; 7 in group 2). Posttraumatic aneurysm formation at the aortic isthmus occurred in 3 patients in group 1. Extent and location of aneurysms varied slightly, with more extensive aneurysms occurring in patients who underwent repair by the open technique (Table 2). For Table 1. Patient History Patient Group”

Hypertension

Group 1 Group 2

16 15

COPD

Previous Cardiac Operation

Previous Aneurysm Operation

5

12

9

8

7 4

Group 1 patients underwent aneurysm repair with the conventional two-clamp technique. Group 2 patients underwent aneurysm repair with open distal anastomosis.

a

COPD = chronic obstructive pulmonary disease.

=

11 2

descending thoracic aorta;

0 1 TAA

9 15 =

11 6

thoracoabdominal aorta

example, larger aneurysms covering the entire descending thoracic aorta occurred more frequently in group 2 than in group 1 patients. Aneurysms confined to the proximal descending thoracic aorta were more common in group 1. Thoracoabdominal aneurysms were slightly more common in group 1 than in group 2 patients. The incidence of a contained rupture was similar for both groups. The intraoperative variables associated with aneurysm resection were similar for both groups. The proximal aortic clamp was located between the left common carotid and left subclavian arteries in 13 of 31 patients (42%) in group 1 and in 8 of 24 patients (33%) in group 2. The clamp was placed on the proximal descending aorta in 8 of 31 patients (26%)in group 1and 10 of 24 patients (42%)in group 2. In the remaining patients, the proximal clamp was placed in the mid or distal descending thoracic aorta. Aortic occlusion times were longer in group 1 (31 2 5 minutes) than in group 2 patients (26 4 minutes), but the difference was not statistically significant ( p = 0.10). Intercostal vessels were incorporated into the new lumen by an oblique anastomosis whenever possible regardless of the selected procedure; individual reattachment of intercostal vessels was not done in either group. In all patients with thoracoabdominal aneurysms, we used a single Carrel patch to incorporate the renal and visceral arteries. The use of heparin (1 mg/kg body weight administered intravenously) was the same for both groups. There was no significant difference in early mortality rates (30 days postoperatively) between the two groups (4 of 31 [13%], group 1; 4 of 24 [17%], group 2). All four deaths in group 1 were caused by multiorgan failure and sepsis. The four deaths in group 2 were attributed to multiorgan failure and sepsis (2) and coexisting coronary artery occlusive disease (2). Spinal cord injury occurred less frequently in group 2 (1 of 24,4%) than in group 1 (4 of 31, 13%),but the difference was not statistically significant. The only case of paraplegia in group 2 was in a 69-year-old man who had undergone infrarenal aneurysm resection several years before this admission. Only 1 patient in group 1 underwent thoracoabdominal aneurysm replacement. All 5 patients in whom paraplegia developed in this series had aortic clamp times of 30 minutes or greater. Renal failure requiring dialysis was not seen in any (0 of 24) patients in group 2, but was seen with a disturbing frequency (8 of 31, 26%) in group 1 ( p = 0.01). Five of the 8 patients in whom renal failure developed had undergone resection of extensive atherosclerotic thoracoabdominal aneurysms. Of the patients having nonthoracoab-

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dominal involvement, those in group 2 had a lower incidence of renal failure (0 of 18) than those in group 1 (3 of 20). Two of the 8 patients with renal failure had aortic clamp times of less than 30 minutes, whereas the other 6 patients had clamp times ranging from 30 to 60 minutes. Postoperative hemorrhage requiring reoperation occurred less frequently in group 2 (3 of 24) than in group 1 (5 of 31), but the difference was not statistically significant. Other sporadic complications included vocal nerve paralysis (2 patients), wound dehiscence (2 patients), and stroke (1 patient), but neither group showed a predilection toward these complications.

Comment The decrease in ischemic complications related to aortic cross-clamping noted in the patients in whom the open distal anastomosis technique was used may be related to the shorter distal ischemic times in that group. Lengthy aortic occlusion times have consistently been shown to increase the incidence of paraplegia and renal failure [4,9, 101. Aortic occlusion times in excess of 30 minutes have correlated with a marked increase in the incidence of paraplegia [4, 91. Although the difference in clamp times in our study between those in whom the open anastomosis was used (26 minutes) and those in whom conventional repair was performed (31 minutes) seems small, this small difference may represent a critical level of spinal ischemic tolerance. The relative protection from ischemic spinal cord injury seen in our patients who underwent procedures with use of open anastomosis creates a challenge to the conventional belief that favors shunting or bypass to augment abdominal aortic pressure [7-9, 11-13]. Improved results with use of an open distal anastomosis that effectively lowers the abdominal aortic pressure to zero underscores the poor correlation between distal aortic pressure and spinal cord blood flow. This may be due to the location of the anterior spinal artery and its dependency on the arteria radicularis magna, which usually originates above the abdominal aorta [lo, 14, 151. At the level of the potential injury, the individual radicular arteries contribute to spinal cord perfusion. This local radicular arterial pressure may not, however, correlate with either the distal aortic pressure or the intercostal artery pressure in an adult human spinal cord that depends on a noncontinuous anterior spinal artery and diseased vessels for its vascular supply. The diminished enthusiasm for shunting [ P 6 , 16, 171 may, in part, be a result of this phenomenon. Equally important to the local arterial pressure in spinal cord perfusion is the local venous pressure. In our early studies of aortic cross-clampingin dogs, the cerebrospinal fluid (CSF) Bressure was noted to rise immediately on cross-clamping and then fall, even though the proximal systemic arterial pressure was elevated [18, 191. These studies led to the conclusion that the CSF pressure reflects the local venous pressure and that a reduction in CSF pressure (by subarachnoid aspiration or a urea-induced diuresis) provides a sufficient perfusion gradient between the local spinal radicular arteries and the local spinal

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venous return to maintain arterial flow into the cord substance, despite critically low pressure in the abdominal aorta [18, 191. In several patients who underwent aneurysm resection by use of the open technique with continuous central venous and CSF pressure monitoring, it has been noted that CSF pressure increases with crossclamping, but decreases to low levels after the aneurysm has been opened and the abdominal aorta decompressed. It is possible, therefore, that allowing the intercostal and lumbar vessels to drain during the open anastomosis reduces the CSF pressure, thereby increasing blood flow to the spinal cord substance and contributing to spinal cord protection. Studies in dogs and humans have confirmed that preoperative CSF drainage has a protective effect against ischemic spinal cord injury during resection of aneurysms of the descending thoracic aorta [2&24]. Investigators have developed adjuncts to minimize spinal cord ischemia, including hypothermia [25, 261, localization of the arteria radicularis magna [lo, 27, 281, and intraoperative somatosensory [8, 271 and motor-evoked potentials [lo, 291. In our experience, however, the factor that consistently relates to decreased mortality and morbidity is a short aortic clamp time. In another review of our cases, Livesay and associates [4] found that the duration of aortic occlusion was the most important factor in minimizing the risk of paraplegia (more than age, extent of the lesion, and rupture). They concluded that the risk of paraplegia would be minimal if surgeons limited cross-clamp time to 30 minutes. In an effort to minimize clamp times with the open technique of anastomosis, use of a large MH needle has been helpful to expedite the open distal anastomosis. In addition, performing an open anastomosis makes the false lumen easier to repair in dissecting aneurysms and minimizes the risks of clamp atheroembolism and clamp trauma [30]. We believe that the open technique for resecting aneurysms involving the descending thoracic aorta is safe and may offer some protection against postoperative spinal cord and renal ischemic injuries. Because good results have been achieved with a distal aortic pressure of zero, the role of shunting and partial cardiopulmonary bypass in spinal cord protection may need to be reevaluated.

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