Ann Thorac Surg 1998;66:1204-1208
© 1998 The Society of Thoracic Surgeons
Original articles: cardiovascular
Effect of extended cross-clamp time during thoracoabdominal aortic aneurysm repair
Hazim J. Safi, MDa,
Anders Winnerkvist, MDa,
Charles C. Miller, III, PhDa,
Dimitrios C. Iliopoulos, MDa,
Michael J. Reardon, MDa,
Rafael Espada, MDa,
John C. Baldwin, MDa
a Department of Surgery, Baylor College of Medicine and The Methodist Hospital, Houston, Texas, USA
Address reprint requests to Dr Safi, Department of Surgery, Baylor College of Medicine, 6550 Fannin, Suite 1603, Houston, TX 77030
e-mail: (hsafi{at}bcm.tmc.edu)
Presented at the Poster Session of the Thirty-fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 26–28, 1998.
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Abstract
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Background. In previous studies of the neurologic outcome of patients undergoing thoracoabdominal aortic aneurysm repair with the simple cross-clamp technique, cross-clamp time of greater than 30 minutes was identified as an important risk factor. We retrospectively examined the effect of clamp time of 30 minutes or greater on outcome for patients undergoing repair with the addition of surgical adjuncts.
Methods. Between February 1991 and June 1996 we operated on 370 patients for thoracoabdominal or descending thoracic aortic aneurysm. Two hundred seventy-one of these patients with cross-clamp times of 30 minutes or greater were included in this study. One hundred twelve patients underwent simple cross-clamp repair, whereas 159 were operated on with the surgical adjuncts of distal aortic perfusion and cerebrospinal fluid drainage.
Results. By multivariate analysis, acute dissection, surgical adjuncts, and aneurysm extent proved most significant in overall patient outcome. The overall rate of early neurologic deficits was 23 of 271 (8.5%). For highest risk patients with type II thoracoabdominal aortic aneurysms, the rate of neurologic deficits was 11 of 29 (38%) for cross-clamp versus 6 of 82 (7.3%) for adjunct operation patients (odds ratio = 0.13; p < 0.001).
Conclusions. The adjuncts of cerebrospinal fluid drainage and distal aortic perfusion decreased the risk of extended cross-clamp time during thoracoabdominal aortic aneurysm repair, particularly for highest risk type II.
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Introduction
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Postoperative neurologic deficit has been recognized as a hazard of thorocoabdominal aortic aneurysm repair since the operation was first carried out, and studies have shown repeatedly that this dreaded complication is highly correlated with ischemic time and aneurysm extent [1–6]. Aneurysms of the total thoracoabdominal aorta are most often referred to as type II, as originally defined by Crawford and associates (Fig 1) [7], and extensive cross-clamp time is most frequently defined as significant at greater than 30 minutes [5]. In an effort to minimize clamp time and decrease neurologic morbidity, the first generation of thoracoabdominal aortic aneurysm operations focused on the speed of the operation. More recently, scientific developments have permitted us to add on methods to improve the tolerance of the spinal cord to ischemia so that lengthy clamp times, often unavoidable in type II repairs, could be used with reduced risk [8–17]. Among these methods are cerebrospinal fluid drainage, sequential clamping using distal aortic perfusion, profound hypothermia, and regional moderate hypothermia as well as the use of pharmacologic agents such as naloxone and corticosteroids. Results, however, vary and the literature offers no agreement as to which of these treatments is superior. The reasons for lack of a clear consensus are many, but one explanation may be the variation in multiple components of patient management from center to center, and the nonuniformities in reporting aneurysm extent and clamp time. In this study we reviewed retrospectively our experience with the combination of distal aortic perfusion and cerebrospinal fluid drainage (hereafter referred to as "adjunct") in patients whose aortic cross-clamp times exceeded 30 minutes.
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Fig 1. Thoracoabdominal aortic aneurysm classification. Type I: below the left subclavian to above the celiac axis or opposite the superior mesenteric and above the renal arteries. Type II: below the left subclavian and including the infrarenal abdominal aorta to the level of the aortic bifurcation. Type III: the sixth intercostal space, tapering to just above the infrarenal abdominal aorta to the iliac bifurcation. Type IV: the twelfth intercostal space, tapering to above the iliac bifurcation. Type V: the sixth intercostal space, tapering to just above the renal arteries.
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Material and methods
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Of 370 patients operated on by one surgeon (H.J.S.) between February 1991 and June 1996 with thoracoabdominal or descending thoracic aortic aneurysms, we studied all patients with aortic cross-clamp times of 30 minutes or more. Two hundred eighty patients met this criterion. The patients had a median age of 68 years, and ranged in age from 8 to 84 years. Ninety-five patients were female and 185 were male. One hundred eleven of 280 patients (41%) had type II thoracoabdominal aortic aneurysms, which put them at highest risk for neurologic morbidity. Associated diseases present before the operation were hypertension in 220 (79%), chronic obstructive pulmonary disease in 86 (31%), renal insufficiency in 51 (18%), cerebrovascular disease in 33 (12%), and acute dissection as the cause of the aneurysm in 20 (7%). Median aortic cross-clamp time was 50 minutes, and it ranged from 30 minutes (the lower limit for inclusion in this study) to 131 minutes.
We describe the operative technique briefly as repair of these aneurysms has been reported previously in detail [1]. The patient was positioned in the thoracoabdominal position with the left side up. A spinal catheter placed at the level of the intervertebral space between L-4 and L-5 drained cerebrospinal fluid and kept spinal fluid pressure in the range of 10 mm Hg, both during the operation and for 3 to 4 days afterward. The mean amount of cerebrospinal fluid drained was 80 mL (range, 0 to 250 mL). The contraindication for cerebrospinal fluid drainage was previous operation on the spinal cord or blood effusion. Emergency procedures also on some occasions made cannulation or catheter insertion impossible. For distal aortic perfusion we prefer left atrial to femoral bypass with the BioMedicus (Minneapolis, MN) pump, but if this was not possible for reasons such as a previous operation, then the lower pulmonary vein or on occasion the upper descending thoracic aorta was used. If the femoral artery was occluded or had previously undergone graft replacement, then the upper abdominal lower or descending thoracic aorta was used for outflow as in the patient illustrated in Figure 2. Patient temperature was permitted to drift downward to a moderate hypothermic temperature of approximately 33°C as measured by rectal and nasopharyngeal probes. The proximal descending thoracic aorta was clamped either proximal or distal to the left subclavian artery depending on the anatomy of the aneurysm. Subsequently, the mid-descending thoracic clamp was applied and the proximal anastomosis was completed. This was followed by clamping of the infrarenal abdominal aorta and perfusion of the visceral arteries (celiac, superior mesenteric, and both renal arteries) with a 9F cannula. The recent addition of active visceral cooling permitted us to lower the patient’s left kidney temperature to 15.0°C (measured with a temperature probe inserted directly into the left kidney). The body temperature was maintained greater than 32°C by the heat exchanger in the BioMedicus pump.
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Fig 2. Illustrations of type II thoracoabdominal aortic aneurysm repair with adjuncts. (A) Computed tomographic scan and aortogram of type II thoracoabdominal aortic aneurysm. (B) Left atrial to femoral bypass with the BioMedicus pump for distal aortic perfusion. Cerebrospinal fluid drainage also was used. (C) Despite aneurysm extent and clamp time greater than 60 minutes, adjuncts permitted ample time for intercostal artery reattachment with graft replacement.
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Results
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In 280 patients there were nine intraoperative deaths (3.2%). Because patients who died intraoperatively could not be evaluated for neurologic deficit, these 9 patients were excluded from the at-risk population. Neurologic deficit (paraplegia or paraparesis), which indicated the failure of the adjunct and was recorded as occurring irregardless of the degree of severity, occurred in 23 of 271 patients (8.5%). Univariate associations between classification variables and neurologic deficit prevalence are shown in Table 1. Significant univariate risk factors for neurologic deficit were type II thoracoabdominal aortic aneurysm (odds ratio, 4.6; p < 0.001) and aortic cross-clamp time (odds ratio, 1.04 per minute beyond 30 minutes; p < 0.02). For highest risk patients with type II thoracoabdominal aortic aneurysms, the rate of neurologic deficits was 11/29 (38%) for cross-clamp versus 6/82 (7.3%) for adjunct operation patients (odds ratio, 0.13; p < 0.001). Significant univariate protective factors were female sex (odds ratio, 0.27; p < 0.03), type I thoracoabdominal aneurysm (odds ratio, 0.13; p < 0.02), and adjunct (odds ratio, 0.28; p < 0.004). Figure 3 shows the relationship between cross-clamp and adjunct for type II aneurysm. Table 2 shows a comparison of predictive factors (risk or benefit) at two different cross-clamp time points. The left side of the table shows variables that predict neurologic deficit at 30 minutes of cross-clamp time and above. The right side of the table shows what the same variables predict at 60 minutes or more. Although the sample size for the 60 minute or greater group is much smaller than that of the 30 minute or greater group (n = 87 versus 271), with a consequent decrease in statistical power, acute dissection and emergency presentation become significant for cases with longer ischemic times. Conversely, female sex and aneurysm extent lose statistical significance in the 60 minutes or greater group. The loss of significance for extent most likely reflects the fact that two thirds of the aneurysms requiring long clamp times are of type II extent.
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Fig 3. Relationship between cross-clamp and adjunct, type II thoracoabdominal aortic aneurysm (TAAA). (A = current study, patients without adjuncts; B = Crawford experience, cross-clamp and go [5]; C = current study, patients with adjuncts.)
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Table 2. Effect of Cross-Clamp Time Criterion on Associations Between Risk Factors and Outcomes Early Neurologic Deficit
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Comment
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Since its inception, surgical treatment of thoracoabdominal aortic aneurysm has been associated with the ever-present threat of neurologic deficit, accompanied by a host of methods designed to avoid paraplegia or paraparesis after the operation. In the mid-1970s none of these efforts were of much success, and following the lead of the monumental work of Dr Stanley Crawford, the simple cross-clamp and go technique became the mainstay of surgical therapy for thoracoabdominal aortic aneurysm [7]. Before 1986 there was also no standardized classification for thoracoabdominal aortic aneurysm, and it was difficult not only to assess risk factors, but also to determine the success or failure of attempted adjuncts. With the Crawford classification we were able to see how the maximum risk in the incidence of neurologic deficit correlated with type I and type II thoracoabdominal aortic aneurysms, particularly in type II [7]. This work was again reviewed in 1991, and again showed a clear relationship in the development of neurologic deficit to aneurysm extent, and also to prolonged cross-clamp time [5]. In our previous reports we showed that the combination of perioperative cerebrospinal fluid drainage and distal aortic perfusion had an impact on lowering the incidence of paraplegia and paraparesis in high-risk patients [1, 2]. The current study clearly shows the influence of adjuncts in patients with ischemic time of more than 30 minutes (p < 0.004) and greater than 60 minutes (p < 0.009). Adjuncts extend the tolerance of the spinal cord to ischemia beyond the 30-minute limitations of the cross-clamp and go technique. With adjuncts the surgeon is able to proceed in an unhurried fashion to perform all anastomoses, as well as implant intercostal arteries, which we believe is of great importance [18]. Moderate hypothermia, which we use for all patients, may also play an important role in extending the tolerance of ischemia in the spinal cord.
Responsible for some of the confusion in the world literature regarding thoracoabdominal aortic aneurysms is the lumping together of all thoracoabdominal aortic aneurysm types with little regard for classification, making comparisons difficult to achieve. We emphasize that proper classification is essential to accurate reporting. Overall results of the morbidity and mortality should be accounted for, whether of descending or thoracoabdominal aortic aneurysm, but studies must focus on type II thoracoabdominal aortic aneurysm in which we find the highest incidence of neurologic complications. With this in mind, the results of recorded series can be deciphered and compared. Within our own series and adhering to classification, we have found that perioperative cerebrospinal fluid drainage and distal aortic perfusion have a great impact in preventing neurologic deficit, most significantly in type II thoracoabdominal aortic aneurysm.
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Acknowledgments
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Special thanks to our editor, Amy Wirtz Newland.
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References
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Abstract
Introduction
