Eur J Cardiothorac Surg 2001;19:411-416
© 2001 Elsevier Science NL
Active cooling during open repair of thoraco-abdominal aortic aneurysms improves outcome
L.K. von Segesser,
B. Marty,
X. Mueller,
P. Ruchat,
P. Gersbach,
F. Stumpe,
A. Fischer
Department for Cardiovascular Surgery, University Hospital Vaudois, CHUV, Lausanne, Switzerland
Received 10 October 2000;
received in revised form 11 February 2001;
accepted 16 February 2001.
Corresponding author. Tel.: +41-21-314-2280; fax: +41-21-314-2278
e-mail: ludwig.von-segesser{at}chuv.hospvd.ch
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Abstract
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Objective: Evaluate impact of active cooling with partial cardiopulmonary bypass (CPB) and low systemic heparinization during open repair of thoracoabdoninal aortic aneurysms. Methods: Prospective analysis of 100 consecutive patients undergoing surgical repair of thoracoabdominal aortic aneurysms. Partial CPB and normothermic (36°C) or hypothermic (29°C) perfusion was selected in accordance to the surgeons preference. In the hypothermic group, aortic cross clamp was applied when the target temperature of the venous blood was achieved and rewarming was started after declamping. Results: 52/100 patients (62.2±10.9 years) received normothermic and 48/100 patients hypothermic perfusion (63.8±10.6 years: NS). Emergent procedures accounted for 18/52 (35%) with normothermia vs. 21/48 (44%: NS) with hypothermia. The number of aortic segments (eight = maximum including arch and bifurcation) replaced was 3.9±1.5 with normothermia vs. 4.1±1.5 with hypothermia (NS); Crawford type II aneurysms accounted for 21/52 patients (40%) for normothermia vs. 20/48 (42%:NS) for hypothermia. Total clamp time was 38±21 min with normothermia vs. 47±28 min with hypothermia (P=0.05). Pump time was 55±28 min with normothermia vs. 84±34 min with hypothermia (P=0.001). Mortality at 30 days was 8/52 patients (15%) with normothermia vs. 2/48 (4%) with hypothermia (P=0.06; odds ratio = 4.1). Parapareses/plegias occurred in 4/52 patients (8%) with normothermia vs. 4/48 (8%) with hypothermia (NS). Revisions for bleeding were required in 4/52 patients (8%) with normothermia vs. 2/48 patients (4%) with hypothermia (P=0.38). Revisions for distal vascular problems were necessary in 5/52 patients (10%) with normothermia vs. 2/48 (4%) with hypothermia (P=0.25). Freedom from death, paraplegia, and surgical revision was 89.9% with normothermia vs. 94.8% with hypothermia (P=0.04; odds ratio 2.0). Conclusions: Active cooling during repair of thoracoabdominal aortic aneurysms allows for longer cross-clamp times, more complex repairs and improves outcome.
Key Words: Thoracoabdominal aortic aneurysm • Aneurysm repair • Paraplegia • Hypothermia • Partial cardiopulmonary bypass
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1. Introduction
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Despite all the progress made in surgical repair of thoracoabdominal aortic aneurysm repair, spinal chord injury remains the Achilles heel of these otherwise well controlled procedures. The incidence of spinal chord injury defined as paraparesis or paraplegia of the lower limbs, either transient or permanent, varies between 1 and 2% for elective infrarenal abdominal aortic aneurysm repair and 48% for extensive Crawford type II thoracoabdominal aortic aneurysms [1]. Likewise a 41% paraplegia rate was reported by Cox et al. for survivors after type II thoracoabdominal aortic aneurysm repair [2]. Numerous attempts with and without [3] adjuncts have been made to reduce the rate of paraplegia in patients undergoing descending thoracic and thoracoabdominal aneurysm repair including cerebrospinal fluid drainage [1], cerebrospinal fluid drainage with intrathecal papaverine [4], profound hypothermia and circulatory arrest [5], regional hypothermic perfusion [6], epidural cooling [7], selective segmental artery perfusion [8], retrograde venous perfusion [9], endovascular stent graft repair [10,11] and others. Despite the progress made, none of the adjuncts cited above allows alone for complete avoidance of spinal cord injury during thoracoabdominal aortic aneurysm repair. Therefore various combinations of spinal cord protecting methods have been studied.
We have previously introduced partial cardiopulmonary bypass (CPB) using heparin surface coated perfusion equipment [12] with low systemic heparinization for proximal unloading and distal protection during surgical repair of descending thoracic and thoracoabdominal aortic aneurysms [13]. The present study was designed to determine whether active cooling during partial CPB provides additional benefits.
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2. Patients and methods
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One hundred consecutive patients undergoing surgical repair of thoracoabdominal aortic aneurysms who required thoracoabdominal exposure (including paracostal desinsertion of the diaphragm) were prospectively analyzed. All procedures were performed with partial cardiopulmonary bypass using heparin coated perfusion equipment and low systemic heparinization (activated coagulation time: ACT >180 s) as described below. Normothermic (35–37°C) or hypothermic (28–30°C) perfusion temperature was selected in accordance to the surgeons preference.
Two classifications for determination of the extent of the aortic aneurysmal disease and the consecutive surgical procedures were used:
(a) The Crawford classification based on type I–IV as published in 1984 [14].
(b) The segmental classification (1–8 aortic segments: one involved aortic arch, three descending thoracic aortic segments, three abdominal aortic segments, one involved aortic bifurcation) with or without crossing of the diaphragm as published in 1988 [15,16] and shown in Fig. 1
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Fig. 1. Segmental classification [15,16] of thoracic and thoracoabdominal aortic aneurysms as a function of the eight aortic segements involved: Aortic arch (involvement of supraaortic vessels) = segment 1, three thoracic segments = segment 2–4, three abdominal aortic segments = segment 5–7, aortic bifurcation (involving iliac vessels) = segment 8. An aneurysm involving the segments 2 throughout 6 (including the visceral and renal arteries) is equivalent to Crawford type II. Based on the segmental classification the extent of aortic disease can be expressed as a continuous variable, which is useful for statistical work-up.
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If the Crawford classification (a) is more widely used in the current literature, the segmental classification (b) has the advantage of providing a continuous variable which is helpful for statistical work-up. In addition, the segmental classification allows for systematic description of more extended aneurysmal formations (proximal and distal) going well beyond the Craford type II aneurysm. Finally, the segmental classification can also be used for description of descending thoracic aortic aneurysms.
2.1. Surgical technique
The surgical procedure was previously reported [13] and shall therefore only roughly be summarized here. A left sided thoraco-phreno-laparotomy following preparation of the left external iliac vessels (see also perfusion technique) was the standard approach. Paracostal desinsertion of the diaphragm and complete exposure of the thoracoabdominal aorta was routine. We used partial cardiopulmonary bypass with heparin coated perfusion equipment (Spiral Gold integrated oxygenator/heat-exchanger structure: formerly Baxter–Bentley, now Jostra–Bentley, Irvine, CA, USA) and low systemic heparinzation in all patients. In the hypothermic group, the aortic cross clamp was applied when the target temperature (28–30°C) was achieved and rewarming was started after completion of the aneurysm repair. Selective perfusion of visceral or renal arteries as well as profound hypothermia and circulatory arrest were not used. Staged aortic cross clamping, orthotopic repair with sealed grafts from proximal to distal, reimplantation of aortic patches holding major intercostal and/or visceral vessels, and graft inclusion were standard. In cases with inadequate autologous tissue for graft inclusion, a glutaraldehyde preserved pericardial xenografts (Edwards, Horw, Lucerne, Switzerland) was used [17].
2.2. Perfusion technique
Partial CPB (external iliac vein to external iliac artery; initial flow: 50% of cardiac output) using tip to tip, heparin coated perfusion equipment (Duraflo II, Baxter-Bentley/Jostra-Bentley, Irvine, CA, USA), low systemic heparinization (Liquemin: Roche, Basel, Switzerland; loading dose: 100 IU/kg bodyweight; priming dose 1000 IU/l of priming volume), and a target ACT of >180 s were routine as previously reported [13]. If a large amount of stagnant blood had to be stored temporarily in the cardiotomy reservoir, the ACT was kept >300 s during this period. Normothermic (35–37°C) or hypothermic (28–30°C) perfusion temperature was selected in accordance to the surgeons preference. After aortic repair, rewarming and weaning from cardiopulmonary bypass, circulating heparin was neutralized with protamine equivalent to heparin loading dose and additional protamine was titrated according to the ACT. A red cell spinning device (Autotrans, Dideco, Mirandola, Italy) was used before and after systemic heparinization as well as for concentration of the oxygenator sump blood at the end of the procedure.
2.3. Data analysis
Continuous variables are expressed as the mean±SD. Comparison of continuous variables was made using Student’s t-test for unpaired variables where appropriate. Freedom of negative events was calculated as fraction of documented negative events based on all negative events possible for the analyzed categories. Univariate analysis of descriptive data was performed using Fisher's exact test. For the latter, odds ratio and 95% confidence intervals (based on the approximation of Woolf) were calculated. Statistical significance was confirmed by a probability value less than 0.05.
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3. Results
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During repair of their thoracoabdominal aortic aneurysm, 52/100 patients (age: 62.2±10.9 years; males: 45/53 (85%)) received normothermic and 48/100 patients (age: 63.8±10.6 years: NS; males: 38/48 (79%): NS) received hypothermic perfusion. Acute events requiring emergent procedures accounted for 18/52 with normothermia (35%) vs. 21/48 with hypothermia (44%: NS). The following main diagnoses were recorded for the two groups: true aortic aneurysms in 32/52 patients (62%) for normothermia vs. 35/48 (72%: NS) for hypothermia, aortic dissection in 18/52 patients (35%) for normothermia vs. 12/48 (25%: NS) for hypothermia, and others in 2/52 patients (4%) for normothermia vs. 1/48 (2%: NS) in hypothermia.
In accordance to the Crawford classification, 19/52 patients (37%) with normothermia had type I aneurysms vs. 17/48 (35%) with hypothermia (NS); 21/52 patients (40%) with normothermia had type II aneurysms as compared to 20/48 (42%) with hypothermia (NS); 8/52 patients (15%) with normothermia had type III aneurysms as compared to 8/48 [17] with hypothermia (NS); 3/52 patients (6%) with normothermia had type IV aneurysms as compared to 3/48 (6%) with hypothermia (NS).
In accordance to the segmental classification (Fig. 1), the number of aortic segments (8 = maximum: 1 = arch, 3 thoracic segments, 3 abdominal segments, 1 = bifurcation) replaced was 3.9±1.5 with normothermia vs. 4.1±1.5 with hypothermia (NS).
Total clamp time as depicted in Fig. 2
, was 38±21 min with normothermia vs. 47±28 min with hypothermia (P=0.05). Pump time was 55±28 min with normothermia vs. 84±34 min with hypothermia (P=0.0010). Ventricular fibrillation occurred in 1/52 patients (2%) with normothermic perfusion and in 1/48 patients (2%: NS) with hypothermic perfusion. In both cases this event occurred after the aneurysm repair, with declamped aorta, during reperfusion and rewarming respectively. Both patients were successfully defibrillated. They are alive and well. No venous reservoir or heat exchanger/oxygenator structure occlusion occurred. However cardiotomy reservoir occlusion or red-cell spinning device reservoir occlusion was occasionally observed and handled by immediate reservoir changeover.
Mortality at 30 days was 8/52 patients (15%) with normothermia vs. 2/48 (4%) with hypothermia (P=0.06, odds ratio 4.1, confidence interval: 0.8–20.8). Parapareses and paraplegias occurred in 4/52 patients (8%) with normothermia vs. 4/48 (8%) with hypothermia (NS). A major stroke was observed in two patients (one in each group) leading ultimately to death (included in the mortality given above). Revisions for bleeding were required in 4/52 patients (8%) with normothermia vs. 2/48 patients (4%) with hypothermia (P=0.38; odds ratio 1.9). Revisions for distal vascular problems were necessary in 5/52 patients (10%) with normothermia vs. 2/48 (4%) with hypothermia (P=0.25; odds ratio 2.4). Freedom from negative events (Fig. 3)
including death, paraparesis, paraplegia, and surgical revision for bleeding or distal vascular problems was 187/208 possible events (89.9%) with normothermia vs. 182/192 possible events (94.8%) with hypothermia (P=0.04; odds ratio 2.0; 95% confidence interval: 0.3–4.4).
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Fig. 3. Freedom from potential negative events including death, paraplegia and parapareses, surgical revision for bleeding, as well as surgical revision for distal vascular problems
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4. Discussion
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Active cooling during repair of thoracoabdominal aortic aneurysms allows for longer cross-clamp times in order to perform more complex aortic reconstructions and improves outcome (Table 1). For the two groups analyzed here, there was no significant difference with regard to the basic parameters like age, sex, main diagnoses, and the proportion of emergency procedures. Likewise, the type and extent of aortic repair was almost equal between the groups for the Crawford classification and this holds especially true for the highest risk type II lesions which occurred 40% for normothermia as compared 42% with hypothermia. In addition, the segmental classification (Fig. 1) shows a similar amount of repaired aortic segments (3.9±1.5 with normothermia vs. 4.1±1.5 with hypothermia: NS). In contrast, total aortic cross-clamp time, and therefore aortic repair time in sensu strictu, was significantly longer for hypothermia (47±28 min vs. 38±21) and so was the pump time (84±34 vs. 55±28 min). It is interesting to note that ventricular fibrillation occurred in one patient of each group during the reperfusion and rewarming phase respectively. Despite the fact, that these patients could be rescued, this type of problem is certainly of major concern during aortic crossclamping and even more so under hypothermic conditions. Under such circumstances, quick proximal arterial cannulation (supra-aortic vessel or ascending aorta) is essential in order to restore cerebral and coronary blood flow.
Regarding perprocedural device complications related to perfusion with low systemic heparinization we have to mention occasional cardiotomy reservoir as well as red cell spinning device reservoir occlusions which were handled by immediate reservoir changeover. Thrombotic material originating from the thoracoabdominal aortic aneurysms as well as major quantities of air/blood mixtures are certainly limiting the performance of cardiotomy reservoirs although those used in this setting were all heparin surface coated. The same type of problems do also occur during major operations without CPB in the filter sections of the various red cell spinning devices. In contrast we have not observed any obstruction of venous reservoirs or heat exchanger/oxygenator structures. These findings are in line with our previous experience [12,13,15] and support that partial cardiopulmonary bypass using low systemic heparinization and active cooling is neither associated with increased coagulation disorders nor thromboembolic events.
The mortality of our group with hypothermic perfusion (4%) compares favorably with other reports on repair of thoracoabdominal aortic aneurysms. Although parapareses and paraplegias occurred in 8% of the patients with normothermic perfusion as well as in 8% of the patients with hypothermic perfusion these results were achieved with a 52% longer cross-clamp time in the latter group. Furthermore, there may have remained hidden some additional neural cord injuries in the group with normothermic perfusion which had a higher mortality (15 vs. 4% for hypothermia).
Interestingly enough, there were less revisons for bleeding and less revisions for distal vascular problems in the patients who had hypothermic perfusion and therefore longer crossclamp and longer perfusion times. Although, this is not a randomized study, the overall outcome, considering freedom from negative events including death, paraparesis, paraplegia, and surgical revision for bleeding or distal vascular problems, was significantly better for patients who underwent thoracoabdominal aneurysm repair with hypothermic perfusion and active core cooling.
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Footnotes
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Presented at the 14th Annual Meeting of the European Association for Cardio-thoracic Surgery, Frankfurt, Germany, October 7–11, 2000.
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Appendix A. Conference discussion
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Dr M. Turina (Zurich, Switzerland): I would just like to make a comment. What is the policy now in your unit concerning the reimplantation of the major intercostal branches in the critical segment of thoracic 10 to 12?
Dr von Segesser: They are reimplanted, or sometimes you can leave them out of the anastomosis. It depends where the level is.
Dr Turina: I was disappointed to see the incidence of paraplegia being the same. The numbers are, of course, small, and, as you say, they could be hidden in the mortality. But Joe Coselli makes a comment during discussion that they had highest incidence of paraplegia in the period where Stanley Crawford was performing surgery in normothermia.
Dr von Segesser: Interestingly enough, there is a paper from Svensson, who comes from the same group, where the paraplegia rate with hypothermia and spinal fluid drainage is 8% at 48 min of cross/clamp time, which is exactly the figure we had here.
Dr H.-J. Schafers (Homburg, Germany): I was a bit surprised. I would have expected the opposite, a somewhat lower paraplegia rate and mortality maybe to be the same. You also had more revisions for distal vascular problems and a shorter cross/clamp time under normothermia. So the question really is, is it the direct influence of temperature or did the surgeon working under normothermic conditions maybe work in a more hurried fashion which then resulted in adverse events?
Dr von Segesser: Probably that is the explanation I would retain here, that if you feel more comfortable, you can do the job as it should be done instead of just looking at 20 min on the clock and you loosen the clamp because 20 min are gone. So probably that plays a role, but it's difficult to prove.
Dr Turina: Did you analyze the surgeon as a risk factor?
Dr von Segesser: No, but there are not many surgeons in this field.
Dr T. Wahlers (Isernhagen, Germany): Let me ask for your rationale. Why don't you cool even deeper than 28 degrees in order to protect better and to reduce your paraplegia rate down to figures even lower than 7.5%?
Dr von Segesser: Well, the problem here is that the procedures were done on partial bypass, so you need the function of the heart to maintain perfusion of the head. If you go below 28 degrees, I think you can do that, but it becomes a less predictable procedure, because at 25 degrees you have to expect fibrillation in most cases.
Dr Wahlers: However, for cardiac perfusion to add a second perfusion line for the upper part of the body might not be cumbersome.
Dr von Segesser: Sure, but then you have to vent the heart. How do you get the air out of there? There are a number of other problems that you have to solve. But it's something that can be tried.
Dr A.k. Sarwat (Cairo, Egypt): Have you tried to anastomose the bigger collaterals?
Dr von Segesser: Yes. That was routine.
Dr A. Arbulu (Detroit, MI, USA): Have you tried regional cooling?
Dr von Segesser: No, we have not, but that is reported in the literature as one way to solve the problem.
Dr Turina: Would you like to make a closing comment?
Dr von Segesser: Well, most of us would agree, I think, that there is still some work to do.
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Abstract
1. Introduction
