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Ann Thorac Surg 2002;74:426-431
© 2002 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery and Center for Diseases of the Thoracic Aorta, Washington University School of Medicine, St. Louis, Missouri, USA
* Address reprint requests to Dr Moon, Division of Cardiothoracic Surgery, Washington University School of Medicine, 3108 Queeny Tower, 1 Barnes-Jewish Pl, St. Louis, MO 63110-1013 USA
e-mail: moonm{at}msnotes.wustl.edu
Presented at the Forty-eighth Annual Meeting of The Southern Thoracic Surgical Association, San Antonio, TX, Nov 8–10, 2001.
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Abstract |
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Methods. From 1996 to 2000, 72 consecutive patients underwent an aortic arch procedure using hypothermic circulatory arrest (HCA) (31 acute dissection or rupture, 41 chronic dissection or aneurysm). Supplemental RCP was used in 36 patients, whereas 36 patients had HCA alone. The groups were similar in age, emergent status, and cardiopulmonary bypass time (p > 0.08), but HCA time was higher with RCP (40 ± 15 minutes versus 29 ± 14 minutes; p < 0.001).
Results. Operative mortality was 10% ± 4% (±70% confidence limit), and adverse outcomes (death or cerebrovascular accident) occurred in 14% ± 4%, but there was no difference between HCA alone (8% ± 5%, 14% ± 6%) and HCA with RCP (11% ± 5%, 14% ± 6%) (p > 0.73). The incidence of transient neurologic dysfunction was also similar (HCA alone, 11% ± 5%; HCA with RCP, 17% ± 6%; p > 0.73). Multivariate risk factors for mortality included emergency operation and HCA time (p < 0.02). Risk factors for adverse outcome included emergency operation and atheromatous ascending aorta (p < 0.03). Risk factors for transient neurologic dysfunction included preexisting cerebrovascular disease and rewarming retrograde (femoral) rather than antegrade (through the graft) (p < 0.03).
Conclusions. Supplemental RCP during HCA did not decrease mortality or neurologic complications. Retrograde rewarming through the femoral artery after completion of the distal anastomosis increased transient neurologic dysfunction. Therefore, RCP remains optional, but reperfusion should be antegrade to improve neurologic recovery.
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Material and methods |
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Operative techniques
All patients underwent median sternotomy and total cardiopulmonary bypass with HCA [19]. Two patients had extension through the left fourth intercostal space to access the mid-descending thoracic aorta, and 1 patient required a simultaneous thoracoabdominal incision to access the aortic bifurcation. Bicaval cannulation was performed if RCP was planned. For initial cooling, femoral artery cannulation was performed in 41 patients (57%), and the ascending aorta was cannulated in 31 patients (43%) who were believed to be free of significant proximal atheromatous disease based on preoperative imaging studies and intraoperative transesophageal echocardiography. The core (bladder) temperature was 18° ± 2°C (range, 12°C to 24°C). Rewarming was performed retrograde through the existing femoral artery cannula in 19 patients (26%) and antegrade in 53 patients (74%) by inserting a new aortic cannula in the graft. The aortic cross-clamp (myocardial ischemia) and cardiopulmonary bypass times were 124 ± 47 minutes and 201 ± 62 minutes, respectively. Mean HCA time was 35 ± 15 minutes (range, 12 to 87 minutes); HCA time was less than or equal to 30 minutes in 32 patients (44%), 30 to 45 minutes in 24 (33%), 45 to 60 minutes in 12 (17%), and more than 60 minutes in 4 patients (6%). The extent of distal aortic resection was the ascending aorta (with an open-distal technique) in 37 patients (51%), hemiarch in 17 (24%), total arch in 15 (21%), and mid-descending thoracic or abdominal aorta in 3 patients (4%). Aortic root replacement or reconstruction with coronary reimplantation was performed in 18 patients (25%), aortic valve replacement in 11 (15%), and coronary artery bypass grafting in 20 patients (28%).
All patients received mineralcorticoids (1,000 mg of methylprednisolone intravenously), thiopental sodium (7 to 10 mg/kg intravenously), magnesium sulfate (5 g intravenously), mannitol (0.25 g/kg intravenously), and head cooling with ice before the initiation of HCA. In 36 patients (50%), supplemental RCP was carried out through an arteriovenous shunt to a 28F to 32 F superior vena cava cannula. The decision to use RCP was variable; one researcher used RCP in all HCA cases, whereas the other, in general, used RCP for procedures in which a prolonged period of HCA was anticipated. When used, RCP was initiated at 100 mL/min and increased to 300 to 500 mL/min to keep the innominate vein pressure (central venous pressure) below 20 to 25 mm Hg. The patient was placed in the Trendelenburg position during RCP, and dark blood was verified emanating from the brachiocephalic orifices in all patients. The temperature of inflow blood during RCP was 10°C.
Data analysis
Surgical outcome was measured in terms of neurologic morbidity and operative mortality. Operative mortality included any death that occurred during the initial hospitalization or within 30 days of operation for discharged patients. Adverse outcome was defined as operative death or permanent neurologic injury at the time of discharge from the hospital, whether focal (embolic stroke) or global (diffuse coma). Transient neurologic dysfunction was defined as the occurrence of prolonged postoperative confusion, agitation, or transient delirium or ischemic deficits.
Continuous data are reported as mean ± one standard deviation, and clinically important ratios with 70% confidence limits. Continuous data were compared between groups using Student’s t test. Univariate analysis (
2 test) and multivariate stepwise regression analysis were used to determine the preoperative and intraoperative risk factors that were significant, independent predictors of neurologic morbidity and mortality (SigmaStat 2.03, SPSS Inc., Chicago, IL). Differences were considered significant at p less than 0.05. Odds ratios (OR) are reported with 75% confidence intervals (CI). Thirty variables were analyzed: age, year of operation, gender, hypertension, diabetes, coronary artery disease, congestive heart failure, family history of heart disease, pulmonary disease, cerebrovascular disease, peripheral vascular disease, chronic renal insufficiency, cigarette smoking, severe ascending aortic atheroma (subjective assessment based on intraoperative findings, etiology of aortic disease, acute/chronic pathology, acute dissection, rupture, elective/emergent status, preoperative shock, extent of resection (ascending/arch), RCP utilization, concomitant coronary artery bypass grafting, concomitant aortic valve replacement, concomitant root replacement, initial cooling antegrade/retrograde, rewarming antegrade/retrograde, low core temperature, cardiopulmonary bypass time, and HCA time.
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Comment |
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In the current series, RCP utilization was variable, and the decision was based on the operation to be performed and the surgeon’s preference; however, all of the operations were performed during a 5-year period. We found no significant difference between HCA alone and HCA with RCP with regard to operative mortality (8% versus 11%, p > 0.95), stroke rate (11% versus 6%, p > 0.67), and the incidence of TND (11% versus 17%, p > 0.73). These findings support the hypothesis that RCP remains optional during procedures involving the arch, as long as the core body temperature is low [25–27]. It may be mandatory, however, when using the technique recently described by the Toronto group of circulatory arrest under only moderate systemic hypothermia (nasopharyngeal temperatures of 19° to 28°C, mean of 23°C) [28]. With the Toronto technique, RCP is necessary to keep the brain cool during brief periods of HCA. It is important to note that when HCA time exceeded 30 minutes in their series, there was a significant increase in the stroke rate (1% versus 23%, p < 0.001) and mortality rate (3% versus 20%, p < 0.01). In the current report, the mortality rate also increased when HCA time exceeded 30 minutes (3% ± 3% versus 15% ± 6%) (see Fig 1), possibly due to the increased complexity of the operations requiring prolonged HCA times. However, although the number of patients in the groups with high HCA times is small, the incidence of neurologic complications remained the same, regardless of the duration of HCA (p > 0.95) (see Fig 2).
The Mount Sinai group has historically been very selective in its application of RCP, using it only in patients with extensive atherosclerotic disease, in whom they believed the embolic risk from atheromatous debris was substantial [11, 29]. Atheromatous disease is clearly important in the development of focal neurologic events after aortic operations [30]. In the current report, the stroke rate was 33% ± 16% for the 9 patients with severe atheromatous disease compared to only 5% ± 3% for patients without significant atheromatous disease (p < 0.03). The degree of atheromatous disease, however, did not influence the TND rate (p > 0.44), suggesting that the effects of atheromatous debris are focal rather than global or diffuse. Clearly it is important during periods of HCA to keep the brain cool and minimize the time in which the metabolic needs of the brain are not met. Antegrade cerebral perfusion is an attractive option to address both of these issues, and a number of recent reports have advocated this technique [26, 31, 32].
David and associates [33] recently reported on 109 patients undergoing emergent repair for acute type A dissections. They noted that the cerebrovascular accident rate decreased from 15% to 4% (p < 0.05) and the mortality rate tended to fall from 20% to 9% (p = 0.10) when rewarming was performed antegrade through the new graft after completion of the distal anastomosis, rather than retrograde through the femoral artery (among other recent improvements in their technique). Similarly, in the current report, multivariate analysis identified rewarming retrograde, rather than antegrade, as an independent risk factor for TND (OR: 3.4, p < 0.03), despite higher HCA times in the rewarming antegrade group. Delayed neurologic recovery occurred in 26% ± 10% with retrograde rewarming compared to 9% ± 4% with antegrade rewarming. It is important to note, however, that these findings may have been influenced somewhat by the initial decision to cannulate through the femoral artery in patients believed to have significant proximal atheromatous disease. New grafts with preattached side limbs have simplified the transition from retrograde to antegrade flow, and more frequent use of axillary artery cannulation in appropriate patients can eliminate the need to reposition the cannula and may improve neurologic recovery.
Potential limitations
The current study was subject to all the limitations inherent to a retrospective, nonrandomized comparison of surgical results, including potential selection bias as to which patients received supplemental RCP. For example, HCA time was increased in the RCP patients, suggesting that RCP was used more often for potentially high-risk patients. Although there was no difference in the degree of atheromatous disease or the degree of coexisting medical disease that was present in either group of patients, selection bias surely existed, as it always does in observational studies. We used multivariate analysis to help account for selection bias and other confounding risk factors, but a possible beneficial effect of RCP may still have been masked by clinical decisions to use RCP in more complex procedures. Again, however, when comparing HCA alone to HCA with RCP patients with similar HCA times, supplemental RCP did not significantly impact mortality or neurologic complications (see Figs 1 and 2). A randomized study comparing all the accepted techniques would be very interesting, but likely would require multiple centers, a difficult proposition, as most surgeons have strong personal bias with regard to cerebral protection and would be unwilling to fluctuate from the method with which they are comfortable. Such attitudes, however, are not unreasonable, because based on the current data and findings from other studies, there remain many acceptable, but not yet perfect, methods to protect the brain during circulatory arrest. Continued research is mandatory to improve neurologic outcomes for arch replacement, potentially including more aggressive use of antegrade selective perfusion and pharmacologic manipulation.
In summary, the current report demonstrated that supplemental RCP during HCA did not decrease mortality or neurologic complications during aortic arch operations when compared to a contemporary group of patients receiving HCA alone. However, rewarming retrograde through the femoral artery was associated with an increased incidence of TND. Therefore, although RCP remains optional during HCA for procedures on the arch, rewarming should be performed antegrade after completion of the distal anastomosis to improve neurologic recovery.
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Discussion |
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I have a few comments to make with regard to experimental work on the subject of retrograde cerebral perfusion, because we, like you, were intrigued by this technique early in the ’90s and hoped that RCP would improve the results over HCA alone. Unfortunately it has been our finding, in the pig model, anyway, that the advantages that can be gained with RCP can be replicated just by complete cooling and packing the head in ice. If one forces more blood through the cerebral circulation by clamping the inferior vena cava during RCP, then the technique itself causes cerebral damage. And finally, if one actually studies the flow through the parenchyma of the brain with fluorescent microspheres, of 100 cc’s or so delivered to the superior vena cava in the pig, approximately 0.01cc (= 0.01%) actually traverses brain capillaries, an amount which cannot really have any metabolic importance at all. Based on these data, we are not very enthusiastic about RCP.
In a retrospective analysis of our own experience over a 10-year period, in which RCP was used intermittently by various surgeons—and which suffers from the same criticisms as your paper because it was not a prospective study—we actually found that RCP increased the incidence of temporary neurological dysfunction when RCP patients were compared to patients with similar lengths of interruption of the antegrade circulation without RCP. Secondly, there was a suggestion that RCP converted small strokes to large strokes. As a consequence, at the present time our feeling is that RCP is not merely optional but that it should probably not be used. But obviously there are other opinions. I would like to ask, if you continue to use it, in what patient groups do you think it should be used?
Finally, the issue of cannulation is an extremely important one. You have identified and shown very nicely that perfusion through the femoral arteries is probably not a good idea. We have had similar prejudices and have switched pretty much to cannulation of the right axillary artery over the past two years. We are convinced, on the basis of still unpublished data, that this does reduce the incidence of adverse outcome, to the point that we believe that right axillary artery cannulation is now the technique of choice for any cardiac operation in which there is disease in the ascending aorta or the arch. I would like to ask Dr. Moon whether he has any feelings about axillary cannulation as well.
Once again, this is a beautiful paper. Thank you.
Dr Moon: Thank you very much, Dr. Griepp. It is hard to comment on anything that Dr. Griepp says since he has been studying this topic for so many years and essentially invented the procedure in 1975.
Our current indication for use of retrograde cerebral perfusion is for patients with atherosclerotic aortic disease, in that it may clear some atherosclerotic debris retrograde while the cross clamp is off. We also feel that it may aid in keeping the head cool during complex reconstructions requiring longer periods of circulatory arrest, although, as you note, packing the head in ice is generally sufficient as long as the rest of the body is cool. There have been some studies from Toronto suggesting they can do this procedure safely with moderate hypothermic arrest as long as they use retrograde cerebral perfusion, but I think the jury is still out on that technique.
We do not have extensive experience with axillary cannulation yet; however, we have started to use it within the last six months for patients with descending atherosclerotic disease and for complex arch procedures. We are pleased thus far, especially with the ease in which we can give antegrade cerebral perfusion during periods of arrest.
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