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Ann Thorac Surg 2004;77:1298-1303
© 2004 The Society of Thoracic Surgeons
a The Michael E. DeBakey Department of Surgery, Division of Cardiothoracic Surgery, Baylor College of Medicine and The Methodist DeBakey Heart Center, Houston, Texas, USA
* Address reprint requests to Dr Coselli, 6560 Fannin, Suite 1100, Houston, TX 77030, USA.
e-mail: jcoselli{at}bcm.tmc.edu
Presented at the Forty-ninth Annual Meeting of the Southern Thoracic Surgical Association, Miami Beach, Florida, Nov 79, 2002. *Recipient of the 2002 Southern Thoracic Surgical Association President's Award.
| Abstract |
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METHODS: Over a 15-year period 387 consecutive patients underwent surgical repair of DTAAs using either the "clamp-and-sew" technique (341 patients, 88.1%) or distal aortic perfusion via a LHB circuit (46 patients, 11.9%). Data regarding patient characteristics, operative variables, and outcomes were retrieved from a prospectively maintained database. The impact of LHB on the frequency of paraplegia was determined using univariate and propensity score analyses.
RESULTS: There were 17 operative deaths (4.4%) including 11 patients (2.8%) who died within 30 days. Paraplegia occurred in 10 patients (2.6%). On univariate analysis increasing age (p = 0.03), increasing aortic clamp time (p < 0.001), increasing red blood cell transfusion requirements (p = 0.01), and acute dissection (p = 0.03) were associated with increased incidence of paraplegia. Patients who received LHB had a similar incidence of paraplegia (2/46, 4%) compared with those treated without LHB (8/341, 2.3%; p = 0.3). Both matching and stratification propensity score analyses confirmed that LHB was not associated with reduced risk of paraplegia.
CONCLUSIONS: On retrospective analysis the use of LHB during DTAA repair did not reduce the incidence of spinal cord injury. The "clamp-and-sew" technique remains an appropriate approach to DTAA repair.
| Introduction |
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Over the last 15 years we have expanded our use of distal perfusion with left heart bypass (LHB) in patients undergoing surgical repair of extensive thoracoabdominal aortic aneurysms and have demonstrated that this adjunct reduces the incidence of paraplegia in this setting [16]. The benefit of LHB during less extensive repairs, however, remains unclear. The purpose of this retrospective analysis was to determine if the use of LHB reduced the incidence of paraplegia in patients who underwent DTAA repair.
| Material and methods |
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Operative technique
The details of our surgical technique have been described elsewhere [17, 18]. All patients underwent DTAA repair via left thoracotomy often with division of the costal margin. We routinely used moderate systemic heparinization (1.0 mg/kg); the heparin was reversed with protamine sulfate after completing all anastomoses. Mild permissive hypothermia (32°34°C, nasopharyngeal) was also used routinely to minimize ischemic complications. To reverse cooling at operative completion the field was irrigated with warm saline. Patent groups of intercostal arteries between T7 and T10 were reattached to the graft in 18 patients (4.7%) usually when larger extents of the descending thoracic aorta were replaced and particularly in patients with previous abdominal aortic graft replacement. Cerebral spinal fluid drainage was used in 24 patients (6.2%). We used LHB with a centrifugal pump in 46 patients (11.9%). In these patients blood was drained via a left atrial cannula (usually placed via the inferior pulmonary vein) and returned through a cannula in the distal descending thoracic aorta or left femoral artery. The closed LHB circuit did not include a cardiotomy reservoir, an oxygenator, or a warming device. In most cases LHB was used only during the proximal anastomosis. Neither somatosensory nor motor-evoked potential monitoring was used [19].
Study variables and definitions
All preoperative, intraoperative, and postoperative data were retrieved from a prospectively maintained database. Aneurysms associated with aortic dissection were considered acute if surgery was performed within 14 days of the onset of pain; after 14 days dissection was considered chronic. Patients were considered symptomatic when any symptom (acute or chronic, severe or mild) related to the aneurysm was present including pain, hoarseness, and dysphagia. Patients with acute presentations were defined as those with acute pain, rupture, contained rupture, or acute dissection. Preoperative renal insufficiency was defined as serum creatinine exceeding 3.0 mg/dl or need for hemodialysis.
The patients involved in this series included only those in whom the descending thoracic aorta, ie, the segment of aorta between the left subclavian artery and the diaphragm, was surgically replaced with a graft in continuity with the aortic lumen. The extent of repair was classified based on the descending thoracic aortic segments that were replaced, ie, proximal one-third (A), middle one-third (B), distal one-third (C), or any combination of these.
In accordance with established guidelines operative mortality included all deaths occurring within 30 days and all deaths occurring during the initial hospitalization. All patients with postoperative neurologic deficits involving the lower extremities were included in the paraplegia category regardless of whether the deficit was weakness (paraparesis) or paralysis, immediate or delayed, transient or permanent. This included patients with unilateral lower extremity deficits unless an associated deficit involving the ipsilateral upper extremityindicating a strokewas present.
Statistical analysis
Continuous variables are presented as mean ± standard deviation. Univariate analysis was performed using
2 or Fischer exact tests for categorical data and Student t tests for continuous data. In an attempt to adjust for the confounding variables and minimize the impact of selection bias, several logistic regression models were constructed to estimate the probability of receiving LHB. The model that most accurately predicted LHB/no LHB was used as the propensity scoring model. This final model, which included 32 variables (Table 1),
was used to calculate propensity scores for 385 patients (Fig 1)
(2 patients with preoperative paraplegia were excluded). Cases with LHB and those without LHB were matched based on their propensity scores (calculated to two decimal places); the frequencies of paraplegia in the matched LHB and non-LHB groups were then compared. The propensity scores were also used for a stratified analysis in which scores for all 385 patients were consecutively ordered and divided into five groups of equal size. Patients within each of these quintiles had similar probabilities of receiving LHB thereby reducing bias (Figure 2).
The frequencies of paraplegia between LHB and non-LHB patients were compared for each quintile. For all analyses, p values less than 0.05 were considered statistically significant.
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| Results |
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| Comment |
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Unfortunately prospective randomized trials are extremely difficult to perform in thoracic aortic surgery, primarily due to low patient volumes and tremendous variability in management strategies between different surgeons and institutions. Therefore we are often forced to rely on retrospective analyses to guide patient care decisions. Whereas statistical tools like propensity score analysis are not without limitations, they can add strength to retrospective studies.
In conclusion, in this retrospective analysis, the use of LHB during DTAA repair did not reduce the incidence of spinal cord injury. The "clamp-and-sew" technique remains an appropriate approach to DTAA repair.
| Acknowledgments |
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| Discussion |
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DR COSELLI: Yes.
DR SUNDT: So statistical analysis having failed to demonstrate predictors of increased risk of paraplegia, and hence on which patients we should use left-heart bypass, maybe you can give us some insight into just what your clinical feeling is. How did you tend to decide during this interval on which patients to use left heart bypass and which not to? Are there some imponderables that cannot be statistically quantified that we can consider as we look at these data?
DR COSELLI: That is a good question. It turns out, from our analysis of this data, that my perceived bias toward using left heart bypass in patients that I thought were going to require longer cross-clamp times did pan out. In cases with longer total clamp times, spinal cord ischemic times, renal ischemic times, etcetera, I had a tendency to use left heart bypass. These were often patients that were operated upon for aortic dissection and patients in whom cross-clamping proximal to the left subclavian artery was required; as you might imagine, there was a great deal of overlap between those two groups.
DR SUNDT: So then could we conclude equally well that, by applying this technique in these higher risk patients, you were actually able to do the operation without an increased risk of paraplegia?
DR COSELLI: That is the initial assumption. If you just do univariate and multivariable analyses comparing the left heart bypass and no left heart bypass groups, that is what is distilled out; but, when you use a propensity score analysis to try to take out the surgical bias, it still holds up that left heart bypass does not have a statistically significant impact.
DR SUNDT: My only concern is the ability to truly model the subtleties of clinical assessment; regardless of the sophistication of the statistical analysis, I am not sure that one can account for that sixth sense that you bring to the table given your incredible experience and expertise in this complex area. I suspect that your own good judgment may play more of a role than you are giving it credit for.
DR COSELLI: Thank you.
DR CONSTANTINE MAVROUDIS (Chicago, IL): Congratulations on a great presentation. It seemed like you hit a home run here. Your statistical analysis is comprehensive and answers questions that any reader might have. You carried the analysis farther than I think any of us would have thought possible.
I rise to ask you a couple of questions and not only about your patient population but how it may relate to patients with coarctation of the aorta. The accumulated experience for repair of coarctation of the aorta has shown that intraoperative temperature elevation, elongated cross-clamp time, and significant decrease of downstream pressure during the cross-clamp are risk factors for the development of paraplegia. In our practice, we measure the pressure in the lower extremity in those cases that are in the older age groups.
Did you think about looking at the temperature of the patients and whether temperature elevations corresponded with paraplegia? Also do you think that measuring pressures distally has any effect on whether to use bypass or not? In other words, when you clamp what is the pressure distally and so forth?
Again congratulations on a great paper.
DR COSELLI: Thank you. These were not patients with coarctation although some patients who had had previous coarctations and later developed aneurysms were in this group.
We have not found temperature to be a predictive variable although due to an earlier experience, we do not put a heat exchanger in the circuit and deliberately keep these patients normothermic or warm. We operate in a relatively cool environment and allow the temperature to fall without trying to correct it.
In these patients we did not usually measure distal pressure so we did not use it as a variable in the analysis. Although, early on in the experience, pressure was one of the measurements we used to regulate pump flow, we found that other criteria are probably equally as important and easily measured, and, therefore, we do not routinely measure pressure distally anymore.
DR JOHN KRATZ (Charleston, SC): Thank you for this important piece of information. I think this might be a trendsetter paper around the country that a number of us will use as a tool.
My question is that most of us do not do 300 cases like this and perhaps our average cross-clamp times are going to be 10 or 15 minutes longer than somebody with your degree of experience. Do you think your data will translate to the average thoracic surgeon at 3 o'clock in the morning dealing with an aortic dissection?
DR COSELLI: Excellent questionI hope so. This does not say, "do not use left heart bypass." I showed a slide of some of the review of the literature, much of which makes rather profound, even dogmatic, statements about what we should and should not use. These statements can, on occasion, rise up to impact us in other ways including medico-legally. I think the importance of looking into this data, particularly in this way, is that it may help balance out some of those other efforts.
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