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Ann Thorac Surg 2006;82:90-96
© 2006 The Society of Thoracic Surgeons
Section of Cardiac Surgery, Department of Surgery, University of Michigan Hospitals, Ann Arbor, Michigan
Accepted for publication February 13, 2006.
* Address correspondence to Dr Patel, University of Michigan Hospitals, Section of Cardiac Surgery, Box 0348 Taubman Center, 1500 E. Medical Center Drive, Ann Arbor, MI 48109-0348 (Email: hjpatel{at}med.umich.edu).
Presented at the Fifty-second Annual Meeting of the Southern Thoracic Surgical Association, Orlando, FL, Nov 10–12, 2005.
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Abstract |
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METHODS: Hypothermic circulatory arrest was utilized if arch or extensive descending thoracic aortic resection was required, or if aortic pathology precluded cross-clamping. One hundred thirty-two patients (mean age, 61.3 years) were identified. Diagnosis included fusiform (41.2%) or saccular aneurysm (10.7%) and acute (4.6%) or chronic (38.9%) dissection. Twenty-one patients presented with rupture. Arch resection (distal arch 100, total arch 11) was required in 111 patients (84.1%). The extent of descending thoracic aortic resection (required in 94%) included proximal third in 41 patients, proximal two-thirds in 6, and complete thoracic aorta in 77. The proximal anastomosis was performed with total body HCA while the distal anastomosis was constructed with lower body HCA only (duration upper body HCA 33.7 ± 8.0 minutes; total duration lower body HCA 71.3 ± 24.2 minutes).
RESULTS: Thirty-day mortality was 6.0%. Neurologic events included stroke (6.8%) and permanent lower extremity paralysis-paresis (4.5%). Temporary dialysis was needed in 7 (5.3%), though only 2 patients required permanent dialysis (1.9%). Independent predictors of a composite endpoint of death, stroke, permanent paralysis, or dialysis included duration of lower body HCA (p = 0.03) and major postoperative infection (p = 0.003).
CONCLUSIONS: Adjunctive use of deep hypothermic circulatory arrest for descending thoracic aortic resection affords excellent preservation of end-organ and spinal cord function with acceptable rates of mortality and significant morbidity.
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Introduction |
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This study was undertaken to analyze the outcomes associated with the use of HCA as a surgical adjunct in the operative therapy of descending thoracic aortic pathology. Indications for use of HCA included requirements of either aortic arch or extensive descending aortic resection, or if aortic pathology precluded cross-clamp application (eg, severe atherosclerosis or calcification at the potential cross-clamp site, or presence of acute dissection). A large consecutive group of patients undergoing DTAR with HCA constituted the study group.
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Material and Methods |
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The operative procedure was conducted as follows. Patients were intubated with a double lumen endotracheal tube. All procedures were performed through a left thoracotomy. The descending thoracic aorta was identified and mobilized to allow for resection of the pathologic segments. If the pathology extended into the transverse arch aorta, this was also mobilized for planned resection. The patient was then placed on cardiopulmonary bypass (CPB). Venous drainage was established by either left femoral vein or the left pulmonary artery cannulation and arterial inflow established through the left femoral artery or, rarely, through the descending thoracic aorta. The patients were cooled to a core (bladder or rectal) temperature of 18°C. Nasopharyngeal temperature was also monitored in all patients, and circulatory arrest later instituted only when both nasopharyngeal and core body temperature were 18°C. All intercostal vessels in the pathologic aortic segment were mobilized for either reimplantation or external ligation and division. At 20°, a "neuroprotective cocktail" of solumedrol (1 gram intravenous [IV]), phenobarbital (1 gram IV), and mannitol (25 grams IV) was administered. When both core body and nasopharyngeal temperatures were 18°C, 40 mEq KCl was administered intravenously to arrest the heart, and CPB was temporarily suspended at that temperature. The aorta was then opened, and the proximal anastomosis carried out with a Hemashield (Meadox Medicals Inc, Oakland, NJ) graft (with a prefabricated single side branch) in an open fashion. The graft was then cannulated through the single side branch, partial CPB flow reinstituted, and the proximal aorta was deaired through the open distal end of the graft with the patient in steep Trendelenburg position. A cross-clamp was then placed just distal to the side branch cannulation site and half normal flow reinstituted to the upper half of the body (while still maintaining deep hypothermia). The pathologic aortic segment was then divided distally. The distal anastomosis was then constructed with the lower body still under HCA. After completion of the anastomosis, full CPB was resumed to both the upper and lower half of the body, and active rewarming initiated. The patient was left in a steep Trendelenburg position and an air needle vent was placed in the aortic graft. The heart was allowed to eject partially for a brief period to ensure evacuation of air in the intracardiac chambers and ascending aorta. The patient was taken out of the Trendelenburg position, and separated from CPB when normothermic. Protamine was administered to return the ACT to baseline. Hemostasis was then obtained and the chest closed in routine fashion.
Postoperative management was conducted along standardized protocols. Lumbar drain use was routine for aortic resection involving more than the proximal third of the descending aorta. When indicated, lumbar drains were placed just after induction of anesthesia, and prior to thoracotomy. If lumbar drain placement yielded bloody cerebrospinal fluid drainage, the operative procedure was aborted. No significant complications identified were directly attributed to lumbar drain placement. All patients were also managed with mild permissive hypertension to keep spinal perfusion pressures at 80 mm Hg or higher (if a lumbar drain was placed), or a mean arterial pressure of 90 to 100 mm Hg (if no lumbar drain was present).
Preoperative demographics and comorbidities were identified. Intraoperative and postoperative outcome data were collected. Postoperative morbidity and 30 day mortality were analyzed. Mortality beyond 30 days was obtained from clinic follow-up or interrogation of the National Death Index.
Statistical Analysis
Data were obtained from the Adult Cardiac Surgery database maintained at the University of Michigan. Mortality and complications were verified through the University of Michigan medical information system.
All continuous data were expressed as the mean ± standard deviation, while dichotomous variables were expressed as a count and percent of the whole group. The primary outcomes of the study were rates of 30 day mortality, stroke, permanent renal failure, and permanent paralysis-paresis.
Variables were evaluated using the 
2 test for dichotomous variables, and one way analysis of variance for continuous variables. Variables with a p value of 0.1 or less on univariate analysis were entered into a multivariate model (logistic regression for dichotomous variables and linear regression for continuous variables) to identify factors that were independently associated with each of the outcomes of interest. The models were constructed using a forward selection process. Similarly, a combined outcome, which contained 30-day mortality, permanent dialysis, permanent paralysis, or stroke was created and evaluated in the manner described above. Long-term survival was analyzed by life table methods. All results with p less than 0.05 were considered statistically significant.
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Results |
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Neurologic Complications
Stroke occurred in 9 patients (6.8%). On univariate analysis, presence of chronic dissection with aneurysmal degeneration, prior aortic procedures, or the presence of postoperative GI complications or major infection (defined as any infection requiring antibiotic therapy; eg, pneumonia, urinary tract infection, wound infection) correlated with stroke (all p < 0.05). However, by multivariate analysis only major postoperative infection was independently associated with a postoperative cerebrovascular accident (CVA) (p = 0.003). Details regarding each patient sustaining a postoperative stroke are listed in Table 2. Importantly, of these 9 patients, 5 (56%) had significant atheromatous burden and (or) thrombus in the arch and had an early diagnosis of CVA. In contrast, of the 123 patients without a postoperative CVA, only 14 (11.4%) were noted to have significant thrombus or atherosclerotic debris in the arch aorta (p= 0.004 by 2 test versus patients without a stroke).
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Postoperative delirium was defined as a prolonged period of confusion (duration of less than 72 hours) that occurred at any point during the hospitalization. Prolonged confusion of greater than 72 hours was defined as a postoperative CVA and was investigated with a computed tomographic scan of the head, which typically demonstrated multiple diffuse infarcts. Postoperative delirium was observed in 24.2% of patients. While univariate analysis revealed that both COPD (p = 0.05) and major postoperative infection (p = 0.04) correlated with postoperative delirium, only COPD was independently associated by multivariate analysis (p = 0.01).
Renal Complications
Temporary dialysis was needed in 7 (5.3%). Of these, four patients expired during the hospital stay, two patients required permanent dialysis (1.9%), and two had complete recovery of renal function. There were an additional 10 patients who had a rise in their creatinine to over 2 mg/dL, but who did not require dialysis. By univariate analysis, variables correlating with temporary dialysis included presence of acute dissection (p = 0.008), extent of arch resection (p = 0.0001), preoperative hematocrit (p = 0.03), a history of active tobacco abuse (p = 0.01), a preoperative ejection fraction of 0.50 or less (p = 0.01), and the presence of postoperative GI complications (p = 0.0001) or major infection (p = 0.002). Of these, none was independently associated by multivariate analysis.
Pulmonary Complications
The median duration of intubation was 21 hours (mean 70.2 ± 131.4). Prolonged (>48 hours) ventilatory support was required in 28 patients (21.2%); tracheostomy was needed in 14 (10.6%). All patients requiring prolonged ventilation and (or) tracheostomy were in the group of patients who had a composite endpoint.
Infectious Complications
Major postoperative infectious complications (ie, defined as those requiring antibiotic therapy) occurred in a total of 32 patients (24.2%). This included a diagnosis of pneumonia in 22 (16.7%), urinary tract infection in 6 (4.5%), or a thoracotomy wound infection in 11 (3 of which required reoperation).
Other Results
Reoperation for bleeding was required in 7 patients (5.8%). Recurrent laryngeal nerve injury (temporary or permanent neuropraxia) was identified in 10 patients (7.6%). Finally, 7 patients (5.8%) had significant GI complications, including visceral ischemia (3), and prolonged ileus requiring nasogastric decompression (4).
Composite Endpoint
In order to generate a sufficient event rate for multivariate analysis, a composite endpoint of 30-day mortality, stroke, permanent paralysis, or dialysis was formulated. Variables significantly associated on univariate analysis with the composite endpoint are listed in Table 3. By multivariate analysis, independent predictors of a composite endpoint of 30-day mortality, stroke, permanent paralysis or dialysis included duration of lower body HCA (p = 0.03) or major postoperative infection (p = 0.003).
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Comment |
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This study demonstrates that adjunctive use of HCA can be performed with low rates of mortality and morbidity. Our rates of paraplegia are among the lowest reported in a series of this size, and the incidence of other major complications such as stroke or permanent renal failure are acceptable. It should be emphasized that half of the patients sustaining a postoperative CVA were noted to have significant atheromatous or thrombus burden in the arch at the time of exploration, a site that likely would not have served well for proximal cross-clamp application. In contrast, only 11% of patients without a postoperative CVA had significant atheroma or thrombus within the arch aorta. Although the risk of stroke was quite high in this group, an alternative approach such as simple cross-clamp application in this diseased segment (with or without distal perfusion) would likely not have improved the outcome.
Whether HCA is really necessary for all descending thoracic aortic repairs remains controversial. Other large series have reported success in prevention of paraplegia using various combinations of distal aortic perfusion, lumbar drainage, selective intercostal artery reimplantation, and avoidance of postoperative hypotension [11–14]. Although there has been no randomized trial comparing HCA with other techniques of spinal cord protection, several clinical and experimental studies have suggested a benefit of deep hypothermic arrest for prevention of paraplegia.
Rokkas and colleagues [6] demonstrated, in a series of primate experiments, that deep hypothermia was protective during spinal cord ischemia when compared with normothermic ischemia. Although the neuroprotective effects of hypothermia are likely related to improved ischemic tolerance by a reduction in metabolic requirements, the mechanism may also involve inhibition of release of excitatory amino acids in the extracellular neuronal space [7]. Clinical series by Kouchoukos and colleagues [4], and Okita and colleagues [10] have reported excellent results with the use of HCA. In a report comparing the effects of different systemic temperatures on the outcome variable of paralysis, Svensson and colleagues [15] demonstrated that moderate or profound hypothermia resulted in fewer neurologic deficits. The study by Carrel and colleagues [8] did demonstrate that in addition to 30-day mortality both postoperative paraplegia and stroke were significantly lower in the group requiring HCA, when compared with another group undergoing proximal cross-clamping and distal aortic perfusion. In contrast, other reports have suggested that use of HCA is associated with prohibitive rates of mortality, stroke, and postoperative pulmonary insufficiency [5]. Our results, as well as other contemporary series, demonstrate the safety of this approach.
In contrast to other reports, arch resection (whether partial or complete) was performed in the majority of patients in our study. Although cross-clamp application in the mid-arch (between the left carotid and subclavian arteries) can potentially be performed, risks of this maneuver include a significant increase in cardiac afterload, atheroembolism from this frequently diseased segment, limited ability to resect all disease at times, and finally the risk for aortic injury at the clamp site. The use of HCA for distal arch resection avoids these pitfalls and allows for easy visualization for construction of the proximal anastomosis. Interestingly, a recent report by Girardi and colleagues [16] demonstrated no significant increase in stroke risk with clamp placement in the mid-arch when compared with a group of patients undergoing clamp placement distal to the left subclavian artery. This warrants further study.
The finding that preoperative aortic insufficiency was an independent risk factor for long-term mortality was surprising. All patients undergoing descending thoracic aortic resection in our institution undergo preoperative transesophageal echocardiograms. If aortic insufficiency of 2+ (moderate) or higher is identified, those patients requiring adjunctive HCA for DTAR undergo aortic valve replacement prior to descending aortic resection (to avoid the risk of ventricular distention with HCA). It is therefore unclear why preoperative aortic insufficiency was a risk factor, and this warrants further study.
With the emerging role of endovascular therapy, a report on descending thoracic aortic resection warrants a comparison of outcomes with endoluminal thoracic aortic repair (ETAR). Although ETAR has been associated with a shorter hospital stay and potential applicability to high risk surgical patients, it is of interest that the larger series of ETAR have reported no improvement in rates of paraplegia when compared with open series utilizing a variey of surgical adjuncts. In addition, the late failure rate of ETAR has been much higher than that reported for open surgery [17–19]. The role of ETAR, however, will likely continue to grow and the results will improve as experience is gained.
In conclusion, this study demonstrates that adjunctive use of hypothermic circulatory arrest for descending thoracic aortic resection can be performed with low rates of both mortality and morbidity. Hypothermic circulatory arrest is therefore advocated for use in complicated descending aortic pathology requiring resection.
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Discussion |
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The problem with deep hypothermic circulatory arrest using femoral artery cannulation in my experience has been a high incidence of neurocognitive deficits. Obviously the hard endpoint of stroke is easy to diagnose, but it is these patients that take several days to wake up; they might have problems with memory and speech afterwards. One of the main things that we found improves that was to use the right subclavian artery with a side graft for an arterial in-flow and to run the pump continuously while we do the arch repair. My question is, did you look also at things like dementia, neurological period to recovery from the surgery, and so on?
DR PATEL: Thank you for your questions, Dr Svensson. We are well aware of your work describing a potential reduction in postoperative neurologic deficits with the use of axillary artery cannulation. We observed postoperative delirium at any point during the hospitalization in approximately 24% of patients, which I believe is not much different from that reported with other arch series (usually performed via a median sternotomy). However, our approach generally has been to utilize femoral cannulation for descending thoracic aortic resection, as the axillary artery approach is a bit more cumbersome when the patient is in a decubitus position. We understand, however, that for approaches that are done through a median sternotomy this may indeed reduce the incidence of neurologic dysfunction as you have described.
DR SVENSSON: Just as a technical point for people interested in doing this, the way to do it is to put the patient about 30 degrees, with some big towels behind the shoulder and the hips, and then make sure when the patient is prepped that he has a space behind there, and you can then prep in the field your right subclavian axillary artery, put a side graft onto that, and then do your operation, rotate the table, and with that you have good access. But great presentation.
DR PATEL: Thank you.
DR JOHN A. KERN (Charlottesville, VA): That was a really nice paper and excellent results. Can you speculate a little bit on the issue of the aortic insufficiency and the fact that it was a predictor of your late events, and how did you handle the AI at the time of surgery. Did you look at the folks with aortic insufficiency at all late postoperatively, with echoes or anything, to see what their function was doing? Did you hurt them at the time of surgery?
DR PATEL: Our approach is to obtain a preoperative transesophageal echocardiogram on every patient undergoing descending thoracic aortic resection. If this identifies moderate or severe aortic insufficiency, and the planned operative procedure requires adjunctive hypothermic circulatory arrest, we elect to perform aortic valve replacement prior to descending aortic resection.
DR KERN: But for those who you couldn't clamp, which involved many in this study, obviously, you vented the heart, correct?
DR PATEL: We do not routinely vent the heart. We identify aortic insufficiency preoperatively and perform AVR (aortic valve replacement) as indicated previously.
DR KERN: Was anyone unable to be weaned off cardiopulmonary bypass?
DR PATEL: No.
DR THORALF SUNDT (Rochester, MN): You said that you used spinal drains in a number of these?
DR PATEL: Yes.
DR SUNDT: And did you insert those spinal drains on the morning of surgery or did you insert them the night before? How do you deal with bloody taps, et cetera? Our anesthesiologists are certainly reluctant to put in a spinal drain when we use circulatory arrest, so we don't use a spinal drain in that case. We only use spinal drains when we are using left heart bypass. And a related question, again, to the issue of paraplegia; it seems like there was a pretty significant rate. What is your approach or your philosophy about reimplantation of intercostal vessels?
DR PATEL: Thank you for your questions. Lumbar drains are inserted generally in the morning of the operation prior to thoracotomy. Our approach with CSF (cerebrospinal fluid) drainage is to utilize a lumbar drain in all patients that require resection of more than the proximal third of their descending thoracic aorta.
The issue of intercostal reimplantation is a different story. For those patients requiring total thoracic aortic replacement, we often bevel the distal anastomosis to include the lower couple of critical intercostals (the peridiaphragmatic intercostals). However, we do not routinely reimplant intercostal arteries for isolated thoracic aortic resections. We typically externally ligate and divide these during the time when the patient is cooling. In contrast, for those patients requiring thoracoabdominal resection (not included in this series), we routinely reimplant at least three sets of peridiaphragmatic intercostals.
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