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Ann Thorac Surg 2000;69:692-695
© 2000 The Society of Thoracic Surgeons

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Original Articles

Outcome of thoracoabdominal aortic operations using deep hypothermia and distal exsanguination

^a Clinic for Cardiovascular Surgery, University Hospital Berne, Berne, Switzerland
^b Institute of Anesthesiology, University Hospital Berne, Berne, Switzerland

Address reprint requests to Dr Carrel, Clinic for Cardiovascular Surgery, University Hospital, CH-3010 Berne, Switzerland
e-mail: thierry.carrel{at}insel.ch

Presented at the Poster Session of the Thirty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Antonio, TX, Jan 25–27, 1999.

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. Operation of the descending and thoracoabdominal aorta may be affected by a significant perioperative morbidity, mainly because of ischemic damage of the spinal cord and malperfusion of the abdominal organs.

Methods. A comparative analysis was performed on two consecutive series of patients operated between 1982 and 1998. Group 1 consisted of 90 patients operated with moderate hypothermic left heart bypass. Group 2 included 38 patients operated using deep hypothermic cardiopulmonary bypass and a period of circulatory arrest while performing the proximal anastomosis and distal exsanguination during confection of the distal anastomosis.

Results. Main demographic factors and causes of the aortic disease were similar in both groups. Early mortality was significantly higher in the group of patients with aortic cross-clamping (15 of 90, 16%) than in those operated with circulatory arrest (2 of 38, 5.2%), p < 0.001. Paraplegia occurred in 8 patients in the group operated with mild hypothermia (8.8%) but in only 1 patient (2.6%) when deep hypothermia had been used.

Conclusions. In our experience, deep hypothermia combined with distal exsanguination significantly improved the early postoperative outcome after operation of the descending and thoracoabdominal aorta. This technique allowed easy confection of proximal and distal anastomoses, and the duration of the operation was not prolonged significantly through this approach.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Operation of the descending and thoracoabdominal aorta may be affected by a considerable perioperative morbidity, mainly because of ischemic damage of the spinal cord, malperfusion of the abdominal organs, and cerebrovascular events. Profound hypothermia is a widely accepted technique for the protection of central nervous system as well as of other organs in different fields of cardiovascular surgery [1–6]. Compared with the frequent use of deep hypothermic circulatory arrest (DHCA) in ascending and aortic arch operations, this technique has received less attention in the surgical treatment of descending and thoracoabdominal aneurysms. There are many reasons why DHCA may be useful: (1) the descending aortic pathology extends into the aortic arch, (2) aortic cross-clamping distal to the subclavian artery or between the left carotid and subclavian artery is difficult or hazardous (because of adhesions, atheromatous material, size or friability of the aortic wall), and (3) to achieve organ protection—most importantly to the spinal cord—through hypothermia itself. However, the use of DHCA requires a prolonged time on cardiopulmonary bypass (CPB) necessary for cooling and rewarming and may lead to an increased risk of coagulopathy and pulmonary complications [7].

This study analyzes the early outcome of patients operated on CPB using DHCA combined with distal exsanguination and compares it with that obtained in patients operated on left heart bypass with moderate hypothermia.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
A comparative analysis was performed on two series of patients operated between 1982 and 1998 and who required replacement of either the descending or thoracoabdominal aorta. Group 1 included 90 patients operated with moderate hypothermic left heart bypass and cross-clamped aorta. Group 2 included 38 patients operated using deep hypothermic CPB and circulatory arrest during confection of the proximal anastomosis, whereas the distal anastomosis was performed during distal exsanguination and proximal reperfusion. The demographics of the patients and extent of the aortic disease are summarized in Tables 1 and 2.

Surgical technique and extracorporeal perfusion when DHCA is used
All patients receive conventional monitoring lines and a double-lumen endotracheal tube. Rectal and tympanic temperature are monitored routinely. High-dose aprotinin is given only after restarting the perfusion following DHCA. Posterolateral thoracotomy is performed and the chest entered in the fifth or sixth intercostal space. In patients undergoing thoracoabdominal aneurysm resection, the incision is extended through the costal margin to the abdominal midline; in these cases, the diaphragm is divided in a circumferential fashion. CPB is instituted after iliac artery (22 or 24F cannula) and vein cannulation (28F long cannula—the tip of it is placed in the right atrium) and cooling starts immediately. Alternatively, the distal aorta and the pulmonary artery are used for cannulation. An additional arterial line to be used for rewarming the upper part of the body is connected through a Y-connector to the arterial inflow of the perfusion system. Cooling and rewarming are accelerated by using generous doses of phentolamine into the bypass circuit to promote peripheral vasodilation. In patients with aortic insufficiency only, a left ventricular vent is introduced through the apex of the left ventricle. Topical cooling of the brain is used routinely. Thiopenthal (15 to 20 mg/kg) is given approximately 3 to 5 minutes before DHCA. Once a tympanic temperature of 20°C to 22°C is reached, the extracorporeal circulation is interrupted. The proximal anastomosis is performed in an open fashion at the level of the distal aortic arch without aortic clamp. While doing this, the distal aorta is clamped at the midthoracic level when feasible and low flow distal perfusion (500 to 1,000 mL/min) is started. After completion of the proximal anastomosis, proximal reperfusion is reinstituted at a flow rate of 2.5 L/min through a cannula introduced into the side arm of the vascular prosthesis (Anteflow, Vaskutek, SulzerMedica, Winterthur, Switzerland), and air and debris are flushed out of the aorta.

Thereafter, the vascular prosthesis is clamped immediately distal to the anastomosis and the distal anastomosis performed in an open fashion, while the patient’s lower body part is exsanguinated. In thoracoabdominal aneurysm operations, reattachment of the intercostal and visceral arteries is performed with sequential blood flow restoration to the spinal cord, to the visceral circulation, and finally to the lower extremities. Rewarming is accelerated by the presence of two arterial lines (the proximal one into the side arm of the prosthesis and the distal one in the iliac artery).

Statistical methods
A total of 12 patients’ or operation-related variables were examined in a univariate analysis to determine potential predictive factors for 30-day mortality and spinal cord dysfunction. Those variables with a value of p less than 0.1 in the univariate analysis were entered into a logistic regression analysis and examined separately for each group of patients. For the final analysis, a value of p less than 0.05 was considered statistically significant. An unpaired t test was used to compare mean values between both groups. All analyses were performed using BMDP statistical software (Los Angeles, CA).

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Main demographic factors, incidence of aortic dissection, and degenerative aortic aneurysmal disease and reoperations (prior elephant trunk procedures excluded) were similar in both groups of patients. Both groups showed a similar incidence of acute and chronic aortic dissection (4.4% acute and 37.6% chronic in group 1; 5.2% acute and 31.6% chronic in group 2). Not surprisingly, a trend to prolonged extracorporeal circulation time was observed in patients operated using deep hypothermia. Early mortality (30-day mortality: 15 of 90, 16.6%) was significantly higher in group 1 than in group 2 (2 of 38, 5.2%), p less than 0.001. Paraplegia occurred in 8 patients from group 1 (8.8%) but in only 1 patient from group 2 (2.6%).

Main CPB data are given in Table 3 and mortality, paraplegia, and main additional complications are summarized in Table 4. Early outcome was not analyzed according to the extent of the aortic lesion for four reasons: (1) the overall number of patients was modest, (2) there was a high variation of pathologies, (3) there were only three major events in group 2, and (4) patients from group 1 were mainly operated between 1982 and 1993, and those from group 2 between 1995 and 1998. Regarding all other complications (myocardial infarction, cardiac arrhythmia, pulmonary dysfunction, renal failure), there were no significant differences between the two groups except for reexploration due to bleeding, which was more frequent in group 1 (10/90, 11% vs 0, p < 0.001). Only a trend to less cerebrovascular accident was found in the group operated using DHCA. In the multivariate analysis, only rupture (p = 0.02) and acute type B dissection (p = 0.01) were found to be predictive factors of early mortality and paraplegia in group 1. No factor could be identified as a predictor for adverse outcome in group 2.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

The risk of paraplegia during aortic operation is determined by the interaction of four independent processes: (1) duration and degree of decreased blood flow to the spinal cord, (2) rate of neuronal metabolism, (3) failure to reestablish blood flow to the spinal cord, and (4) postischemic reperfusion injury [12, 17]. Consequently, efforts to protect the spinal cord during ischemia have ranged from purely mechanical (full CPB, temporary left heart bypass, cerebrospinal fluid drainage, reimplantation of intercostal arteries) to purely pharmacologic (vasodilators, oxygen radical scavengers, perfluorocarbon infusion into the subarachnoidal space).

Hypothermia results in an overall reduction of the metabolic requirement at the cellular level, which prolongs the tolerance of tissues to ischemia. In addition, hypothermia has been shown to delay membrane failure—which manifests through an inability to maintain ionic gradients—by slowing the appearance of membrane leaks and thus conserving high-energy phosphates.

The largest experience with deep hypothermic circulatory arrest for repair of descending or thoracoabdominal aneurysms has been reported by Rokkas and Kouchoukos [5] as well as by Safi and associates from Houston [6]. Although in contemporary reports the 30-day mortality rates range between 14% and 33% and the paraplegia rates range from 7% to 14%, Rokkas and Kouchoukos [5] reported a 30-day mortality of 7.3% and a 3.3% incidence of paraplegia. DHCA offers some advantages compared with operations using left heart bypass: absence of surgical dissection of the proximal aorta (minimizing the risk of recurrent paresis), no aortic clamp in the way, excellent and easy access to the aortic arch, and a bloodless field. Identification and proper elimination of the site of the intimal tear—in acute and chronic dissection—are almost always easier than when distal aortic arch remains clamped. At the biochemical level, hypothermia has been shown to inhibit the release of excitatory amino acids in the extracellular space, which may cause irreversible neuronal damage, and to reduce lactate concentration in the cerebrospinal fluid [18, 19].

In contrast to authors who advocate the use of this technique for the majority of descending and thoracoabdominal aortic procedures, Coselli and Svensson [12, 14, 15] recommend DHCA only if there is a need for concomitant repair of the transverse aortic arch and if proximal control is hazardous because of rupture or atheromatous debris. Otherwise, left heart bypass allowing proximal decompression and distal perfusion is performed [20–22].

Our results, obtained in a moderate-sized institution, compare very favorably with those of larger series. Early mortality has been very acceptable and the rate of paraplegia is low. The perfusion technique itself is simple and access to every aortic segment is easy.

We have found deep hypothermic CPB and circulatory arrest to be safe adjuncts in descending and thoracoabdominal aortic operations. The combination of DHCA with distal exsanguination, advised by Cooley [23, 24], during completion of the distal anastomosis offers the advantages of maximal exposure while the heart and brain are already reperfused. In our institution, the combination of these two techniques has contributed to significantly improve the early postoperative outcome after this type of surgical procedure. Moreover, this approach seems to confirm the hypothesis that multiple combinations of techniques may contribute to reduce further the risk of paraplegia [12].

	Footnotes

 
This article has been selected for the open discussion forum on the STS Web site: http://www.sts.org/section/atsdiscussion/

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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