Continuous Selective Cold Perfusion in Thoracoabdominal Aneurysm Repair
ABSTRACT
Fifteen patients with a mean age of 57 ± 17 years underwent thoracoabdominal aortic aneurysm repair under continuous selective blood perfusion of the intercostal and visceral arteries. Three aneurysms were Crawford type I, 6 were type II, and 6 were type III. Surgery was performed on an emergency basis in 5 cases. All operations were carried out using distal perfusion with mild hypothermia (> 32°C) in 13 cases and deep hypothermia (< 20°C) in 2 cases when a proximal clamp was undesirable. During aortic replacement, the intercostal arteries between the eighth thoracic and first lumbar vertebrae and the visceral arteries were reconstructed separately with a prosthetic graft under selective cold blood perfusion (22°C to 26°C). Flow was maintained above 100 mL•min–1. The durations of operation, selective intercostal and visceral perfusion, and distal perfusion were 9 ± 2 hours, 70 ± 35 minutes, and 170 ± 80 minutes, respectively. There was one operative death (mortality, 6.7%) due to respiratory failure and one case of delayed paraparesis. There was no paraplegia, acute hepatorenal failure, or bowel ischemia postoperatively. This experience suggests that continuous selective cold blood spinal and visceral perfusion during thoracoabdominal aneurysm repair can provide adequate organ protection. INTRODUCTION
Patients undergoing surgical treatment of a thoraco-abdominal aortic aneurysm (TAAA) continue to suffer morbidity associated with postoperative neurological deficit and organ failure, especially renal dysfunction.(1,2) Optimal organ protection during TAAA repair is still controversial.(3-5) There are several principles for reducing the frequency and severity of ischemic organ injury. Preservation or reimplantation of critical intercostal arteries is one of the major principles for spinal cord protection.(6,7) Reduction of the frequency or severity of ischemia is also important for both the spinal cord and visceral organs. This may be achieved by segmental aortic clamping, drainage of cerebrospinal fluid (CSF), hypo-thermia, distal aortic perfusion, and continuous blood perfusion to each vessel.(3,8-12) Our experience of con-tinuous selective cold blood perfusion during TAAA repair was reviewed to evaluate the efficacy of this technique.
PATIENTS AND METHODS
From January 1996 to March 1999, 15 consecutive patients with TAAA underwent surgery using continuous selective cold blood perfusion. There were 12 men (80%) and 3 women (20%) and the mean age was 57 ± 17 years (range, 27 to 80 years). Five patients (33%) had Marfan’s syndrome and all of these had chronic dissections. Nine patients (60%) had previous operations (Table 1), of whom 3 had to undergo total aortic replacement between the aortic root and the terminal aorta. The etiology and types of aneurysm are summarized in Table 2. Surgery was performed on an emergency basis in 5 cases. A double-lumen endotracheal tube was used to deflate the left lung during the operation on the thoracic segment of the aneurysm. Radial and dorsalis pedis arterial pressures and central venous pressure were routinely monitored. A transesophageal echocardiography probe was inserted to monitor cardiac function and aortic conditions. We did not employ CSF drainage nor did we monitor sensory evoked potential. Patients were positioned in a right lateral decubitus position to maintain the shoulders and upper thorax at 60° with the hips more supine at approximately 30°. In patients with Crawford type I and II aneurysms, the thorax was opened through the fourth or fifth intercostal space and the short segment of the fifth or sixth rib was resected for extension of the surgical field. For Crawford type III aneurysms, an incision through the seventh or eighth intercostal space was employed. The abdominal portion was continued as a paramedian incision. Dissection was carried out retroperitoneally, mobilizing the viscera to the right. The diaphragm was divided in a circumferential fashion, leaving a rim of 2 cm of diaphragm laterally on the chest wall.
Distal perfusion via femorofemoral bypass and employing a reservoir, oxygenator, and heat exchanger was applied in all cases, with systemic heparinization. Thirteen patients were cooled to mild systemic hypothermia between 32°C and 34°C; 2 patients in whom proximal aortic clamping was not feasible because of severe adhesions, received open proximal anastomosis under deep-hypothermic (< 20°C) circulatory arrest. Aortic crossclamping was carried out segmentally if possible, to avoid ischemia of the spinal cord and visceral organs. As many patent intercostal and lumbar arteries as possible were re-constructed between the eighth thoracic and first lumbar vertebrae. Almost all branches of the patent intercostal and visceral arteries were reconstructed separately with small prosthetic grafts (8 to 10 mm) and reattached to the tube graft. Collagen-impregnated grafts (Hemashield, Boston Scientific, Natic, MA, USA) were employed routinely. During this procedure, intercostal and lumbar arteries and the visceral branches were selectively perfused through a self-inflated balloon catheter (8F to 12F; Research Medical, Inc., Kobe, Japan) as outlined in Figure 1. The catheters were located in the attached graft for intercostal or lumbar arteries or inserted directly into the visceral arteries initially and altered through the grafts after distal anastomosis. These small grafts were attached to the tube graft under selective perfusion and the position of the aortic clamp was moved distal to the site of the reattached grafts. Selective blood perfusion was gravity-fed at a height of 70 to 100 cm to maintain a flow rate above 100 mL•min–1 in each visceral branch and above 50 mL•min–1 in the intercostal and lumbar arteries. The temperature of selective perfusion was 22°C to 26°C, except in the first 2 patients who were perfused under mild hypothermia. In the case of open proximal anas-tomosis, systemic rewarming was carried out at the same time as selective cold perfusion. Finally, distal anastomosis was performed and distal perfusion was terminated immediately after completion of aortic reconstruction.
RESULTS
Operative data are summarized in Table 3. The number of reconstructed intercostal or lumbar arteries averaged 3 pairs (range, 1 to 5 pairs). There was 1 hospital death due to adult respiratory distress syndrome of unknown cause (mortality, 6.7%). One patient (6.7%) developed delayed paraparesis 10 days after surgery. He was treated with intravenous glycerol administration for a week and discharged able to walk. There were no cerebral com-plications, paraplegia, hepatic failure, or bowel ischemia in this series. Postoperative renal failure with an increase in serum creatinine above 30 mg•L–1 developed in one patient and was managed with mild hypothermic perfusion; this patient needed no hemodialysis. There was no postoperative renal failure in the 13 patients who had selective cold blood perfusion. Two patients suffered wound infection that required reoperation.
DISCUSSION
Thoracoabdominal aortic aneurysms involve both the thoracic and abdominal aorta in continuity. Repair of TAAA has become much safer with a gradual reduction in the mortality rate.(6,13–16) However, patients undergoing surgical treatment of TAAA still suffer morbidity associated with postoperative renal dysfunction and neurological deficits such as paraplegia or paraparesis. The incidence of postoperative renal failure and spinal injury reported in several large series ranged from 4% to 27%.(2,5,13) In our previous 9 consecutive cases of TAAA repair from 1989 to 1995, there was a high mortality rate (33%) and high morbidity from postoperative paraplegia or paraparesis (33%) and renal failure (22%). These procedures were performed under normothermic distal perfusion with or without normothermic visceral perfusion. We consider the high mortality and morbidity to be related to visceral organ and spinal cord protection.
The risk of neurological deficit was noted to be influenced by aortic crossclamp time, the extent of aortic replacement, and the presence of aortic dissection.(17) Reduction of spinal cord ischemia can be accomplished by a combination of several methods. There is evidence that CSF drainage improves spinal cord perfusion.(3,9) However, Crawford and colleagues18 reported no benefit from CSF drainage in a randomized study. Reimplantation of as many intercostal arteries as is technically feasible increases the possibility of maintaining blood supply to the spinal cord.(6,7) Some studies on identification of critical intercostal and lumbar arteries used preoperative spinal cord arteriography, monitoring of sensory evoked potential, or hydrogen ion injection into the ostia of the intercostal arteries.(19,20) These are not always possible, especially in the emergency setting that carries its own risks, and they have not been demonstrated to reduce spinal cord complications. Reconstruction of as many intercostal and lumbar arteries as possible seems to be a simple and reliable strategy.(6,7)
Hypothermia reduces the metabolic rate and has protective effects on the spinal cord and visceral organs. Metabolism decreases by approximately 5% for every degree centi-grade below normal temperature.(5,8) Deep-hypothermic circulatory arrest during TAAA repair was reported by Kouchoukos and colleagues.10 It is a simple method of providing a bloodless operative field with protection of organ function. However, this procedure needs a prolonged cardiopulmonary bypass time and may be associated with postoperative pulmonary insufficiency and coagulopathy. Frank and colleagues(11) described a technique where partial bypass is employed with mild to moderate hypothermia for organ protection during aortic clamping. Colon and colleagues(21) developed hypothermic regional perfusion for protection of the spinal cord during ischemia in the pig model. They cooled the blood to 25.5°C and perfused the thoracic and upper lumbar aorta isolated between clamps, for 30 minutes, with satisfactory results. We think that if the spinal cord and visceral organs are cooled selectively by continuous perfusion, ischemic injury can be minimized even in the setting of mild systemic hypothermia.
Selective cold blood perfusion of the intercostal, lumbar, and visceral arteries during reconstruction can provide not only oxygenated blood but also hypothermia in the spinal cord and visceral organs. Celiac, superior mesen-teric, and both renal arteries are perfused continuously with cold oxygenated blood during reconstruction, while maintaining the systemic temperature above 32°C, thus avoiding ischemia in these vessels. As perfusion is gravity-fed, the flow rate in each vessel is self-limiting due to peripheral resistance. Excessive perfusion pressure in each organ is avoidable, as with the use of a centrifugal pump. The perfusionist can easily control this system because there is no need for flow control. Although the perfusion system seems to be somewhat hazardous because of its complexity, we are familiar with this method because we routinely perform antegrade cerebral perfusion in the same fashion during circulatory arrest for aortic arch repair. From this experience, we believe that there is no time limitation during selective cold blood organ perfusion.
Postoperative serum creatinine was elevated only in one patient (6.7%) perfused under mild hypothermia early in the series. Blood for selective perfusion was routinely cooled to between 22°C and 26°C separately thereafter; the fact that no patient with selective hypothermic perfusion suffered creatinine elevation postoperatively supports the renal protective effect of this method. Mild systemic hypothermia maintains its own cardiac rhythm and eliminates the need for full cardiopulmonary bypass. This also reduces the time required for cooling and re-warming. Distal perfusion can be terminated immediately after completion of the procedure. Both operation and perfusion times were extensive due to the number of patients with previous operations and because of our initial learning curve. Extended operation time may have contributed to the high incidence of wound complications.
The number of cases studied was relatively small and further investigation is required to assess the efficacy and safety of this method. There still remains the problem of how to determine the optimal flow rate and temperature for selective perfusion of intercostal and visceral arteries. However, acceptable results were obtained with this method, suggesting that distal perfusion under mild hypothermia can provide adequate organ protection during thoracoabdominal aortic aneurysm repair.
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