Asian Cardiovasc Thorac Ann 1998;6:95-100
© 1998 Asia Publishing EXchange Pte Ltd
Repair of Thoracic Aortic Aneurysm and Dissection Using Deep-Hypothermic Circulatory Arrest
Adrian E Manapat, MD,
Jorge M Garcia, MD,
Joseph B Barril, MD,
Gary A Lopez, MD,
Diomedes A Talavera , MD
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Makati Heart Foundation Makati, Metro Manila, Philippines
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For reprint information contact: Adrian E Manapat, MDMakati Heart FoundationSuite 441 Makati Medical Center2 Amorsolo StreetMakati, Metro Manila 1200, Philippines Te1: 63 2 894 4002 Fax: 63 2 894 4001
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ABSTRACT
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From October 1989 to September 1997, 14 patients underwent repair of a thoracic aortic aneurysm or dissection using deep-hypothermic circulatory arrest. There were 10 males and 4 females with a mean age of 58 years (range, 43 to 82 years). The diagnoses included one ascending aortic aneurysm, one ascending aortic and arch aneurysm, 2 aortic arch and descending aortic aneurysms, 4 descending aortic aneurysms, 2 chronic aortic dissections of type A and 4 of type B. The involved aortic segment was replaced with a woven Dacron tube graft in 11 patients and repaired with a patch of woven Dacron in the other 3. Concomitant procedures were coronary artery bypass grafting in 2 cases; one aortic valve replacement, and one wedge resection of the left-upper lobe of the lung. A median sternotomy approach was used in 6 patients of whom 5 had right atrial-femoral artery bypass and 1 had right atrial-ascending aortic bypass. In addition to sternotomy, one patient had a left anterolateral thoracotomy. Seven patients had a left posterolateral thoracotomy with femorofemoral bypass. The mean circulatory arrest time was 35 minutes (range, 13 to 59 minutes). The lowest perfusion temperature ranged from 7°C to 16°C. Retrograde cerebral perfusion was used in 5 patients. There was one operative death from massive bleeding. Early complications included stroke in 2 patients, vocal cord paralysis in one, prolonged ventilatory support in one, reoperation for bleeding in one, and pleural effusion in 3 patients. There were 2 late deaths and the 11 surviving patients (78%) have been followed up for a mean period of 18 months. Deep-hypothermic circulatory arrest was found to be a useful technique in the repair of aortic aneurysm and dissection. We consider retrograde cerebral perfusion to be safe and easily performed. It probably decreased the incidence of stroke in patients with involvement of the aortic arch.
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INTRODUCTION
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Surgical repair of thoracic aortic aneurysms, particularly those involving the aortic arch, remains a formidable task for the cardiovascular surgeon. Although the reported operative mortality for aneurysms of the aortic arch had reached as high as 50%1, advances in the field have improved the operative milieu for the surgeon and consequently resulted in better overall results.2,3 Foremost is the use of deep-hypothermic circulatory arrest. Although Weiss and colleagues4 reported the use of hypothermic circulatory arrest for cardiac surgery in 1960, early subsequent use of the technique was limited to repair of congenital cardiac anomalies in infants and children. In 1964, Borst and colleagues5 reported using it to repair a traumatic aneurysm of the distal aortic arch. In the 1970s, Griepp and colleagues6 established the value of this technique for resection and grafting of more extensive aneurysms of the aortic arch and since the 1980s more surgeons have used it for aortic arch surgery.7 Currently, some surgeons use it routinely in all cases of aortic dissection.8 Retrograde cerebral perfusion (RCP), which was initially used to treat air embolism during cardiopulmonary bypass has gained many advocates because of its potential benefit in reducing the incidence of stroke in patients who undergo repair of aortic arch abnormalities under circulatory arrest. We report our clinical experience with the use of these two techniques in managing this challenging problem.
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PATIENTS AND METHODS
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Sixteen patients underwent repair of a thoracic aortic aneurysm or dissection from October 1989 to September 1997 in our institute. All except 2 of these patients were subjected to deep-hypothermic circulatory arrest because of involvement of the aortic arch or technical difficulty in placement of the aortic cross-clamp. Of the 14 patients included in this report, there were 10 males and 4 females with a mean age of 58 years (range, 43 to 82 years). The indications for operation are summarized in Table 1
. The most common presentation was chest pain which was present in 64% of our patients. Twenty-one percent were asymptomatic and 14% had vocal cord paralysis.
Patients with involvement of the ascending aorta and aortic arch were approached via a median sternotomy, while those with primary involvement of the descending aorta were approached via a left thoracotomy. One patient who had an aortic arch and descending thoracic aortic aneurysm with coronary artery disease underwent a left anterolateral thoracotomy in addition to a median sternotomy. After adequate exposure and safe mobilization of the aneurysm, heparin was administered at 300 units per kg of body weight. In patients with involvement of the ascending aorta and aortic arch, the right atrium was cannulated for venous access. Separate cannulation of the superior vena cava (SVC) and the inferior vena cava was performed when retrograde cerebral perfusion was planned. The left femoral artery was usually cannulated for arterial access unless a suitable spot was found on the distal ascending aorta (as in one of our patients) or the aortic arch. In patients with primary involvement of the descending aorta, the left femoral artery and vein were usually cannulated using standard femoral cannulae. Recently, we have used a long venous catheter that can be passed up to the level of the right atrium to improve venous drainage and to allow us to deliver retrograde cerebral perfusion (albeit not as selective in perfusing the head as a SVC cannula). For the purpose of RCP, the SVC cannula (or the long venous catheter) was connected to a 3/8 inch x 3/8 inch connector with a Luer lock that was connected to 1/4 inch tubing (RCP line) through which oxygenated blood was delivered by a separate roller pump (Figure 1). Occasionally, a left ventricular vent was placed at the apex to prevent ventricular distension when the heart stopped ejecting during the cooling period. Cardiopulmonary bypass was then instituted and systemic cooling was achieved for approximately 35 to 40 minutes at a nasopharyngeal temperature of 16°C or less. As part of the protocolfor hypothermic circulatory arrest, the following drugs were administered intravenously by the anesthesiologist: sodium pentothal 200 mg, dexamethasone 4 mg, and mannitol 100 mL of 20% (w/v) solution. The patient's head was also packed in ice.
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Figure 1. Extracorporeal cardiopulmonary bypass circuit with provi-sion for retrograde cerebral perfusion via the superior vena cava. IVC = inferior vena cava, LV = left ventricle, RV = right ventricle, SVC = superior vena cava.
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With the patient in the Trendelenburg position, cardiopulmonary bypass was discontinued and RCP started(if used) at a rate of 300 to 400 mLámin–1 or up to a maximum central venous pressure of 30 mm Hg via the SVC cannula (or long venous catheter). The aorta was opened and a decision was made whether to replace the aortic segment with a tube graft or simply patch a localized defect with a piece of woven Dacron. The effluent from the branch vessels was returned to the cardiotomy reservoir. The graft (whether tube or patch) was anastomosed to the aorta using single-layer continuous running 4/0 polypropylene sutures. Before the last knot was tied, de-airing was performed by gradually resuming cardiopulmonary bypass and allowing the aorta to fill with blood. RCP was discontinued and the patient was rewarmed and gradually weaned from cardiopulmonary bypass. The opened aortic wall was wrapped around the tube graft and reapproximated with a continuous running suture. Protamine was administered to reverse the effect of heparin. The cannulae were removed and the cannulation sites were meticulously repaired. The incisions were closed in routine fashion after placement of appropriate drainage tubes.
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RESULTS
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Table 2 summarizes the operations performed and their outcome. In 11 patients, the involved aortic segment was replaced with a tube graft and in 3 patients the aorta was repaired with a patch. The mean hypothermic circulatory arrest time was 35 minutes; mean circulatory arrest time was 37 minutes for tube grafting and 20 minutes for patch grafting. Seven patients developed complications; one died intraoperatively due to uncontrollable bleeding. Stroke occurred on the 5th postoperative day in a 72-year-old man who underwent 25 minutes of hypothermic circulatory arrest for repair of a descending aortic aneurysm and on the 17th postoperative day in another 72-year-old man who underwent coronary artery bypass grafting and ascending aortic replacement with 41 minutes of hypothermic circulatory arrest. Minor complications included pleural effusion that required thoracentesis and prolonged ventilatory support. Figure 2 shows the different locations of aneurysms seen in this series and their appearance after tube graft replacement. Figure 3 illustrates the patch repair operation for a saccular aneurysm of the proximal descending aorta.
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Figure 2. Examples of different types of aneurysms seen in this series. Drawings on the left show the appearance before repair while those on the right illustrate repair with woven Dacron tube graft. (A) Ascending aortic aneurysm in a 56-year-old female (patient no. 1). (B) Aneurysm of the ascending aorta and transverse aortic arch in a 59-year-old female (patient no. 6). (C) Chronic type B aortic dissection in a 45-year-old male showing a redundant and aneurysmal descending aorta (patient no. 10).
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Figure 3. Repair of a saccular aneurysm in a 59-year-old male (patient no. 8) with involvement of the proximal descending aorta showing the appearance: (A) before repair, and (B) after repair with a patch of woven Dacron.
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There were 2 late deaths. One patient died of hemoptysis 2 months postoperatively, probably from an aortobronchial fistula (this patient had a descending aortic patch repair and wedge resection of an adherent portion of the left upper lobe of the lung). Another patient died from a possible cardiac cause 5 months postoperatively. At a mean follow-up period of 18 months (range, 2 to 26 months), 11 patients were alive and well with no symptoms of thoracic aortic disease warranting repeated intervention, except for a 34-year-old male who had a small asymptomatic abdominal aneurysm needing repair in the future.
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DISCUSSION
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The current method of repairing aortic arch aneurysms or dissections employs circulatory arrest with varying degrees of hypothermia depending on the surgeon (profound: less than 10°C; deep: 12°C to 18°C; or moderate: 20°C to 24°C). This is in contrast to the old method where separate perfusion lines were used for cerebral and visceral perfusion during cardiopulmonary bypass. In other instances, the arch itself may not be directly involved, such as in ascending aortic or proximal descending aortic aneurysms. However, there may not be enough room to apply the aortic clamp. In a severely atherosclerotic or friable aorta and in aortic dissection, it is wise to employ the "no touch" technique whereby manipulation including clamping of the diseased aortic segment is avoided to prevent atheroemboli and injury at the cross-clamp site. These are the indications for circulatory arrest in aortic surgery.
The use of hypothermic circulatory arrest is not without caveats. The incidence of neurologic complications also increases directly with the duration of ischemia or circulatory arrest. These complications range from mild confusional states to frank coma and death (for cases of aortic arch disease) or paraplegia (for cases of descending aortic disease). Clinical experience has shown that 45 minutes or less is considered the safe duration of circulatory arrest at a temperature of 15°C to 20°C.7 The technique of hypothermic circulatory arrest requires sufficient time for systemic cooling and later rewarming, resulting in increased duration of cardiopulmonary bypass. Prolonged cardiopulmonary bypass may lead to problematic bleeding as a result of hemolysis, platelet depletion and dysfunction, as well as fibrinolysis.9 One of our patients was reoperated for bleeding that was secondary to coagulopathy.
Retrograde cerebral perfusion whereby oxygenated blood is delivered to the brain via the venous system (SVC) was initially used as a technique to treat air embolism during cardiopulmonary bypass.10 Recently, it has been used in conjunction with hypothermic circulatory arrest to protect the brain by selectively perfusing it during this period.11–13 Blood drained from the head vessels is easily returned to the cardiotomy reservoir by suction. Although the exact mechanism of RCP has not been elucidated and its efficacy is questioned by some surgeons, RCP is theoretically beneficial in that it provides oxygen and metabolic substrates to the brain, it maintains constant cooling of the brain, and most importantly it flushes out air and microemboli from the cerebral circulation.13,14 Advocates of RCP believe that it prolongs the safe period of hypothermic circulatory arrest. The recovery of venous blood from the branch vessels implies oxygen extraction and is probably the best rationale for the use of RCP in conjunction with hypothermic circulatory arrest.
In this series of 14 patients, there was one operative mortality. This patient had a large aneurysm involving the aortic arch and almost the entire descending aorta. He also had concomitant coronary artery disease for which coronary bypass was carried out (left anterior descending coronary artery and two obtuse marginal branches) using saphenous veins. He succumbed to uncontrollable bleeding from coagulopathy. He had a circulatory arrest time of 59 minutes, the longest in the series, and retrograde cerebral perfusion was used. In retrospect, the two operations probably should not have been performed at the same time. The 4 other patients who had retrograde cerebral perfusion had circulatory arrest times of 31, 46, 48, and 59 minutes. RCP was delivered at a flow rate of 300 to 400 mLámin–1. These patients and 9 others recovered uneventfully from anesthesia a few hours postoperatively without any neurologic deficits. No patient developed spinal cord injury.
However, 2 patients suffered strokes as a result of a cardioembolic phenomenon from atrial fibrillation. One was a 72-year-old male who had a stroke on the 5th postoperative day. He also developed vocal cord paralysis from iatrogenic injury to the left recurrent laryngeal nerve. He eventually recovered from his stroke but had permanent hoarseness that required a Teflon injection in the vocal cord. The other patient underwent surgery for an ascending aortic aneurysm and coronary artery bypass grafting and developed a stroke on the 17th postoperative day. He also suffered from recurrent pleural effusion that required thoracentesis on 3 occasions. He recovered fully from the stroke.
A patient who had hypothermic circulatory arrest for 20 minutes at 13°C for ascending aortic replacement and aortic valve replacement, presented with troublesome coagulopathy that necessitated multiple blood-product transfusions and reoperation. The rest of her hospital stay was uneventful. One of the patients with an aortic arch lesion had preexisting pulmonary tuberculosis and required prolonged ventilatory support and a tracheostomy. He was eventually weaned from the ventilator, extubated, and discharged.
Our experience has shown that surgical repair of aneurysms and dissections of the aorta is facilitated by the use of deep-hypothermic circulatory arrest. Although this technique dictates a longer duration of operation with attendant adverse effects, we believe that these are manageable and are outweighed by the benefit of a relatively bloodless field and avoidance of trauma to an already diseased aorta. The exact mechanism and the benefit derived from retrograde cerebral perfusion remains unknown. Since the duration of hypothermic circulatory arrest in the patients who had retrograde cerebral perfusion was within the range considered safe, we cannot attribute the absence of neurologic complications in the immediate postoperative period solely to RCP. However, we have found that RCP is safe and easily performed and we would continue to use it in the future, particularly in patients with involvement of the aortic arch and in those where a prolonged duration of hypothermic circulatory arrest is anticipated.
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ABSTRACT
INTRODUCTION
