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Hypothermic thoracic and thoracoabdominal aneurysm operation: A central cannulation technique
Hypothermic Thoracic and Thoracoabdominal Aneurysm Operation: A Central Cannulation Technique Stephen Westaby, FRCS Oxford Heart Centre, John Radcliffe Hospital, Oxford, England
Surgical resection of the descending thoracic and thoracoabdominal aorta is associated with the risk of spinal cord ischemic injury, particularly in patients with aortic dissection. Hypothermic total cardiopulmonary bypass with periods of circulatory arrest has been advocated for spinal cord protection with encouraging early results. However, techniques for this procedure are relatively complex. An alternative cannulation technique with venous return from the right atrium through the internal jugular vein and arterial return to the aortic arch is described. This has been used in 6 patients for replacement of the descending thoracic or thoracoabdominal aorta. Despite profound hypothermia and preservation of the principal spinal radicular artery, 1 patient suffered early paraparesis with some recovery but eventually died
P
rolonged unprotected normothermic cross clamping of the descending thoracic aorta is associated with considerable perioperative morbidity and mortality. Hypertension proximal to the clamps causes subendocardial ischemia and left ventricular failure. Spinal cord ischemia may result in paraparesis or paraplegia, and interruption of renal blood flow produces acute tubular necrosis [l]. After cross-clamp release reperfusion is often followed by acute circulatory collapse caused by release of ischemic metabolites and the vasodilatation of reactive hyperemia [2, 31. Methods of perfusion have evolved in an attempt to attenuate the adverse effects of descending thoracic and thoracoabdominal aortic resection. Shunt techniques and left atriofemoral bypass at normothermia provide perfusion distal to the aortic cross-clamps but do not always protect the spinal cord or kidneys when resection involves the thoracoabdominal segment [ 4 9 ] . Cross-clamping of the dissected thoracic aorta is particularly hazardous while the heart supports the circulation. In ideal circumstances the same conditions of controlled flow, pressure reduction, and hypothermic organ protection used for ascending aortic operations could provide similar benefits for the descending thoracic and abdominal aorta [lo, 111. In particular, hypothermia and reimplantation of the Accepted for publication Dec 24, 1991. Address reprint requests to Mr Westaby, Oxford Heart Centre, John Radcliffe Hospital, Oxford OX3 9DU, England.
0 1992 by The Society of Thoracic Surgeons
of multisystem failure. A second elderly patient with severe obstructive airways disease died of respiratory failure 11 days postoperatively. Four patients made a good recovery including 1 with a ruptured thoracoabdominal aneurysm who subsequently required gut resection for ischemic necrosis present preoperatively. This cannulation technique together with profound hypothermia has greatly improved the operating conditions for extensive aneurysms of the thoracoabdominal aorta. Paraparesis occurring despite hypothermic protection and attempted preservation of the spinal cord arterial supply suggests that unfavorable vascular anatomy still predominates in the risk factors for ischemic injury. (Ann Tkorac Surg 1992;54:253-8)
critical spinal radicular vessels might protect against paraplegia [121. Recently hypothermic cardiopulmonary bypass techniques with or without periods of total circulatory arrest have been described for major thoracic and thoracoabdominal aortic resection [13, 141. These were applied clinically after animal experiments showed profound hypothermia to have a marked protective effect on spinal cord function during prolonged periods of aortic occlusion [15, 161. However, established methods have distinct disadvantages. Femorofemoral bypass cannot provide blood flow to the cerebral and coronary circulation when the cross-clamps are applied, and in some patients with small femoral vessels flow rates may be limited. Although retrograde femoral arterial perfusion is used routinely for patients with type A dissection, it can be hazardous in patients with type B dissection or severe aortoiliac disease and cannot be used safely in an emergency when a descending thoracic aneurysm has ruptured. Central cannulation is therefore desirable. The recently described Kouchoukos technique is effective but requires dual cannulation of the femoral vein and right ventricle for venous return. Arterial return is by the femoral artery, followed by secondary central arterial cannulation when the proximal descending aortic anastomosis is completed [13]. This report describes a central cannulation technique that allows continuous hypothermic perfusion of the coronary and brachiocephalic vessels while affording hypothermic protection of the spinal cord and abdominal organs during aortic cross-clamping. Circulatory arrest 0003-4975/92/$5.00
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"s, v
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massive thoracoabdominal aneurysm and a chronic descending (type B) aortic dissection, respectively (Fig 1). All patients were at risk of spinal cord injury, particularly those who underwent full-length thoracic or thoracoabdominal resection. The first patient already had suspected ischemic gut at the time of operation and required endarterectomy and reimplantation of the celiac axis, renal arteries, and superior mesenteric artery. He underwent simultaneous left fourth space thoracotomy and left seventh space thoracoabdominal incisions, which provided excellent access to the full length of the arch, descending thoracic, and abdominal components of the aorta. In the 5 remaining patients a single fifth interspace thoracotomy or thoracoabdominal incision was used. The patient undergoing elective thoracoabdominal repair had previously had a leak from his aneurysm. The resection avoided reimplantation of the renal and celiac vessels but required intercostal inclusion by oblique anastomosis to conserve the major spinal radicular artery at T11. This vessel was two to three times the diameter of neighboring intercostal vessels. The remaining 4 patients underwent resection and replacement of between 15 and 20 cm of descending thoracic aorta for acute or chronic type B dissection and a ruptured syphilitic aortic aneurysm.
Perfusion Technique
Fig 1. Descending thoracic pathology and surgical replacement in (A) 1 patient ( B ) 2 patients and (C) 3 patients operated on by the central cannulation method.
can be used intermittently to reduce bleeding through collateral vessels or for open anastomosis techniques. The methods described evolved during emergency operations for ruptured thoracic and thoracoabdominal aortic aneurysms. We had previously used cannulation of the right atrium through the right internal jugular vein together with femoral venous return for patients requiring urgent perfusion for an intrathoracic catastrophe that precluded safe sternotomy (171.
Material and Methods
Patients Hypothermic cardiopulmonary bypass (20°C) with or without circulatory arrest was used in four emergency operations and two elective procedures on the descending thoracic or thoracoabdominal aorta. All patients were men aged between 63 and 76 years. The emergency operations were performed on 1 patient with a ruptured abdominal component of an extensive thoracoabdominal aneurysm, 1 patient with a ruptured descending thoracic aneurysm, and 2 patients with leaking type B aortic dissections. The fifth and sixth patients underwent elective repair of a
Anesthesia was induced with midazolam and fetanyl and maintained with fetanyl and isoflurane. Thiopentone and nimodipine were given prophylactically for neurological protection. Central venous lines were inserted through the left internal jugular vein, and a radial arterial cannula was placed in the right radial artery. A double-lumen endotracheal tube was used to allow deflation of the left lung during the surgical approach. At this stage the patient was positioned supine on the operating table with the neck extended and turned to the left. The neck was prepared for surgical approach to the right internal jugular vein. This was exposed using a longitudinal incision at the anterior border of the right sternomastoid muscle, and the incision was extended to the suprasternal notch. The patient was fully systemically heparinized, and snares were placed above and below the proposed jugular incision. A standard 32F two-stage venous cannula was then inserted into the right internal jugular vein and advanced into the right atrium and inferior vena cava, care being taken to avoid air embolism (Fig 2). This cannula was then connected to the venous re turn line to the bypass circuit but kept clamped until cardiopulmonary bypass was started. The tissues were then loosely approximated over the cannula and covered by an adhesive drape, which helped to prevent displacement during positioning for left thoracotomy. This approach to right atrial cannulation adds no more than 15 minutes to the anesthetic preparation time. The patient was then repositioned in the left lateral position for thoracotomy (sternum to spine) or thoracoabdominal incision. A fourth interspace approach in particular affords good access to the ascending aorta and aortic arch and can be combined with an eighth interspace incision for access to the thoracoabdominal segment. A
WESTABY HYPOTHERMIC THORACOABDOMINAL ANEURYSM SURGERY
Ann Thorac Surg 1992;54:25%3
c
Fig 2. Central venous cannulation through the right internal jugular vein and arterial return to the aortic arch. This approach allows continued perfusion to the corona y and carotid vessels and hypothermic protection of the spinal cord and abdominal organs during resection of the descending thoracic aorta.
double pursestring was then placed in healthy proximal transverse aorta with the tip of the cannula pointing toward the aortic valve. In patients with type B dissection, care was taken to avoid the damaged distal arch. Cardiopulmonary bypass was then established with full calculated adult flow rates of 2.2 L * mp2 min-', which provides rapid cooling. With controlled pressure and flow, appropriate dissection was carried out to allow proximal aortic crossclamping either between the left carotid and subclavian vessels or just distal to the left subclavian artery. The distal limit of dissection and those vessels for reimplantation were identified during the cooling period. Cooling was continued until the nasopharyngeal temperature reached 15°C and the rectal temperature reached 20°C. This was achieved within 20 minutes of perfusion. During cooling the heart fibrillates, and care was taken to palpate for left ventricular distention. However, with reduced flow rates at profound hypothermia and in the presence of a competent aortic valve, left ventricular venting was not required. The pericardium was kept intact for all 6 patients. When profound hypothermia was secure, the aortic cross-clamps were applied and the rate of perfusion decreased appropriately to supply continual blood flow to the coronary and brachiocephalic vessels (approximately 0.8 L * min-' * m-'). With the aorta open blood was retrieved from the operative site using a Cell Saver (Haemonetics, Braintree, MA), and short periods of low flow or circulatory arrest were employed to control collateral inter-costal bleeding. The generous thoracotomy incision
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does not allow accumulation of blood to a depth sufficient for effective cardiotomy suction. Those vessels requiring reimplantation were identified and mobilized from the native aorta. Appropriate lengths of collagen-impregnated woven Dacron (Hemashield, Meadox) were used for aortic replacement. No preclotting was required. The first patient, who had a rupture of the abdominal portion of an extensive thoracoabdominal aneurysm, underwent endarterectomy of the superior mesenteric and renal vessels before implantation into the graft. When appropriate, attempts were made to preserve the major spinal radicular artery or to include or reimplant it into the graft. On completion of the anastomoses with continuous Prolene (Ethicon, Somerville, NJ) suture, air was removed from the graft and perfusion to the lower body was restored. The longest aortic cross-clamp time was 61 minutes, and the longest total period of circulatory arrest was 16 minutes. Rewarming to a rectal temperature of 34°C was invariably achieved within 30 minutes, and in all patients ventricular fibrillation reverted or was converted to sinus rhythm between 25" and 30°C. Cardiopulmonary bypass was discontinued without difficulty in each case. After removal of the aortic cannula heparin was reversed with protamine. When satisfactory hemostasis was achieved, two chest drains were inserted and the thoracotomy incisions closed. The patients were then turned back to the supine position, and the venous cannula was removed from the right internal jugular vein. There was no sign of clot formation within the cannula. Clamps applied to this vessel were temporarily released to exclude thrombus formation, then the vessel was repaired directly.
Results There were no adverse effects from either venous or arterial cannulation. When the clamps were released to flush the jugular vein, prompt flow without clots was noted. All patients survived the operative procedure, although 1 suffered spinal cord injury. There were two hospital deaths caused by respiratory and renal complications at 11and 23 days postoperatively. The first occurred in the 72-year-old patient after elective thoracoabdominal aneurysm resection with reimplantation of the principal spinal radicular artery. After an uncomplicated procedure, diffuse abnormal bleeding delayed closure of the thoracotomy. When this was adequately controlled, the jugular venous cannula was removed uneventfully and the patient returned to the recovery area. However, bleeding continued into the right chest through an interpleural communication, and more than 20 units of transfused blood plus platelets and fresh frozen plasma were required before the bleeding stopped. He then required prolonged positive-pressure ventilation and drainage of the right chest. When he regained consciousness paraparesis was noted. During the next 14 days there was gradual improvement in his spinal cord function, and he regained leg movements. By that time however, renal and respiratory failure supervened and he died on the 23rd postoperative day. The second death
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occurred in a 74-year-old patient with acute type B aortic dissection which ruptured into the left chest. This patient had very poor respiratory function before acute dissection (forced expiratory volume in 1 second, 0.9 L), and after a satisfactory initial recovery with early extubation, he required reintubation and died of respiratory then renal failure followed by systemic sepsis 11 days postoperatively. The remaining 4 patients were each extubated in less than 12 hours postoperatively. Three made a rapid, uneventful recovery. The patient with the ruptured abdominal component of a thoracoabdominal aneurysm suffered prolonged ileus with feeding difficulties. A repeat aortogram showed improved blood supply to the gut through the reimplanted endarterectomized vessels. However, when the white blood cell count rose to 25 x 10'lL (25,OOO/pL) on the 8th postoperative day, laparotomy was performed and a length of necrotic gut resected. After this he made an uneventful recovery. The 4 hospital survivors are alive and well between 9 months and 2.5 years postoperatively.
Comment In the 3 years during which this perfusion technique has been employed, 23 other adults have undergone repair of coarctation or traumatic aortic transection with one death caused by multiple trauma and one case of paraplegia. Another patient underwent successful repair of a descending thoracic aneurysm without paraplegia. All of these patients were operated on without shunt or bypass techniques, and none had an aortic cross-clamp time of greater than 30 minutes. We use hypothermic perfusion only when prolonged cross-clamp times are expected and for emergency situations where control of pressure, flow, and temperature are important. Nevertheless, hypothermic perfusion with only one cannula in the operative field has much improved the operating conditions for these extensive procedures. The method affords control over pressure and flow and minimizes blood loss during the course of the operation. The site of the arterial cannula depends on the condition of the aortic wall. An extensive left fourth or fifth interspace thoracotomy gives access to the whole ascending and transverse aorta, and a nonpathological area is chosen. Dissection extending into the ascending aorta precludes this technique, although a separate ascending aneurysm or atheroma should be negotiable. We have not encountered this situation as yet. If safe clamping of the transverse or descending aorta is considered improbable the open-ended method with total circulatory arrest can be employed. The central cannulation technique allows continuous hypothermic perfusion of the coronary and brachiocephalic vessels and eliminates the time constraint otherwise imposed by total circulatory arrest. Meanwhile during aortic cross-clamping the spine and kidneys are protected by profound hypothermia. Circulatory arrest is unnecessary for most patients and is restricted to short periods to facilitate surgical exposure by reducing bleeding.
Ann Thorac Surg 1992;54:25>8
Control of pressure and flow is important at the time of cross-clamp application, particularly for patients with aortic dissection, in whom further damage to the vessel wall is likely when pressure is excessive [18]. As with other perfusion techniques cardiac workload and subendocardial ischemia are reduced during aortic crossclamping. The central cannulation technique cannot be safely employed in the presence of important aortic valvular regurgitation. Normal hearts tolerate hypothermic fibrillatory arrest, and for minimal degrees of aortic regurgitation, left ventricular venting can be used. However, serious aortic regurgitation or diffuse coronary disease may substantially impair myocardial perfusion, and in these patients either aortic valve replacement or coronary bypass grafting should be performed before elective aneurysm repair. We experienced no problems from cannulation and temporary occlusion of the right internal jugular vein. Right internal jugular venous flow was interrupted for periods up to 180 minutes in these and previous patients but restored by careful repair. The vessel was opened just below the apex of the anterior triangle of the neck allowing collateral flow from the proximal segment through the common facial, pharyngeal, superior thyroid, and external and anterior jugular veins. In addition there is extensive collateral potential in the venous sinuses of the skull. Intravenous lines were inserted in the left arm and jugular veins. Postoperatively we did not identify facial edema or signs of cerebral irritability, although others have observed unilateral facial edema after long-term interruption of internal jugular venous flow (personal communication). We have used permanent ligation of the internal jugular vein uneventfully for control of bleeding in patients with complicated penetrating injuries of the neck. We anticipated potential thrombotic complications from the continued presence of the venous cannula in the right atrium after heparin reversal. This was addressed by intermittently releasing the clamp on the venous line, allowing the line to bleed a small volume, thus avoiding complete stasis. Brisk flow over the external aspect presumably precludes thrombosis within this time frame. In practice we could not conclusively rule out pulmonary microemboli, but we have no clinical evidence for this. All patients had a prompt restoration of urine flow after removal of the aortic clamps and passed good-quality urine in the early postoperative period. Success with 3 of 4 patients requiring urgent operation with this technique prompted its use for elective resection of the thoracoabdominal aorta. Unfortunately one otherwise uneventful procedure was subsequently complicated by excessive bleeding, which led to a large volume of blood transfusion and multisystem failure. Also, despite an aortic crossclamp time of 50 minutes at less than 20°C, paraparesis occurred. Circulatory arrest was not used at any stage in this patient, and the artery of Adamkiewicz was thought to be preserved by identification and inclusion. Paraparesis therefore reinforced my suspicion that anatomical factors provide the greatest constraint to the spinal out-
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come after operation on t h e descending thoracic aorta [8]. The contrary view is that hypothermia is protective a n d m a y h a v e prevented paraplegia i n others i n this group. Although t h e separate reports of Kouchoukos [13], Mahfood [lo], a n d Massimo [19] a n d their colleagues collectively d i d n o t include a n episode of spinal cord injury in a total of 1 2 patients u n d e r g o i n g hypothermic perfusion w i t h circulatory arrest, Crawford a n d colleagues [6] reported paraplegia i n 2 of 18 patients i n whom femorofemoral bypass h a d been u s e d . However, t h e d e p t h of hypothermia, extent of resection, a n d reimplantation of strategic intercostal a n d lumbar vessels w e r e not mentioned i n Crawford's series. In experimental situations venoarterial bypass a n d i n particular hypothermia has been shown t o h a v e a clear protective effect on spinal cord function [1.520]. Both limited surface cooling a s u s e d i n Oxford for high-risk coarctation r e p a i r a n d direct p e r f u s i o n cooling a r e t h o u g h t t o prolong t h e tolerance of t h e spinal cord t o ischemia. Whereas t h e use of somatosensory evoked potentials m a y suggest a n i m p e n d i n g cord problem, it is difficult t o imagine that i n practice this m e t h o d might expedite cross-clamp removal [21]. The Kouchoukos g r o u p h a s shown t h a t low-flow cardiopulmonary bypass combined w i t h hypothermia d u r i n g aortic cross-damping provide superior protection to cardiopulmonary bypass a t 37°C (Kouchoukos NT, personal communication). However, if critical blood s u p p l y is interrupted by a n e u r y s m resection, t h e n spinal cord ischemia and paraplegia m a y follow rewarming. Late-onset paraplegia has been reported after operation on t h e thoracoabdominal aorta w i t h simple unprotected aortic cross-clamping techniques [22]. T h e pathogenesis of delayed ischemic injury is uncertain. In experimental studies of reperfusion after aortic cross-clamping (in baboons and dogs) a p r o f o u n d hyperemic response occurred i n t h e spinal cord. This was significantly greater a m o n g animals that became paraplegic compared with those t h a t d i d not. Profound hyperemia results i n spinal cord e d e m a and possible irreversible compression injury. Cerebrospinal fluid drainage reduces intrathecal pressure a n d h a s a protective effect [23]. Paradoxically Svensson a n d colleagues [24] have advocated t h e use of intrathecal papaverine i n clinical practice. In summary, t h e rationale for t h e use of cardiopulmon a r y b y p a s s and hypothermia i n thoracoabdominal aneur y s m resection is t o increase t h e safe duration of spinal cord ischemia. This s h o u l d allow reimplantation of critical intercostal and lumbar vessels within a reasonable time f r a m e before t h e o n s e t of p e r m a n e n t cord injury. Paraparesis h a s multifactorial origins, a n d no firm conclusions c a n be d r a w n from its occurrence i n o u r patient. Nevertheless we suspect that hypothermia alone cannot reliably protect against paraplegia t h r o u g h hyperemia and e d e m a i n t h e ischemic cord. Postoperative respiratory problems a r e predictable i n elderly patients w i t h poor lung function. In an attempt t o minimize p u l m o n a r y complications, collapse of t h e left
WESTABY HYPOTHERMIC THORACOABDOMINAL ANEURYSM SURGERY
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l u n g is advocated so that persistent retraction is n o t necessary.
References 1. Crawford ES, Crawford JL, Safi HJ, et al. Thoraco-abdominal
aortic aneurysms: pre operative and intra-operative factors determining intermediate and long term results in 605 patients. J Vasc Surg 1980;3:389-404. 2. Najafi H, Javid H, Hunter J, Serry C, Monson D. Descending aortic aneurysmectomy without adjuncts to avoid ischemia. Ann Thorac Surg 1980;30:32630. 3. Barone GW, Joob AW, Flanagan TL, Dunn CE, Kron IL. The effect of hyperemia on spinal cord function after temporary thoracic aortic occlusion. J Vasc Surg 1988;8:535-40. 4. Donahoo JS, Brawley RK, Gott VL. The heparin-coated vascular shunt for thoracic aortic and great vessel procedures. A ten year experience. Ann Thorac Surg 1977;23: 507-10.
5. Kouchoukos NT, Lell WA, Karp RB, Samuelson PN. Hemodynamic effects of aortic clamping and decompression with a temporary shunt for resection of the descending thoracic aorta. Surgery 1979;85:22-7. 6. Crawford ES, Coselli JS, Safi HJ. Partial cardiopulmonary bypass, hypothermic circulatory arrest, and posterolateral exposure for thoracic aortic aneurysm operation. J Thorac Cardiovasc Surg 1987;94:824-7. 7. May IA, Ecker RR, Iverson LIG. Heparinless femoral venoarterial bypass with an oxygenator for surgery of the descending thoracic aorta. J Thorac Cardiovasc Surg 1977;73:387-91. 8. Hamerlijnck R, De Geest R, Brutal de la Riviere A, Defauw J, Knaepen P, Vermeulen F. Surgical correction of descending thoracic aortic aneurysms with shunt or bypass techniques versus simple aortic cross-clamping. Eur J Cardiothorac Surg 1989;3:3743. 9. Verdant A, Page A, Cossette R, Dontigny L, Page P, Baillot
R. Surgery of the descending thoracic aorta: spinal cord protection with the Gott shunt. Ann Thorac Surg 1988;46: 147-54.
10. Mahfood S, Qazi A, Garcia J, Mispireta L, Corso P, Smyth N. Management of aortic arch aneurysm using profound hypothermia and circulatory arrest. Ann Thorac Surg 1985;39: 412-7. 11. Massimo CG, Presenti LF, Marranci P, et al. Extended and
12.
13.
14.
15. 16. 17. 18.
total aortic resection in the surgical treatment of acute type A aortic dissection: experience with 54 patients. Ann Thorac Surg 1988;46:420-4. De Mol B, Hamerlijnck R, De Geest R, Vermeulen FEE. Assessment of risk factors for spinal cord ischaemia in surgery of thoracoabdominal aneurysms without use of adjuncts. Eur J Cardiothorac Surg 1989;3:449-55. Kouchoukos NT, Wareing TH, Izumoto H, Klausing W, Abboud N. Elective hypothermic cardiopulmonary bypass and circulatory arrest for spinal cord protection during operations on the thoracoabdominal aorta. J Thorac Cardiovasc Surg 1990;99:65944. Caramutti VM, Dantur JR, Favaloro MR, Weinshcelbaum EE, Favaloro RG. Deep hypothermia and circulatory arrest as an elective technique in the treatment of type B dissecting aneurysm of the aorta. J Card Surg 1989;4:20615. Colon R, Frazier OH, Cooley DA, McAllister HA. Hypothermic regional perfusion for protection of the spinal cord during periods of ischemia. Ann Thorac Surg 1987;43:63943. Robertson CS, Foltz R, Grossman RG, Goodman JC. Protection against experimental ischemic spinal cord injury. J Neurosurg 1986;44:63342. Westaby S. Extrathoracic cannulation for urgent cardiopulmonary bypass in cardiac tamponade. Use of the internal jugular vein. J Cardiovasc Surg 1987;29:10>5. Crawford ES, Svensson LG, Coselli JS, Saft HJ, Hess KR. Aortic dissection and dissecting aortic aneurysms. Ann Surg 1988;208:25P73.
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19. Massimo CG, Poma AG, Viligiardi RR, Duranti A, Colucci M, Favi PP. Simultaneous total aortic replacement from arch to bifurcation: experience with six cases. J Tex Heart Inst 1986;13:147-51. 20. Grossi EA, Krieger KH, Cunningham J N Jr, et al. Preservation of spinal cord function and prevention of paralysis during aortic occlusion via veno-arterial bypass. J Cardiovasc Surg 1989;30:95-8. 21. Fava E, Bortaline EM, Ducati A, Roberti U. Evaluation of spinal cord functions by means of lower limb somatosensory evoked potentials in reparative aortic surgery. J Cardiovasc Surg 1988;29:421-7. 22. Crawford ES, Snyder DM, Cho GC, Roehm ]OF. Progress in
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treatment of thoracoabdominal and abdominal aortic aneurysms involving coeliac, superior mesenterio and renal arteries. Ann Surg 1978;188:404-22. 23. Bower TC, Murray MJ, Gloviczki P, Yaksh TL, Hollier LH, Pariolero PL. Effects of thoracic aortic occlusion and cerebrospinal fluid drainage on regional spinal cord blood flow in dogs: correlation with neurologic outcome. J Vasc Surg 1989;9:13-4. 24. Svensson LG, Stewart RW, Cosgrove DM 111, et al. Intrathecal papaverine for the prevention of paraplegia after operation on the thoracic or thoraco-abdominal aorta. J Thorac Cardiovasc Surg 1988;96:823-9.
Surgical resection of the descending thoracic and thoracoabdominal aorta is associated with the risk of spinal cord ischemic injury, particularly in patients with aortic dissection. Hypothermic total cardiopulmonary bypass with periods of circulatory arrest has been advocated for spinal cord protection with encouraging early results. However, techniques for this procedure are relatively complex. An alternative cannulation technique with venous return from the right atrium through the internal jugular vein and arterial return to the aortic arch is described. This has been used in 6 patients for replacement of the descending thoracic or thoracoabdominal aorta. Despite profound hypothermia and preservation of the principal spinal radicular artery, 1 patient suffered early paraparesis with some recovery but eventually died
P
rolonged unprotected normothermic cross clamping of the descending thoracic aorta is associated with considerable perioperative morbidity and mortality. Hypertension proximal to the clamps causes subendocardial ischemia and left ventricular failure. Spinal cord ischemia may result in paraparesis or paraplegia, and interruption of renal blood flow produces acute tubular necrosis [l]. After cross-clamp release reperfusion is often followed by acute circulatory collapse caused by release of ischemic metabolites and the vasodilatation of reactive hyperemia [2, 31. Methods of perfusion have evolved in an attempt to attenuate the adverse effects of descending thoracic and thoracoabdominal aortic resection. Shunt techniques and left atriofemoral bypass at normothermia provide perfusion distal to the aortic cross-clamps but do not always protect the spinal cord or kidneys when resection involves the thoracoabdominal segment [ 4 9 ] . Cross-clamping of the dissected thoracic aorta is particularly hazardous while the heart supports the circulation. In ideal circumstances the same conditions of controlled flow, pressure reduction, and hypothermic organ protection used for ascending aortic operations could provide similar benefits for the descending thoracic and abdominal aorta [lo, 111. In particular, hypothermia and reimplantation of the Accepted for publication Dec 24, 1991. Address reprint requests to Mr Westaby, Oxford Heart Centre, John Radcliffe Hospital, Oxford OX3 9DU, England.
0 1992 by The Society of Thoracic Surgeons
of multisystem failure. A second elderly patient with severe obstructive airways disease died of respiratory failure 11 days postoperatively. Four patients made a good recovery including 1 with a ruptured thoracoabdominal aneurysm who subsequently required gut resection for ischemic necrosis present preoperatively. This cannulation technique together with profound hypothermia has greatly improved the operating conditions for extensive aneurysms of the thoracoabdominal aorta. Paraparesis occurring despite hypothermic protection and attempted preservation of the spinal cord arterial supply suggests that unfavorable vascular anatomy still predominates in the risk factors for ischemic injury. (Ann Tkorac Surg 1992;54:253-8)
critical spinal radicular vessels might protect against paraplegia [121. Recently hypothermic cardiopulmonary bypass techniques with or without periods of total circulatory arrest have been described for major thoracic and thoracoabdominal aortic resection [13, 141. These were applied clinically after animal experiments showed profound hypothermia to have a marked protective effect on spinal cord function during prolonged periods of aortic occlusion [15, 161. However, established methods have distinct disadvantages. Femorofemoral bypass cannot provide blood flow to the cerebral and coronary circulation when the cross-clamps are applied, and in some patients with small femoral vessels flow rates may be limited. Although retrograde femoral arterial perfusion is used routinely for patients with type A dissection, it can be hazardous in patients with type B dissection or severe aortoiliac disease and cannot be used safely in an emergency when a descending thoracic aneurysm has ruptured. Central cannulation is therefore desirable. The recently described Kouchoukos technique is effective but requires dual cannulation of the femoral vein and right ventricle for venous return. Arterial return is by the femoral artery, followed by secondary central arterial cannulation when the proximal descending aortic anastomosis is completed [13]. This report describes a central cannulation technique that allows continuous hypothermic perfusion of the coronary and brachiocephalic vessels while affording hypothermic protection of the spinal cord and abdominal organs during aortic cross-clamping. Circulatory arrest 0003-4975/92/$5.00
254
WESTABY HYPOTHERMIC THORACOABDOMINAL ANEURYSM SURGERY
"s, v
Ann Thorac Surg 1992:54:253-8
massive thoracoabdominal aneurysm and a chronic descending (type B) aortic dissection, respectively (Fig 1). All patients were at risk of spinal cord injury, particularly those who underwent full-length thoracic or thoracoabdominal resection. The first patient already had suspected ischemic gut at the time of operation and required endarterectomy and reimplantation of the celiac axis, renal arteries, and superior mesenteric artery. He underwent simultaneous left fourth space thoracotomy and left seventh space thoracoabdominal incisions, which provided excellent access to the full length of the arch, descending thoracic, and abdominal components of the aorta. In the 5 remaining patients a single fifth interspace thoracotomy or thoracoabdominal incision was used. The patient undergoing elective thoracoabdominal repair had previously had a leak from his aneurysm. The resection avoided reimplantation of the renal and celiac vessels but required intercostal inclusion by oblique anastomosis to conserve the major spinal radicular artery at T11. This vessel was two to three times the diameter of neighboring intercostal vessels. The remaining 4 patients underwent resection and replacement of between 15 and 20 cm of descending thoracic aorta for acute or chronic type B dissection and a ruptured syphilitic aortic aneurysm.
Perfusion Technique
Fig 1. Descending thoracic pathology and surgical replacement in (A) 1 patient ( B ) 2 patients and (C) 3 patients operated on by the central cannulation method.
can be used intermittently to reduce bleeding through collateral vessels or for open anastomosis techniques. The methods described evolved during emergency operations for ruptured thoracic and thoracoabdominal aortic aneurysms. We had previously used cannulation of the right atrium through the right internal jugular vein together with femoral venous return for patients requiring urgent perfusion for an intrathoracic catastrophe that precluded safe sternotomy (171.
Material and Methods
Patients Hypothermic cardiopulmonary bypass (20°C) with or without circulatory arrest was used in four emergency operations and two elective procedures on the descending thoracic or thoracoabdominal aorta. All patients were men aged between 63 and 76 years. The emergency operations were performed on 1 patient with a ruptured abdominal component of an extensive thoracoabdominal aneurysm, 1 patient with a ruptured descending thoracic aneurysm, and 2 patients with leaking type B aortic dissections. The fifth and sixth patients underwent elective repair of a
Anesthesia was induced with midazolam and fetanyl and maintained with fetanyl and isoflurane. Thiopentone and nimodipine were given prophylactically for neurological protection. Central venous lines were inserted through the left internal jugular vein, and a radial arterial cannula was placed in the right radial artery. A double-lumen endotracheal tube was used to allow deflation of the left lung during the surgical approach. At this stage the patient was positioned supine on the operating table with the neck extended and turned to the left. The neck was prepared for surgical approach to the right internal jugular vein. This was exposed using a longitudinal incision at the anterior border of the right sternomastoid muscle, and the incision was extended to the suprasternal notch. The patient was fully systemically heparinized, and snares were placed above and below the proposed jugular incision. A standard 32F two-stage venous cannula was then inserted into the right internal jugular vein and advanced into the right atrium and inferior vena cava, care being taken to avoid air embolism (Fig 2). This cannula was then connected to the venous re turn line to the bypass circuit but kept clamped until cardiopulmonary bypass was started. The tissues were then loosely approximated over the cannula and covered by an adhesive drape, which helped to prevent displacement during positioning for left thoracotomy. This approach to right atrial cannulation adds no more than 15 minutes to the anesthetic preparation time. The patient was then repositioned in the left lateral position for thoracotomy (sternum to spine) or thoracoabdominal incision. A fourth interspace approach in particular affords good access to the ascending aorta and aortic arch and can be combined with an eighth interspace incision for access to the thoracoabdominal segment. A
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c
Fig 2. Central venous cannulation through the right internal jugular vein and arterial return to the aortic arch. This approach allows continued perfusion to the corona y and carotid vessels and hypothermic protection of the spinal cord and abdominal organs during resection of the descending thoracic aorta.
double pursestring was then placed in healthy proximal transverse aorta with the tip of the cannula pointing toward the aortic valve. In patients with type B dissection, care was taken to avoid the damaged distal arch. Cardiopulmonary bypass was then established with full calculated adult flow rates of 2.2 L * mp2 min-', which provides rapid cooling. With controlled pressure and flow, appropriate dissection was carried out to allow proximal aortic crossclamping either between the left carotid and subclavian vessels or just distal to the left subclavian artery. The distal limit of dissection and those vessels for reimplantation were identified during the cooling period. Cooling was continued until the nasopharyngeal temperature reached 15°C and the rectal temperature reached 20°C. This was achieved within 20 minutes of perfusion. During cooling the heart fibrillates, and care was taken to palpate for left ventricular distention. However, with reduced flow rates at profound hypothermia and in the presence of a competent aortic valve, left ventricular venting was not required. The pericardium was kept intact for all 6 patients. When profound hypothermia was secure, the aortic cross-clamps were applied and the rate of perfusion decreased appropriately to supply continual blood flow to the coronary and brachiocephalic vessels (approximately 0.8 L * min-' * m-'). With the aorta open blood was retrieved from the operative site using a Cell Saver (Haemonetics, Braintree, MA), and short periods of low flow or circulatory arrest were employed to control collateral inter-costal bleeding. The generous thoracotomy incision
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does not allow accumulation of blood to a depth sufficient for effective cardiotomy suction. Those vessels requiring reimplantation were identified and mobilized from the native aorta. Appropriate lengths of collagen-impregnated woven Dacron (Hemashield, Meadox) were used for aortic replacement. No preclotting was required. The first patient, who had a rupture of the abdominal portion of an extensive thoracoabdominal aneurysm, underwent endarterectomy of the superior mesenteric and renal vessels before implantation into the graft. When appropriate, attempts were made to preserve the major spinal radicular artery or to include or reimplant it into the graft. On completion of the anastomoses with continuous Prolene (Ethicon, Somerville, NJ) suture, air was removed from the graft and perfusion to the lower body was restored. The longest aortic cross-clamp time was 61 minutes, and the longest total period of circulatory arrest was 16 minutes. Rewarming to a rectal temperature of 34°C was invariably achieved within 30 minutes, and in all patients ventricular fibrillation reverted or was converted to sinus rhythm between 25" and 30°C. Cardiopulmonary bypass was discontinued without difficulty in each case. After removal of the aortic cannula heparin was reversed with protamine. When satisfactory hemostasis was achieved, two chest drains were inserted and the thoracotomy incisions closed. The patients were then turned back to the supine position, and the venous cannula was removed from the right internal jugular vein. There was no sign of clot formation within the cannula. Clamps applied to this vessel were temporarily released to exclude thrombus formation, then the vessel was repaired directly.
Results There were no adverse effects from either venous or arterial cannulation. When the clamps were released to flush the jugular vein, prompt flow without clots was noted. All patients survived the operative procedure, although 1 suffered spinal cord injury. There were two hospital deaths caused by respiratory and renal complications at 11and 23 days postoperatively. The first occurred in the 72-year-old patient after elective thoracoabdominal aneurysm resection with reimplantation of the principal spinal radicular artery. After an uncomplicated procedure, diffuse abnormal bleeding delayed closure of the thoracotomy. When this was adequately controlled, the jugular venous cannula was removed uneventfully and the patient returned to the recovery area. However, bleeding continued into the right chest through an interpleural communication, and more than 20 units of transfused blood plus platelets and fresh frozen plasma were required before the bleeding stopped. He then required prolonged positive-pressure ventilation and drainage of the right chest. When he regained consciousness paraparesis was noted. During the next 14 days there was gradual improvement in his spinal cord function, and he regained leg movements. By that time however, renal and respiratory failure supervened and he died on the 23rd postoperative day. The second death
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occurred in a 74-year-old patient with acute type B aortic dissection which ruptured into the left chest. This patient had very poor respiratory function before acute dissection (forced expiratory volume in 1 second, 0.9 L), and after a satisfactory initial recovery with early extubation, he required reintubation and died of respiratory then renal failure followed by systemic sepsis 11 days postoperatively. The remaining 4 patients were each extubated in less than 12 hours postoperatively. Three made a rapid, uneventful recovery. The patient with the ruptured abdominal component of a thoracoabdominal aneurysm suffered prolonged ileus with feeding difficulties. A repeat aortogram showed improved blood supply to the gut through the reimplanted endarterectomized vessels. However, when the white blood cell count rose to 25 x 10'lL (25,OOO/pL) on the 8th postoperative day, laparotomy was performed and a length of necrotic gut resected. After this he made an uneventful recovery. The 4 hospital survivors are alive and well between 9 months and 2.5 years postoperatively.
Comment In the 3 years during which this perfusion technique has been employed, 23 other adults have undergone repair of coarctation or traumatic aortic transection with one death caused by multiple trauma and one case of paraplegia. Another patient underwent successful repair of a descending thoracic aneurysm without paraplegia. All of these patients were operated on without shunt or bypass techniques, and none had an aortic cross-clamp time of greater than 30 minutes. We use hypothermic perfusion only when prolonged cross-clamp times are expected and for emergency situations where control of pressure, flow, and temperature are important. Nevertheless, hypothermic perfusion with only one cannula in the operative field has much improved the operating conditions for these extensive procedures. The method affords control over pressure and flow and minimizes blood loss during the course of the operation. The site of the arterial cannula depends on the condition of the aortic wall. An extensive left fourth or fifth interspace thoracotomy gives access to the whole ascending and transverse aorta, and a nonpathological area is chosen. Dissection extending into the ascending aorta precludes this technique, although a separate ascending aneurysm or atheroma should be negotiable. We have not encountered this situation as yet. If safe clamping of the transverse or descending aorta is considered improbable the open-ended method with total circulatory arrest can be employed. The central cannulation technique allows continuous hypothermic perfusion of the coronary and brachiocephalic vessels and eliminates the time constraint otherwise imposed by total circulatory arrest. Meanwhile during aortic cross-clamping the spine and kidneys are protected by profound hypothermia. Circulatory arrest is unnecessary for most patients and is restricted to short periods to facilitate surgical exposure by reducing bleeding.
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Control of pressure and flow is important at the time of cross-clamp application, particularly for patients with aortic dissection, in whom further damage to the vessel wall is likely when pressure is excessive [18]. As with other perfusion techniques cardiac workload and subendocardial ischemia are reduced during aortic crossclamping. The central cannulation technique cannot be safely employed in the presence of important aortic valvular regurgitation. Normal hearts tolerate hypothermic fibrillatory arrest, and for minimal degrees of aortic regurgitation, left ventricular venting can be used. However, serious aortic regurgitation or diffuse coronary disease may substantially impair myocardial perfusion, and in these patients either aortic valve replacement or coronary bypass grafting should be performed before elective aneurysm repair. We experienced no problems from cannulation and temporary occlusion of the right internal jugular vein. Right internal jugular venous flow was interrupted for periods up to 180 minutes in these and previous patients but restored by careful repair. The vessel was opened just below the apex of the anterior triangle of the neck allowing collateral flow from the proximal segment through the common facial, pharyngeal, superior thyroid, and external and anterior jugular veins. In addition there is extensive collateral potential in the venous sinuses of the skull. Intravenous lines were inserted in the left arm and jugular veins. Postoperatively we did not identify facial edema or signs of cerebral irritability, although others have observed unilateral facial edema after long-term interruption of internal jugular venous flow (personal communication). We have used permanent ligation of the internal jugular vein uneventfully for control of bleeding in patients with complicated penetrating injuries of the neck. We anticipated potential thrombotic complications from the continued presence of the venous cannula in the right atrium after heparin reversal. This was addressed by intermittently releasing the clamp on the venous line, allowing the line to bleed a small volume, thus avoiding complete stasis. Brisk flow over the external aspect presumably precludes thrombosis within this time frame. In practice we could not conclusively rule out pulmonary microemboli, but we have no clinical evidence for this. All patients had a prompt restoration of urine flow after removal of the aortic clamps and passed good-quality urine in the early postoperative period. Success with 3 of 4 patients requiring urgent operation with this technique prompted its use for elective resection of the thoracoabdominal aorta. Unfortunately one otherwise uneventful procedure was subsequently complicated by excessive bleeding, which led to a large volume of blood transfusion and multisystem failure. Also, despite an aortic crossclamp time of 50 minutes at less than 20°C, paraparesis occurred. Circulatory arrest was not used at any stage in this patient, and the artery of Adamkiewicz was thought to be preserved by identification and inclusion. Paraparesis therefore reinforced my suspicion that anatomical factors provide the greatest constraint to the spinal out-
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come after operation on t h e descending thoracic aorta [8]. The contrary view is that hypothermia is protective a n d m a y h a v e prevented paraplegia i n others i n this group. Although t h e separate reports of Kouchoukos [13], Mahfood [lo], a n d Massimo [19] a n d their colleagues collectively d i d n o t include a n episode of spinal cord injury in a total of 1 2 patients u n d e r g o i n g hypothermic perfusion w i t h circulatory arrest, Crawford a n d colleagues [6] reported paraplegia i n 2 of 18 patients i n whom femorofemoral bypass h a d been u s e d . However, t h e d e p t h of hypothermia, extent of resection, a n d reimplantation of strategic intercostal a n d lumbar vessels w e r e not mentioned i n Crawford's series. In experimental situations venoarterial bypass a n d i n particular hypothermia has been shown t o h a v e a clear protective effect on spinal cord function [1.520]. Both limited surface cooling a s u s e d i n Oxford for high-risk coarctation r e p a i r a n d direct p e r f u s i o n cooling a r e t h o u g h t t o prolong t h e tolerance of t h e spinal cord t o ischemia. Whereas t h e use of somatosensory evoked potentials m a y suggest a n i m p e n d i n g cord problem, it is difficult t o imagine that i n practice this m e t h o d might expedite cross-clamp removal [21]. The Kouchoukos g r o u p h a s shown t h a t low-flow cardiopulmonary bypass combined w i t h hypothermia d u r i n g aortic cross-damping provide superior protection to cardiopulmonary bypass a t 37°C (Kouchoukos NT, personal communication). However, if critical blood s u p p l y is interrupted by a n e u r y s m resection, t h e n spinal cord ischemia and paraplegia m a y follow rewarming. Late-onset paraplegia has been reported after operation on t h e thoracoabdominal aorta w i t h simple unprotected aortic cross-clamping techniques [22]. T h e pathogenesis of delayed ischemic injury is uncertain. In experimental studies of reperfusion after aortic cross-clamping (in baboons and dogs) a p r o f o u n d hyperemic response occurred i n t h e spinal cord. This was significantly greater a m o n g animals that became paraplegic compared with those t h a t d i d not. Profound hyperemia results i n spinal cord e d e m a and possible irreversible compression injury. Cerebrospinal fluid drainage reduces intrathecal pressure a n d h a s a protective effect [23]. Paradoxically Svensson a n d colleagues [24] have advocated t h e use of intrathecal papaverine i n clinical practice. In summary, t h e rationale for t h e use of cardiopulmon a r y b y p a s s and hypothermia i n thoracoabdominal aneur y s m resection is t o increase t h e safe duration of spinal cord ischemia. This s h o u l d allow reimplantation of critical intercostal and lumbar vessels within a reasonable time f r a m e before t h e o n s e t of p e r m a n e n t cord injury. Paraparesis h a s multifactorial origins, a n d no firm conclusions c a n be d r a w n from its occurrence i n o u r patient. Nevertheless we suspect that hypothermia alone cannot reliably protect against paraplegia t h r o u g h hyperemia and e d e m a i n t h e ischemic cord. Postoperative respiratory problems a r e predictable i n elderly patients w i t h poor lung function. In an attempt t o minimize p u l m o n a r y complications, collapse of t h e left
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l u n g is advocated so that persistent retraction is n o t necessary.
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