ORIGINAL ARTICLE

     SPINAL PROTECTION WITH VENO-ARTERIAL BY-PASS FOR SURGERY OF
      THORACIC AORTA:26-YEAR EXPERIENCE

    THE IMPACT OF GRAFT SELECTION ON OUTCOME OF CORONARY
      BYPASS SURGERY AND INFLUENCE OF SURGICAL EXPERIENCE

     SPINAL PROTECTION WITH VENO-ARTERIAL BY-PASS FOR SURGERY OF
      THORACIC AORTA:26-YEAR EXPERIENCE

R. Gregorio, MD, A. Renzulli, MD, FECTS, M. De Feo, MD, F. Onorati, MD, c. Quarto, MD, J. Marmo, MD, A. della Corte, MD, M. Cotrufo, MD, FECTS Department of Cardiothoracic Sciences, Second University of Naples, V. Monaldi Hospital, Naples – ITALY

   ABSTRACT

   Introduction

   Materials and Methods

   TABLE 1. Indications for surgery
  Results

   TABLE 2. Mortality and causes of death
   DISCUSSION
   References

ABSTRACT

Authors report their experience with surgical treatment of descending thoracic aortic aneurysms using femoro-femoral by-pass for spinal protection. Between June 1976 and December 2001, 650 patients with thoracic aortic aneurysm were seen and in 170 of them the descending thoracic aorta was involved. Surgery was needed in 73 patients, among whom 34 had fusiform chronic aneurysm of thoracic aorta, with involvement of proximal abdominal aorta in 12 cases, and 27 had type B aortic dissection. Emergency surgical treatment was needed in 38 patients. Resection of the diseased aorta was performed in 71 patients, patch repair of the intimal tear in 2. Spinal protection was achieved with femoro-femoral by-pass in all cases. Nineteen cases (26.02%) of post-operative death were observed. There were four cases of lower limbs motor deficit reported, two in thoraco-abdominal aortic aneurysms, and two in patients with type B aortic dissection. Clinical experience shows that veno-arterial by-pass achieves low incidence of post-operative paraplegia. 

(Heart Views. 2002;3(3):113-117) © 2002 Gulf Heart Association.

Key Words:

   Femoro-femoral by-pass   Post-operative paraplegia     Type B aortic dissection

   Thoracic aortic aneurysm

Introduction

Surgical treatment of descending thoracic aortic aneurysms is still a challenge to the surgeon because of the complexity of the disease, the high incidence of postoperative complications and the grave general condition with which the patients usually present at the operation, which is, in most of cases, performed as an emergency (1). The operation generally consists of graft replacement of an aortic segment of variable length. In almost all cases, this technique requires blood flow interruption downstream to the diseased segment (2,3). Clamping the aortic isthmus causes severe hypotension and ischemic injury to splanchnic and spinal tissues (4). Therefore, protection measures are necessary to avoid postoperative ischemic complications (2 – 4). Graft replacement of descending thoracic aorta was initially performed without extracorporeal circulation (5,6). Later, femoro-femoral by-pass has been the most commonly employed technique. Many other techniques have been suggested, but none seems to more strongly reduce either operative mortality and morbidity or long-term complications rate. In this study, we report our 26-year experience with femoro-femoral by-pass as circulatory support in surgical treatment of descending thoracic aortic aneurysms.

Materials and Methods

Between June 1976 and December 2001, 650 patients underwent medical or surgical treatment of an aortic aneurysm or dissection in our Institution. The descending thoracic aorta was involved in 170 (26.15 %) of patients. Fifty-two of them (30.58%) had fusiform aneurysm and 118 of them (69.4%) type B dissection. Patients with traumatic injury of the aortic isthmus, in which a different approach was needed, were excluded from this study. Patients with retrograde extension of dissection to the aortic arch and the ascending aorta were excluded as well. Patients with fusiform aortic aneurysm underwent surgery in all cases, whereas the first approach in patients with aortic dissection was medical treatment with intravenous hypotensive therapy: beta-blocking agents, nitrates, sodium nitroprusside. Indications for surgery in case of type B aortic dissection were: hemothorax, persistent or recurrent pain, echocardiographic finding of progression of the dissection, progressive renal failure, and resistant hypertension. Surgical treatment was indicated in 73 patients (42.94 %), among whom 46 (63.01%) had descending thoracic aortic aneurysm and 27 (36.98%) had type B aortic dissection. Sixty-seven (91.78%) patients were male and 5 (8.12%) female, with age ranging from 16 to 80 years (mean age 63.2 ± 9.7 years). Chronic aneurysm involved the aortic isthmus in 6 cases, the whole thoracic aorta in 14 cases, and the thoraco-abdominal tract in 12 cases. In this subgroup of patients, the dilatation extended to the subdiaphragmatic segment in 6 cases (Crawford’s type 1) and below the origin of the renal arteries in 6 cases (Crawford’s type 2). Diagnosis was based on history, clinical examination and aortography in 9 cases; on transthoracic and transesophageal echocardiographic study only, in the last 25 cases. In 27 patients, transferred to our Institution from other hospitals, the first diagnosis of aortic aneurysm or dissection was made with CT scan. In the group of patients with descending aortic aneurysm, the indications for surgical treatment were: aortic dilatation of >5.5 cm in all cases, associated fissuration in 9 cases and peripheral embolism in 2. In the group of patients with aortic type B dissection, indications were: rupture of the false lumen in 8 cases, progression of the dissection with opioid-resistant pain in 8, paraplegia in 2, mesenteric ischemia in 2, lower limb ischemia in 5, and renal failure in 2 (Tab. 1). Emergency surgical treatment, within 6 hours after admission or diagnosis of complication was performed in 27 patients. The aneurysm was approached through a thoracotomy at the 5th left intercostal space in 43 patients, with a second thoracotomy at the 7th left intercostal space in 6 of them. In the other 6 patients, a thoraco-freno-laparotomy was performed to approach a more extended aortic aneurysm. To allow lower body perfusion, during aortic cross clamping, femoro-femoral by-pass was employed in all cases. Cannulation of the left femoral artery and vein was performed in 40 patients (81.6%); in the other 9 patients, venous drainage was obtained with Cannulation of the pulmonary artery. Mean arterial pressure in the upper body was maintained above 60 mm Hg to achieve sufficient brain perfusion. Rectal temperature was kept at 34°C to allow further spinal protection. Oxygenation was performed by a bubble oxygenator in 15 cases (30.5%) and by a membrane oxygenator in 34 (69%). Cross-clamp time ranged from 27 and 83 minutes (mean time 43 ± 7.5 minutes). In all cases replacement of the dilated descending aortic segment with a tubular prosthesis was performed except for 2 patients with type B aortic dissection in which intimal tear repair with a patch of pericardium was performed. In 27 patients with aortic dissection aortic wall layers were reinforced with Teflon pledgets (18 cases) or resorcin glue (9 cases).

TABLE 1. Indications for surgery

Results

Hospital mortality was 26.02% (19 cases). Causes of death were: low cardiac output in 4 patients, post-operative bleeding in 4, renal failure in 4, multi-organ failure in 5, respiratory failure in 1 and myocardial infarction in 1 (Tab.2). Operative mortality was slightly higher in patients with aortic dissection (9 of 27, 33.3%), compared to patients with fusiform aneurysm (10 of 46, 21.7%). As far as the incidence of neurological complications due to spinal ischemia were concerned: four cases of paraplegia, one in a patient with post-operative low output syndrome and severe hypotension, a global motor deficit involving lower limbs, suggesting a spinal lesion was observed. Nevertheless, it was difficult to establish how much post-operative hypotension had increased spinal lesion due to intra-operative ischemia.

TABLE 2. Mortality and causes of death

The patient died 72 hours after the operation for low cardiac output, thus it was not possible to know whether his neurological lesion was reversible or not. Two other patients with acute type B aortic dissection underwent emergency surgical treatment for neurological dysfunction to the lower limbs and developed paraplegia post-operatively. One patient undergwent successfull resection of thoracoabdominal aortic aneurysm but on the 7th postoperative day, developed massive bleeding from the chest drain and required surgical re-exploration. Following such complication, the patient developed paraplegia, probably caused by severe hypotension. Post-operative complications included: post-operative bleeding requiring reoperation in 6 cases, left diaphragm paresis in 4, recurrent left pleural effusion in 6 cases, and chylothorax requiring i.v. feeding for 3 weeks in 1 case.

DISCUSSION

Surgical treatment of descending thoracic aortic aneurysms is associated with such a high mortality and morbidity rate that medical treatment is still recommended as the first approach in case of non-complicated type B dissection. Post-operative paraplegia is the most dreadful complication of surgical treatment (4, 8). The spinal cord is certainly the most vulnerable organ to ischemic injury. It has been stated that complete arrest of blood supply for 10-15 minutes is followed by paraplegia in most cases (9). The spinal cord is supplied by the anterior and posterior spinal arteries, which arise from vertebral arteries or their branches and form an arterial circle around and along the spinal cord (10). The anterior spinal artery supplies two-thirds of spinal tissue and it usually gets thinner at its distal portion; thoracic and lumbar segments of the spinal cord are predominantly supplied by segmental spinal arteries, which arise from the posterior branches of intercostal and lumbar arteries respectively (11,12). Adamkievicz’ artery (arteria radicularis magna), which gives an important contribution to anterior spinal vasculature, in most cases joins the anterior spinal artery between T9 and T12, less frequently between L1 and L2, rarely more distal (13). Therefore surgical interruption of intercostal or lumbar arteries is an important risk factor for postoperative paraplegia and it is absolutely necessary to spare as many intercostal and lumbar arteries as possible, especially between T8 and T12 (14,15). The reported incidence of paraplegia or paraparesis after operation for thoraco-abdominal aneurysm ranges from 4 to 32%, being related to extension of the disease, presence of dissection or rupture, and cross-clamp time (2 – 4). Spinal perfusion pressure decreases during aortic cross clamping. Moreover, opening the aneurysm induces a blood steal from spinal arteries (with high resistances) to intercostal vessels. As anterior spinal artery pressure decreases, cerebrospinal fluid pressure increases because of intracranial arterial hypertension and reduction of venous capacitance caused by aortic cross-clamping (16). It is still debated whether reduction of cerebrospinal fluid pressure can increase blood flow in the anterior spinal artery, with a lower risk of spinal ischemia, or not. Nevertheless some authors have suggested cerebrospinal fluid continuous drainage as a preventive maneuver for post-operative paraplegia (15, 17 –19). Clinical aspects of post-operative paraplegia (tendon areflexia, preservation of epicritic sensibility and urinary functions, and the peculiar topography of anesthesia) suggest that mainly the central spinal gray is involved. The lesion is generally incomplete and it involves 2 to 10 metamers, but it can occasionally extend down to the terminal cone, causing complete flaccid paraplegia (20). Spinal ischemic damage is more severe in surgical treatment of acute dissections than in atherosclerotic aneurysms. In case of aneurysm without dissection, chronic obstruction of intercostal arteries can lead to development of collateral circulation, which partially protects the spinal cord against ischemic injury (2, 21). Clinical trials have studied evoked spinal cord potentials (ESCPs) and myogenic motor evoked potentials (MEPs) variations during surgical treatment of aortic aneurysms; this allowed early detection and management of spinal ischemia in many cases (22 – 24). Three main maneuvers have been studied (25,26) in order to reduce spinal (and splanchnic) ischemic risk:: 1) providing blood flow in the vessels downstream to aortic clamp, and preventing upstream hypertension; 2) restoring blood flow in all main branches of the descending aorta; and 3) reducing spinal and visceral temperature during the ischemic period. Several techniques have been proposed to protect the spinal cord. “Clamp and go” technique, without extracorporeal circulation (5,6), requires only partial heparinization, thus reducing operative blood loss, but intraoperative recovery of blood is not possible and hypertension in upper body vessels needs accurate pharmacological management. “Gott’s Shunt” is another suggested technique to avoid heparinization and extracorporeal circulation, although it does not address the problem of hypertension upstream to aortic clamp. It cannot be used in case of dissecting aneurysms, and nowadays it is suitable only in case of traumatic lesions of the aortic isthmus, to avoid high heparinization in patients with multiple lesions in other organs (27). Connection of left atrium to femoral artery by means of a centrifugal pump, without an oxygenator has been proposed (6), which should reduce “blood stress”. However heparinization is needed, and recovery of blood losses can be difficult without a reservoir (28, 29). Cooley and colleagues (25,30) suggested to use deep hypothermia in surgical treatment of De Bakey’s type III dissecting aneurysms. Brain metabolism reduces to 23% at 15°C, and if temperature is near 20°C, circulation can be arrested for 30 minutes (30). This procedure allows to perform an easier anastomosis with open technique, and it allows a better spinal protection; on the other hand the need of prolonged by-pass time and hypothermia make the risk of coagulopathy and post-operative respiratory failure higher. Femoro-femoral by-pass and its modification with venous drainage from the pulmonary artery have been used for 30 years in the surgical treatment of descending thoracic aortic aneurysms: it allows resection of intercostal arteries and extended cross-clamp time, providing splanchnic and spinal retrograde perfusion. Blood reaches the spinal cord through lumbar arteries and proximal to the aortic clamp through the superior intercostal arteries originating from the subclavian artery. With this technique, a rapid intraoperative infusion of blood losses following aneurysm incision and backflow from the intercostal arteries is possible. A drawback of this technique is heparinization, with increased risk of post-operative bleeding. The dreadful ischemic complications of descending aortic surgery evidently need further investigation. Nevertheless the association of techniques such as distal aortic perfusion, surgical reimplantation of intercostal arteries, hypothermia, blood glucose control, and, if possible, cerebrospinal fluid drainage, can significantly reduce the risk of such complications. Although relatively high mortality rate reduces the possibility to estimate the real incidence of paraplegia, femoro-femoral by-pass, as shown by our experience, seems to be a suitable technique to reduce the incidence of paraplegia and likelihood of ischemic complications of descending thoracic aortic surgery. However operative risk is still high, therefore in case of type B dissection the first approach is still medical treatment. Nevertheless, the good results obtained with femoro-femoral by-pass support the principle thatif complications develop or medical treatment fails, early surgical intervention can be performed with a good rate of success and low incidence of complications.

References

1. Miller DC: The continuing dilemma concerning medical versus surgical management of patients with acute type B dissections. Semin Thorac Cardiovasc Surg 1993; 5: 33.

2.Crawford ES, Crawford JL, Safi HJ, Coselli JS, Hess KR, Brooks B, Norton HJ, Glaeser DH: Thoracoabdominal aortic aneurysms: preoperative and intraoperative factors determining immediate and long-term results of operation in 605 patients. J Vasc Surg 1986; 3: 389-404.

3. Svensson LG, Crawford ES, Hess KR, Coselli JS, Safi HJ: Experience with 1509 patients undergoing thoracoabdominal aortic operations. J Vasc Surg 1993; 17: 357-68.

4. Panneton JM, Hollier LH: Basic data underlying clinical decision-making. Section ed. Lloyd M Taylor Jr. Ann Vasc Surg 1995; 9: 503.

5. Cooley DA: Single-clamp repair of aneurysms of the descending thoracic aorta: Semin Thorac Cardiovasc Surg 1998; 10(1): 87-90.

6. Schepens MA, Defauw SS, Hamerdjnck RP, De Geest R, Vermeulen FE: Surgical treatment of thoracoabdominal aortic aneurysms by simple cross- clamping. Risk factors and results. J Thorac Cardiovasc Surg: 1994; 107(1): 134-42.

7. Glower DD, Fann JI, Speier RH: Comparison of medical and surgical therapy for uncomplicated descending aortic dissection. Circulation 1990; 82: 34-39.

8. Natali J: Forensis medical implications of vascular accidents related to the practice of conventional vascular surgery. J Vasc Surg 1996; 21(4): 216-19.

9. Carrel A: On the aortic experimental surgery of the thoracic aorta and the heart. Ann Surg 1910; 52: 83-95.

10. Gillilan LA: The arterial blood supply of the human spinal cord. J Comp Neurol 1958; 110:75.

11. Brochestein B, Johns L, Gewetz BL: Blood supply to the spinal cord: anatomic and physiologic correlations. Ann Vasc Surg 194; 8:394.

12. Acher CW, Wynn MM: Multifactorial nature of spinal cord circulation. Semin Thorac Cardiovasc Surg 1998; 10(1): 7-10.

13. Adams HD, Von Gertruyden HH: Neurological complications of aortic surgery. Ann Surg 1956; 144: 574.

14. Connolly JE: Prevention of paraplegia secondary to operations on the aorta. J Cardiovasc Surg 1986; 27: 410-17.

15. Safi HJ, Miller CC III, Carr C, Iliopulos DC, Dorsay DA: Importance of intercostal artery reattachment during thoracoabdominal aortic aneurysm repair. J Vasc Surg 1998; 27(1): 58-66.

16. Kazama S, Masaki Y, Maruyama S, Ishihara A: Effect of altering cerebrospinal fluid pressure on spinal cord blood flow. Ann Thorac Surg 1994; 58(1): 112-5.

17. Acher CW, Wynn MM, Hoch JR, Popic P, Archibald J, Turnipseed WD: Combined use of cerebral spinal fluid drainage and Naloxone reduces the risk of paraplegia in thoracoabdominal aneurysm repair. J Vasc Surg 1994; 19(2): 236-248.

18. Hill AB, Kalman PG, Johnston KW, Vosu HA: Reversal of delayed-onset paraplegia after aortic surgery with cerebrospinal fluid drainage. J Vasc Surg 1994; 20(2): 315-7.

19. Wisselink W, Becher MO, Nguyen JH, Money SR, Hollier LH: Protecting the ischaemic spinal cord during aortic clamping: the influence of selective hypothermia and spinal cord perfusion pressure. J Vasc Surg 1994; 19(5): 788-96.

20. Mathe JF, Richard I, Roger JC, Potagas M, El Masry WS, Verbe B: Ischaemic myelopathy following aortic surgery or traumatic laceration of the aorta. Spinal Cord 1998; 36(2):110-6.

21. Svensson LG, Crawford ES: Aortic dissection and aortic aneurysm surgery: clinical observations, experimental investigations, and statistical analyses. Curr Probl Surg 1992; 29: 913.

22. Yamamoto N, Takano H, Kitagawa H, Kawaguchi Y, Tsuji H, Uozaki Y: Monitoring for spinal cord ischaemia by use of the evoked spinal cord potentials during aortic aneurysm surgery. J Vasc Surg 1994; 20(5): 826-33.

23. Matsui Y, Shiiya N, Ishii K, Murashita T, Sasaki S, Sakuma M, Yasuda K: The reliability of evoked spinal cord potentials elicited by direct stimulation of the cord as a monitor of spinal cord ischaemia during temporary occlusion of the thoracic aorta. Paraminerva Med 1997; 39(2): 78-84.

24. Haan P, Kalman CJ, Jacobs MJ: Spinal cord monitoring with myogenic motor evoked potentials: early detection of spinal cord ischemia during thoracoabdominal aneurysm surgery. Semin Thorac Cardiovasc Surg 1998; 10(1): 19-24.

25. Cooley DA: Surgical treatment of aneurysms of the descending thoracic aorta: an analysis of 85 patients, by Carlson DE et al. Discussion. Ann Thorac Surg 1983; 35: 67.

26. De Bakey ME, McCollum CH, Crawford ES, Morris GC Jr, Howell J, Noon GP, Lawrie G: Dissection and dissecting aneurysms of the aorta: 20-year follow-up of 527 patients treated surgically. Surgery 1982; 92: 1118- 34.

27. Verdant A, Cosette R, Page A, Baillot R, Dontigny L, Page P: Aneurysms of the descending thoracic aorta: 366 consecutive cases resected without paraplegia. J Vasc Surg 1995; 21(3): 385-91.

28. Biglioli P, Spirito R, Pompilio G, Agrifoglio C, Arena V, Sisillo E: Descending thoracic aorta aneurysmectomy: left-left centrifugal pump versus simple clamp technique. Cardiovasc Surg 1995; 3(5): 511-8.

29. Robertazzi RR, Acinapaura AJ: The efficacy of left atrial to femoral artery by-pass in the prevention of spinal cord ischemia during aortic surgery. Semin Thorac Cardiovasc Surg 1998; 10(1): 67-71.

30. Salzano RP Jr, Ellison LH, Antonji PF: Regional deep hypothermia of the spinal cord protects against ischaemic injury during thoracic aorta cross-clamping. Ann Thorac Surg 1994; 56: 57-65.

Address correspondence to: Attilio Renzulli, MD, Via Aquila 144, 80143- Napoli. Tel: 39 081 5539035 Fax :39 081 5536350 E-mail: arenzul@tin.it