Symposium on Surgical Techniques
Carotid Endarterectomy
Edwin G. Beven, M.D.
Carotid endarterectomy is by far the most common of all the procedures performed in the surgical treatment of extracranial occlusive disease, accounting for at least 90 per cent of all the operations for patients with cerebral vascular symptoms. There are many reasons for this. The most common site of occlusive disease in the extracranial tree is the carotid bifurcationP Furthermore, the symptoms produced by such a lesion are frequently dramatic and profound, thus eliciting concern and fear in the patient, and leading him to seek medical help early. In addition, the symptoms that result from a carotid lesion are usually well defined and the diagnosis is obvious. The clini~al diagnosis is frequently strengthened by the presence of a carotid bruit on auscultation of the neck. 7 Finally, from a technical consideration, the carotid bifurcation atheroma is usually well localized and therefore suited for excision by simple endarterectomy, in contrast to more complicated surgical procedures that are necessary for the correction of lesions in other sites of the extracranial arterial vasculature. Chronologically the first successful carotid reconstructive procedure was performed by Carrea and associates in 1951, but reported in 1955.6 Strully and co-workers in 1953 published a report of a case of an unsuccessful carotid thromboendarterectomy,22 and in 1954 Eastcott, Pickering, and Rob published the first successful carotid reconstruction.10 It is interesting to note that of these three reports, the two successful cases were accomplished by excision and re-anastomosis, while in the unsuccessful case, the procedure employed was an endarterectomy which has since become the procedure of choice. Over the past two decades carotid endarterectomy has become a most valuable tool in the armamentarium of the vascular surgeon. The technical details have become standardized and will be described in this article. The description is based upon the experience accumulated with more than 700 operations performed at the Cleveland Clinic. The anesthetic technique and the methods for cerebral protection From the Department of Vascular Surgery, The Cleveland Clinic Foundation and The Cleveland Clinic Educational Foundation, Cleveland, Ohio
Surgical Clinics of North America- Vol. 55, No. 5, October 1975
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during the operative carotid clamping, however, have remained controversial. Therefore, discussion of these methods will also be included.
GENERAL CONSIDERATIONS SELECTION OF PATIENTS
The criteria for selection of patients for carotid endarterectomy have gradually evolved with experience accumulated during the past decade. In this regard, there appears to be uniformity of opinion among the majority of vascular surgeons.
Indications Our current indications for carot:h:l. endarterectomy are: 1. Patients with transient ischemic attacks in whom arteriography demonstrates an arteriosclerotic lesion in the appropriate carotid artery. Since emboli from even small ulcerated plaques can be the source of cerebral or retinal ischemic symptoms, carotid endarterectomy is indicated regardless of the degree of stenosis.'s· '" 2. Patients with a completed stroke who demonstrate severe stenosis of the appropriate internal carotid artery and who, in time, have demonstrated good neurologic recovery. 3. Asymptomatic patients with a carotid stenosis of greater than 70 per cent, who are to undergo an unrelated major operation that could be associated with the risk of hypotension which might result in thrombosis of the carotid artery. 4. Asymptomatic patients with severe stenosis of one internal carotid and total occlusion of the contralateral carotid artery. Prophylactic carotid endarterectomy for the stenotic side is indicated in this group of patients because of the fear that thrombosis of the remaining carotid artery could result in a major stroke. These patients, however, should be highly selected, should be relatively young, and should lack any serious associated disease that may affect their long-term survival.
Contraindications We believe that carotid endarterectomy is contraindicated in the following situations: 1. Patients with a stroke in evolution or with a recent acute stroke. Experience has shown that in these patients, carotid endarterectomy is associated with a high mortality. 2 • 23 2. Patients with a remote stroke associated with a poor neurologic recovery. Reconstructive surgery, even if feasible, should be avoided because of the high incidence of aggravation of the previous neurologic deficit, or the production of a new one! 3. Patients with a stenosis in the cervical carotid artery who, in addition to this lesion, have a severe obstruction of the ipsilateral intracranial carotid artery. It is postulated that excision of the accessible cervical plaque does not improve the flow through the second intracranial stenosis. 4. Patients with total occlusion of the internal carotid artery. We no longer recommend operation in such cases, since the success rate is low. 26 Instead, attention should be focused on stenotic lesions in other extracranial arteries.
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INTRAOPERATIVE CEREBRAL PROTECTIVE TECHNIQUES
Most patients undergoing carotid endarterectomy have adequate cerebral collateral circulation and can tolerate temporary carotid occlusion without problems. About 10 per cent of patients, however, are intolerant of operative carotid clamping.3· 21 The earliest technique devised to circumvent this problem was the use of the intraluminal shunt that permitted carotid endarterectomy while maintaining blood flow to the brain through the shunt. Although the routine use of a shunt is preferred by some surgeons,8· 18· 23 others believe that it interferes with a technically adequate endarterectomy.4· 9 • 26 General hypercarbic anesthesia and controlled hypertension, first introduced by Wells, Keats, and Cooley in 1963,24 permitted carotid endarterectomy without a shunt. The cerebral protection by this method is based on the improved oxygenation and the decrease in oxygen consumption by the brain during general anesthesia, the increased cerebral blood flow resulting from the vasodilatation of hypercarbia, and the increased cerebral perfusion from the induced hypertension. We have used a slight modification of their technique since 1964P· 26 Experimental evidence, however, suggests that hypercarbia may produce a deleterious effect by creating an intracerebral steal. 5 Furthermore, Ehrenfeld and co-workers investigating the effects of different levels of Pco 2 on the internal carotid back pressure, suggested that hypocarbia increased cerebral perfusion to the ischemic areas while hypercarbia did not. For these reasons the authors abandoned hypercarbic general anesthesia. They recommend the use of hypocarbia, deliberate hypertension, and general anesthesia.20 Although local anesthesia allows neurologic evaluation of the patient while the carotid artery is clamped, and thus permits selection of patients who require shunting, general anesthesia has become the method of choice of most surgeons. Since neurologic evaluation of the anesthetized patient is not possible, Moore and Hall21 investigated the operative measurement of the internal carotid back pressure, or stump pressure, as a test for adequacy of cerebral perfusion. The authors reported a positive correlation of a low internal carotid back pressure and the incidence of ischemic cerebral symptoms. The critical pressure found was 25 mm Hg. Hays and associates14 and Hobson and coworkers15 corroborated these findings but noted that the critical pressure range obtained by them was 41 to 50 mm Hg and 60 to 70 mm Hg respectively. The evidence accumulated thus far indicates that measurement of the stump pressure is the most reliable index to predict when shunting is necessary in the anesthetized patient. However, the minimum safe pressure has not yet been clearly established. In an attempt to confirm this test we have begun a prospective study in patients undergoing endarterectomy. The stump pressure is determined in all patients. In one group of patients, selected by admission to a particular surgical service, a shunt is used if the stump pressure
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measures less than 50 mm Hg. In the other group of patients, shunting is not utilized, regardless of the stump pressure obtained.
SURGICAL TECHNIQUE After induction of anesthesia a cannula is inserted percutaneously into the radial artery at the wrist. This is done to monitor the mean arterial systemic pressure and to provide access to arterial blood samples for blood gas analysis in order to follow the degree of hypercarbia. The patient is positioned with the head slightly extended and rotated to the opposite side and the incision is made along the anterior border of the sternocleidomastoid muscle (Fig. 1). The carotid bifurcation should lie in the midportion of the incision. A glance at the lateral carotid arteriogram is helpful at this point, since it will show the relationship of the carotid bifurcation to the angle of the mandible. The incision is carried through platysma muscle and along the anterior border of the sternomastoid muscle. With further dissection this structure is retracted laterally and posteriorly. Deeper dissection is then carried through until the internal jugular vein is visualized. The facial vein is identified and divided between suture ligatures. By means of a pursestring suture, a catheter is inserted into the internal jugular vein and introduced in a cephalad direction for approximately 8 em. This will provide access to the venous return from the brain and permits periodic determinations of the P v0 2 as well as the oxygen saturation throughout the procedure (Fig. 2). This provides a gross measure of the increased total cerebral flow as a result of the induced hypercarbia. Attention is then directed to the common carotid artery which has a medial relationship to the internal jugular vein. The artery is dissected in the lowermost portion of the incision and the dissection carried proximally towards the carotid bifurcation. Utmost care should be exercised
Figure 1. Positioning of the patient is important for proper exposure. The head is extended and turned to the opposite side. The dotted line shows the placement of the incision.
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Figure 2. After exposure of the internal jugular vein, a catheter is introduced to monitor the Pvo2 and 0 2 saturation.
in dissecting the carotid artery from the surrounding structures. Excessive manipulation of the carotid artery is avoided in order to prevent embolization from the atherosclerotic plaque (Fig. 3). The vagus nerve should be identified and protected from unnecessary trauma. It should be gently dissected from the posterior lateral aspect of the common carotid artery when it is adherent to this vessel. This maneuver is necessary to avoid incorporating the vagus nerve with the artery when the vascular clamp is applied. Clamping of the nerve is a common cause of the ipsilateral vocal cord paralysis occurring in a small number of patients undergoing carotid endarterectomy. The descending branch of the hypoglossal nerve is identified as it courses anteriorly and it is isolated and preserved by retracting it to one side (Fig. 4). The dissection is then extended proximally along the common carotid artery. Once the bifurcation is approached, the dissection is carried out along the anterior aspect, and to a minimal degree along the sides of the carotid bulb, the superior thyroid and external carotid arteries. The posterior aspect of the carotid bifurcation, as well as the area of the carotid body between the internal and external carotid arteries, are left undisturbed. This maneuver prevents excessive manipulation of the carotid bifurcation and thus minimizes the danger of embolization from the arteriosclerotic lesion. It also protects the superior laryngeal nerve as it courses deep to the carotid bifurcation.
Figure 3. The carotid arteriogram demonstrates an ulcerated plaque with a probable thrombus. Manipulation of the carotid artery during the surgical dissection should be minimal in order to avoid the danger of cerebral embolization.
Figure 4. Exposure of the carotid artery. The descending branch of the hypoglossal nerve is seen in its usual location.
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The internal carotid artery is then isolated and dissected free as high above the lesion as is practical. Although it is tempting to palpate the internal carotid artery in order to ascertain the extent of the lesion, this maneuver should be avoided because it can easily dislodge loose fragments and result in cerebral embolization (see Fig. 3). Instead the surgeon should be guided by the arteriogram which should demonstrate the extent of the plaque in the internal carotid artery. During the course of the dissection of the internal and external carotid arteries, the hypoglossal nerve should be identified as it courses superficial to these arteries, curving down and anteriorly. When retracting this area the blade of the retractor should be carefully placed in order to avoid trauma to the nerve. In patients with a high carotid bifurcation it may be necessary to extend the upper end of the incision to dissect the internal carotid artery adequately above the lesion. The extension of the incision should be 1 em posterior to the angle of the jaw. Dissection of the deeper structures should be directed somewhat posteriorly into the anterior aspect of the sternocleidomastoid muscle in order to avoid trauma to the mandibular branch of the facial nerve. A deeper dissection will encounter the internal jugular vein and usually the maxillary vein as it runs anteriorly and superficial to the internal carotid artery. This vein should be mobilized and divided between suture ligatures. The internal carotid artery can then be mobilized without difficulty. At this stage of the dissection, hypercarbia should be at an optimum level. The arterial Pco 2 should be between 70 and 90 mm Hg. while the jugular venous Po 2 should be greater than 80 mm Hg. Heparin is now administered intravenously (200 units per kg of body weight). After a few minutes, measurement of the internal carotid back pressure (stump pressure) is determined. The common carotid, external carotid, and superior thyroid arteries are clamped and a 22 gauge needle, connected through tubing to a strain gauge, is introduced into the common carotid. The needle should enter the artery at a suitable point between the common carotid clamp and the lesion. Once the stump pressure is determined, the needle is withdrawn and the arterial clamps are released. The occlusion time for this procedure is usually less than 30 seconds. A few minutes should be allowed to perfuse the brain before reapplying the clamps to perform the endarterectomy.
CAROTID ENDARTERECTOMY WITHOUT A SHUNT
As previously mentioned, a stump pressure of 50 mm Hg has been arbitrarily selected as the minimal pressure required in patients in whom carotid endarterectomy can be performed without a shunt. The internal carotid artery is occluded with a vascular clamp as far cephalad as possible and at least 1 em beyond the end of the arteriosclerotic plaque. The common carotid, external carotid, and superior thyroid arteries are similarly clamped. A short longitudinal arteriotomy is performed with a No. 15 blade on the anterolateral wall of the common carotid artery below the plaque. The arteriotomy is then extended
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with the angled Potts scissors across the lesion and into the first portion of the internal carotid artery. The arteriotomy should be placed away from the origin of the external carotid artery in order to avoid the carotid body. The arteriotomy is terminated at the most cephalad end of the arteriosclerotic plaque. Similarly, the arteriotomy is extended caudally and should also terminate at the end of the plaque. In some patients the thickened intima extends throughout the common carotid artery. In this situation the arteriotomy should be terminated approximately 5 mm from the common carotid clamp. The endarterectomy is then initiated by grasping the adventitia of the artery away from the plaque at its most thickened portion. With the use of the blunt Cannon endarterectomy knife the plaque is lifted away from the artery and this plane is then developed. The dissection along this plane is extended circumferentially down the common carotid artery to the lowermost portion of the arteriotomy. The plaque is lifted anteriorly and away from the posterior wall of the artery with the use of a Moynihan clamp and is cleanly transected with Strully scissors. Since we have not observed retrograde dissection of the common carotid, it is not necessary to transfix the intima to the artery. The divided plaque is then lifted and the dissection is carried cephalad to the origin of the external carotid artery. The endarterectomy should be carried circumferentially around the origin of the extemal carotid artery. With slight traction on the plaque and with the release of the external carotid clamp the plaque separates from the normal intima beyond and is delivered into the lumen of the artery. The external carotid clamp is reapplied. Attention is then directed to the internal carotid artery. With gentle traction on the plaque, the wall of the artery is pushed away from the plaque until the normal dissection plane disappears. At this point the plaque easily separates from the normal intima. Once the specimen is delivered, attention is focused on the normal intima at the point of separation. The intima should be adherent to the artery if dissection by the blood stream is to be avoided when flow to the internal carotid artery is re-established. In most patients the cephalad end of the plaque is usually tapered and the normal intima is adherent to the wall. In a few patients, however, the intima is thickened and dissection could result in occlusion of the lumen after the vascular clamps are released. To avoid this complication the intima is sutured down to the wall of the internal carotid artery by means of interrupted doublearmed 7-0 sutures. One needle is inserted through the intima while the other is placed just caudad to the intimal edge and tied outside the artery. Usually five sutures accomplishes the objective. After completion of the endarterectomy the denuded surface is inspected for residual fragments that may remain attached to the artery. These are carefully removed. The arterial clamps are then momentarily released in order to flush any debris that may be trapped by them. The arteriotomy is closed, beginning at the cephalad end, with a continuous 6-0 nonabsorbable arterial suture. Just before completing the closure the internal carotid clamp is temporarily released in order to flush air and minute debris. The last suture is then inserted and tied, closing the arteriotomy. The external carotid clamp is opened first, followed by the
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clamp occluding the common carotid artery. Any trapped fragments will flow into the external artery and eliminate the danger of cerebral embolization. After a few moments the int-ernal carotid clamp is released. Any bleeding that may occur from the arteriotomy is controlled with interrupted 7- 0 sutures. The removal of the atheromatous lesion usually results in a normal or larger than normal carotid bulb and therefore eliminates the necessity of applying a patch for closure of arteriotomy (Fig. 5, A and B). Very rarely, when faced with a small internal carotid artery or with a lesion that extends high into it, a saphenous vein patch is necessary to avoid creating a stenosis. Because of the potential danger of infection we do not use a patch of prosthetic material. At the end of the procedure heparin is partially neutralized with protamine sulphate and a Jackson-Pratt suction drain'~ is placed in the operative field through a stab wound below the incision. The platysma, subcutaneous tissue, and skin are closed separately with interrupted sutures. CAROTID ENDARTERECTOMY WITH A SHUNT
In selected patients who demonstrate an internal carotid back pressure of less than 50 mm Hg, operative carotid clamping is shortened by the use of a shunt. Only the technique of the insertion and the removal of the shunt will be outlined in this section since this is the only variation from that previously described. *Heyer-Schulte Corporation.
Figure 5. A, Preoperative arteriogram demonstrating severe carotid stenosis. B, Carotid arteriogram following endarterectomy in the same patient. The lumen has been restored to a normal diameter and a patch graft is therefore unnecessary.
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Figure 6. The shunt has been introduced through the arteriotomy and it is secured with the Javid clamps.
Although several shunts are available, we prefer the loop shunt* because the ends of this particular shunt are rounded and smooth and thus allow insertion into the artery with minimal risk of producing intimal damage. In addition, its greater flexibility permits easier retraction of the shunt during the endarterectomy with no danger of angulation and obstruction of blood flow. The coiled metal spring embedded in its wall prevents kinking. Lastly, it is available in various diameters that permit a better match to the lumen of the artery. After the internal, common, and external carotid arteries are clamped, the arteriotomy is extended beyond the cephalad end of the plaque. The internal carotid clamp is released and the shunt is introduced into the artery and secured in place with a small Javid clamp. While back bleeding is occurring through the shunt, its lower end is inserted into the common carotid artery until it meets the clamp that occludes this vessel. The large Javid clamp is applied to secure the shunt and the common carotid clamp is released, initiating blood flow to the brain (Fig. 6). This entire maneuver usually takes less than 1 minute. After the completion of the endarterectomy, the arteriotomy is closed over the shunt beginning at the upper end (Figs. 7 and 8). When *Heyer-Schulte Corporation.
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Figure 7. The endarterectomy plane is developed with the use of a Cannon endarterectomy knife.
Figure 8. The arteriotomy is closed over the shunt with a continuous 6-0 vascular suture.
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the closure has reached the common carotid artery, the suture is interrupted. The lower portion of the arteriotomy is then closed in a similar manner. When no further closure is possible because of the shunt, the lower suture is similarly interrupted. A clamp is applied to the common carotid artery below the end of the shunt, the large Javid clamp is released, and the lower end of the shunt is withdrawn. The small Javid clamp is then released and the shunt is removed. The internal carotid artery is clamped to stop retrograde bleeding. Traction is then exerted on the ends of the sutures partially closing the arteriotomy, elevating the carotid artery, and a Statinsky clamp is applied in such a manner as to partially occlude the lumen of the artery. The external carotid and the common carotid clamps are released, permitting flow into the external carotid artery. A few moments later the internal carotid clamp is opened, restoring circulation to the brain. Closure of the arteriotomy can then be completed and the Statinsky clamp is removed.U
POSTOPERATIVE CARE Careful monitoring of the patient's blood pressure is most important in the immediate postoperative care. Therefore, the radial artery cannula is removed only after the patient has awakened from the anesthetic and the blood pressure has remained stable. Serious hypotension may cause thrombosis of the recently operated carotid artery. Mild hypotension usually responds to simple fluid replacement while more severe degrees of hypotension should be treated with use of vasopressors. Metaraminol bitartrate (10 mg in 500 ml of dextrose solution) is administered by the intravenous drip method. Severe hypertension occurs less frequently and should be controlled in order to avoid cerebral edema or bleeding from the operative site. The intravenous administration of sodium nitroprusside (50 mg in 500 ml of dextrose solution) by the drip technique will lower the blood pressure. Neurologic evaluation of the patient should be performed early when the level of consciousness is adequate to permit proper examination. Mild neurologic deficits may be apparent early but usually disappear by the time the patient is fully awake. Anticoagulants and antibiotics are not administered routinely. The suction drain is removed in the first postoperative day and most patients are discharged from the hospital 5 days after the operation.
COMPLICATIONS The most common complication of carotid endarterectomy is a wound hematoma. Fortunately most hematomas are small and require no treatment. Rapidly expanding or large hematomas that displace the trachea, however, should be evacuated in the operating room. In our experience the routine use of the suction drain has eliminated this complication. Although secondary infection of a hematoma is a potential danger, we have never seen this problem.
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Postoperative dysfunction of the hypoglossal, the mandibular branch of the facial, and the vagus nerves does not require specific treatment. In our experience, return of function after a variable length of time has been observed in all patients. A voiding trauma to these nerves during the operation should eliminate the occurrence of this complication. The most serious complication of carotid endarterectomy is the production of a stroke or the aggravation of one present preoperatively. Mild neurologic deficits apparent on examination of a patient awakening from anesthesia are frequently temporary, while major deficits are more likely to be permanent and are associated with a significant mortality. The most common causes of this complication are: cerebral embolization during the operation, cerebral ischemia due to operative carotid clamping, and thrombosis of the operated carotid artery. In most instances, however, it is difficult to define the actual mechanism implicated. Nevertheless, thrombosis of the carotid artery is the most likely cause in patients who, after having recovered from the operation, develop a sudden severe neurologic deficit affecting the hemisphere supplied by the operated carotid artery. In this situation, immediate reoperation is indicated for proper diagnosis and treatment. The artery should be explored through a small, transverse arteriotomy below the previous endarterectomy. If a fresh thrombus is not found and brisk retrograde bleeding from the internal carotid artery is observed, the arteriotomy is simply closed. If, however, carotid thrombosis is confirmed, thrombectomy with Fogarty and suction catheters is performed. The cause for the thrombosis should be determined and corrected. Anticoagulation with heparin should be administered intraoperatively and continued for a few days to prevent the recurrence of thrombosis.
SUMMARY During the last 20 years carotid endarterectomy has become an important method of treatment for selected patients with arteriosclerotic cerebrovascular disease. Improvement in selection of patients for operation, in anesthetic management, and in surgical techniques has resulted in a decline in complications associated with the operation. The steps of the operation are described in detail. The causes, prevention, and treatment of the surgical complications are discussed.
REFERENCES 1. Bauer, R. B., Meyer, J. S., Fields, W. S., Remington R., MacDonald, M. C., and Callen, P.: Joint study of extracranial arterial occlusion. III. Progress report of controlled study of long-term survival in patients without operation. J.A.M.A., 208:509, 1969. 2. Blaisdell, F. W., Clauss, R. H., Galbraith, J. G., Imparato, A. M., and Wylie, E. J.: Joint study of extracranial arterial occlusion. IV. A review of surgical considerations. J.A.M.A., 209:1889, 1969. 3. Bland, j. E., Chapman, R. D., and Wylie, E. j.: Neurological complications of carotid artery surgery. Ann. Surg., 171 :459, 1970.
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4. Bloodwell, R. D., Hallman, G. L., Keats, A. S., and Cooley, D. A.: Carotid endarterectomy without a shunt. Arch. Surg., 96:644, 1968. 5. Brawley, B. W., Strandness, D. E., and Kelley, W. A.: The physiologic response to therapy in experimental cerebral ischemia. Arch. Neurol., 17:180, 1967. 6. Carrea, R., Molins, M., and Murphy, G.: Surgical treatment of spontaneous thrombosis of the internal carotid artery in the neck. Carotid-carotideal anastomosis: Report of a case. Acta Neurol. Latinoamer., 1:71, 1955. 7. David, T. E., Humphries, A. W., Young, J. R., and Beven, E. G.: A correlation of neck bruits and arteriosclerotic carotid arteries. Arch. Surg., 107:729, 1973. 8. DeBakey, M. E., Crawford, E. S., Cooley, D. A., Morris, G. C., Jr., Garrett, H. E., and Fields, W. S.: Cerebral arterial insufficiency: One to eleven year results following arterial reconstructive operation. Ann. Surg., 161:921, 1965. 9. DeWeese, J. A., Rob, C. G., Satran, R., Norris, F. H., Lipchik, E. 0., Zehl, D. N., and Long, J. M.: Surgical treatment for occlusive disease of the carotid artery. Ann. Surg., 168:85, 1968. 10. Eastcott, H. H. G., Pickering, G. W., and Rob, C. G.: Reconstruction of the internal carotid artery. Lancet, 2:994, 1954. 11. Ehrenfeld, W. K.: Personal communication. 12. Ehrenfeld, W. K., Hamilton, F. N., Larson, C. P., Jr., Hickey, R. F., and Severinghaus, J. W.: Effect of CO, and systemic hypertension on downstream cerebral arterial pressure during carotid endarterectomy. Surgery, 67:87, 1970. 13. Hass, W. K., Fields, W. S., North, R. R., Kricheff, I. 1., Chase, N. E., and Bauer, R. B.: Joint study of extracranial arterial occlusion. II. Arteriography, techniques, sites, and complications. J.A.M.A., 203:961, 1968. 14. Hays, R. J., Levinson, S. A., and Wylie, E. J.: Intraoperative measurement of carotid back pressure as a guide to operative management for carotid endarterectomy. Surgery, 72:953:960, 1972. 15. Hobison, R. W., Wright, C. B., Sublett, J. W., Fedde, W. C., and Rich, N. M.: Carotid artery back pressure and endarterectomy under regional anesthesia. Arch. Surg., 109:682, 1974. 16. Hollenhorst, R. W.: Significance of bright plaques in the retinal arterioles. J.A.M.A., 178:23, 1961. 17. Homi, J., Humphries, A. W., Young, J. R., Beven, E. G., and Smart, J. F.: Hypercarbic anesthesia in cerebrovascular surgery. Surgery, 59:57, 1966. 18. Javid, H., Ostermiller, W. E., Hengesh, J. W., Dye, W. S., Hunter, J. A., Najafi, H., and Julian, 0. C.: Natural history of carotid bifurcation atheroma. Surgery, 67:80, 1970. 19. Julian, 0. C., Dye, W. S., Javid, H., and Hunter, J. A.: Ulcerative lesions of the carotid artery bifurcation. Arch. Surg., 86:803, 1963. 20. Larson, C. P.: Anesthesia and control of the cerebral circulation. In Wylie, E. J., and Ehrenfeld, W. K. (eds.): Extracranial Occlusive Cerebrovascular Disease. Philadelphia, W. B. Saunders Co., 1970, p. 174. 21. Moore, W. S., and Hall, A. D.: Carotid artery back pressure. A test of cerebral tolerance to temporary carotid occlusion. Arch. Surg., 99:702, 1969. 22. Strully, K. J., Hurwitt, E. S., and Blankenberg, H. W.: Thromboendarterectomy of thecarotid artery in the neck. J. Neurosurg., 10:474, 1953. 23. Thompson, J. E., Austin, D. J., and Patman, R. D.: Carotid endarterectomy for cerebrovascular insufficiency: Long term results in 592 patients followed up to thirteen years. Ann. Surg., 172:663, 1970. 24. Wells, B. A., Keats, A. S., and Cooley, D. A.: Increased tolerance to cerebral ischemia produced by general anesthesia during temporary carotid occlusion. Surgery, 54:216, 1963. 25. Young, J. R., Humphries, A. W., DeWolfe, V. G., Beven, E. G., and LeFevre, F. A.: Extracranial cerebrovascular disease treated surgically. Arch. Surg., 89:848, 1964. 26. Young, J. R., Humphries, A. W., Beven, E. G., and DeWolfe, V. G.: Carotid endarterectomy without a shunt. Arch. Surg., 99:293, 1969. Department of Vascular Surgery The Cleveland Clinic Foundation 9500 Euclid Avenue Cleveland, Ohio 44106
Carotid Endarterectomy
Edwin G. Beven, M.D.
Carotid endarterectomy is by far the most common of all the procedures performed in the surgical treatment of extracranial occlusive disease, accounting for at least 90 per cent of all the operations for patients with cerebral vascular symptoms. There are many reasons for this. The most common site of occlusive disease in the extracranial tree is the carotid bifurcationP Furthermore, the symptoms produced by such a lesion are frequently dramatic and profound, thus eliciting concern and fear in the patient, and leading him to seek medical help early. In addition, the symptoms that result from a carotid lesion are usually well defined and the diagnosis is obvious. The clini~al diagnosis is frequently strengthened by the presence of a carotid bruit on auscultation of the neck. 7 Finally, from a technical consideration, the carotid bifurcation atheroma is usually well localized and therefore suited for excision by simple endarterectomy, in contrast to more complicated surgical procedures that are necessary for the correction of lesions in other sites of the extracranial arterial vasculature. Chronologically the first successful carotid reconstructive procedure was performed by Carrea and associates in 1951, but reported in 1955.6 Strully and co-workers in 1953 published a report of a case of an unsuccessful carotid thromboendarterectomy,22 and in 1954 Eastcott, Pickering, and Rob published the first successful carotid reconstruction.10 It is interesting to note that of these three reports, the two successful cases were accomplished by excision and re-anastomosis, while in the unsuccessful case, the procedure employed was an endarterectomy which has since become the procedure of choice. Over the past two decades carotid endarterectomy has become a most valuable tool in the armamentarium of the vascular surgeon. The technical details have become standardized and will be described in this article. The description is based upon the experience accumulated with more than 700 operations performed at the Cleveland Clinic. The anesthetic technique and the methods for cerebral protection From the Department of Vascular Surgery, The Cleveland Clinic Foundation and The Cleveland Clinic Educational Foundation, Cleveland, Ohio
Surgical Clinics of North America- Vol. 55, No. 5, October 1975
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during the operative carotid clamping, however, have remained controversial. Therefore, discussion of these methods will also be included.
GENERAL CONSIDERATIONS SELECTION OF PATIENTS
The criteria for selection of patients for carotid endarterectomy have gradually evolved with experience accumulated during the past decade. In this regard, there appears to be uniformity of opinion among the majority of vascular surgeons.
Indications Our current indications for carot:h:l. endarterectomy are: 1. Patients with transient ischemic attacks in whom arteriography demonstrates an arteriosclerotic lesion in the appropriate carotid artery. Since emboli from even small ulcerated plaques can be the source of cerebral or retinal ischemic symptoms, carotid endarterectomy is indicated regardless of the degree of stenosis.'s· '" 2. Patients with a completed stroke who demonstrate severe stenosis of the appropriate internal carotid artery and who, in time, have demonstrated good neurologic recovery. 3. Asymptomatic patients with a carotid stenosis of greater than 70 per cent, who are to undergo an unrelated major operation that could be associated with the risk of hypotension which might result in thrombosis of the carotid artery. 4. Asymptomatic patients with severe stenosis of one internal carotid and total occlusion of the contralateral carotid artery. Prophylactic carotid endarterectomy for the stenotic side is indicated in this group of patients because of the fear that thrombosis of the remaining carotid artery could result in a major stroke. These patients, however, should be highly selected, should be relatively young, and should lack any serious associated disease that may affect their long-term survival.
Contraindications We believe that carotid endarterectomy is contraindicated in the following situations: 1. Patients with a stroke in evolution or with a recent acute stroke. Experience has shown that in these patients, carotid endarterectomy is associated with a high mortality. 2 • 23 2. Patients with a remote stroke associated with a poor neurologic recovery. Reconstructive surgery, even if feasible, should be avoided because of the high incidence of aggravation of the previous neurologic deficit, or the production of a new one! 3. Patients with a stenosis in the cervical carotid artery who, in addition to this lesion, have a severe obstruction of the ipsilateral intracranial carotid artery. It is postulated that excision of the accessible cervical plaque does not improve the flow through the second intracranial stenosis. 4. Patients with total occlusion of the internal carotid artery. We no longer recommend operation in such cases, since the success rate is low. 26 Instead, attention should be focused on stenotic lesions in other extracranial arteries.
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INTRAOPERATIVE CEREBRAL PROTECTIVE TECHNIQUES
Most patients undergoing carotid endarterectomy have adequate cerebral collateral circulation and can tolerate temporary carotid occlusion without problems. About 10 per cent of patients, however, are intolerant of operative carotid clamping.3· 21 The earliest technique devised to circumvent this problem was the use of the intraluminal shunt that permitted carotid endarterectomy while maintaining blood flow to the brain through the shunt. Although the routine use of a shunt is preferred by some surgeons,8· 18· 23 others believe that it interferes with a technically adequate endarterectomy.4· 9 • 26 General hypercarbic anesthesia and controlled hypertension, first introduced by Wells, Keats, and Cooley in 1963,24 permitted carotid endarterectomy without a shunt. The cerebral protection by this method is based on the improved oxygenation and the decrease in oxygen consumption by the brain during general anesthesia, the increased cerebral blood flow resulting from the vasodilatation of hypercarbia, and the increased cerebral perfusion from the induced hypertension. We have used a slight modification of their technique since 1964P· 26 Experimental evidence, however, suggests that hypercarbia may produce a deleterious effect by creating an intracerebral steal. 5 Furthermore, Ehrenfeld and co-workers investigating the effects of different levels of Pco 2 on the internal carotid back pressure, suggested that hypocarbia increased cerebral perfusion to the ischemic areas while hypercarbia did not. For these reasons the authors abandoned hypercarbic general anesthesia. They recommend the use of hypocarbia, deliberate hypertension, and general anesthesia.20 Although local anesthesia allows neurologic evaluation of the patient while the carotid artery is clamped, and thus permits selection of patients who require shunting, general anesthesia has become the method of choice of most surgeons. Since neurologic evaluation of the anesthetized patient is not possible, Moore and Hall21 investigated the operative measurement of the internal carotid back pressure, or stump pressure, as a test for adequacy of cerebral perfusion. The authors reported a positive correlation of a low internal carotid back pressure and the incidence of ischemic cerebral symptoms. The critical pressure found was 25 mm Hg. Hays and associates14 and Hobson and coworkers15 corroborated these findings but noted that the critical pressure range obtained by them was 41 to 50 mm Hg and 60 to 70 mm Hg respectively. The evidence accumulated thus far indicates that measurement of the stump pressure is the most reliable index to predict when shunting is necessary in the anesthetized patient. However, the minimum safe pressure has not yet been clearly established. In an attempt to confirm this test we have begun a prospective study in patients undergoing endarterectomy. The stump pressure is determined in all patients. In one group of patients, selected by admission to a particular surgical service, a shunt is used if the stump pressure
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measures less than 50 mm Hg. In the other group of patients, shunting is not utilized, regardless of the stump pressure obtained.
SURGICAL TECHNIQUE After induction of anesthesia a cannula is inserted percutaneously into the radial artery at the wrist. This is done to monitor the mean arterial systemic pressure and to provide access to arterial blood samples for blood gas analysis in order to follow the degree of hypercarbia. The patient is positioned with the head slightly extended and rotated to the opposite side and the incision is made along the anterior border of the sternocleidomastoid muscle (Fig. 1). The carotid bifurcation should lie in the midportion of the incision. A glance at the lateral carotid arteriogram is helpful at this point, since it will show the relationship of the carotid bifurcation to the angle of the mandible. The incision is carried through platysma muscle and along the anterior border of the sternomastoid muscle. With further dissection this structure is retracted laterally and posteriorly. Deeper dissection is then carried through until the internal jugular vein is visualized. The facial vein is identified and divided between suture ligatures. By means of a pursestring suture, a catheter is inserted into the internal jugular vein and introduced in a cephalad direction for approximately 8 em. This will provide access to the venous return from the brain and permits periodic determinations of the P v0 2 as well as the oxygen saturation throughout the procedure (Fig. 2). This provides a gross measure of the increased total cerebral flow as a result of the induced hypercarbia. Attention is then directed to the common carotid artery which has a medial relationship to the internal jugular vein. The artery is dissected in the lowermost portion of the incision and the dissection carried proximally towards the carotid bifurcation. Utmost care should be exercised
Figure 1. Positioning of the patient is important for proper exposure. The head is extended and turned to the opposite side. The dotted line shows the placement of the incision.
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Figure 2. After exposure of the internal jugular vein, a catheter is introduced to monitor the Pvo2 and 0 2 saturation.
in dissecting the carotid artery from the surrounding structures. Excessive manipulation of the carotid artery is avoided in order to prevent embolization from the atherosclerotic plaque (Fig. 3). The vagus nerve should be identified and protected from unnecessary trauma. It should be gently dissected from the posterior lateral aspect of the common carotid artery when it is adherent to this vessel. This maneuver is necessary to avoid incorporating the vagus nerve with the artery when the vascular clamp is applied. Clamping of the nerve is a common cause of the ipsilateral vocal cord paralysis occurring in a small number of patients undergoing carotid endarterectomy. The descending branch of the hypoglossal nerve is identified as it courses anteriorly and it is isolated and preserved by retracting it to one side (Fig. 4). The dissection is then extended proximally along the common carotid artery. Once the bifurcation is approached, the dissection is carried out along the anterior aspect, and to a minimal degree along the sides of the carotid bulb, the superior thyroid and external carotid arteries. The posterior aspect of the carotid bifurcation, as well as the area of the carotid body between the internal and external carotid arteries, are left undisturbed. This maneuver prevents excessive manipulation of the carotid bifurcation and thus minimizes the danger of embolization from the arteriosclerotic lesion. It also protects the superior laryngeal nerve as it courses deep to the carotid bifurcation.
Figure 3. The carotid arteriogram demonstrates an ulcerated plaque with a probable thrombus. Manipulation of the carotid artery during the surgical dissection should be minimal in order to avoid the danger of cerebral embolization.
Figure 4. Exposure of the carotid artery. The descending branch of the hypoglossal nerve is seen in its usual location.
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The internal carotid artery is then isolated and dissected free as high above the lesion as is practical. Although it is tempting to palpate the internal carotid artery in order to ascertain the extent of the lesion, this maneuver should be avoided because it can easily dislodge loose fragments and result in cerebral embolization (see Fig. 3). Instead the surgeon should be guided by the arteriogram which should demonstrate the extent of the plaque in the internal carotid artery. During the course of the dissection of the internal and external carotid arteries, the hypoglossal nerve should be identified as it courses superficial to these arteries, curving down and anteriorly. When retracting this area the blade of the retractor should be carefully placed in order to avoid trauma to the nerve. In patients with a high carotid bifurcation it may be necessary to extend the upper end of the incision to dissect the internal carotid artery adequately above the lesion. The extension of the incision should be 1 em posterior to the angle of the jaw. Dissection of the deeper structures should be directed somewhat posteriorly into the anterior aspect of the sternocleidomastoid muscle in order to avoid trauma to the mandibular branch of the facial nerve. A deeper dissection will encounter the internal jugular vein and usually the maxillary vein as it runs anteriorly and superficial to the internal carotid artery. This vein should be mobilized and divided between suture ligatures. The internal carotid artery can then be mobilized without difficulty. At this stage of the dissection, hypercarbia should be at an optimum level. The arterial Pco 2 should be between 70 and 90 mm Hg. while the jugular venous Po 2 should be greater than 80 mm Hg. Heparin is now administered intravenously (200 units per kg of body weight). After a few minutes, measurement of the internal carotid back pressure (stump pressure) is determined. The common carotid, external carotid, and superior thyroid arteries are clamped and a 22 gauge needle, connected through tubing to a strain gauge, is introduced into the common carotid. The needle should enter the artery at a suitable point between the common carotid clamp and the lesion. Once the stump pressure is determined, the needle is withdrawn and the arterial clamps are released. The occlusion time for this procedure is usually less than 30 seconds. A few minutes should be allowed to perfuse the brain before reapplying the clamps to perform the endarterectomy.
CAROTID ENDARTERECTOMY WITHOUT A SHUNT
As previously mentioned, a stump pressure of 50 mm Hg has been arbitrarily selected as the minimal pressure required in patients in whom carotid endarterectomy can be performed without a shunt. The internal carotid artery is occluded with a vascular clamp as far cephalad as possible and at least 1 em beyond the end of the arteriosclerotic plaque. The common carotid, external carotid, and superior thyroid arteries are similarly clamped. A short longitudinal arteriotomy is performed with a No. 15 blade on the anterolateral wall of the common carotid artery below the plaque. The arteriotomy is then extended
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with the angled Potts scissors across the lesion and into the first portion of the internal carotid artery. The arteriotomy should be placed away from the origin of the external carotid artery in order to avoid the carotid body. The arteriotomy is terminated at the most cephalad end of the arteriosclerotic plaque. Similarly, the arteriotomy is extended caudally and should also terminate at the end of the plaque. In some patients the thickened intima extends throughout the common carotid artery. In this situation the arteriotomy should be terminated approximately 5 mm from the common carotid clamp. The endarterectomy is then initiated by grasping the adventitia of the artery away from the plaque at its most thickened portion. With the use of the blunt Cannon endarterectomy knife the plaque is lifted away from the artery and this plane is then developed. The dissection along this plane is extended circumferentially down the common carotid artery to the lowermost portion of the arteriotomy. The plaque is lifted anteriorly and away from the posterior wall of the artery with the use of a Moynihan clamp and is cleanly transected with Strully scissors. Since we have not observed retrograde dissection of the common carotid, it is not necessary to transfix the intima to the artery. The divided plaque is then lifted and the dissection is carried cephalad to the origin of the external carotid artery. The endarterectomy should be carried circumferentially around the origin of the extemal carotid artery. With slight traction on the plaque and with the release of the external carotid clamp the plaque separates from the normal intima beyond and is delivered into the lumen of the artery. The external carotid clamp is reapplied. Attention is then directed to the internal carotid artery. With gentle traction on the plaque, the wall of the artery is pushed away from the plaque until the normal dissection plane disappears. At this point the plaque easily separates from the normal intima. Once the specimen is delivered, attention is focused on the normal intima at the point of separation. The intima should be adherent to the artery if dissection by the blood stream is to be avoided when flow to the internal carotid artery is re-established. In most patients the cephalad end of the plaque is usually tapered and the normal intima is adherent to the wall. In a few patients, however, the intima is thickened and dissection could result in occlusion of the lumen after the vascular clamps are released. To avoid this complication the intima is sutured down to the wall of the internal carotid artery by means of interrupted doublearmed 7-0 sutures. One needle is inserted through the intima while the other is placed just caudad to the intimal edge and tied outside the artery. Usually five sutures accomplishes the objective. After completion of the endarterectomy the denuded surface is inspected for residual fragments that may remain attached to the artery. These are carefully removed. The arterial clamps are then momentarily released in order to flush any debris that may be trapped by them. The arteriotomy is closed, beginning at the cephalad end, with a continuous 6-0 nonabsorbable arterial suture. Just before completing the closure the internal carotid clamp is temporarily released in order to flush air and minute debris. The last suture is then inserted and tied, closing the arteriotomy. The external carotid clamp is opened first, followed by the
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clamp occluding the common carotid artery. Any trapped fragments will flow into the external artery and eliminate the danger of cerebral embolization. After a few moments the int-ernal carotid clamp is released. Any bleeding that may occur from the arteriotomy is controlled with interrupted 7- 0 sutures. The removal of the atheromatous lesion usually results in a normal or larger than normal carotid bulb and therefore eliminates the necessity of applying a patch for closure of arteriotomy (Fig. 5, A and B). Very rarely, when faced with a small internal carotid artery or with a lesion that extends high into it, a saphenous vein patch is necessary to avoid creating a stenosis. Because of the potential danger of infection we do not use a patch of prosthetic material. At the end of the procedure heparin is partially neutralized with protamine sulphate and a Jackson-Pratt suction drain'~ is placed in the operative field through a stab wound below the incision. The platysma, subcutaneous tissue, and skin are closed separately with interrupted sutures. CAROTID ENDARTERECTOMY WITH A SHUNT
In selected patients who demonstrate an internal carotid back pressure of less than 50 mm Hg, operative carotid clamping is shortened by the use of a shunt. Only the technique of the insertion and the removal of the shunt will be outlined in this section since this is the only variation from that previously described. *Heyer-Schulte Corporation.
Figure 5. A, Preoperative arteriogram demonstrating severe carotid stenosis. B, Carotid arteriogram following endarterectomy in the same patient. The lumen has been restored to a normal diameter and a patch graft is therefore unnecessary.
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Figure 6. The shunt has been introduced through the arteriotomy and it is secured with the Javid clamps.
Although several shunts are available, we prefer the loop shunt* because the ends of this particular shunt are rounded and smooth and thus allow insertion into the artery with minimal risk of producing intimal damage. In addition, its greater flexibility permits easier retraction of the shunt during the endarterectomy with no danger of angulation and obstruction of blood flow. The coiled metal spring embedded in its wall prevents kinking. Lastly, it is available in various diameters that permit a better match to the lumen of the artery. After the internal, common, and external carotid arteries are clamped, the arteriotomy is extended beyond the cephalad end of the plaque. The internal carotid clamp is released and the shunt is introduced into the artery and secured in place with a small Javid clamp. While back bleeding is occurring through the shunt, its lower end is inserted into the common carotid artery until it meets the clamp that occludes this vessel. The large Javid clamp is applied to secure the shunt and the common carotid clamp is released, initiating blood flow to the brain (Fig. 6). This entire maneuver usually takes less than 1 minute. After the completion of the endarterectomy, the arteriotomy is closed over the shunt beginning at the upper end (Figs. 7 and 8). When *Heyer-Schulte Corporation.
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Figure 7. The endarterectomy plane is developed with the use of a Cannon endarterectomy knife.
Figure 8. The arteriotomy is closed over the shunt with a continuous 6-0 vascular suture.
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the closure has reached the common carotid artery, the suture is interrupted. The lower portion of the arteriotomy is then closed in a similar manner. When no further closure is possible because of the shunt, the lower suture is similarly interrupted. A clamp is applied to the common carotid artery below the end of the shunt, the large Javid clamp is released, and the lower end of the shunt is withdrawn. The small Javid clamp is then released and the shunt is removed. The internal carotid artery is clamped to stop retrograde bleeding. Traction is then exerted on the ends of the sutures partially closing the arteriotomy, elevating the carotid artery, and a Statinsky clamp is applied in such a manner as to partially occlude the lumen of the artery. The external carotid and the common carotid clamps are released, permitting flow into the external carotid artery. A few moments later the internal carotid clamp is opened, restoring circulation to the brain. Closure of the arteriotomy can then be completed and the Statinsky clamp is removed.U
POSTOPERATIVE CARE Careful monitoring of the patient's blood pressure is most important in the immediate postoperative care. Therefore, the radial artery cannula is removed only after the patient has awakened from the anesthetic and the blood pressure has remained stable. Serious hypotension may cause thrombosis of the recently operated carotid artery. Mild hypotension usually responds to simple fluid replacement while more severe degrees of hypotension should be treated with use of vasopressors. Metaraminol bitartrate (10 mg in 500 ml of dextrose solution) is administered by the intravenous drip method. Severe hypertension occurs less frequently and should be controlled in order to avoid cerebral edema or bleeding from the operative site. The intravenous administration of sodium nitroprusside (50 mg in 500 ml of dextrose solution) by the drip technique will lower the blood pressure. Neurologic evaluation of the patient should be performed early when the level of consciousness is adequate to permit proper examination. Mild neurologic deficits may be apparent early but usually disappear by the time the patient is fully awake. Anticoagulants and antibiotics are not administered routinely. The suction drain is removed in the first postoperative day and most patients are discharged from the hospital 5 days after the operation.
COMPLICATIONS The most common complication of carotid endarterectomy is a wound hematoma. Fortunately most hematomas are small and require no treatment. Rapidly expanding or large hematomas that displace the trachea, however, should be evacuated in the operating room. In our experience the routine use of the suction drain has eliminated this complication. Although secondary infection of a hematoma is a potential danger, we have never seen this problem.
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Postoperative dysfunction of the hypoglossal, the mandibular branch of the facial, and the vagus nerves does not require specific treatment. In our experience, return of function after a variable length of time has been observed in all patients. A voiding trauma to these nerves during the operation should eliminate the occurrence of this complication. The most serious complication of carotid endarterectomy is the production of a stroke or the aggravation of one present preoperatively. Mild neurologic deficits apparent on examination of a patient awakening from anesthesia are frequently temporary, while major deficits are more likely to be permanent and are associated with a significant mortality. The most common causes of this complication are: cerebral embolization during the operation, cerebral ischemia due to operative carotid clamping, and thrombosis of the operated carotid artery. In most instances, however, it is difficult to define the actual mechanism implicated. Nevertheless, thrombosis of the carotid artery is the most likely cause in patients who, after having recovered from the operation, develop a sudden severe neurologic deficit affecting the hemisphere supplied by the operated carotid artery. In this situation, immediate reoperation is indicated for proper diagnosis and treatment. The artery should be explored through a small, transverse arteriotomy below the previous endarterectomy. If a fresh thrombus is not found and brisk retrograde bleeding from the internal carotid artery is observed, the arteriotomy is simply closed. If, however, carotid thrombosis is confirmed, thrombectomy with Fogarty and suction catheters is performed. The cause for the thrombosis should be determined and corrected. Anticoagulation with heparin should be administered intraoperatively and continued for a few days to prevent the recurrence of thrombosis.
SUMMARY During the last 20 years carotid endarterectomy has become an important method of treatment for selected patients with arteriosclerotic cerebrovascular disease. Improvement in selection of patients for operation, in anesthetic management, and in surgical techniques has resulted in a decline in complications associated with the operation. The steps of the operation are described in detail. The causes, prevention, and treatment of the surgical complications are discussed.
REFERENCES 1. Bauer, R. B., Meyer, J. S., Fields, W. S., Remington R., MacDonald, M. C., and Callen, P.: Joint study of extracranial arterial occlusion. III. Progress report of controlled study of long-term survival in patients without operation. J.A.M.A., 208:509, 1969. 2. Blaisdell, F. W., Clauss, R. H., Galbraith, J. G., Imparato, A. M., and Wylie, E. J.: Joint study of extracranial arterial occlusion. IV. A review of surgical considerations. J.A.M.A., 209:1889, 1969. 3. Bland, j. E., Chapman, R. D., and Wylie, E. j.: Neurological complications of carotid artery surgery. Ann. Surg., 171 :459, 1970.
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4. Bloodwell, R. D., Hallman, G. L., Keats, A. S., and Cooley, D. A.: Carotid endarterectomy without a shunt. Arch. Surg., 96:644, 1968. 5. Brawley, B. W., Strandness, D. E., and Kelley, W. A.: The physiologic response to therapy in experimental cerebral ischemia. Arch. Neurol., 17:180, 1967. 6. Carrea, R., Molins, M., and Murphy, G.: Surgical treatment of spontaneous thrombosis of the internal carotid artery in the neck. Carotid-carotideal anastomosis: Report of a case. Acta Neurol. Latinoamer., 1:71, 1955. 7. David, T. E., Humphries, A. W., Young, J. R., and Beven, E. G.: A correlation of neck bruits and arteriosclerotic carotid arteries. Arch. Surg., 107:729, 1973. 8. DeBakey, M. E., Crawford, E. S., Cooley, D. A., Morris, G. C., Jr., Garrett, H. E., and Fields, W. S.: Cerebral arterial insufficiency: One to eleven year results following arterial reconstructive operation. Ann. Surg., 161:921, 1965. 9. DeWeese, J. A., Rob, C. G., Satran, R., Norris, F. H., Lipchik, E. 0., Zehl, D. N., and Long, J. M.: Surgical treatment for occlusive disease of the carotid artery. Ann. Surg., 168:85, 1968. 10. Eastcott, H. H. G., Pickering, G. W., and Rob, C. G.: Reconstruction of the internal carotid artery. Lancet, 2:994, 1954. 11. Ehrenfeld, W. K.: Personal communication. 12. Ehrenfeld, W. K., Hamilton, F. N., Larson, C. P., Jr., Hickey, R. F., and Severinghaus, J. W.: Effect of CO, and systemic hypertension on downstream cerebral arterial pressure during carotid endarterectomy. Surgery, 67:87, 1970. 13. Hass, W. K., Fields, W. S., North, R. R., Kricheff, I. 1., Chase, N. E., and Bauer, R. B.: Joint study of extracranial arterial occlusion. II. Arteriography, techniques, sites, and complications. J.A.M.A., 203:961, 1968. 14. Hays, R. J., Levinson, S. A., and Wylie, E. J.: Intraoperative measurement of carotid back pressure as a guide to operative management for carotid endarterectomy. Surgery, 72:953:960, 1972. 15. Hobison, R. W., Wright, C. B., Sublett, J. W., Fedde, W. C., and Rich, N. M.: Carotid artery back pressure and endarterectomy under regional anesthesia. Arch. Surg., 109:682, 1974. 16. Hollenhorst, R. W.: Significance of bright plaques in the retinal arterioles. J.A.M.A., 178:23, 1961. 17. Homi, J., Humphries, A. W., Young, J. R., Beven, E. G., and Smart, J. F.: Hypercarbic anesthesia in cerebrovascular surgery. Surgery, 59:57, 1966. 18. Javid, H., Ostermiller, W. E., Hengesh, J. W., Dye, W. S., Hunter, J. A., Najafi, H., and Julian, 0. C.: Natural history of carotid bifurcation atheroma. Surgery, 67:80, 1970. 19. Julian, 0. C., Dye, W. S., Javid, H., and Hunter, J. A.: Ulcerative lesions of the carotid artery bifurcation. Arch. Surg., 86:803, 1963. 20. Larson, C. P.: Anesthesia and control of the cerebral circulation. In Wylie, E. J., and Ehrenfeld, W. K. (eds.): Extracranial Occlusive Cerebrovascular Disease. Philadelphia, W. B. Saunders Co., 1970, p. 174. 21. Moore, W. S., and Hall, A. D.: Carotid artery back pressure. A test of cerebral tolerance to temporary carotid occlusion. Arch. Surg., 99:702, 1969. 22. Strully, K. J., Hurwitt, E. S., and Blankenberg, H. W.: Thromboendarterectomy of thecarotid artery in the neck. J. Neurosurg., 10:474, 1953. 23. Thompson, J. E., Austin, D. J., and Patman, R. D.: Carotid endarterectomy for cerebrovascular insufficiency: Long term results in 592 patients followed up to thirteen years. Ann. Surg., 172:663, 1970. 24. Wells, B. A., Keats, A. S., and Cooley, D. A.: Increased tolerance to cerebral ischemia produced by general anesthesia during temporary carotid occlusion. Surgery, 54:216, 1963. 25. Young, J. R., Humphries, A. W., DeWolfe, V. G., Beven, E. G., and LeFevre, F. A.: Extracranial cerebrovascular disease treated surgically. Arch. Surg., 89:848, 1964. 26. Young, J. R., Humphries, A. W., Beven, E. G., and DeWolfe, V. G.: Carotid endarterectomy without a shunt. Arch. Surg., 99:293, 1969. Department of Vascular Surgery The Cleveland Clinic Foundation 9500 Euclid Avenue Cleveland, Ohio 44106
