Surgical Management of Extracranial Carotid Artery Disease

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Chapter 66 Surgical Management of Extracranial Carotid Artery Disease

Since the first description of a carotid endarterectomy (CEA) for the prevention of stroke,¹ the operation has been widely debated and often criticized; yet the numbers of endarterectomy procedures performed annually have steadily increased.² Early studies suggested that medical management was superior to surgical intervention.^3,⁴ This is clearly no longer the case. Gratifying and unimpeachable results from recent multicenter trials have advocated surgical therapy over medical management in specific cases⁵^–⁷ of both asymptomatic and symptomatic carotid stenosis. The North American Symptomatic Carotid Endarterectomy Trial data indicate that CEA has benefit for all symptomatic patients with lesions of more than 70% linear stenosis and for specific subgroups of symptomatic patients with more than 50% stenosis. The Asymptomatic Carotid Atherosclerosis Study indicates that asymptomatic patients with more than 60% stenosis have a better outcome with CEA than with medical management.⁸

In this chapter, we describe our standard technique for CEA and discuss the various surgical options and different variations of the procedure. Although there are numerous ways to perform a CEA, one must adhere to several basic principles of carotid reconstruction. The surgeon must have complete preoperative knowledge of the patient’s vascular anatomy, must maintain complete vascular control at all times, must have sufficient working anatomic knowledge to prevent harm to adjacent structures, and must assure the patient of a repair that is widely patent and free of technical errors.

Surgical Technique

Surgical Magnification

We perform the operation with 3.5× loupe-magnified technique. Microscopic repair of the internal carotid artery (ICA), which we have also tried, allows a primary repair that is unquestionably finer than a loupe-magnified technique,^3,⁹^–¹¹ but which in our experience did not alter the overall patient outcome or incidence of restenosis or acute occlusion. In the ongoing effort to reduce morbidity, we have instead adopted universal patch grafting with collagen-impregnated Dacron (Hemashield graft), which has essentially eliminated the problem of acute postoperative thrombosis or rapid restenosis. In our opinion, the graft procedure is more easily and expeditiously accomplished with 3.5× magnification rather than the microscope. There is no doubt that the suture lines are not as fine with this method, but the added lumen diameter with patch angioplasty renders the microscopic technique unnecessary in our routine practice.

Anesthetic Technique

General anesthesia and local anesthesia are both in common use for CEA. We routinely use general anesthesia with both full-channel electroencephalographic and concurrent somatosensory-evoked potential (SSEP) monitoring. Proponents of local anesthesia cite the advantages of patient response to questioning as a superior method of assessing the need for intraoperative shunting while minimizing anesthetic risks, reducing postoperative morbidity, and shortening length of stay. The patient has local anesthesia with light sedation, which allows the patient to perform a simple task with the contralateral hand during cross-clamping. The disadvantages include risk of contamination and patient movement during the procedure, along with the increased psychological stress of remaining awake. A recent review comparing our technique with that of an institutional vascular surgeon using local anesthesia showed a decreased incidence of electroencephalographic changes and intraoperative shunting with local anesthesia. However, there was no difference in stroke rate, complications, length of stay, or overall outcome.^12,¹³

We prefer general anesthesia for a number of reasons, not the least of which is the controlled environment. Additionally, all commonly used inhalational anesthetic agents and intravenous barbiturates significantly reduce the cerebral metabolic rate of oxygen consumption,¹⁴ giving a theoretical protective effect in the setting of cerebral ischemia. We keep our patients normocapnic. Although there has been much interest in arterial levels of carbon dioxide, nonphysiologic hypercapnia and hypocapnia provide no cerebral protection.¹⁵^–¹⁸ Gross and colleagues¹⁹ found that there was a 40% decrease in electroencephalographic changes with cross-clamping in those patients receiving either one or two units of 6% hetastarch (500 to 1000 ml). They had acceptable outcomes with a postoperative stroke and mortality rate of 1.3%. We ourselves have not adopted this technique because of our policy of shunting quickly without hesitation for any hint of an EEG or SSEP change. Finally, blood pressure is maintained at normotensive levels with a tolerance of as high as a 20% increase in systolic pressure.¹¹ Although some surgeons prefer to induce hypertension at cross-clamping if there are electroencephalographic changes and then shunt if no improvement is seen in the electro-encephalographic recordings, we are not trying to avoid shunt use, and as mentioned we have a policy to shunt immediately if any monitoring changes are evident.

Monitoring Techniques

Monitoring techniques can be divided into two categories: (1) tests of vascular integrity, such as stump pressure measurements, xenon regional cerebral blood flow studies, transcranial Doppler and, to a lesser extent, intraoperative oculoplethysmography (OPG), Doppler/duplex scanning, and angiography; and (2) tests of cerebral function, such as electroencephalography, electroencephalographic derivatives, and/or SSEP monitoring. The newly described near-infrared spectroscopy technique bridges both categories. We use a full-channel electroencephalography interpreted by a neurologist. After completion of arteriotomy closure, an intraoperative Doppler examination is performed of the common carotid artery (CCA), the ICA, and the external carotid artery (ECA).^20,²¹

Intraoperative Shunting

Generally speaking, there are three schools of thought about intraoperative shunting.²² Carotid surgeons shunt in every case, shunt when indicated by some form of intraoperative monitoring, or never place a shunt.²³ In our institution, we perform monitor-dependent shunting based on electroencephalographic criteria. We use a custom commercial shunt of our own design (Loftus shunt, Integra Neurocare, Plainfield, NJ).²⁴ In our experience, we shunt approximately 15% of CEAs. This increases to approximately 25% if the contralateral carotid is occluded. After the shunt is placed, the monitoring should return to baseline. If this does not occur, the shunt must be inspected for possible kinking, thrombosis, or misplacement. We always auscultate the shunt with a Doppler probe that confirms patency and shunt flow.

Proponents of universal shunting tout the benefits of the maximal degree of cerebral protection in every case while eliminating dependence on specialized intraoperative monitoring techniques. They assert that shunt placement is benign and allows extra time to ensure meticulous intimal dissection and arteriotomy repair.²⁵^–³⁰

Proponents of nonshunting believe that shunt placement is not benign. In one series, there was a higher stroke rate with shunting compared with nonshunting,³¹ indicating that embolization from shunt placement, especially by surgeons inexperienced in the procedure, is a real risk. Another documented concern is distal intimal damage leading to embolization or carotid artery dissection.³²

Many surgeons, in part because of the concerns previously discussed, choose not to shunt. There have been multiple series that have good surgical results with no shunts being used.³³^–⁴⁰ These authors do not deny the existence of postoperative stroke, but they strongly believe that neurologic deficits from carotid artery surgery are invariably embolic rather than hemodynamic in nature and that intraoperative monitoring and/or shunt placement will not further reduce the already low morbidity in their series.³⁹

As discussed previously, we prefer to shunt when there are changes in the EEG and/or SSEP with cross-clamping. This policy has been well supported by several reports of large series of patients.^41,⁴² Of note, there are also several authors who normally practice selective shunting but who advocate shunting all patients who have had recent strokes or reversible neurologic events (due to their belief that intraoperative monitoring is unreliable in the face of recent ischemic events).⁴³^–⁴⁵ Whereas we understand their concerns, this has not been our practice.

Patch Graft Angioplasty

Almost all carotid surgeons perform patch angioplasty for recurrent carotid stenosis. Many will also use selective patching in cases in which the internal carotid is small, where the arteriotomy may have extended far up the ICA, or in any similar case in which compromise of the lumen and a high risk of thrombosis is anticipated. We have taken this policy one step further, and for a number of years have used a Hemashield patch graft primarily in all our patients. We have not encountered any restenosis or acute occlusions since using the patch universally. There are several other synthetic grafts available depending on surgeon preference, and of course autologous sapenous vein grafts can be used, but we prefer Hemashield, mindful of the real concern of central patch rupture with autologous vein, especially in women and patients with diabetes. Rupture risk can be reduced by harvesting the graft from a high femoral site rather than at the ankle.⁴⁶

Heparinization

A single dose of intravenous heparin is given to the patient at some point before cross-clamping. This dose is between 2500 and 10,000 U of heparin, depending on the surgeon’s preference. There are no published reports to support one dose versus another; however, Poisik and colleagues ³⁸ recently reported their results using weight-based dosing of heparin at 85 U/kg. Although they did not see any statistically significant differences between fixed-dose heparinization (5000 U) and weight-based dosing, there were trends of decreased complications of hematoma formation and neuropsychometric testing differences. Some individuals reverse the heparinization with protamine after the operation.^39,⁴⁰ We have not found any benefit in this practice. For those patients who come to the operating room on a continuous heparin drip, we continue the infusion until the arteriotomy closure is finished. With meticulous technique, bleeding in these cases has not been a problem.

Tacking Sutures

Tandem sutures to secure the distal intima in the ICA after plaque removal are considered a great advance by some ²⁶ and are deemed unnecessary by others^27,^39,⁴⁰ The concern with tacking sutures is that they may narrow the lumen, but to us this risk seems small compared with the concern of intimal dissection from an unsecured intimal flap. Several authors^28,^39,⁴⁰ state that, if the arteriotomy is carried far enough to see normal intima distal to the plaque, the tacking sutures are unnecessary. We strongly agree with an arteriotomy that extends past the plaque, but we are not always satisfied with how the intimal plaque tapers at the distal endpoint. In recent years, because of negative experiences with plaque that does not feather cleanly when pulled down from the distal ICA, we have adopted the use of fine scissors to “trim” the plaque cleanly in the ICA as it is removed. When this is done, tacking sutures are rarely necessary. We estimate that we now selectively place tacking sutures in the distal ICA in approximately 10% of cases.

Surgery

We think that the meticulous anatomic dissection and identification of vital cervical structures needed to minimize postoperative complications can be achieved only with a bloodless field. Accordingly, we do not consider elapsed time to be a factor in the performance of carotid artery surgery. In our institution, CEA requires from 2 to 2.5 hours of operating time and the average cross-clamp time is between 30 and 40 minutes. No untoward effects from the length of the procedure have been observed in any patient, and we are convinced that the risk of cervical nerve injury or postoperative complications related to hurried closure of the suture line is significantly reduced by meticulous attention to detail.⁴⁷

Two surgeons trained in the procedure are always present during carotid surgery. Both surgeons may stand on the operative side, the primary surgeon facing cephalad and the assistant facing the patient’s feet, or the surgeons may stand on each side of the table. The operative nurse may stand either behind or across the table from the primary surgeon. The patient is positioned supine on the operating room table with the head extended and turned away from the side of operation. Several folded pillowcases are placed between the shoulder blades to facilitate extension of the neck, and the degree of rotation of the head is determined by the relationship of the ECA and the ICA on preoperative angiography or magnetic resonance angiography. The carotid vessels are customarily superimposed in the anteroposterior plane, and moderate rotation of the head will swing the ICA laterally into a more surgically accessible position. In those patients in whom the ICA can be seen angiographically to be laterally placed, the head rotation need not be as great. Conversely, occasional patients will demonstrate an ICA that is rotated medially under the ECA (sometimes called the “twisted” or “side-by-side” carotid configuration), and in such cases, no degree of head rotation will yield a satisfactory exposure. When faced with such a case, the surgeon must be prepared to mobilize the ECA more extensively and swing it medially to expose the underlying internal carotid (even tacking it up to medial soft tissues if necessary).

The position of the carotid bifurcation has been likewise determined before surgery from the angiogram and the skin incision is planned accordingly. We always use a linear incision along the anterior portion of the sternocleidomastoid muscle (Fig. 66-1). This may go as low as the suprasternal notch and as high as the retroaural region depending on the level of the bifurcation. The skin and subcutaneous tissues are divided sharply to the level of the platysma, which is always identified and divided sharply as well. Hemostasis often requires the generous use of bipolar electrocautery. If careful attention is paid to all bleeding points during the opening, there will be little or no bleeding when heparin is administered and the closure will be much simpler.

FIGURE 66-1 Positioning and surgical incision planning in a left carotid endarterectomy are shown. The incision parallels the anterior border of the sternomastoid muscle. The L-shaped mark indicates the angle of the mandible.

Self-retaining retractors are next placed and the underlying fat is dissected to identify the anterior edge of the sternocleidomastoid muscle. Retractors are left superficial at all times on the medial side to prevent retraction injury to the recurrent laryngeal nerve in the traceo-esophageal groove, but laterally they may be more deeply placed. Dissection proceeds in the midportion of the wound down the sternomastoid muscle until the jugular vein is identified. Care must be taken under the sternomastoid muscle, however, to prevent injury to the spinal accessory nerve, which can be inadvertently transected or stretched.

It is to be emphasized that the jugular vein is the key landmark in this exposure and complete dissection of the medial jugular border should always be carried out before proceeding to the deeper structures. In some corpulent individuals, the vein is not readily apparent and a layer of fat between it and the sternomastoid must be entered to locate the jugular itself. If this is not done, it is possible to fall into an incorrect plane lateral and deep to the jugular vein. As soon as the jugular is identified, dissection is shifted to come along the medial jugular border and the vein is held back with blunt retractors.⁴⁸ The importance of the blunt retractor in preventing vascular injury at this point cannot be overemphasized. In this process, several small veins and one large common facial vein are customarily crossing the field and need to be doubly ligated and divided (Fig. 66-2). The underlying carotid artery is soon identified once the jugular is retracted. Most often we come upon the CCA first, and at the point of first visualization, the anesthesiologist is instructed to give 5000 U of intravenous heparin, which, as discussed previously, is never reversed. Dissection of the carotid complex is then straightforward, and the CCA, ECA, and ICA are isolated with the gentlest possible dissection and encircled with 00 silk ties (or vessel loops, if preferred) passed with a right-angle clamp. We no longer routinely inject the carotid sinus; however, the anesthesiologist is notified when the bifurcation is being dissected, and if any changes in vital signs ensue, the sinus can be injected with 2 to 3 ml of 1% plain Xylocaine through a short 25-gauge needle (this has not been necessary for the past several years). Although the carotid complex is completely exposed, the CCA and ECA are not routinely dissected free from their underlying beds to prevent postoperative kinking and coiling of these vessels. These arteries are dissected circumferentially only in those areas where silk ties or clamps are placed around them. Posterior dissection is more extensive in the region of the ICA, where in an occasional case posterior tacking sutures may later be placed and tied.

FIGURE 66-2 Intraoperative photograph shows the right jugular vein with a forcep behind the right common facial vein. The carotid cannot be visualized yet.

The CCA 0 silk is passed through a wire loop that is then pulled through a rubber sleeve (Rummel tourniquet), thereby facilitating constriction of the vessel around an intraluminal shunt if this becomes necessary. The ECA and ICA ties or loops are merely secured with mosquito clamps. Particular attention is paid to the superior thyroid artery, which is dissected free and secured with a double loop 00 silk ligature (some prefer an aneurysm clip for this). A hanging mosquito clamp keeps tension on this occlusive Potts tie. Occasionally, multiple branches of this artery are identified on the preoperative angiogram and must be individually dealt with so that no troublesome back-bleeding will ensue during the procedure through ignorance of these vessels. It is also essential that the ECA silk tie (and subsequent cross-clamp) be placed proximal to any major external branches, lest unacceptable back-bleeding occur during the arteriotomy and repair.

Proper placement of the retractors facilitates the control of the carotid system. The hanging mosquitoes and silk ties are draped over these retractor handles to keep the field uncluttered. Of particular note is a blunt, hinged (modified Richards) retractor, which is invaluable in exposing the ICA when a far distal exposure is necessary. Dissection of the ICA must be complete and clearly beyond the distal extent of the plaque before cross-clamping is performed. A clear plane can be developed if the jugular vein is followed distally and dissection follows the plane between the lateral carotid wall and the medial jugular border. By following this plane, the hypoglossal nerve is readily identified as it swings down medial to the jugular and crosses toward the midline over the ICA. The nerve is mobilized along its lateral wall adjacent to the jugular vein, after which it can be isolated with a vessel loop and gently retracted from the field. Hypoglossal paresis is rare and seems to result instead in cases in which the nerve is not visualized and is blindly retracted. On occasion, adequate mobilization of the hypoglossal nerve requires ligation of a small arterial branch of the ECA to the sternocleidomastoid muscle, which loops over the nerve. We have never seen inadvertent transection of the hypoglossal nerve.

There are several nerves that can be injured during carotid exposure and CEA. The spinal accessory and hypoglossal nerves have already been discussed. The vagus nerve lies deep to the carotid in the carotid sheath and can be inadvertently cross-clamped if not identified. The marginal mandibular branch of the facial nerve can be stretched by medial retraction in the high exposure of the ICA. The greater auricular nerve is at risk with a high incision, leaving the patient with a troublesome numb ear if it is transected. We have seen Horner’s syndrome (always transient) from unrecognized injury to the pericarotid sympathetic chain. Cutaneous sensory nerves will always be transected with the skin incision, and we advise patients that the anterior triangle of their neck will be numb for approximately 6 months after endarterectomy, after which sensation customarily reverts to normal.

It is vital to have adequate exposure of the ICA and control distal to the plaque before opening the vessel. The extent of the plaque can be readily palpated with some experience by a moistened finger. There is also a visual cue when the vessel becomes pinker (instead of hard and yellow) and more normal appearing distal to the extent of the plaque. If high exposure is needed, the posterior belly of the digastric muscle can be cut with impunity, although this is necessary only in a small percentage of cases. When complete exposure is achieved, the final step in preparation for cross-clamping is to ensure that the shunt clamp can be fitted around the ICA to secure the shunt if one is used. We designed and use a custom commercial spring-loaded pinch clamp (Loftus carotid shunt clamp, Scanlan Instruments, St. Paul, MN), which is available in several angles and has a special head exactly sized to grasp the ICA and indwelling shunt without leakage from back-bleeding. The Loftus shunt clamp is illustrated in Fig. 66-3.

FIGURE 66-3 The Loftus shunt clamp. This customized spring-loaded clamp is slightly angled with an encircling atraumatic end. This clamp is used to secure the indwelling shunt in the internal carotid artery.

We also use a sterile marking pen to draw the proposed arteriotomy line along the vessel, which is helpful in preventing a jagged or curving suture line (Fig. 66-4). The arteriotomy is made on the anterior surface of the ICA to facilitate the subsequent repair.

FIGURE 66-4 The carotid system has been cleanly dissected, and the arteriotomy site has been marked with a black marking pen. In the left upper quadrant, the hypoglossal nerve has been dissected and isolated with a vessel loop. The external carotid and superior thyroid arteries have silk ties around them. At the left edge, the internal carotid artery that is plaque free has a silk tie around it.

The monitoring systems (we use concurrently both EEG and SSEP now) are then rechecked, and the technicians are notified of impending cross-clamping. Once a suitable period of baseline has been recorded, the CCA is occluded with a large DeBakey vascular clamp and small, straight bulldog clamps or Yasargil aneurysm clips are used to occlude the ICA and ECA. We always occlude the ICA first in the belief that this approach has the lowest risk of embolization associated with clamping. A no. 11 blade is then used to begin the arteriotomy in the CCA and when the lumen is identified, a Potts scissors is used to cut straight up along the marked line into the region of the bifurcation and then up into the internal until normal ICA is entered (Fig. 66-5). In severely stenotic vessels with friable plaque, the lumen is not always easily discerned and false planes within the lesion are often encountered; great care must be taken to ensure that the back wall of the carotid is not lacerated and that the true lumen is identified before attempted shunt insertion.

FIGURE 66-5 After the vessel has been opened, the plaque can best be seen by gently everting the edges of the artery with vascular forceps.

Changes in the electroencephalogram mandate a rapid trial of induced hypertension for some surgeons, but for an intraluminal shunt is placed for any change on any monitor. The wisdom of shunt use is discussed elsewhere in the text. Numerous shunt types are available. We now use and recommend a customized indwelling shunt, the Loftus carotid endarterectomy shunt (Integra Neurocare, Plainsboro, NJ) (Fig. 66-6). This is a 15-cm straight silicone tube, singly packed in two diameters (10 Fr and 12 Fr), with tapered ends for easy insertion and a bulb at the proximal end to facilitate anchoring by the Rummel tourniquet. This shunt has a black marker band directly in the center of the shunt, so that cephalad shunt migration can be readily discerned and corrected. The shunt is first inserted into the CCA and secured by pulling up on the silk ties; a mosquito clamp then holds the rubber sleeve in place to snug the silk around both the vessel and the intraluminal shunt. The shunt tubing is held closed at its midportion with a heavy vascular forceps and then briefly opened to confirm blood flow and evacuate any debris in the shunt tubing. Suction is then used by the assistant to elucidate the lumen of the ICA, and the distal end of the shunt tubing is placed therein. After the shunt is again bled, flushing any debris from the ICA, the bulldog clamp is removed and the shunt is advanced up the ICA until the black dot lies in the center of the arteriotomy. The shunt, if properly placed, should slide easily into the ICA, and no undue force should be employed to prevent intimal damage and possible dissection. The Loftus shunt clamp is then used to secure the shunt distally in the ICA. Visualization of the dot in the center of the arteriotomy confirms constant correct positioning of the shunt (Fig. 66-7). A handheld Doppler probe can be applied to the shunt tubing to audibly confirm flow.

FIGURE 66-6 The Loftus shunt set. The set contains two shunts of differing diameters to allow for sizing preferences and a special scissors (disposable) to hook and cut the shunt cleanly for removal without damaging the back wall of the carotid. The shunt is a straight silicone tube beveled and rounded at both ends for safe insertion. A built-up bulb is present on the proximal (common carotid artery) end to anchor the shunt within the Rummel tourniquet.

FIGURE 66-7 The Loftus shunt in place. The shunt is secured at the common carotid artery end by a Rummel tourniquet and in the internal carotid artery by the Loftus shunt clamp. The black band indicates the center of the shunt and helps prevent unrecognized shunt migration (which should also be prevented by the fat bulb on the common carotid artery end anchored by the Rummel tourniquet).

With or without the shunt, the plaque is next dissected from the arterial wall with a Freer elevator. A vascular pickup is used to hold the wall, and the Freer elevator is moved from side to side developing a plane first in the lateral wall of the arteriotomy (Fig. 66-8). The plaque is usually readily separated in a primary case, and we go approximately half way around the wall before proceeding to the other side. The plaque is then dissected on the medial side of the CCA and transected proximally with a Potts or Church scissors. A clean feathering away of the plaque is almost never possible in the CCA, and the goal here is to transect the plaque sharply, leaving a smooth transition zone. We like to pass a right-angle clamp between the plaque and the normal vessel and cut sharply along the clamp blade with the no. 15 knife (Fig. 66-9). It is important to note that, despite the direction of flow, the proximal end point can create a flap and the surgeon should ensure that the CCA end point is adherent. Attention is then directed to the ICA where likewise the plaque is dissected first laterally and then medially and then an attempt is made to feather the plaque down smoothly from the ICA (Fig. 66-10). However, we find that, in some cases no matter how far up the ICA we go, a shelf of normal intima remains and tacking sutures are required. Attention is finally directed to the final point of plaque attachment at the orifice of the ECA. The vascular pickup is used to grip across the entire plaque at the ECA opening, and, with some traction on the plaque, the ECA can be everted such that the plaque can be dissected quite far up into that vessel (Fig. 66-11). The eversion of the external and thus optimal plaque removal can be facilitated by “pushing” the distal external artery proximally with the clamp or forceps. The plaque is often tethered in the ECA by the clamp and as long as the lumen is held closed with the heavy forceps, this clamp can be removed without untoward bleeding, allowing avulsion of the distal plaque. The clamp must be quickly reapplied to stem back-bleeding that occurs when the plaque is removed from the ECA. It should be stressed that if plaque removal is inadequate in the ECA, thrombosis may ensue, which can occlude the entire carotid tree with disastrous results. If there is any question of incomplete removal of the external plaque, we do not hesitate to extend the arteriotomy up the ECA itself and close it via a separate suture line.