Optimal Outcome for “High-Risk” Carotid Endarterectomy

Thomas Anthony, MD, Kaj Johansen, MD, Se&e. Washin~ron

Wbile carotid endarterectomy (CEA) can often be accomplished with a very low stroke risk, certain scenario+prior ipsilateral stroke, con- tralateral carotid occlusion, or acute cerebral is- chemia-have been associated with neurologic morbidity and mortality rates exceeding 10%. The routine use of temporary intral&al carotid shunts has been thought to be obligatory in such patients, notwithstanding the fact that these devices are obtrusive and may be associ- ated with an increased risk of perioperative stroke. Among 175 patients undergoing CEA, 68 could be &ssi&d as “high-risk” (contralat- eral carotid occlusion, n = 24; prior ipsilateral stroke, n = 28; acute cerebral ischemia, n = 16). CEA was performed under regional or local anesthetic block in all 68 patients. Sixty-six pa- tients (97%), ineluding 22 of 24 (92%) with contralateral carotid occlusion, underwent CEA (carotid occlusion times averaging 22 minutes [range: 12 to 42 minutes]) without insertion of a carotid shunt. Two patients (2.9%) with con- tralateral carotid occlusion lost consciousness 7 and 10 minutes after carotid clamping, but re- gained neurologic normalcy after shunt inser- tion. A single patient (1.5%) experienced a fatal stroke due to heparin-induced “white clot” syn- drome. Rates of shunt insertion and of perioper- ative stroke did not differ from those in 107 “low-risk” CEA patients.

Cerebral collateral circulation is well developed even in compromised CEA patients. The neces- sity for temporary carotid shunts may be re- duced by the use of “awake” anesthesia in such cases. Carotid shunting may be no more neces- sary, and operative outcome no less favorable, in “high-risk” than in uncomplicated CEA patients.

e T”

goal of carotid endarterectomy (CEA) is to minimize the risk of future stroke. To maximize the benefits of

CEA, the procedure must be performed with an absolute min- imum of perioperative neurologic morbidity and mortality.

Patients undergoing CEA may be separated into two risk groups based on the natural history of the untreated disease and the risk of perioperative neurologic complications. The lower-risk category includes patients with transient is-

From the Department of Surgery, University of Washington Affiliated Hospitals, Seattle, Washington.

Requests for reprints should be addressed to Kaj Johansen, MD, PhD, Providence Medical Center, P.O. Box 34008, Seattle, Washington 98 124.

Presented at the 80th Annual Meeting of the North Pacific Surgical Association, Vancouver. British Columbia, Canada, November 12-l 3, 1993.

chemic attacks (TIAs) refractory to medical management and those with asymptomatic carotid stenosis. In such pa- tients the risk of stroke varies between 1% to 8% per yeare5; perioperative stroke risk varies from 0% to 5%.3-5

Patients who have contralateral occlusion of the internal carotid artery (ICA), prior major or recent ipsilateral stroke, stroke-in-evolution, reversible ischemic neurologic deficits (RINDS), or “crescendo” TIAs are considered to be at higher risk: such patients’ annual stroke incidence varies from 8% to more than 40%.6-‘o Ideally, these would be the patients most likely to benefit from CEA. Unfortunately, this population of patients is also at high- est risk for perioperative neurologic deficits: numerous studies have found such patients’ perioperative stroke risk to be in excess of 10%.9-‘2 To improve the efficacy of CEA in these high-risk patients, it would be useful to adopt a treatment strategy that identifies potentially controllable sources of perioperative neurologic morbidity.

Inadequate cerebral collateral blood flow is thought to be the common denominator predisposing high-risk CEA pa- tients to perioperative neurologic complications. Many strategies have been adopted to assure cerebral perfusion during carotid clamping and thereby decrease the risk of stroke. Routine carotid shunting should theoretically be highly effective as a means of overcoming inadequate cere- bral collateral flow; excellent results are possible with this technique, leading some vascular surgeons to conclude that shunts are obligatory in such compromised CEA patients.’ ’

In an attempt to evaluate the adequacy of cerebral col- lateral flow in these high-risk individuals, and to determine whether or not “high-risk” CEA patients require tempo- rary shunts, we have reviewed our own experience with such patients.

PATIENTS AND METHODS We retrospectively reviewed the records of 175 consec-

utive patients undergoing CEA under local or regional anesthesia in the past decade. High-risk individuals were identified as those with contralateral occlusion and ipsi- lateral high-grade stenosis, prior major cerebral stroke referable to an ipsilateral carotid stenosis, or signs of acute ischemia (stroke-in-evolution, RIND, or crescendo TIAs). CEA was performed utilizing local or regional (“awake”) anesthesia. Carotid arteriotomy was performed following demonstration of neurologic normalcy after 1 minute of carotid occlusion; an intra-arterial shunt was inserted only when a change in consciousness or motor function was noted. The operations were performed by senior surgical residents supervised by a single vascular surgeon. We com- pared outcome and the necessity for shunt insertion in high-risk CEA patients versus all other (“low-risk”) CEA patients in this series, using chi-square analysis and as- suming statistical significance for P <O.OS.

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“HIGH-RISK” CAROTID ENDARTERECTOMY/ANTHONY AND JOHANSEN

TABLE

“High-risk” CEA “Low-risk” CEA

Comparison of High-Risk and Low-Risk CEA Patients

n No shunts (%) Shunts (%) Stroke (%)

68 66/68 (97.1) 2/68 (2.9) l/68 (1.5) 107 104/107 (97.2) 3/107 (2.8) l/107 (0.9)

RESULTS We identified 68 “high-risk” CEA patients. Twenty-eight

of these patients had prior ipsilateral stroke; 24 patients had contralateral occlusion (documented by either duplex scan- ning, 4-vessel cerebral angiography, or both); 16 patients had crescendo TIAs, a RIND, or stroke-in-evolution. One hundred seven CEA patients did not meet these criteria and are termed “low-risk.” Results are listed in the Table.

Of the 68 “high-risk” patients, none required conversion to general anesthesia. Sixty-six patients (97%) underwent uneventful CEA without change in neurologic status or in- sertion of a carotid shunt. This included all 28 (100%) pa- tients with prior ipsilateral stroke, 22 of 24 (92%) of those with contralateral carotid occlusion, and all 16 (100%) with acute cerebral ischemia. Mean cross-clamp time was 22 minutes (range: 12 to 42 minutes).

Two “high-risk” patients required insertion of a tempo- rary carotid shunt. Both had contralateral carotid occlusion and high-grade ipsilateral stenosis. In both these patients (2.9% of all “high-risk” CEA patients and 8.3% of those with contralateral carotid occlusion) operation began with- out the use of a shunt. However, at 7 and 10 minutes af- ter cross-clamping, loss of consciousness developed. After expeditious placement of an intraarterial shunt, both re- gained consciousness and CEA proceeded without com- plication. Both of these patients had an uneventful post- operative course.

The single death among “high-risk” CEA patients oc- curred in a patient with contralateral carotid occlusion and ipsilateral high-grade carotid stenosis. He developed hep- arm-induced “white-clot” syndromeI with recurrent thrombosis of the entire ICA. Despite numerous attempts at thrombectomy and repair, the patency of the carotid artery could not be maintained; the patient sustained a large ipsilateral hemispheric stroke resulting in death on the sec- ond postoperative day. This resulted in a combined stroke/death rate of 1.5% for this series.

satisfactory endarterectomy, most surgeons would agree that the two most important factors under surgical control during CEA are maintenance of adequate intraoperative cerebral blood flow and prevention of embolic events.

One solution which should guarantee adequate cerebral perfusion during carotid artery clamping might be the rou- tine insertion of a temporary shunt, an approach champi- oned by some.14’15 Such an approach relieves the surgeon of the need to utilize complex intraoperative monitoring technologies to assure adequate cerebral perfusion: rou- tine carotid shunting reduces the urgency to complete the CEA, and presence of a shunt may help ensure that arte- riotomy closure will not unduly narrow the ICA.

On the other hand, shunts are sometimes difficult to in- sert, and may be obtrusive. Most importantly, they may malfunction, resulting in thrombosis of the carotid artery or embolization into the brain. Halsey, writing for the International Transcranial Doppler Study Group, noted among CEA patients without severe clamp-induced cere- bral ischemia an 8.8% incidence of intraoperative stroke when shunts were used, in contrast to a 2.1% incidence in nonshunted patients (P <O.OOl). The conclusion is un- avoidable from this study that risk of intraoperative stroke, presumably on an embolic basis, rises with carotid shunt insertion.

Among “low-risk” CEA patients, three (2.8%) required shunt insertion-each because of loss of consciousness or contralateral motor function within the first minute fol- lowing carotid cross-clamping. Each patient regained neu- rologic normalcy following shunt insertion. One patient (0.9%) experienced a mild postoperative stroke due to ICA thrombosis. No significant difference was determined be- tween “high-risk” and “low-risk” CEA patients in terms of shunt use (2.9% versus 2.8%, P N.99) or perioperative stroke (1.5% versus 0.9%, P >0.60).

COMMENTS To minimize the risk of perioperative neurologic com-

plications during CEA, a thorough understanding of their etiology is necessary. Presuming an otherwise technically

Most surgeons shunt CEA patients selectively, utilizing one of numerous monitoring technologies to assure ade- quate cerebral perfusion during cross-clamping of the carotid artery. Carotid stump pressure measurement, jugu- lar vein oxygen saturation, computer analyzed EEG, trans- cranial Doppler, regional cerebral blood flow determina- tion, and others have all been advocated. None of these techniques has clearly emerged as superior; in fact, each has been found occasionally to provide inaccurate infor- mation, leading some patients with adequate cerebral per- fusion to receive a shunt, while others needing a tempo- rary shunt fail to have one inserted.3~y~‘7~‘s

An alternative technique which allows direct, continu- ous, accurate monitoring of neurologic functioning is the use of local/regional (“awake”) anesthesia during CEA. Multiple series of patients undergoing CEA under “awake” anesthesia have been reported, with excellent results.5,1X-22 CEA performed in this fashion also appears to result in lower rates of postoperative blood pressure lability as well as shorter hospitalization.23

Given the crucial importance of assuring adequate cere- bral blood flow while preventing shunt-associated cerebral ischemia, we believe that the most effective CEA strategy in high-risk patients incorporates the use of “awake” anes- thesia, with selective use of shunts for those few patients (2.9% in our series) who develop neurologic deficits after cross-clamping. Our results compare favorably with pub-

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“HlC,H-RISK” CAROTID ENDARTERECTOMY /ANTHONY AND JOHANSEN ___ _ __ ____. -. .._ __._~.~~.

lished series concerning the performance of CEA in low- or high-risk individuals, and suggest at the least that em- piric or anatomic criteria indicating the necessity for carotid shunt insertion may not be accurate.

We have shown that surprisingly few CEA patients con- ventionally considered to be at high risk because of criti- cally-reduced cerebral collateral circulation actually de- velop neurologic deficits during carotid cross-clamping. While some series suggest that, in the presence of con- tralateral carotid occlusion, a shunt is needed in up to 46% of cases,22,24-26 other series, like ours, demonstrate that 85% to 100% of such patients can undergo CEA without shunt insertion.3.20*2’.27 These results imply development of a ro- bust cerebral collateral circulation in the vast majority of even “high-risk” CEA patients: intraarterial shunting may be no more necessary in such patients than in lower-risk, uncomplicated CEA patients. A diminished use of shunts in high-risk patients may reduce the rate of perioperative neurologic morbidity and maximize the favorable outcome of CEA in these patients.

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