Prediction of Cerebral Ischemic Tolerance During Carotid Cross-clamping by Angiographic Criteria

Predictors of cross-clamp-induced intraoperative monitoring changes during carotid endarterectomy using both electroencephalography and somatosensory evoked potentials

OBJECTIVE

The efficacy of selective shunting during carotid endarterectomy (CEA) using intraoperative monitoring (IOM) for detection of cerebral ischemia is well established. There is mounting evidence that monitoring of both electroencephalography (EEG) and somatosensory evoked potentials (SSEPs) increases the sensitivity of cerebral ischemia detection. Predictors of cerebral ischemia requiring selective shunt placement using IOM of both EEG and SSEPs have not been previously identified.

METHODS

Consecutive patients who underwent CEA between January 1, 2000, and December 31, 2010, were retrospectively analyzed. Primary end points were IOM changes at any time during the operation or IOM changes with carotid cross-clamping. Risk factors assessed included demographics; baseline comorbidities; severity of ipsilateral and contralateral disease; symptomatic status; and use of statin, antiplatelet, and beta-blocker medications. Univariate and multivariate logistic regression was used for analysis.

RESULTS

During the 11-year study period, a total of 758 patients underwent 804 CEAs (mean age, 70.6 ± 9.5 years; 59.8% male; 39.2% symptomatic) using IOM of both SSEPs and EEG for selective shunting guidance. Postoperative stroke rate was 1.37%; 27.1% of patients had significant SSEP or EEG changes, and 49.1% of these were clamp induced (within 5 minutes of cross-clamping). Of these patients, 83.2% received a shunt (11.4% overall). The most common reason that a shunt was not placed after cross-clamp-induced changes was that the changes resolved with further blood pressure elevation (8 of 17 patients). Clamp-induced IOM changes were predictive of postoperative stroke (odds ratio [OR], 5.5; P = .005). Risk factors for clamp-induced IOM changes were contralateral carotid occlusion (OR, 2.5; P = .01), symptomatic stenosis (OR, 1.8; P = .006), and diabetes (OR, 1.6; P = .03), whereas there was a trend toward increased risk with female sex (OR, 1.5; P = .08). Risk factors for any IOM change (clamp and nonclamp induced) were symptomatic carotid stenosis (OR, 1.8; P < .001), use of beta blockers (OR, 1.5; P = .03), and female sex (OR, 1.5; P = .02).

CONCLUSIONS

Whereas some patients can be expected to experience IOM changes by monitoring of SSEPs and EEG, a much smaller percentage will receive a shunt. Contralateral carotid occlusion, symptomatic stenosis, diabetes, and female sex increase the risk of clamp-induced IOM changes and should be anticipated to need a shunt. Patients receiving beta blockers are likely to experience IOM changes during the operation that are not associated with clamping.

Interaction of cerebrovascular disease and contralateral carotid occlusion in prediction of shunt insertion during carotid endarterectomy

INTRODUCTION

To assess the possible role and the interaction of cerebrovascular disease and vascular stenosis on the necessity of shunt insertion during carotid endarterectomy (CEA).

MATERIAL AND METHODS

Eighty consecutive patients undergoing CEA under regional anaesthesia were prospectively enrolled. Patients were divided into two groups depending on whether they were shunted or not. The measured end-points were co-morbidities degree of contralateral and carotid stenosis and other intra- and postoperative outstanding parameters. ANOVA, Student's t and χ(2) tests were used (p<0.05). Variables differing significantly between groups and potential confounders were used in backward stepwise logistic regression to estimate the relative risk (RR, 95% CI) of shunt. In addition Wald's test (p<0.05) with and without adjustments for potential confounders was used with various different multivariate analysis models.

RESULTS

Contralateral stenosis and cerebral vascular accidents (CVA) were more frequently observed in shunted patients. The RR for patients with contralateral stenosis ≥ 50% was 1.3 (95% CI 1.0-1.5) and for patients with previous CVA was 1.2 (95% CI 1.0-1.4). For contralateral stenosis and CVA together the RR increased to 7.7 (95% CI 1.0-14.4). A model based on contralateral stenosis and CVA was found to be statistically significant (p=0.003) for shunt (RR=1.1, 95% CI 1.0-2.1). Relative excess risk due to interaction of both factors was 6.2.

CONCLUSIONS

The findings suggest that patients with contralateral stenosis ≥ 50% and previous CVA have a higher risk of requiring shunt use during CEA than patients with these risk factors separately.

The Hypothesis Regarding the Benefit of Carotid Endarterectomy Under Locoregional Anesthesia in Prevention of Stroke May be Unanswered

A recent trial attempted to investigate the role of locoregional anesthesia (LA) in carotid endarterectomy (CEA) compared with general anesthesia. The hypothesis regarding the advantage of LA is based on the intraprocedural neurologic evaluation and the early identification of neurologic deficit. The trial has not demonstrated the superiority of the rocoregional anesthesia versus general anesthesia and revealed equal results concerning the prevention of stroke. We analyze the reasons which explain why the hypothesis regarding the advantage of LA in CEA, in comparison to general anesthesia cannot be answered.

Stump pressure and somatosensory evoked potentials for predicting the use of shunt during carotid surgery

The aim of this study is to compare measurement of stump pressure (SP) and somatosensory evoked potentials (SSEP) made during carotid surgery as criteria upon which to base the decision whether or not to use a shunt. We included 288 patients who underwent for carotid surgery under general anaesthesia. We performed 247 endarterectomies with patch closure (85.7%), 25 carotid transsection with reimplantation (8.7%), and 16 carotid bypasses (5.6%). SSEP monitoring showed no modification in 225/288 patients (78.1%), moderate modification in 32/288 patients (11.1%), and severe modification in 31/288 patients (10.8%). Shunt was used if there was moderate or severe SSEP modification in response to carotid clamping, which represents 63 patients in our series. A shunt was used in 47/288 patients (16.3%). In 16 patients, despite SSEP modifications, the shunt was not used because these SSEP modifications occurred only in the last minutes of the procedure just before off clamping the carotid. The mean SP for all patients was 51 mm Hg. In the shunted patients, the mean SP was 33 mm Hg. Variation of SP was correlated with the SSEP modifications. There was just one perioperative stroke in this series (1/288 = 0.3%). We concluded that the threshold of SP below which shunting is indicated in our study was 44 mm Hg with 81% sensibility and 68% specificity.

Increased incidence of cerebral clamping ischemia during early contralateral carotid endarterectomy

OBJECTIVES

The aim of our study was to assess the influence of previous contralateral carotid endarterectomy (CEA) and of the timing of the procedures on cerebral clamping ischemia during the second operation in patients undergoing staged bilateral CEA.

METHODS

We reviewed the 251 patients who presented with bilateral carotid stenosis of > or =70% at the time of the first admission and underwent staged bilateral CEA between January 2001 and December 2004. Surgery was performed under locoregional anesthesia. Cerebral perfusion was monitored with mental status and contralateral motor function evaluation in awake patients. Selective carotid shunting was performed for patients who manifested neurologic deficits. Univariate and multivariate analyses were performed for the variables of interest.

RESULTS

Twenty-two patients (8.8%) required carotid shunting during the first procedure and 28 (11.1%) during the second one. Nine of the latter also had shunts during the first CEA, whereas 19 tolerated cross-clamping during the first operation. Among the patients who underwent contralateral CEA < or =30 days, 23 of 146 required carotid shunting; between 31 and 60 days, 4 of 73; and after 61 days, 1 of 32 (P = .023; univariate analysis). The chi2 for trend was statistically significant (P = .009). Patients operated on the second side < or =30 days had a nearly fourfold risk of shunting during the second procedure compared with patients operated on > or =31 days. The highest risk was observed in patients with a shunt during the first operation who underwent the second CEA < or =30 days. Multivariate analysis also identified the time intervals between CEAs and the need of shunting during the first procedure as independent risk factors (P = .042 and P < .001).

CONCLUSIONS

These data show an increased incidence of cerebral clamping ischemia during contralateral endarterectomy performed < or =30 days; whereas after longer intervals between CEAs, the need for shunting is significantly reduced.

Review of developments in anesthesia for carotid endarterectomy

PURPOSE OF REVIEW

Analysis of recent data indicates a clear benefit of carotid endarterectomy for symptomatic patients with high-grade carotid artery stenosis, and a marginal benefit for asymptomatic patients. Despite myriad challenges presented by patients undergoing carotid endarterectomy, excellent outcomes have been achieved and many centers have shown the technique to be safe as an outpatient procedure for specific populations. Greater attention to comorbidities and their management in the perioperative period is increasingly important as older and more complex patients present for invasive treatment of carotid disease. Scientific study aimed at defining which characteristics merit our attention will only lead to improved outcomes and greater understanding of carotid disease, endarterectomy and anesthesia. While controversial, the efficacy, safety, and durability of stenting and angioplasty have improved in recent years. Potential advantages of stenting and angioplasty of the carotid artery include avoiding cranial nerve damage, wound hematoma, and general anesthesia. Staying abreast of the science regarding such endovascular therapies will be increasingly important.

RECENT FINDINGS

The major areas of investigative interest include patient selection, anesthetic technique, and monitoring for carotid endarterectomy, and durability of stenting and angioplasty of the carotid artery.

SUMMARY

Patients with significant comorbidities may be managed safely by a variety of anesthetic techniques. Maintaining hemodynamic stability and monitoring cerebral oxygen delivery remain important goals of perioperative management. Recent data regarding the durability and safety of stenting and angioplasty of the carotid artery suggest that outcomes may approach those of carotid endarterectomy.