Somatosensory Evoked Potentials and Electroencephalography during Carotid Endarterectomy Predict Late Stroke but not Death

Can NIRS be a surrogate indicator of elective shunt in carotid endarterectomy? A single-center observational retrospective study says no

BACKGROUND

Neuromonitoring during carotid endarterectomy (CEA) under general anesthesia is desirable and may be useful for preventing brain ischemia, but the selection of the most appropriate method remains controversial.

PURPOSE

To determine the effectiveness of near infrared spectroscopy (NIRS) compared to multimodality intraoperative neuromonitoring (IONM) in indicating elective shunts and predicting postoperative neurological status.

METHODS

This is a retrospective observational study including 86 consecutive patients with CEA under general anesthesia. NIRS and multimodality IONM were performed during the procedure. IONM included electroencephalography (EEG), somatosensory evoked potentials (SSEPs) and transcranial motor-evoked potentials (TcMEPs). Sensitivity, specificity, and positive and negative predictive values (PPV and NPV) were calculated for each neuromonitoring modality.

RESULTS

NIRS presented a sensitivity and a specificity for detecting brain ischemia of 77.7% and 89.6%, respectively (PPV = 46.6% and NPV = 97.2%). In contrast, a 100% sensitivity and specificity for multimodality IONM was determined (PPV and NPV = 100%). No significant difference (in demographical or clinical data) between "true positive" and "false-positive" patients was identified. Among the methods included in multimodality IONM, EEG showed the best results for predicting postoperative outcome after CEA (PPV and NPV=100%).

CONCLUSION

NIRS is inferior to multimodality IONM in detecting brain ischemia and predicting postoperative neurological status during CEA under general anesthesia.

Role of Intraoperative Neurophysiological Monitoring in Preventing Stroke After Cardiac Surgery

BACKGROUND

Perioperative stroke after cardiac surgical procedures carries significant morbidity. Dual intraoperative neurophysiological monitoring with electroencephalography (EEG) and somatosensory-evoked potentials detects cerebral hypoperfusion and predicts postoperative stroke in noncardiac procedures. We further evaluated preoperative risk factors and intraoperative neuromonitoring ability to predict postoperative stroke after cardiac operations.

METHODS

All patients who underwent cardiac operations with intraoperative neurophysiological monitoring from 2009 to 2020 at a single academic medical center were retrospectively analyzed. Patients with circulatory arrest were excluded. Risks factors analyzed were sex, age, tobacco use, hypertension, diabetes mellitus, dyslipidemia, atrial fibrillation, prior cerebrovascular accident, cerebrovascular disease, antiplatelet/anticoagulant use, abnormal somatosensory-evoked potentials and EEG baselines, and significant somatosensory-evoked potentials and EEG change as well as their permanence. Patients were divided into 2 groups by 30-day postoperative stroke occurrence. Univariate and multivariate logistical regressions were used for postoperative stroke significant predictors, and Kaplan-Meier curves estimated survival.

RESULTS

The study included 620 patients (67.6% men), mean age 65.1 ± 14.1 years, with stroke in 5.32%. In univariate analysis, diabetes (odds ratio [OR], 2.62) and permanence of EEG change (OR, 5.35) were each associated with increased postoperative stroke odds. In multivariate analysis, diabetes (OR, 2.64) and permanent EEG change (OR, 4.22) were independently significantly associated with postoperative stroke. Overall survival was significantly better for patients with no intraoperative neurophysiological monitoring changes (P < .005).

CONCLUSIONS

Permanent EEG change and diabetes were significant postoperative stroke predictors in cardiac operations. Furthermore, overall survival out to 10 years postoperatively was significantly higher in the group without intraoperative neurophysiological monitoring changes, emphasizing its important predictive role.

Which sites better represent the sensory function of hands in convalescent stroke patients? A study based on electrophysiological examination

Background

Assessing hand sensation in stroke patients is necessary; however, current clinical assessments are time-consuming and inaccurate.

Objective

This study aimed to explore the nature of light touch sensation and two-point discrimination (2-PD) of different hand sites in convalescent stroke patients based on somatosensory evoked potentials (SEP).

Methods

Light touch sensation and 2-PD of the thumb, the index finger, the little finger, thenar, and hypothenar were measured (n = 112) using sensory measurement tools. Sensory differences among the hand sites were then compared. The correlation analysis between SEP and the hemiplegic hand function was made. Sensory functions were divided into three levels: sensory intactness, sensory impairment, and sensory loss.

Results

Light touch sensations were mainly associated with sensory impairment in the finger and palm region. The 2-PD of the finger region was mainly sensory loss and that of the palm region was mainly sensory impairment. There was no statistical difference in the light touch sensation among the sites of the hand. The correlation coefficients between the 2-PD and SEP N20 amplitudes differed. The correlation coefficients of the thenar and hypothenar were the smallest, and that of the finger was the largest. Light touch sensation and 2-PD in patients with stroke were related to the hemiplegic hand function.

Conclusion

Any site on the hand could be selected as the measurement site for light touch sensation. The little finger and hypothenar may be appropriate sites when screening for 2-PD. To improve the patient's recovery they could receive more sensory stimulation of the hand.

Monitoring in carotid endarterectomy

Cerebral ischemia during carotid endarterectomy occurs via several mechanisms: inadequate collateral blood flow during carotid cross-clamping, thromboembolism due to carotid manipulation, and/or rethrombosis at the surgical site. Perioperative strokes increase not only the morbidity of endarterectomy but also its short- and long-term mortality. However, while several predictors of cerebral ischemia have been identified, precise individual risk is hard to assess. Since nonselective shunting during carotid cross-clamping is neither risk-free nor eliminates perioperative stroke, it is advisable to apply intraoperative monitoring techniques for detection and reversal of cerebral ischemia, which may occur at various stages of the procedure. This chapter addresses the methods available for monitoring, with an emphasis on neurophysiologic techniques, which are preferable given their direct assessment of how a decrease in cerebral blood flow impacts brain function. These include electroencephalography, somatosensory evoked potentials, and transcranial motor evoked potentials. Details regarding the methodology, advantages, disadvantages, and interpretation of these tests will be discussed within the anatomic, physiologic, surgical, and anesthetic contexts.

Intraoperative neurophysiologic monitoring during aortic arch surgery

OBJECTIVE

To evaluate the ability of intraoperative neurophysiologic monitoring (IONM) during aortic arch reconstruction with hypothermic circulatory arrest (HCA) to predict early (<48 hours) adverse neurologic events (ANE; stroke or transient ischemic attack) and operative mortality.

METHODS

This was an observational study of aortic arch surgeries requiring HCA from 2010 to 2018. Patients were monitored with electroencephalogram (EEG) and somatosensory evoked potentials (SSEP). Baseline characteristics and postoperative outcomes were compared according to presence or absence of IONM changes, which were defined as any acute variation in SSEP or EEG, compared with baseline. Multivariable logistic regression analysis was used to assess the association of IONM changes with operative mortality and early ANE.

RESULTS

A total of 563 patients underwent aortic arch reconstruction with HCA and IONM. Of these, 119 (21.1%) patients had an IONM change, whereas 444 (78.9%) did not. Patients with IONM changes had increased operative mortality (22.7% vs 4.3%) and increased early ANE (10.9% vs 2.9%). In multivariable analysis, SSEP changes were correlated with early ANE (odds ratio [OR], 4.68; 95% confidence interval [CI], 1.51-14.56; P = .008), whereas EEG changes were not (P = .532). Permanent SSEP changes were correlated with early ANE (OR, 4.56; 95% CI, 1.51-13.77; P = .007), whereas temperature-related SSEP changes were not (P = .997). Finally, any IONM change (either SSEP or EEG) was correlated with operative mortality (OR, 5.82; 95% CI, 2.72-12.49; P < .001).

CONCLUSIONS

Abnormal IONM events during aortic arch reconstruction with HCA portend worse neurologic outcomes and operative mortality and have a negative predictive value of 97.1%. SSEP might be more sensitive than EEG for predicting early ANE, especially when SSEP changes are permanent.

Anaesthesia and multimodality intraoperative neuromonitoring in carotid endarterectomy. Chronological evolution and effects on intraoperative neurophysiology

Contingency data was retrospectively collected to evaluate the historical and current ability to provide multimodality intraoperative neurophysiological monitoring during carotid endarterectomy under two conditions: total intravenous anaesthesia (TIVA) and low dose halogenated anaesthesia (SEVO). 229 patients were monitored during carotid endarterectomy procedures under general anaesthesia between 2012 and 2020. 121 Patients were monitored with SEVO at a minimum alveolar concentration less than 0.7 and 108 were monitored using TIVA, according to common anaesthetic practice standards in our hospital across the years. Multimodality IONM was established with electroencephalography, somatosensory evoked potentials and motor evoked potentials. As compared to TIVA, patients monitored with SEVO showed significantly higher motor evoked potential thresholds (313.52 ± 77.74 SEVO and 218.93 V ± 103.2 V TIVA p < 0.05) and lower reproducibility. Electroencephalography and somatosensory evoked potentials showed no significant differences among the groups. When using SEVO, multimodality intraoperative neurophysiological monitoring during carotid endarterectomy could mask or miss a motor isolated change in patients in spite of low dose minimum alveolar concentration and of apparently adequate electroencephalography and somatosensory evoked potentials for monitoring. Given these difficulties, we believe the chronological transfer to TIVA could have improved our ability to establish multimodality intraoperative neurophysiological monitoring during carotid endarterectomy in recent times.

Surgical Technique for Carotid Endarterectomy: Current Methods and Problems

Over the last 60 years, many reports have investigated carotid endarterectomy (CEA) and techniques have thus changed and improved. In this paper, we review the recent literature regarding operational maneuvers for CEA and discuss future problems for CEA. Longitudinal skin incision is common, but the transverse incision has been reported to offer minimal invasiveness and better cosmetic effects for CEA. Most surgeons currently use microscopy for dissection of the artery and plaque. Although no monitoring technique during CEA has been proven superior, multiple monitors offer better sensitivity for predicting postoperative neurological deficit. To date, data are lacking regarding whether routine shunt or selective shunt is better. Individual surgeons thus need to select the method with which they are more comfortable. Many surgical techniques have been reported to obtain distal control of the internal carotid artery in patients with high cervical carotid bifurcation or high plaque, and minimally invasive techniques should be considered. Multiple studies have shown that patch angioplasty reduces the risks of stroke and restenosis compared with primary closure, but few surgeons in Japan have been performing patch angioplasty. Most surgeons thus experience only a small volume of CEAs in Japan, so training programs and development of in vivo training models are important.

Temporary Reversal of Blood Flow During Transcarotid Artery Revascularization Does Not Change Brain Electrical Activity in Lead-In Cases of the ROADSTER 1 Multicenter Trial

Purpose: To evaluate any intraoperative electroencephalographic (EEG) changes accompanying reversed flow with the ENROUTE Transcarotid Neuroprotection System during transcarotid artery revascularization (TCAR). Methods: A post hoc analysis was performed of the first 81 consecutive lead-in patients (mean age 72.8±8 years; 61 men) enrolled in the ROADSTER 1 trial at 5 participating institutions. All patients had high-grade carotid artery stenosis [53 (59.3%) left sided; 12 (14.8%) contralateral occlusions] and high-risk criteria for carotid endarterectomy. A third had symptoms of either stroke (13, 16.0%) or transient ischemic attack (14, 17.3%). This subset of early patients underwent EEG monitoring to detect any cerebral changes during reversed flow as an added safety measure mandated by the ROADSTER 1 trial protocol. Results: Mean flow reversal time was 12.9±8.2 minutes. The goal mean arterial pressure during reversed flow was 100 mm Hg, but 7 (8.6%) patients suffered hypotension. One (1.2%) patient had slight EEG changes secondary to blood pressure fluctuation; these resolved with blood pressure elevation. No other EEG changes were noted. One (1.2%) patient had a postoperative stroke and another (1.2%) had postoperative myocardial infarction (MI), leading to 2.5% 30-day stroke/death/MI rate. Conclusion: Temporary reversal of blood flow during TCAR is a safe maneuver and does not cause cerebral ischemia in the vast majority of patients, including those with contralateral carotid occlusion. Carotid stenting performed with reversed blood flow mitigates cerebral embolization and periprocedural stroke without concern for brain ischemia.

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.