Monitoring of somatosensory evoked potentials during carotid endarterectomy

A systematic review & meta-analysis on perioperative cerebral and hemodynamic monitoring methods during carotid endarterectomy

OBJECTIVE

To compare outcomes between different strategies of perioperative cerebral and hemodynamic monitoring during carotid endarterectomy.

DATA SOURCES

MEDLINE, EMBASE, CINAHL, and Cochrane CENTRAL databases were searched.

METHODS

This review was performed according to the PRISMA guidelines and prospectively registered in the international prospective register of systematic reviews (CRD42021241891). The GRADE approach was used to describe the methodological quality of the studies and certainty of the evidence. The primary outcome was 30-day stroke rate. Secondary outcomes measures are 30-day ipsilateral stroke, 30-day mortality, shunt rate and complication rates.

RESULTS

The search identified 3 460 articles. Seventeen RCTs, three prospective observational studies and seven registries were included, reporting on 236 983 patients. The overall pooled 30-day stroke rate is 1.8% (95% CI 1.4 - 2.2%), ranging from 0 - 12.6%. In RCT's the pooled 30-day stroke rate is 2.7% (95% CI 1.6 - 3.7%) compared to 1.3% (95%CI 0.8 - 1.8%) in the registries. The overall stroke risk decreased from 3.7% before the year 2000 to 1.6% after 2000. No significant differences could be identified between different monitoring and shunting strategies, although a trend to higher stroke rates in routine no shunting arms of RCTs was observed. Overall 30-day mortality, myocardial infarction and nerve injury rates are 0.6% (95%CI 0.4 - 0.8), 0.8% (95%CI 0.6-1.0) and 1.3% (95%CI 0.4-2.2), respectively.

CONCLUSIONS

No significant differences between the compared shunting and monitoring strategies are found. However, routine no shunting is not recommended. The available data is too limited to prefer one method of neuromonitoring over another method when selective shunting is applied.

Motor evoked potential monitoring can evaluate ischemic tolerance to carotid artery occlusion during surgery

Balloon test occlusion (BTO) is a useful examination for evaluating ischemic tolerance to internal carotid artery (ICA) occlusion. The aim of this study was to investigate the relationships between intraoperative motor evoked potential (MEP) monitoring and the results of preoperative BTO. Between 2013 and 2017, 32 patients undergoing surgery under general anesthesia with intraoperative MEP monitoring, in whom preoperative BTO was performed, were identified. A receiver operator characteristic (ROC) analysis was performed to determine the appropriate cutoff value of MEP amplitude for BTO-positive. Furthermore, the accuracy of MEP monitoring for BTO-positive was compared with electroencephalogram (EEG) and somatosensory evoked potential (SEP) monitoring. Four of 32 (12.5%) patients were BTO-positive. The cutoff value of MEP amplitude for BTO-positive was a > 80% reduction from the baseline level, which showed sensitivity of 100% and specificity of 100%. Thus, the sensitivity and specificity for BTO-positive were significantly higher for MEP than for EEG (100% and 72.0%, p = 0.02) in 28 patients, but they were not significantly different compared with SEP (33.3% and 100%, p = 0.48) in 21 patients. MEP monitoring might be one of the alternatives for evaluating ischemic tolerance to ICA occlusion during surgery. The cutoff value of MEP amplitude was a > 80% reduction.

The Effect of Xenon-Based Anesthesia on Somatosensory-Evoked Potentials in Patients Undergoing Carotid Endarterectomy

OBJECTIVES

The aim of this study was to investigate the influence of xenon-based anesthesia on somatosensory-evoked potentials.

DESIGN

Observational cohort study.

SETTING

University hospital.

PARTICIPANTS

Twenty subsequent adult patients undergoing elective carotid endarterectomy.

INTERVENTIONS

Xenon-based anesthesia.

MEASUREMENTS AND MAIN RESULTS

Cortical-evoked responses to median nerve stimulation were quantified by measurement of the amplitude and latency of the N20 wave, which are typically assessed during carotid surgery to detect intraoperative cerebral hypoperfusion and ischemia. Primary (N20 amplitude and latency) and secondary (mean arterial pressure, norepinephrine requirements and depth of anesthesia) were assessed during (1) propofol/remifentanil and (2) subsequent xenon/remifentanil anesthesia. Xenon at an inspiratory fraction of 62.5 ± 7% decreased norepinephrine requirement (0.067 ± 0.04 v 0.028 ± 0.02 µg/kg/min, p < 0.001), and mean arterial pressure was unchanged (90.6 ± 15.0 v 93.1 ± 9.6 mmHg, p = 0.40). Somatosensory-evoked potentials were available in all patients during xenon/remifentanil. Despite similar depth of anesthesia (Narcotrend index 38.4 ± 6.2 v 38.5 ± 5.8) during propofol and xenon, N20 amplitude was reduced after xenon wash-in from 3.7 ± 1.7 to 1.4 ± 2.8 µV, p < 0.001 on the surgical and 3.6 ± 1.6 to 1.4 ± 0.6 µV, p < 0.001 on the contralateral side. N20 latency remained unchanged during xenon (22.9 ± 2.1 v 22.5 ± 2.8 ms, p = 0.34 and 22.9 ± 2.0 v 22.9 ± 3.0, p = 0.97).

CONCLUSIONS

Xenon influences somatosensory-evoked potentials measurement by reducing N20 wave amplitude but not latency. When xenon is considered as an anesthetic for carotid endarterectomy, wash-in needs to be completed before carotid surgery is commenced to provide stable baseline somatosensory-evoked potential measurement.

Across the consciousness continuum-from unresponsive wakefulness to sleep

Advances in the development of new paradigms as well as in neuroimaging techniques nowadays enable us to make inferences about the level of consciousness patients with disorders of consciousness (DOC) retain. They, moreover, allow to predict their probable development. Today, we know that certain brain responses (e.g., event-related potentials or oscillatory changes) to stimulation, circadian rhythmicity, the presence or absence of sleep patterns as well as measures of resting state brain activity can serve the diagnostic and prognostic evaluation process. Still, the paradigms we are using nowadays do not allow to disentangle VS/UWS and minimally conscious state (MCS) patients with the desired reliability and validity. Furthermore, even rather well-established methods have, unfortunately, not found their way into clinical routine yet. We here review current literature as well as recent findings from our group and discuss how neuroimaging methods (fMRI, PET) and particularly electroencephalography (EEG) can be used to investigate cognition in DOC or even to assess the degree of residual awareness. We, moreover, propose that circadian rhythmicity and sleep in brain-injured patients are promising fields of research in this context.

[Intraoperative electrophysiological monitoring with evoked potentials]

During the last 30 years intraoperative electrophysiological monitoring (IOEM) has gained increasing importance in monitoring the function of neuronal structures and the intraoperative detection of impending new neurological deficits. The use of IOEM could reduce the incidence of postoperative neurological deficits after various surgical procedures. Motor evoked potentials (MEP) seem to be superior to other methods for many indications regarding monitoring of the central nervous system. During the application of IOEM general anesthesia should be provided by total intravenous anesthesia with propofol with an emphasis on a continuous high opioid dosage. When intraoperative MEP or electromyography guidance is planned, muscle relaxation must be either completely omitted or maintained in a titrated dose range in a steady state. The IOEM can be performed by surgeons, neurologists and neurophysiologists or increasingly more by anesthesiologists. However, to guarantee a safe application and interpretation, sufficient knowledge of the effects of the surgical procedure and pharmacological and physiological influences on the neurophysiological findings are indispensable.