Somatosensory Evoked Potentials versus Locoregional Anaesthesia in the Monitoring of Cerebral Function During Carotid Artery Surgery: Preliminary Results of a Prospective Study

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.

Effects of regional anesthesia techniques on local anesthetic plasma levels and complications in carotid surgery: a randomized controlled pilot trial

BACKGROUND

The ultrasound guided intermediate cervical plexus block with perivascular infiltration of the internal carotid artery (PVB) is a new technique for regional anesthesia in carotid endarterectomy (CEA). We conducted a pilot study investigating the effects of deep cervical block (DCB), intermediate cervical block alone (ICB) and PVB on perioperative complications in patients undergoing elective CEA. We hypothesized, that the ropivacaine plasma concentration is higher in patients receiving DCB compared to PVB and ICB.

METHODS

In a randomized controlled pilot study thirty patients scheduled for elective CEA were randomly assigned into three groups: DCB receiving 20 mL ropivacaine 0.5% (n = 10), ICB receiving 20 mL ropivacaine 0.5% (n = 10) and PVB receiving 20 mL ropivacaine 0.5% and 10 mL ropivacaine 0,3% (n = 10). As primary outcome, plasma levels of ropivacaine were measured with high performance liquid chromatography before, 5, 10, 20, 60, and 180 min after the injection of ropivacaine. Secondary outcomes were vascular and neurological complications as well as patients' and surgeons' satisfaction. All analyses were performed on an intention-to-treat basis. Statistical significance was accepted at p < 0.05.

RESULTS

No conversion to general anesthesia was necessary and we observed no signs of local anesthetic intoxication or accidental vascular puncture. Plasma concentration of ropivacaine was significantly higher in the DCB group compared to PVB and ICB (p < 0.001) and in the PVB group compared to ICB (p = 0.008). Surgeons' satisfaction was higher in the PVB group compared to ICB (p = 0.003) and patients' satisfaction was higher in the PVB group compared to ICB (p = 0.010) and DCB group (p = 0.029). Phrenic nerve paralysis was observed frequently in the DCB group (p < 0.05). None of these patients with hemi-diaphragmatic paralysis showed signs of respiratory distress.

CONCLUSION

The ultrasound guided PVB is a safe and effective technique for CEA which is associated with lower plasma levels of local anesthetic than the standard DCB. Considering the low rate of complications in all types of regional anesthesia for CEA, larger randomized controlled trials are warranted to assess potential side effects among the blocks.

TRIAL REGISTRATION

The trial was registered at German Clinical Trials Register (DRKS) on 04/05/2019 (DRKS00016705, retrospectively registered).

Intraoperative management of carotid endarterectomy

First reports on surgical treatment of cerebrovascular atherosclerosis date to the early 1950s. With advancements in surgical technique, carotid endarterectomy (CEA) has become the treatment of choice for patients with both symptomatic and asymptomatic severe carotid stenosis. Given the benefits that surgery offers beyond medical management, the number of CEA procedures continues to increase. The intraoperative management of patients undergoing CEA is challenging because of the combination of patient and surgical factors. This article explores and reviews the literature on anesthetic management and considerations of patients undergoing CEA.

[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.

The role of somatosensory evoked potentials in detecting cerebral ischaemia during carotid endarterectomy

BACKGROUND AND OBJECTIVE

The generation of shunt criteria by somatosensory evoked potentials is controversial. This study was designed to validate somatosensory evoked potentials' tracings and their derived shunt criteria compared with clinical-neurological examination.

METHODS

We prospectively studied the somatosensory evoked potentials' tracing in 102 patients who underwent carotid endarterectomy under cervical plexus blockade, comparing different somatosensory evoked potentials' derived thresholds of impaired cerebral blood flow with the neurological examination.

RESULTS

The 50% reduction of the primary cortical response to median nerve stimulation as threshold of critical cerebral blood flow showed a sensitivity of 87% and a specificity of 66%. In case of total collapse of primary cortical response, we observed a sensitivity of 85% and a specificity of 89%. Concerning the prolongation of central conduction time between the spinal response at N13 and the cortical response at N20/P25 as critical threshold of impaired cerebral blood flow, the sensitivity was 87% and specificity 40%. The need-to-shunt index with its threshold at >0.5 showed a sensitivity of 85% and a specificity of 88%.

CONCLUSION

Compared to other studies, we have shown a much lower sensitivity and specificity of somatosensory evoked potentials in detecting critical cerebral perfusion; thus its use remains controversial and has to be assessed in further investigations.

SELECTIVE VERSUS ROUTINE INTRAOPERATIVE SHUNTING DURING CAROTID ENDARTERECTOMY

OBJECTIVE

The use of intraluminal shunting during carotid endarterectomy (CEA) remains controversial. Over the years, different shunting strategies have been used. More recently, the use of intraoperative electroencephalography and somatosensory evoked potential monitoring with selective intraluminal shunting has been explored. No studies have assessed the independent association of selective versus routine intraluminal shunting to outcomes after CEA.

METHODS

The clinical and radiological records of all patients undergoing CEA from 1994 to 2006 at an academic institution were reviewed retrospectively to assess outcomes at 72 hours. The independent association of selective intraluminal carotid artery shunting during CEA and perioperative stroke within 72 hours was assessed through multivariate logistic regression analysis.

RESULTS

In 1411 patients with both symptomatic and asymptomatic extracranial carotid artery disease, there were a total of 49 (3.5%) perioperative strokes after CEA. There were two (1%) cases of perioperative strokes among 194 patients in the selective shunting group compared with 47 out of 1217 (4%) in the routine shunting group (P = 0.04). Symptomatic carotid artery disease was associated with a twofold increase in the odds of experiencing perioperative stroke (odds ratio, 1.95; 95% confidence interval, 1.08–3.52; P = 0.03). Patients undergoing electrophysiological monitoring with selective intraluminal carotid artery shunting were more than seven times less likely to experience a perioperative stroke (odds ratio, 0.05; 95% confidence interval, 0.01–0.40; P &lt; 0.01). Increasing cumulative surgical volume, particularly more than 200 total cases, was associated with more than a twofold decrease in perioperative stroke (odds ratio, 0.38; 95% confidence interval, 0.20–0.74; P &lt; 0.01).

CONCLUSION

Regardless of symptomatic carotid artery disease or cumulative surgical volume, patients undergoing CEA with intraoperative electroencephalography and somatosensory evoked potential monitoring with selective intraluminal carotid artery shunting had a stroke rate lower than that of the routine shunting group. Selective shunting based on electroencephalography and somatosensory evoked potential monitoring may be superior to the nonselective strategy.

Superficial or deep cervical plexus block for carotid endarterectomy: a systematic review of complications †

Carotid endarterectomy is commonly conducted under regional (deep, superficial, intermediate, or combined) cervical plexus block, but it is not known if complication rates differ. We conducted a systematic review of published papers to assess the complication rate associated with superficial (or intermediate) and deep (or combined deep plus superficial/intermediate). The null hypothesis was that complication rates were equal. Complications of interest were: (1) serious complications related to the placement of block, (2) incidence of conversion to general anaesthesia, and (3) serious systemic complications of the surgical-anaesthetic process. We retrieved 69 papers describing a total of 7558 deep/combined blocks and 2533 superficial/intermediate blocks. Deep/combined block was associated with a higher serious complication rate related to the injecting needle when compared with the superficial/intermediate block (odds ratio 2.13, P = 0.006). The conversion rate to general anaesthesia was also higher with deep/combined block (odds ratio 5.15, P < 0.0001), but there was an equivalent incidence of other systemic serious complications (odds ratio 1.13, P = 0.273; NS). We conclude that superficial/intermediate block is safer than any method that employs a deep injection. The higher rate of conversion to general anaesthesia with the deep/combined block may have been influenced by the higher incidence of direct complications, but may also suggest that the superficial/combined block provides better analgesia during surgery.

Cerebral Monitoring of Somatosensory Evoked Potentials during Carotid Surgery: A Review of 100 Cases

The purpose of this study was to evaluate immediate and middle-term results of surgical carotid artery revascularization (CAR) with cerebral monitoring of intraoperative somatosensory evoked potentials (SEPs). Between 1998 and 2004, a total of 100 CARs in 86 patients were performed under general anesthesia with SEP monitoring. A shunt was inserted if SEP amplitude decreased by 50% or latency time increased by 10%. Immediate and middle-term results were analyzed retrospectively. The shunt insertion rate was 5%. Two transient ischemic attacks were observed, and one patient died postoperatively due to myocardial infarction. The cumulative stroke and death rate was 1% at 30 days. Intraoperative SEP monitoring with selective shunt placement can be used safely for carotid surgery. Randomized studies will be necessary to determine the respective indications for various cerebral monitoring techniques.

Posterior tibial nerve and median nerve somatosensory evoked potential monitoring during carotid endarterectomy

PURPOSE

Somatosensory evoked potential (SSEP) monitoring using the median nerve (MN) modality during carotid endarterectomy is well established. This study assessed the usefulness of monitoring the posterior tibial nerve (PTN) SSEP as an adjunct to MNSSEP for detection of cerebral ischemia and as an indicator for the insertion of a shunt in patients undergoing a carotid endarterectomy.

METHODS

All patients undergoing carotid endarterectomy during three years who had routine bilateral MNSSEP were also monitored with bilateral PTNSSEP. Patients received a shunt if there was a significant change (> 50% decrease in amplitude of cortical peak (N20) in the MNSSEP after cross clamping. The incidence, timing, and duration of all PTNSSEP changes were compared to MNSSEP changes.

RESULTS

One hundred fifty-three patients were studied. Significant changes in MNSSEP after cross clamp lead to insertion of a shunt in six patients. Changes in PTNSSEP occurred at almost the same time in three patients, four minutes before MNSSEP in one, three minutes later in one and no change in one patient. Good quality baseline tracings were obtained in 99% MNSSEP as compared to 88% PTNSSEP (P < 0.05). New postoperative neurological deficits occurred in four patients (2.6%), only one had significant evoked potential changes.

CONCLUSION

Monitoring of PTNSSEP is feasible and may be considered for an adjunct to MNSSEP or as an alternative modality if there are difficulties with MNSSEP. However, there may be a greater incidence of poor quality baseline tracings for PTNSSEP.

Intraoperative management: carotid endarterectomies

The management of anesthesia for patients undergoing carotid endarterectomy is challenging and dynamic. Effective management and good outcome requires the anesthesiologist's understanding of cerebral physiology, knowledge of neck anatomy, and understanding of the rapid pathophysiologic changes that occur during carotid artery manipulations. The anesthesiologist must be flexible in the management of patients, who frequently have underlying multiorgan pathology and cardiovascular compromise. Good communication between the anesthetic and surgical teams is needed to avoid irreversible debilitating consequences for the patient.

Near Infrared Spectroscopy Monitoring During Carotid Endarterectomy: Which Threshold Value is Critical?

OBJECTIVES

Retrospectively to verify which decreasing percentage in regional oxygen saturation (rSO(2)) identified patients with good collateralisation during carotid artery cross clamp.

MATERIALS AND METHODS

During 594 endarterectomies under general anaesthesia the decreasing percentage from preclamp value to value detected in the first 2 min after clamping the CCA and/or ICA was calculated in real time. No temporary shunt was placed in any case. ROC analysis was performed to determine the optimal cut-off for rSO(2) decrease to identify the occurrence of neurological complications.

RESULTS

A cut-off of 11.7% was identified as optimal. Sensitivity and specificity were 75% (95% CI 71-78) and 77% (95% CI 74-80), respectively. The cut-off of 20% had a lower sensitivity (30%) and a higher specificity (98%) to identify patients with complications, with positive and negative predictive value of 37 and 98%, respectively.

CONCLUSIONS

The study suggest that a relative decrease in rSO(2) of <20% from preclamp to early cross clamp value has a high negative predictive value, i.e. if rSO(2) does non decrease more than 20%, ischemia by hypoperfusion is unlikely and a shunt should not be necessary. Moreover, a relative decrease >20% may not always indicate intraoperative neurological complications.