Benefits, shortcomings, and costs of EEG monitoring

Skin preparation-free, stretchable microneedle adhesive patches for reliable electrophysiological sensing and exoskeleton robot control

High-fidelity and comfortable recording of electrophysiological (EP) signals with on-the-fly setup is essential for health care and human-machine interfaces (HMIs). Microneedle electrodes allow direct access to the epidermis and eliminate time-consuming skin preparation. However, existing microneedle electrodes lack elasticity and reliability required for robust skin interfacing, thereby making long-term, high-quality EP sensing challenging during body movement. Here, we introduce a stretchable microneedle adhesive patch (SNAP) providing excellent skin penetrability and a robust electromechanical skin interface for prolonged and reliable EP monitoring under varying skin conditions. Results demonstrate that the SNAP can substantially reduce skin contact impedance under skin contamination and enhance wearing comfort during motion, outperforming gel and flexible microneedle electrodes. Our wireless SNAP demonstration for exoskeleton robot control shows its potential for highly reliable HMIs, even under time-dynamic skin conditions. We envision that the SNAP will open new opportunities for wearable EP sensing and its real-world applications in HMIs.

Solvent-Free and Skin-Like Supramolecular Ion-Conductive Elastomers with Versatile Processability for Multifunctional Ionic Tattoos and On-Skin Bioelectronics

The development of stable and biocompatible soft ionic conductors, alternatives to hydrogels and ionogels, will open up new avenues for the construction of stretchable electronics. Here, a brand-new design, encapsulating a naturally occurring ionizable compound by a biocompatible polymer via high-density hydrogen bonds, resulting in a solvent-free supramolecular ion-conductive elastomer (SF-supra-ICE) that eliminates the dehydration problem of hydrogels and possesses excellent biocompatibility, is reported. The SF-supra-ICE with high ionic conductivity (>3.3 × 10-2  S m-1 ) exhibits skin-like softness and strain-stiffening behaviors, excellent elasticity, breathability, and self-adhesiveness. Importantly, the SF-supra-ICE can be obtained by a simple water evaporation step to solidify the aqueous precursor into a solvent-free nature. Therefore, the aqueous precursor can act as inks to be painted and printed into customized ionic tattoos (I-tattoos) for the construction of multifunctional on-skin bioelectronics. The painted I-tattoos exhibit ultraconformal and seamless contact with human skin, enabling long-term and high-fidelity recording of various electrophysiological signals with extraordinary immunity to motion artifacts. Human-machine interactions are achieved by exploiting the painted I-tattoos to transmit the electrophysiological signals of human beings. Stretchable I-tattoo electrode arrays, manufactured by the printing method, are demonstrated for multichannel digital diagnosis of the health condition of human back muscles and spine.

Utilizing EEG and fNIRS for the detection of sleep-deprivation-induced fatigue and its inhibition using colored light stimulation

Drowsy driving is a common, but underestimated phenomenon in terms of associated risks as it often results in crashes causing fatalities and serious injuries. It is a challenging task to alert or reduce the driver's drowsy state using non-invasive techniques. In this study, a drowsiness reduction strategy has been developed and analyzed using exposure to different light colors and recording the corresponding electrical and biological brain activities. 31 subjects were examined by dividing them into 2 classes, a control group, and a healthy group. Fourteen EEG and 42 fNIRS channels were used to gather neurological data from two brain regions (prefrontal and visual cortices). Experiments shining 3 different colored lights have been carried out on them at certain times when there is a high probability to get drowsy. The results of this study show that there is a significant increase in HbO of a sleep-deprived participant when he is exposed to blue light. Similarly, the beta band of EEG also showed an increased response. However, the study found that there is no considerable increase in HbO and beta band power in the case of red and green light exposures. In addition to that, values of other physiological signals acquired such as heart rate, eye blinking, and self-reported Karolinska Sleepiness Scale scores validated the findings predicted by the electrical and biological signals. The statistical significance of the signals achieved has been tested using repeated measures ANOVA and t-tests. Correlation scores were also calculated to find the association between the changes in the data signals with the corresponding changes in the alertness level.

Real-time noise cancellation with deep learning

Biological measurements are often contaminated with large amounts of non-stationary noise which require effective noise reduction techniques. We present a new real-time deep learning algorithm which produces adaptively a signal opposing the noise so that destructive interference occurs. As a proof of concept, we demonstrate the algorithm's performance by reducing electromyogram noise in electroencephalograms with the usage of a custom, flexible, 3D-printed, compound electrode. With this setup, an average of 4dB and a maximum of 10dB improvement of the signal-to-noise ratio of the EEG was achieved by removing wide band muscle noise. This concept has the potential to not only adaptively improve the signal-to-noise ratio of EEG but can be applied to a wide range of biological, industrial and consumer applications such as industrial sensing or noise cancelling headphones.

Routine or selective carotid artery shunting for carotid endarterectomy (and different methods of monitoring in selective shunting)

BACKGROUND

Temporary interruption of cerebral blood flow during carotid endarterectomy can be avoided by using a shunt across the clamped section of the carotid artery. The shunt may improve the outcome. This is an update of a Cochrane review originally published in 1996 and previously updated in 2002, 2009, and 2014.

OBJECTIVES

To assess the effect of routine versus selective or no shunting, and to assess the best method for selective shunting on death, stroke, and other complications in people undergoing carotid endarterectomy under general anaesthesia.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (last searched April 2021), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2021, Issue 4), MEDLINE (1966 to April 2021), Embase (1980 to April 2021), and the Science Citation Index Expanded (SCI-EXPANDED) (1980 to April 2021). We also searched ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform, and handsearched relevant journals, conference proceedings, and reference lists.

SELECTION CRITERIA

Randomised and quasi-randomised trials of routine shunting compared with no shunting or selective shunting, and trials that compared different shunting policies in people undergoing carotid endarterectomy.

DATA COLLECTION AND ANALYSIS

Three independent review authors performed data extraction, selection, and analysis. A pooled Peto odds ratio (OR) and 95% confidence interval (CI) were computed for all outcomes of interest. Best and worse case scenarios were also calculated in case of unavailable data. Two authors independently assessed risk of bias, and quality of evidence using GRADE.

MAIN RESULTS

No new trials were found for this updated review. Thus, six trials involving 1270 participants are included in this latest review: three trials involving 686 participants compared routine shunting with no shunting, one trial involving 200 participants compared routine shunting with selective shunting, one trial involving 253 participants compared selective shunting with and without near-infrared refractory spectroscopy monitoring, and the other trial involving 131 participants compared shunting with a combination of electroencephalographic and carotid pressure measurement with shunting by carotid pressure measurement alone. Only three trials comparing routine shunting and no shunting were eligible for meta-analysis. Major findings of this comparison found that the routine shunting had less risk of stroke-related death within 30 days of surgery (best case) than no shunting (Peto odds ratio (OR) 0.13, 95% confidence interval (CI) 0.02 to 0.96, I² not applicable, P = 0.05, low-quality evidence), the routine shunting group had a lower stroke rate within 24 hours of surgery (Peto odds ratio (OR) 0.15, 95% CI 0.03 to 0.78, I² = not applicable, P = 0.02, low-quality evidence), and ipsilateral stroke within 30 days of surgery (best case) (Peto OR 0.41, 95% CI 0.18 to 0.97, I² = 52%, P = 0.04, low-quality evidence) than the no shunting group. No difference was found between the groups in terms of postoperative neurological deficit between selective shunting with and without near-infrared refractory spectroscopy monitoring. However, this analysis was inadequately powered to reliably detect the effect. There was no difference between the risk of ipsilateral stroke in participants selected for shunting with the combination of electroencephalographic and carotid pressure assessment compared with pressure assessment alone, although again the data were limited.

AUTHORS' CONCLUSIONS

This review concluded that the data available were too limited to either support or refute the use of routine or selective shunting in carotid endarterectomy when performed under general anaesthesia. Large-scale randomised trials of routine shunting versus selective shunting are required. No method of monitoring in selective shunting has been shown to produce better outcomes.

Automatic annotation correction for wearable EEG based epileptic seizure detection

OBJECTIVE

Video-electroencephalography (vEEG), which defines the ground truth for the detection of epileptic seizures, is inadequate for long-term home monitoring. Thanks to their advantages in comfort and unobtrusiveness, wearable EEG devices have been suggested as a solution for home monitoring. However, one of the challenges in data-driven automated seizure detection with wearable EEG data is to have reliable seizure annotations. Seizure annotations on the gold-standard 25-channel vEEG recordings may not be optimal to delineate seizure activity on the concomitantly recorded wearable EEG, due to artifacts or absence of ictal activity on the limited set of electrodes of the wearable EEG. This paper aims to develop an automatic approach to correct the imperfect annotations of seizure activity on wearable EEG, which can be used to train seizure detection algorithms.

APPROACH

This paper first investigates the effectiveness of correcting the seizure annotations for the training set with a visual annotation correction. Then a novel approach has been proposed to automatically remove non-seizure data from wearable EEG in epochs annotated as seizures in gold-standard video-EEG recordings. The performance of the automatic annotation correction approach was evaluated by comparing the seizure detection models trained with 1. original vEEG seizure annotations, 2. visually corrected seizure annotations, and 3. automatically corrected seizure annotations.

RESULTS

The automatic seizure detection approach trained with automatically corrected seizure annotations was more sensitive and had fewer false-positive detections compared to the approach trained with visually corrected seizure annotations, and the approach trained with the original seizure annotations from gold-standard vEEG.

SIGNIFICANCE

The wearable EEG seizure detection approach performs better when trained with automatic seizure annotation correction.

Distinct spatio-temporal and spectral brain patterns for different thermal stimuli perception

Understanding the human brain's perception of different thermal sensations has sparked the interest of many neuroscientists. The identification of distinct brain patterns when processing thermal stimuli has several clinical applications, such as phantom-limb pain prediction, as well as increasing the sense of embodiment when interacting with neurorehabilitation devices. Notwithstanding the remarkable number of studies that have touched upon this research topic, understanding how the human brain processes different thermal stimuli has remained elusive. More importantly, very intense thermal stimuli perception dynamics, their related cortical activations, as well as their decoding using effective features are still not fully understood. In this study, using electroencephalography (EEG) recorded from three healthy human subjects, we identified spatial, temporal, and spectral patterns of brain responses to different thermal stimulations ranging from extremely cold and hot stimuli (very intense), moderately cold and hot stimuli (intense), to a warm stimulus (innocuous). Our results show that very intense thermal stimuli elicit a decrease in alpha power compared to intense and innocuous stimulations. Spatio-temporal analysis reveals that in the first 400 ms post-stimulus, brain activity increases in the prefrontal and central brain areas for very intense stimulations, whereas for intense stimulation, high activity of the parietal area was observed post-500 ms. Based on these identified EEG patterns, we successfully classified the different thermal stimulations with an average test accuracy of 84% across all subjects. En route to understanding the underlying cortical activity, we source localized the EEG signal for each of the five thermal stimuli conditions. Our findings reveal that very intense stimuli were anticipated and induced early activation (before 400 ms) of the anterior cingulate cortex (ACC). Moreover, activation of the pre-frontal cortex, somatosensory, central, and parietal areas, was observed in the first 400 ms post-stimulation for very intense conditions and starting 500 ms post-stimuli for intense conditions. Overall, despite the small sample size, this work presents novel findings and a first comprehensive approach to explore, analyze, and classify EEG-brain activity changes evoked by five different thermal stimuli, which could lead to a better understanding of thermal stimuli processing in the brain and could, therefore, pave the way for developing a real-time withdrawal reaction system when interacting with prosthetic limbs. We underpin this last point by benchmarking our EEG results with a demonstration of a real-time withdrawal reaction of a robotic prosthesis using a human-like artificial skin.

Ultra-conformal skin electrodes with synergistically enhanced conductivity for long-time and low-motion artifact epidermal electrophysiology

Accurate and imperceptible monitoring of electrophysiological signals is of primary importance for wearable healthcare. Stiff and bulky pregelled electrodes are now commonly used in clinical diagnosis, causing severe discomfort to users for long-time using as well as artifact signals in motion. Here, we report a ~100 nm ultra-thin dry epidermal electrode that is able to conformably adhere to skin and accurately measure electrophysiological signals. It showed low sheet resistance (~24 Ω/sq, 4142 S/cm), high transparency, and mechano-electrical stability. The enhanced optoelectronic performance was due to the synergistic effect between graphene and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which induced a high degree of molecular ordering on PEDOT and charge transfer on graphene by strong π-π interaction. Together with ultra-thin nature, this dry epidermal electrode is able to accurately monitor electrophysiological signals such as facial skin and brain activity with low-motion artifact, enabling human-machine interfacing and long-time mental/physical health monitoring.

Novel dry electrodes with enhanced mechano-electrical stability and conformability are attractive for long-time electrophysiological signal monitoring. Here, the authors report polymer-covered CVD-grown graphene with enhanced optoelectronic performance for biopotential monitoring.

Cost-effectiveness of genome-wide sequencing for unexplained developmental disabilities and multiple congenital anomalies

PURPOSE

Genetic testing is routine practice for individuals with unexplained developmental disabilities and multiple congenital anomalies. However, current testing pathways can be costly and time consuming, and the diagnostic yield low. Genome-wide sequencing, including exome sequencing (ES) and genome sequencing (GS), can improve diagnosis, but at a higher cost. This study aimed to assess the cost-effectiveness of genome-wide sequencing in Ontario, Canada.

METHODS

A cost-effectiveness analysis was conducted using a discrete event simulation from a public payer perspective. Six strategies involving ES or GS were compared. Outcomes reported were direct medical costs, number of molecular diagnoses, number of positive findings, and number of active treatment changes.

RESULTS

If ES was used as a second-tier test (after the current first-tier, chromosomal microarray, fails to provide a diagnosis), it would be less costly and more effective than standard testing (CAN$6357 [95% CI: 6179-6520] vs. CAN$8783 per patient [95% CI: 2309-31,123]). If ES was used after standard testing, it would cost an additional CAN$15,228 to identify the genetic diagnosis for one additional patient compared with standard testing. The results remained robust when parameters and assumptions were varied.

CONCLUSION

ES would likely be cost-saving if used earlier in the diagnostic pathway.

Benefit of selective shunt use during carotid endarterectomy under regional anesthesia

Objectives

Carotid cross-clamping during endarterectomy exposes the patient to intraoperative neurological deficits due to embolism or cerebral hypoperfusion. To prevent further cerebrovascular incidents, resorting to shunt is frequently recommended. However, since this method is also considered a stroke risk factor, the use is still controversial. This study aims to shed some light on the best approach regarding the use of shunt in symptomatic cerebral malperfusion after carotid artery cross-clamping.

Methods

From January 2012 to January 2018, 79 patients from a tertiary referral hospital who underwent carotid endarterectomy with regional anesthesia for carotid artery stenosis and manifested post-clamping neurologic deficits were prospectively gathered. Shunt use was left to the decision of the surgeon and performed in 31.6% (25) of the patients. Demographics, comorbidities, imaging tests, and clinical/intraoperative features were evaluated. For data assessment, univariate analysis was performed.

Results

Regarding 30-day stroke, 30-day postoperative complications (stroke, surgical hematoma, hyperperfusion syndrome), and cranial nerve injury, no significant differences were found ( P = 0.301, P = 0.460, and P = 0.301, respectively) between resource to shunt and non-shunt. Clamping and surgery times were significantly higher in the shunt group ( P < 0.001 and P = 0.0001, respectively).

Conclusions

Selective-shunting did not demonstrate superiority for patients who developed focal deficits regarding stroke or other postoperative complications. However, due to the limitations of this study, the benefit of shunting cannot be excluded. Further randomized trials are recommended for precise results on this matter with current sparse clinical evidence.

Decoding of Pain Perception using EEG Signals for a Real-Time Reflex System in Prostheses: A Case Study

In recent times, we have witnessed a push towards restoring sensory perception to upper-limb amputees, which includes the whole spectrum from gentle touch to noxious stimuli. These are essential components for body protection as well as for restoring the sense of embodiment. Notwithstanding the considerable advances that have been made in designing suitable sensors and restoring tactile perceptions, pain perception dynamics and its decoding using effective bio-markers, are still not fully understood. Here, using electroencephalography (EEG) recordings, we identified and validated a spatio-temporal signature of brain activity during innocuous, moderately more intense, and noxious stimulation of an amputee's phantom limb using transcutaneous nerve stimulation (TENS). Based on the spatio-temporal EEG features, we developed a system for detecting pain perception and reaction in the brain, which successfully classified three different stimulation conditions with a test accuracy of 94.66%, and we investigated the cortical activity in response to sensory stimuli in these conditions. Our findings suggest that the noxious stimulation activates the pre-motor cortex with the highest activation shown in the central cortex (Cz electrode) between 450 ms and 750 ms post-stimulation, whereas the highest activation for the moderately intense stimulation was found in the parietal lobe (P2, P4, and P6 electrodes). Further, we localized the cortical sources and observed early strong activation of the anterior cingulate cortex (ACC) corresponding to the noxious stimulus condition. Moreover, activation of the posterior cingulate cortex (PCC) was observed during the noxious sensation. Overall, although this is a single case study, this work presents a novel approach and a first attempt to analyze and classify neural activity when restoring sensory perception to amputees, which could chart a route ahead for designing a real-time pain reaction system in upper-limb prostheses.

Genome-Wide Sequencing for Unexplained Developmental Disabilities or Multiple Congenital Anomalies: A Health Technology Assessment

BACKGROUND

People with unexplained developmental disabilities or multiple congenital anomalies might have had many biochemical, metabolic, and genetic tests for a period of years without receiving a diagnosis. A genetic diagnosis can help these people and their families better understand their condition and may help them to connect with others who have the same condition. Ontario Health (Quality), in collaboration with the Canadian Agency for Drugs and Technologies in Health (CADTH) conducted a health technology assessment about the use of genome-wide sequencing for patients with unexplained developmental disabilities or multiple congenital anomalies. Ontario Health (Quality) evaluated the effectiveness, cost-effectiveness, and budget impact of publicly funding genome-wide sequencing. We also conducted interviews with patients and examined the quantitative evidence of preferences and values literature to better understand the patient preferences and values for these tests.

METHODS

Ontario Health (Quality) performed a systematic literature search of the clinical evidence. We assessed the risk of bias of each included study using the Risk of Bias Assessment tool for Non-randomized Studies (RoBANS) and the quality of the body of evidence according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group criteria. We also performed a search of the quantitative evidence and undertook direct patient engagement to ascertain patient preferences for genetic testing for unexplained developmental disabilities or multiple congenital anomalies. CADTH performed a review of qualitative literature about patient perspectives and experiences, and a review of ethical issues.Ontario Health (Quality) performed an economic literature review of genome-wide sequencing in people with unexplained developmental disabilities or multiple congenital anomalies. Although we found eight published cost-effectiveness studies, none completely addressed our research question. Therefore, we conducted a primary economic evaluation using a discrete event simulation model. Owing to its high cost and early stage of clinical implementation, whole exome sequencing is primarily used for people who do not have a diagnosis from standard testing (referred to here as whole exome sequencing after standard testing; standard testing includes chromosomal microarray and targeted single-gene tests or gene panels). Therefore, in our first analysis, we evaluated the cost-effectiveness of whole exome sequencing after standard testing versus standard testing alone. In our second analysis, we explored the cost-effectiveness of whole exome and whole genome sequencing used at various times in the diagnostic pathway (e.g., first tier, second tier, after standard testing) versus standard testing. We also estimated the budget impact of publicly funding genome-wide sequencing in Ontario for the next 5 years.

RESULTS

Forty-four studies were included in the clinical evidence review. The overall diagnostic yield of genome-wide sequencing for people with unexplained development disability and multiple congenital anomalies was 37%, but we are very uncertain about this estimate (GRADE: Very Low). Compared with standard genetic testing of chromosomal microarray and targeted single-gene tests or gene panels, genome-wide sequencing could have a higher diagnostic yield (GRADE: Low). As well, for some who are tested, genome-wide sequencing prompts some changes to medications, treatments, and referrals to specialists (GRADE: Very Low).Whole exome sequencing after standard testing cost an additional $3,261 per patient but was more effective than standard testing alone. For every 1,000 persons tested, using whole exome sequencing after standard testing would lead to an additional 240 persons with a molecular diagnosis, 272 persons with any positive finding, and 46 persons with active treatment change (modifications to medications, procedures, or treatment). The resulting incremental cost-effectiveness ratios (ICERs) were $13,591 per additional molecular diagnosis. The use of genome-wide sequencing early in the diagnostic pathway (e.g., as a first- or second-tier test) can save on costs and improve diagnostic yields over those of standard testing. Results remained robust when parameters and assumptions were varied.Our budget impact analysis showed that, if whole exome sequencing after standard testing continues to be funded through Ontario's Out-of-Country Prior Approval Program, its budget impact would range from $4 to $5 million in years 1 to 5. If whole exome sequencing becomes publicly funded in Ontario (not through the Out-of-Country Prior Approval Program), the budget impact would be about $9 million yearly. We also found that using whole exome sequencing as a second-tier test would lead to cost savings ($3.4 million per 1,000 persons tested yearly).Participants demonstrated consistent motivations for and expectations of obtaining a diagnosis for unexplained developmental delay or congenital anomalies through genome-wide sequencing. Patients and families greatly value the support and information they receive through genetic counselling when considering genome-wide sequencing and learning of a diagnosis.

CONCLUSIONS

Genome-wide sequencing could have a higher diagnostic yield than standard testing for people with unexplained developmental disabilities or multiple congenital anomalies. Genome-wide sequencing can also prompt some changes to medications, treatments, and referrals to specialists for some people tested; however, we are very uncertain about this. Genome-wide sequencing could be a cost-effective strategy when used after standard testing to diagnose people with unexplained developmental disabilities or multiple congenital anomalies. It could also lead to cost savings when used earlier in the diagnostic pathway. Patients and families consistently noted a benefit from seeking a diagnosis through genetic testing.

Somatosensory Evoked Potential and Transcranial Doppler Monitoring to Guide Shunting in Carotid Endarterectomy

OBJECTIVE

 Clamping of the internal carotid artery (ICA) during carotid endarterectomy (CEA) is a critical step. In our neurosurgical department, CEAs are performed with transcranial Doppler (TCD) and somatosensory evoked potential (SEP) monitoring with a 50% flow velocity/amplitude decrement warning criteria for shunting. The aim of our study was to evaluate our protocol with immediate neurologic deficits after surgery for the primary end point.

METHODS

 This is a single-center retrospective cohort study of symptomatic and asymptomatic ICA stenosis patients from January 2012 to June 2015. Only those cases in which CEA was performed with both modalities (TCD and SEP) were included. The Mann-Whitney U test was applied to evaluate TCD and SEP ratios based on immediate postoperative neurologic deficits.

RESULTS

 A total of 144 patients were included, 120 (83.3%) with symptomatic ICA stenosis. The primary end point was met by six patients (4.2%); all of them were patients with a symptomatic ICA stenosis. The stroke and death rate was 1.4%. Ratios of SEP amplitudes demonstrated significant differences between patients with and without an immediate postoperative neurologic deficit at the time of ICA clamping (p = 0.005), ICA clamping at 10 minutes (p = 0.044), and ICA reperfusion (p = 0.005). Ratios of TCD flow velocity showed no significant difference at all critical steps.

CONCLUSION

 In this retrospective series of simultaneous TCD and SEP monitoring during CEA surgery of predominantly symptomatic ICA stenosis patients, the stroke and death rate was 1.4%. SEP seemed to be superior to TCD in predicting the need for an intraoperative shunt and for predicting temporary postoperative deficits. Further prospective studies are needed.

Cerebral Neuromonitoring during Carotid Endarterectomy and Impact of Contralateral Internal Carotid Occlusion

BACKGROUND

The aim of this study was to identify the reliability of carotid artery stump pressure (SP) in predicting the neurologic changes and correlation with contralateral internal carotid artery (ICA) occlusion in patients undergoing eversion carotid endarterectomy (CEA). The optimal method for monitoring cerebral perfusion during CEA, performed under either local or general anesthesia, is still controversial.

METHODS

We prospectively analyzed 118 consecutive patients undergoing eversion CEA under local anesthesia. We had 78 symptomatic (66%) and 40 asymptomatic patients (33.9%). Selective shunting was performed in patients who developed neurologic changes after carotid clamping regardless of SP. Correlation of preoperative symptom status, a degree of stenosis, status of contralateral ICA, arterial blood pressure, SP value, and the intraoperative need for shunting due to neurologic changes was evaluated for both groups: shunted and nonshunted.

RESULTS

Selective shunting was performed in 12 patients (10%). There was no significant difference among the groups regarding the demographic characteristics. Mean carotid clamping time was 14.57 minutes. We had no perioperative mortality, stroke, or myocardial infarction. None of the patients required conversion to general anesthesia. We found a mean SP of 31 mm Hg as a reliable threshold for shunting (P < .001; sensitivity 92.3%; specificity 91.3%). Contralateral carotid occlusion was correlated with the significantly lower SP (27 ± 13 mm Hg; P = .001) and the higher need for shunt (50%).

CONCLUSIONS

SP measurement is a reliable and simple method for monitoring the collateral cerebral perfusion and can predict the need for shunting during CEA. Patients with the contralateral ICA occlusion showed significantly lower SP, although it did not have impact on the outcome.

Cost-Effectiveness of Two Decision Strategies for Shunt Use During Carotid Endarterectomy

Background

Arterial shunting during carotid endarterectomy (CEA) is essential in some patients because of insufficient cerebral perfusion during cross-clamping. However, the optimal diagnostic modality identifying these patients is still debated. None of the currently used modalities has been proved superior to another. The aim of this study was to assess the cost-effectiveness of two modalities, stump pressure measurement (SPM) versus electroencephalography (EEG) combined with transcranial Doppler (TCD) during CEA.

Methods

Two retrospective cohorts of consecutive patients undergoing CEA with different intraoperative neuromonitoring strategies (SPM vs. EEG/TCD) were analyzed. Clinical data were collected from patient hospital records. Primary clinical outcome was in-hospital stroke or death. Total admission costs were calculated based on volumes of healthcare resources. Analyses of effects and costs were adjusted for clinical differences between patients by means of a propensity score, and cost-effectiveness was estimated.

Results

A total of 503 (239 SPM; 264 EEG/TCD) patients were included, of whom 19 sustained a stroke or died during admission (3.3 vs. 4.2%, respectively, adjusted risk difference 1.3% (95% CI −2.3–4.8%)). Median total costs were €4946 (IQR 4424–6173) in the SPM group versus €7447 (IQR 6890–8675) in the EEG/TCD group. Costs for neurophysiologic assessments were the main determinant for the difference.

Conclusions

Given the evidence provided by this small retrospective study, SPM would be the favored strategy for intraoperative neuromonitoring if cost-effectiveness was taken into account when deciding which strategy to adopt.

Cerebral Oximetry Monitoring During Carotid Endarterectomy: Effect of Carotid Clamping and Shunting

Cerebral oximetry is a simple method of measuring regional cerebral oxygen saturation (rSO2). One promising application is its use during carotid endarterectomy (CEA) to help minimize the risk of perioperative stroke. The authors used the INVOS-4100 cerebral oximeter at several steps during CEA to measure the effect of carotid clamping and shunting on rSO2. The authors prospectively evaluated 42 consecutive CEAs in 40 patients. All had CEA under general anesthesia with the routine use of a Javid shunt. The INVOS-4100 oximeter was used to measure rSO2 before clamping (t1), after clamping but before shunting (t2), 5 minutes after shunt insertion (t3), and after patch closure with reestablished flow (t4). The Wilcoxon signed-rank and rank-sum tests were used for analysis. Clamping of the internal carotid artery (t1 vs t2) resulted in a drop of ipsilateral rSO2 by –12.3% (p<0.001). Shunt insertion (t2 vs t3) increased rSO2 by 10.9% (p< 0.001). Contralateral rSO2 for the same time periods was insignificant. Patients with preoperative neurologic symptoms had a greater decrease in rSO2 after clamping (–18.4%) compared with a decrease of –10.4% in asymptomatic patients (p=0.037). Cerebral oximetry monitoring is simple and inexpensive. The study showed statistically significant changes in rSO2 as a result of clamping and shunting of the carotid artery. Symptomatic patients had a greater drop in rSO2.

Correlation of Cerebral Oximetry Measurement with Carotid Artery Stump Pressures During Carotid Endarterectomy

Cerebral oximetry and internal carotid artery stump pressures were measured during carotid endarterectomy to assess whether cerebral oximetry could be used as a noninvasive and reliable alternative to monitor cerebral blood flow and the need for selective carotid artery shunting. Carotid endarterectomy procedures were performed in 27 patients wherein a cerebral oximeter was placed on the ipsilateral forehead preoperatively. Stump pressure data as well as cerebral oximetry readings at baseline and before and after carotid artery clamping were gathered. The differences between baseline and clamped carotid artery oximetry readings were calculated for each subject and divided by the baseline reading to provide an adjusted measure of percent oximetry change. This normalized percent change in cerebral oximetry readings was then correlated with stump pressure. Carotid artery stump pressures correlated closely with the normalized change in cerebral oximetry readings ( r = -0.57, p = 0.002). Based on the regression analysis, stump pressure readings of 50 and 25 mm Hg were predicted by at least a 15% and 30% drop in cerebral oximetry readings, respectively. Based on low intraoperative stump pressure and changes in cerebral oximetry readings, arterial shunt placement was used in eight patients. There was no morbidity or mortality from the 27 carotid endarterectomy procedures performed. Carotid endarterectomy can be performed safely with cerebral oximetry as a simple, noninvasive, and reliable alternative to internal carotid artery stump pressure measurements in determining the need for selective carotid artery shunting.

Monitoring cerebral ischemia during carotid endarterectomy and stenting

Current therapy for carotid stenosis mainly includes carotid endarterectomy and endovascular stenting, which may incur procedure-related cerebral ischemia. Several methods have been employed for monitoring cerebral ischemia during surgery, such as awake neurocognitive assessment, electroencephalography, evoked potentials, transcranial Doppler, carotid stump pressure, and near infrared spectroscopy. However, there is no consensus on the gold standard or the method that is superior to others at present. Keeping patient awake for real time neurocognitive assessment is effective and essential; however, not every surgeon adopts it. In patients under general anesthesia, cerebral ischemia monitoring has to rely on non-awake technologies. The advantageous and disadvantageous properties of each monitoring method are reviewed.

A novel volume integral equation for solving the Electroencephalography forward problem

In this paper, a novel volume integral equation for solving the Electroencephalography forward problem is presented. Differently from other integral equation methods standardly used for the same purpose, the new formulation can handle inhomogeneous and fully anisotropic realistic head models. The new equation is obtained by a suitable use of Green's identities together with an appropriate handling of all boundary conditions for the EEG problem. The new equation is discretized with a consistent choice of volume and boundary elements. Numerical results shows validity and convergence of the approach, together with its applicability to real case models obtained from MRI data.

Ionic liquid gel-assisted electrodes for long-term cutaneous recordings

The integration of an ionic liquid gel on conformal electrodes is investigated for applications in long-term cutaneous recordings. Electrodes made of Au and the conducting polymer PEDOT:PSS coated with the gel show a low impedance in contact with the skin that maintains a steady value over several days, paving the way for non-invasive, long-term monitoring of human electrophysiological activity.

Routine or selective carotid artery shunting for carotid endarterectomy (and different methods of monitoring in selective shunting)

BACKGROUND

Temporary interruption of cerebral blood flow during carotid endarterectomy can be avoided by using a shunt across the clamped section of the carotid artery. This may improve outcome. This is an update of a Cochrane review originally published in 1996 and previously updated in 2009.

OBJECTIVES

To assess the effect of routine versus selective or no shunting during carotid endarterectomy, and to assess the best method for selecting people for shunting.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (last searched August 2013), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2013, Issue 8), MEDLINE (1966 to August 2013), EMBASE (1980 to August 2013) and Index to Scientific and Technical Proceedings (1980 to August 2013). We handsearched journals and conference proceedings, checked reference lists, and contacted experts in the field.

SELECTION CRITERIA

Randomised and quasi-randomised trials of routine shunting compared with no shunting or selective shunting, and trials that compared different shunting policies in people undergoing carotid endarterectomy.

DATA COLLECTION AND ANALYSIS

Three review authors independently performed the searches and applied the inclusion criteria. For this update, we identified two new relevant randomised controlled trials.

MAIN RESULTS

We included six trials involving 1270 participants in the review: three trials involving 686 participants compared routine shunting with no shunting, one trial involving 200 participants compared routine shunting with selective shunting, one trial involving 253 participants compared selective shunting with and without near-infrared refractory spectroscopy monitoring, and the other trial involving 131 participants compared shunting with a combination of electroencephalographic and carotid pressure measurement with shunting by carotid pressure measurement alone. In general, reporting of methodology in the included studies was poor. For most studies, the blinding of outcome assessors and the report of prespecified outcomes were unclear. For routine versus no shunting, there was no significant difference in the rate of all stroke, ipsilateral stroke or death up to 30 days after surgery, although data were limited. No significant difference was found between the groups in terms of postoperative neurological deficit between selective shunting with and without near-infrared refractory spectroscopy monitoring, However, this analysis was inadequately powered to reliably detect the effect. There was no significant difference between the risk of ipsilateral stroke in participants selected for shunting with the combination of electroencephalographic and carotid pressure assessment compared with pressure assessment alone, although again the data were limited.

AUTHORS' CONCLUSIONS

This review concluded that the data available were too limited to either support or refute the use of routine or selective shunting in carotid endarterectomy. Large scale randomised trials of routine shunting versus selective shunting are required. No method of monitoring in selective shunting has been shown to produce better outcomes.

Is Near-Infrared Spectroscopy a Reliable Method to Evaluate Clamping Ischemia during Carotid Surgery?

Guidelines do not include cerebral oximetry among monitoring for carotid endarterectomy (CEA). The purpose of this study was to evaluate the reliability of near-infrared spectroscopy (NIRS) in the detection of clamping ischemia and in the prevention of clamping-related neurologic deficits using, as a cutoff for shunting, a 20% regional cerebral oxygen saturation (rSO(2)) decrease if persistent more than 4 minutes, otherwise a 25% rSO(2) decrease. Bilateral rSO(2) was monitored continuously in patients undergoing CEA under general anesthesia (GA). Data was recorded after clamping, declamping, during shunting and lowest values achieved. Preoperative neurologic, CT-scan, and vascular lesions were recorded. We reviewed 473 cases: 305 males (64.5%) mean age 73.3 ± 7.3. Three patients presented transient ischemic deficits at awakening, no perioperative stroke or death; 41 (8.7%) required shunting: 30 based on the initial rSO(2) value and 11 due to a decrease during surgery. Using the ROC curve analysis we found, for a >25% reduction from baseline value, a sensitivity of 100% and a specificity of 90.6%. Reliability, PPV, and NPV were 95.38%, 9%, and 100%, respectively. In conclusion, this study indicates the potential reliability of NIRS monitoring during CEA under GA, using a cutoff of 25% or a cutoff of 20% for prolonged hypoperfusion.

Effectiveness of near-infrared spectroscopy during surgical repair of tracheo-innominate artery fistula

Monitoring regional cerebral oxygen saturation (rSO(2)) by use of near-infrared spectroscopy (NIRS) is a useful method for detecting cerebral ischemia. Tracheo-innominate artery fistula is a rare but life-threatening complication of tracheostomy. The surgical procedures for management of tracheo-innominate artery fistula include direct or patch closure of the fistula, ligation or division of the innominate artery, and anatomical or extra-anatomical reconstruction of the flow of the innominate artery. Division of the innominate artery is the best method to prevent postoperative recurrence of bleeding and infection. However, cutting off the innominate artery flow may cause brain ischemia. We present the case of a patient with tracheo-innominate artery fistula successfully treated by dividing the innominate artery while the rSO(2) was monitored. In this case report, we have shown that NIRS is a useful method for deciding the surgical maneuver for tracheo-innominate artery fistula.

Correlation of Cerebral Oximetry With Internal Carotid Artery Stump Pressures in Carotid Endarterectomy

Objective: This study compares internal carotid artery (ICA) mean stump pressures (SPs) with cerebral oximetry monitoring during carotid endarterectomy (CEA). Methods: A total of 104 consecutive patients undergoing CEA under general anesthesia (GA) during a 10-month period were prospectively evaluated. Baseline and postcarotid clamp regional cerebral oxygen saturation (rSO2) and mean ICA SPs were measured. Demographic, surgical, and medical variables were recorded for each case. Results: There were no postoperative strokes. Thirteen patients were excluded because of incomplete data. Of the 40 patients who had <10% drop in rSO2, 6 had SP <40 mm Hg. Regional cerebral oxygen saturation with a 15% saturation drop threshold was 76.3% sensitive and 81.1% specific in detecting patients with SP <40 mm Hg. With a threshold of 20% drop, sensitivity and specificity were 57.9% and 86.8%, respectively. Conclusions: Relative drop in rSO 2 is neither sensitive nor specific in detecting patients with mean SP <40 mm Hg. These data do not support the use of cerebral oximetry as the sole monitoring modality during carotid endarterectomy under GA.

Prospective randomized trial of routine versus selective shunting in carotid endarterectomy based on stump pressure

BACKGROUND

The use of shunting in carotid endarterectomy (CEA) is controversial. This randomized trial compared the results of routine (RS) vs selective shunting (SS) based on stump pressure (SP).

METHODS

Two-hundred CEA patients under general anesthesia were randomized into RS (98 patients) or SS (102 patients), where shunting was used only if systolic SP (SSP) was <40 mm Hg. Clinical and demographic characteristics were comparable in both groups. Patients underwent immediate and 30-day postoperative duplex ultrasound follow-up. Analysis was by intention-to-treat.

RESULTS

Of 102 SS patients, 29 (28%) received shunting. Indications for CEA were similar (42% symptomatic for RS; 47% for SS, P = .458). The mean internal carotid artery diameter was comparable (5.5 vs 5.5 mm, P = .685). Mean preoperative ipsilateral and contralateral stenosis was 76% and 38% for RS (P = .268) vs 78% and 40% for SS (P = .528). Mean preoperative ipsilateral and contralateral stenosis was 79% and 56% in the shunted (P = .634) vs 78% and 34% in the nonshunted subgroup of SS patients (P = .002). The mean SSP was 55.9 mm Hg in RS vs 56.2 for SS (P = .915). The mean SSP was 33 mm Hg in the shunted vs 65 in the nonshunted subgroup (P < .0001). Mean clamp time in the nonshunted subgroup of SS was 32 minutes. Mean shunt time was 35 minutes in RS and 33 in SS (P = .354). Mean operative time was 113 minutes for RS and 109 for SS (P = .252), and 111 minutes in shunted and 108 in the nonshunted subgroup (P = .586). Mean arteriotomy length was 4.4 cm for RS and 4.2 for SS (P = .213). Perioperative stroke rate was 0% for RS vs 2% for SS (one major and one minor stroke, both related to carotid thrombosis; P = .498). No patients died perioperatively. Combined perioperative transient ischemic attack (TIA) and stroke rates were 2% in RS vs 2.9% in SS (P > .99). The overall perioperative complication rates were 8.3% in RS (2 TIA, 3 hemorrhage, 1 myocardial infarction [MI], and 1 asymptomatic carotid thrombosis) vs 7.8% in SS (2 strokes, 1 TIA, 3 hemorrhage, 1 MI, and 1 congestive heart failure; P = .917).

CONCLUSIONS

RS and SS were associated with a low stroke rate. Both methods are acceptable, and surgeons should select the method with which they are more comfortable.

Routine or selective carotid artery shunting for carotid endarterectomy (and different methods of monitoring in selective shunting)

BACKGROUND

Temporary interruption of cerebral blood flow during carotid endarterectomy can be avoided by using a shunt across the clamped section of the carotid artery. This may improve outcome. This is an update of a Cochrane Review originally published in 1996 and previously updated in 2001.

OBJECTIVES

To assess the effect of routine versus selective, or never, shunting during carotid endarterectomy, and to assess the best method for selecting patients for shunting.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (last searched September 2008), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 1, 2009), MEDLINE (1966 to November 2008), EMBASE (1980 to November 2008) and Index to Scientific and Technical Proceedings (1980 to November 2008). We handsearched journals and conference proceedings, checked reference lists, and contacted experts in the field.

SELECTION CRITERIA

Randomised and quasi-randomised trials of routine shunting compared with no shunting or selective shunting, and trials that compared different shunting policies in patients undergoing carotid endarterectomy.

DATA COLLECTION AND ANALYSIS

Two review authors independently performed the searches and applied the inclusion criteria. We identified one new relevant randomised controlled trial.

MAIN RESULTS

We included four trials in the review: three trials involving 686 patients compared routine shunting with no shunting; the other trial involving 131 patients compared shunting with a combination of electroencephalographic and carotid pressure measurement with shunting by carotid pressure measurement alone. Allocation was adequately concealed in one trial, and one trial was quasi-randomised. Analysis was by intention-to-treat where possible. For routine versus no shunting, there was no significant difference in the rate of all stroke, ipsilateral stroke or death up to 30 days after surgery, although data were limited. There was no significant difference between the risk of ipsilateral stroke in patients selected for shunting with the combination of electroencephalographic and carotid pressure assessment compared to pressure assessment alone, although again the data were limited.

AUTHORS' CONCLUSIONS

This review concluded that the data available were too limited to either support or refute the use of routine or selective shunting in carotid endarterectomy. It was suggested that large scale randomised trials between routine shunting versus selective shunting were required. No one method of monitoring in selective shunting has been shown to produce better outcomes.

Cerebral oximetry does not correlate with electroencephalography and somatosensory evoked potentials in determining the need for shunting during carotid endarterectomy

OBJECTIVE

Several reports in the literature have described the value of regional cerebral oximetry (rSO(2)) as a neuromonitoring device during carotid endarterectomy (CEA). The use of rSO(2) is enticing because it is simpler and less expensive than other neuromonitoring modalities. This study was performed to compare the efficacy of rSO(2) with electroencephalography (EEG) and median nerve somatosensory evoked potentials (SSEP) in determining when to place a shunt during CEA.

METHODS

From October 2000 to June 2006, 323 CEAs were performed under general anesthesia by six surgeons. Shunting was done selectively on the basis of EEG and SSEP monitoring under the auspices of an intraoperative neurophysiologist. All patients were retrospectively reviewed to see if significant discrepancies existed between EEG/SSEP and rSO(2).

RESULTS

Twenty-four patients (7.4%) showed significant discrepancies. Sixteen patients showed no significant EEG/SSEP changes, but profound changes occurred in rSO(2), and no shunt was placed. In seven patients there was no change in rSO(2) but a profound change occurred in EEG/SSEP, and shunts were placed. In one patient early in the series, the EEG and SSEP were unchanged but the rSO(2) dropped precipitously, and a shunt was placed. In the 299 patients who showed no discrepancies, 285 were not shunted and 14 required a shunt. Two strokes occurred in the entire series (0.6%), none intraoperatively. Shunts were placed in 23 patients (7%). The sensitivity of rSO(2) compared with EEG/SSEP was 68%, and the specificity was 94%. This gave a positive-predictive value of 47% and a negative-predictive value of 98%.

CONCLUSIONS

Relying on rSO(2) alone for selective shunting is potentially dangerous and might have led to intraoperative ischemic strokes in seven patients and the unnecessary use of shunts in at least 16 patients in this series. The use of rSO(2) adds nothing to the information already provided by EEG and SSEP in determining when to place a shunt during CEA.

Significant correlation between cerebral oximetry and carotid stump pressure during carotid endarterectomy

Limited information on a correlation between carotid stump pressure and cerebral oximetry changes associated with cross-clamping of carotid vessels during carotid endarterectomy (CEA) prompted us to prospectively evaluate 38 consecutive CEAs in 37 patients. The authors used the INVOS-4100 cerebral oximeter to measure cerebral oximetry (cerebral oxygen saturation) before (t1) and after (t2) cross-clamping along with carotid stump pressure. All patients had CEA under general anesthesia with the routine use of a Javid shunt. Cross-clamping (t1 vs. t2) resulted in statistically significant changes (p < 0.0001) on the operated side of 6.03 units or a percent change of 9.2% when analyzed using the nonparametric signed-rank test. The nonoperated side had insignificant change (p = 0.71). Spearman correlation analysis revealed significant correlation (r = -0.63) between cerebral oximetry changes on the operated side and carotid stump pressure such that a larger change in cerebral oximetry due to cross-clamping was strongly and significantly correlated with lower carotid stump pressure. Using regression analysis, stump pressures of 25 and 50 mm Hg were predicted by cerebral oximetry changes of 28.5 or 8.8 units, respectively. This is equivalent to a percent change from baseline (t1) of 41.1% or 13.1%, respectively. Taken together, these findings suggest that cerebral oximetry can be used as an alternative to carotid stump pressure to provide noninvasive, inexpensive, and continuous real-time monitoring during CEA.

Prospective evaluation of electroencephalography, carotid artery stump pressure, and neurologic changes during 314 consecutive carotid endarterectomies performed in awake patients

OBJECTIVE

This study attempted to correlate neurologic changes in awake patients undergoing carotid endarterectomy (CEA) under cervical block anesthesia (CBA) with electroencephalography (EEG) and measurement of carotid artery stump pressure (SP).

METHODS

Continuous EEG and SP monitoring was measured prospectively in 314 consecutive patients undergoing CEA between April 1, 2003, and July 30, 2006, under CBA. Indications for CEA were asymptomatic 70% to 99% internal carotid artery stenosis in 242 (77.1%), transient ischemic attacks (including transient monocular blindness) in 45 (14.3%), and prior stroke in 27 (8.6%). Mean common carotid artery pressure before clamping, mean SP after carotid clamping, and intraarterial pressure were continuously monitored in all patients. An indwelling shunt was placed when neurologic events (contralateral motor weakness, aphasia, loss of consciousness, or seizures) occurred, regardless of SP or EEG changes.

RESULTS

Shunt placement was necessary because of neurologic changes in 10% (32/314) of all CEAs performed under CBA. Only 3 patients (1.4%) of 216 required shunt placement if SP was 50 mm Hg or more, vs 29 (29.6%) of 98 if SP was less than 50 mm Hg (P < .00001; sensitivity, 29.8%; specificity, 98.6%). In patients with SP of 40 mm Hg or more, 7 (2.6%) of 270 required shunt placement, vs 25 (56.8%) of 44 if SP was less than 40 mm Hg (P < .00001; sensitivity, 56.8%; specificity, 97.4%). Ischemic EEG changes were observed in 19 (59.4%) of 32 patients (false-negative rate, 40.6%) requiring shunt placement under CBA. Three patients had false-positive EEG results and did not require shunt placement (false-positive rate, 1.0%). The perioperative stroke/death rate was 4 (1.2%) in 314. All strokes occurred after surgery and were unrelated to cerebral ischemia or lack of shunt placement.

CONCLUSIONS

Ten percent of patients required a shunt placement during CEA under CBA. Shunt placement was necessary in 56.8% of patients with SP less than 40 mm Hg. EEG identified cerebral ischemia in only 59.4% of patients needing shunt placement, with a false-positive rate of 1.0% and a false-negative rate of 40.6%. Both SP and EEG as a guide to shunt placement have poor sensitivity. Intraoperative monitoring of the awake patients under regional anesthesia (CBA) is the most sensitive and specific method to identify patients requiring shunt placement.

Cerebral monitoring in the operating room and the intensive care unit: an introductory for the clinician and a guide for the novice wanting to open a window to the brain. Part I: The electroencephalogram

While there is an increasing body of knowledge in regard to central nervous system function and/or the mode of action of centrally active agents on neuronal function, little is done to develop new techniques on how to measure such changes. Also, monitoring of the cardiovascular system in the past has made extensive progress especially when it comes to evaluate the failing heart. In contrast monitoring of the central nervous system is only done in rare cases where operative procedures likely impede nervous function integrity. Since in the past decade the aging population undergoing operation has rise considerably, the risk of cerebral malperfusion or minute signs of degradation of the aging central nervous system (CNS) to anesthetics and agents being used in the operation room (OR) or the intensive care unit (ICU), needs continuous monitoring of an organ which presents the highest vulnerability and is likely to deteriorate faster than the cardiovascular system. In spite the rapid improvement in technology regarding the electroencephalogram (EEG) and evoked potential monitoring, physicians still are reluctant to use a technology on a routine base, which will give them insight information into brain function and activity. Such "windows to the brain" now not just are reserved to specialists working in the area of neurology and/or psychiatry. More so, cerebral monitoring is getting an integrated part in the overall therapy in patients undergoing operation or who need ventilatory support in the ICU as it effects the well-being and the outcome. The present book therefore, is intended for the practitioners who work with the patient, guide the clinician in his decision making and outlining those situations where cerebral monitoring presents an integrated part in the diagnosis and therapy of patient care. Without going too much into the technical details, representative cases underline the potential use of cerebral monitoring in the underlying clinical situation where either the patient presents borderline perfusion of the CNS, undergoes vascular surgery, or where monitoring of cerebral function in the intensive care in a head trauma patients is an integrated part in therapy. The book therefore is meant for all those clinicians who have to deal with the CNS in a day-to-day situation. This may be the anesthesiologist, the surgeon, the intensive care therapist, the nurse anesthetist as well as all other medical personal involved in intensive care therapy. The aim of the book therefore is to outline the possibilities, the limitations, and the options for therapy when the windows to the brain are opened, how to interpret the data in the light of other physiological parameters and aid the user in the technical details of how to avoid artifacts in recording which may have an impact on final decision making. Therefore, emphasis is placed on the electrode placement, artifact and electrical noise reduction, as well as data interpretation so that cerebral function diagnosis can be made on reliable grounds. The following serves as an introduction to and as a reference guide for Cerebral Monitoring in the OR and the ICU: Gives complete coverage of EEG power spectra analysis. Describes in detail the EEG machines available to be used in the OR and ICU setting. Describes in detail the major features of EEG power spectra and evoked potential measurements, including amplifiers, filter setting and microprocessor algorithm for data reduction. Gives suggestions for assessing and improving signal quality, including noise and artifact rejection, which usually are encountered in the operation room and the intensive care unit, both of which can be considered as electrically contaminated. Gives examples of EEG power spectra and evoked potential monitoring related to different types of anesthesia, in coma, after head trauma, and for the detection of ischemic events. In addition, gives complete coverage of those machines being available for the OR and the ICU, including a list of parameters regarding latency and amplitude in evoked potential As an introductory, recommendations are given for the novice to start cerebral monitoring and guide the beginner in setting up cerebral monitoring in the clinical environment.

Correlation of carotid artery stump pressure and neurologic changes during 474 carotid endarterectomies performed in awake patients

PURPOSE

A carotid artery stump pressure (SP) of < 50 mm Hg and abnormal electroencephalography (EEG) changes have been suggested as indications for selective shunting in patients undergoing carotid endarterectomy (CEA) under general anesthesia. We attempted to determine the optimal SP threshold that correlated with neurologic changes in awake patients undergoing CEA using cervical block anesthesia (CBA) and performed a cost comparison with EEG monitoring.

METHODS

Between July 1, 1995, and December 31, 2004, SP was measured during 474 CEAs performed under CBA by inserting a 19-gauge butterfly needle into the common carotid artery. A saline-filled intravenous bag in the patient's contralateral hand was connected to pressure tubing to generate waveforms with hand squeezing that could be visualized on a monitor. Systemic pressure was maintained approximately 10 mm Hg higher than baseline. Accurate SPs were confirmed by the finding of flatline waveforms after internal carotid artery clamping. Selective shunting was performed when neurologic changes occurred (aphasia, inability to squeeze the contralateral hand, decreased consciousness), regardless of SP. During this same period, 142 patients underwent CEA using GA, and SP was also measured.

RESULTS

Shunting was necessary because of neurologic changes in 7.2% (34/474) of all CEAs performed using CBA: 0.9% (3/335) with SPs > or = 50 mm Hg systolic vs 1.0% (4/402) with SPs > or = 40 mm Hg systolic, and 22% (31/139) with SPs < 50 mm Hg systolic vs 42% (30/72) with SPs < 40 mm Hg systolic. If these 474 CEAs had been performed using GA, shunts would have been used in 29% (139/474) of patients for a SP < 50 mm Hg systolic vs 15% (72/474) for a SP < 40 mm Hg systolic. In patients not shunted, the perioperative stroke/death rate was 1.2% in patients (4/332) with SPs > or = 50 mm Hg vs 1.0% (4/398) with SPs > or = 40 mm Hg. Three of the four strokes occurred > 24 hours postoperatively and were unrelated to lack of shunting and ischemia. There was no significant difference in the percentage of patients with SPs > or = 50 mm Hg who underwent CEA using CBA (70%, 335/474) vs GA (67%, 96/142) during this time period. At our hospital, charges for SPe measurement, including anesthesia charges and tubing, were 229 dollars per case vs 3439 dollars per case for EEG monitoring. Use of SP measurements in these 474 patients would have resulted in reduced charges of 1,521,540 dollars compared with EEG monitoring if CEA had been performed under GA.

CONCLUSION

Using 40 mm Hg systolic as a threshold, the need for shunting (15%) and the false-negative rate (1.0%) for SP in our series were equivalent to the results of EEG monitoring during CEA reported in the literature. However, charges for SP measurements are dramatically lower compared with EEG monitoring. Our results suggest that a carotid artery SP > or = 40 mm Hg systolic may be considered as an equally reliable but more cost-effective method to predict the need for carotid shunting during CEA under GA compared with EEG monitoring, but further investigation is warranted.

Selective shunting during carotid endarterectomy

Carotid endarterectomy (CEA) is an effective treatment for significant carotid atherosclerosis. Perioperative stroke, a devastating complication, may be partially circumvented by shunting. However, routine shunt use is not without complications and does not benefit every patient. Our study is designed to determine whether CEA under general anesthesia, without cerebral monitoring, can be safely done with shunting only in the presence of poor internal carotid artery back-bleeding or contralateral carotid occlusion or critical stenosis. The medical records of 995 carotid operations were reviewed. A subset of 117 operations was performed on 112 patients using selective shunting. Data were analyzed and outcomes compared. For the selective shunt group, indications for redo operations (n=13) were recurrent asymptomatic high-grade stenosis in 69% and amaurosis fugax or transient ischemic attack in 31%. Indications for primary CEA (n=104) were asymptomatic high-grade stenosis in 59%, amaurosis fugax or transient ischemic attack in 36%, previous stroke in 3%, and global ischemia in 2%. A selective shunt was used in 29% of all symptomatic and 11% of all asymptomatic patients. No cerebral monitoring was used. There were no perioperative deaths and no permanent cranial nerve injuries, and there was one stroke (0.8%) from postoperative carotid thrombosis in a shunted patient. The average length of stay was 1.6 days for the non-shunt group and 2.2 days for the shunt group. The routine shunt group (n=878) had an overall stroke rate of 0.7%, no permanent cranial nerve deficits, and a mean hospital stay of 2.6 days. CEA under general anesthesia with selective shunting can be performed safely without cerebral monitoring.

Electroencephalography (EEG) and somatosensory evoked potentials (SEP) to prevent cerebral ischaemia in the operating room

We review the principal aspects of EEG and SEP to detect and prevent cerebral ischaemia in the operating room during interventions at risk. EEG and SEP are variables that indirectly reflect cerebral blood flow (CBF) provided that anaesthetic regimen, body temperature, and arterial blood pressure of the patient are stable. When CBF decreases and reaches the functional threshold, slowing and/or attenuation of EEG occurs while the amplitude and the latency of cortical SEP are, respectively decreased and lengthened. Based on these changes, numerous criteria corresponding to critical thresholds have been defined. A decrease in EEG amplitude greater than 30% or EEG changes lasting more than 30 s have been considered as significant by clinicians. The main criteria resulting from computerized EEG analysis were a reduction in total power and/or in spectral edge frequency. Regarding SEP, a more than 50% decrease in N20 amplitude and/or a more than 1 ms increase in central conduction time were the most frequently used criteria. According to the bulk of literature, it may be concluded that processed EEG analysis is more sensitive than visual EEG analysis to detect cerebral ischaemia, and that SEP are not less sensitive than conventional EEG. Moreover, literature shows that SEP are as specific as computerized EEG analysis to disclose ischaemia during carotid endarterectomy.

The evolution of extracranial carotid artery surgery as seen by one surgeon over the past 40 years

Carotid endarterectomy is one of the most common vascular and neurosurgical operations. Controversies regarding its indications and safety have required several decades before general resolution, while its methodology is still debated. The first operations are described with particular emphasis on the epic successful procedure in 1954 by Eastcott and Rob. Early procedures were on patients with frank strokes with poor results. The development of carotid endarterectomy was slow because neurologists were unsure of its effectiveness and safety as the mortality and stroke results recorded by untrained surgeons were unacceptable. It was not until some 35 years after its introduction that randomised controlled trials, both in North America and Europe, defined its indications and demonstrated its benefits for both symptomatic and asymptomatic carotid stenosis. Clamping of the carotid vessels, required during endarterectomy, may result in various degrees of cerebral ischaemia. Methods to determine which patients need shunting are compared. The author has employed local neck block anesthesia since 1972, which is the only method that provides constant neurological assessment for selective shunting during carotid cross clamping. Evidence is presented showing that local anaesthesia also reduces complications of general anaesthesia, especially myocardial infarction. The technique of neck block, conventional endarterectomy and two varieties of eversion endarterectomy for carotid disease are described. Each of these techniques of endarterectomy is advantageous in certain circumstances, suggesting that vascular surgeons should ideally be proficient in each. Likewise, the management of early stroke after operation, stenotic or occluded external carotid the presence of retinal Hollenhorst plaques, and the totally occluded internal carotid, is presented. Finally, observations on some famous figures who suffered from cerebrovascular complications secondary to carotid disease and what effect it may have had on world history is discussed.

Carotid endarterectomy with routine electroencephalography and selective shunting: Influence of contralateral internal carotid artery occlusion and utility in prevention of perioperative strokes

OBJECTIVE

Carotid endarterectomy (CEA) is associated with a risk of cerebral ischemia during carotid clamping, particularly in the face of contralateral internal carotid artery (ICA) occlusion. We examined the results of CEA with continuous electroencephalography in patients without and with contralateral ICA occlusion.

DESIGN AND SETTING

We reviewed 564 primary CEAs with routine electroencephalography and general anesthesia performed between April 1, 1989, and March 31, 1999, in a community teaching medical center. Main outcome measures were perioperative stroke, temporary lateralizing neurologic deficit, and death. Shunts were placed primarily for significant electroencephalographic changes after carotid clamping but also selectively for contralateral ICA occlusion, prior stroke, or surgeon choice. CEA was performed for asymptomatic disease in 35% of cases.

RESULTS

Significant electroencephalographic changes occurred in 16% versus 39% (P <.001) and shunts were placed in 13% versus 55% (P <.001) of patients with patent (n = 507) versus occluded contralateral ICA (n = 57), respectively. The fraction of CEAs with significant electroencephalographic changes during clamping was stable, but shunt use declined slightly over time as our confidence in electroencephalography increased. Patches were placed more often (86% versus 65%; P =.002), but other operative details were similar when the contralateral ICA was occluded. Five early (30 days) strokes (0.9%) and eight early temporary postoperative neurologic events (1.4%) occurred, all ipsilateral to CEA and all after the patient left the operating room with none in patients with contralateral ICA occlusion. Two perioperative deaths occurred, one in a patient without and one in a patient with contralateral ICA occlusion. Neither of these deaths was related to ipsilateral stroke. No increase in stroke rate with decreased shunt use over time was seen.

CONCLUSION

Routine use of electroencephalography was associated with apparent complete elimination of intraoperative strokes and less than 1% risk of perioperative strokes. These observations appear to be true even in the face of contralateral ICA occlusion. Electroencephalography is a sensitive detector of cerebral ischemia and a valuable tool for determination of need for shunting during CEA. Surgeons should consider routine use of electroencephalography and selective shunting for significant electroencephalographic changes with clamping.

Routine or selective carotid artery shunting for carotid endarterectomy (and different methods of monitoring in selective shunting)

BACKGROUND

Temporary interruption of cerebral blood flow during carotid endarterectomy can be avoided by using a shunt across the clamped section of the carotid artery. This may improve outcome.

OBJECTIVES

The objective of this review was to assess the effect of routine versus selective, or never, shunting during carotid endarterectomy, and to assess the best method for selecting patients for shunting.

SEARCH STRATEGY

For the original review the authors searched the Cochrane Stroke Group trials register, Medline (1966 to 1994), Embase (1980 to 1995) and Index to Scientific and Technical Proceedings (1980 to 1994). They also hand searched Annals of Surgery (1981 to 1995), British Journal of Surgery (1985 to 1995), European Journal of Vascular Surgery (1988 to 1995) and World Journal of Surgery (1978 to 1995). For the updated review, for the dates January 1994 - December 2000 we: 1. Repeated all these searches performed for the original review and developed more comprehensive search strategies for Medline and Embase. The Cochrane Stroke Group Trials Register was last searched in May 2001. 2. Hand searched the Journal of Vascular Surgery, Stroke, Annals of Vascular Surgery, American Journal of Surgery and Cardiovascular Surgery. 3. Hand searched the abstracts from the International Stroke Conference, AGM of the Vascular Surgical Society (UK), AGM of the Association of Surgeons of Great Britain and Ireland and the Annual Meeting of the Society for Vascular Surgery (USA). 4. Searched reference lists from all relevant trials All the authors of studies included in the initial review, and other authors known to have published relevant work, were contacted requesting information about further published or unpublished data.

SELECTION CRITERIA

Randomised and quasi-randomised trials of routine shunting compared with no shunting or selective shunting, and trials that compared different shunting policies in patients undergoing carotid endarterectomy.

DATA COLLECTION AND ANALYSIS

For the original review two reviewers independently performed the searches and applied the inclusion criteria. The data were extracted by one reviewer and double-checked. Trial quality was assessed. During the update, two reviewers independently performed the searches and applied the inclusion criteria. No new relevant randomised controlled trials were found.

MAIN RESULTS

Despite recommendation from the original review that further studies were required, no new trials of adequate quality and fitting the inclusion criteria were found. The initial review included three trials. Two trials involving 590 patients compared routine shunting with no shunting. The other trial involving 131 patients compared shunting with a combination of electroencephalographic and carotid pressure measurement, with shunting by carotid pressure measurement alone. Allocation was adequately concealed in one trial, and one trial was quasi-randomised. Analysis was by intention-to-treat where possible. For routine versus no shunting, there was no significant difference in the rate of all stroke, ipsilateral stroke or death up to 30 days after surgery, although data were limited. There was no significant difference between the risk of ipsilateral stroke in patients selected for shunting with the combination of electroencephalographic and carotid pressure assessment compared to pressure assessment alone, although again the data were limited.

REVIEWER'S CONCLUSIONS

When first published in 1995, this review concluded that the data available were too limited to either support or refute the use of routine or selective shunting in carotid endarterectomy. It was suggested that large scale randomised trials using no shunting as the control group were required. No one method of monitoring in selective shunting has been shown to produce better outcomes. No further prospective randomised or quasi-randomised trials have been performed since then and the conclusions therefore remain unchanged.

EEG changes during awake carotid endarterectomy

To determine the reason for differing shunt rates based on electroencephalographic (EEG) and neurologic changes during general and regional anesthetic, respectively, we compared simultaneous EEG tracings and neurologic status in 135 patients undergoing carotid endarterectomy (CEA) under cervical block over a 30-month period. The decision to shunt in these patients was made on the basis of neurologic changes only irrespective of EEG findings. This group was then compared to the 288 patients undergoing CEA under general anesthetic with EEG monitoring over the same period. EEG changes occurred in 7.4% of awake patients and 15.3% of asleep patients (p < 0.03). The rates of ipsilateral hemispheric changes were similar, but no awake patient manifested global EEG changes with clamping while 3.5% of patients under general anesthesia did (p < 0.04). Global, but not hemispheric, changes were correlated with systolic blood pressure variability during clamping. This implies that global EEG changes in anesthetized patients may be the result of the anesthetic technique itself, and that cervical block may in fact be cerebroprotective.