Bispectral index monitoring may not reliably indicate cerebral ischaemia during awake carotid endarterectomy † †This study was conducted in the Department of Neurosurgery, Newcastle General Hospital, Newcastle Upon Tyne NE4 6BE, UK. Preliminary results were presented at the British Neurosurgery Research Group Meeting, Sheffield, March 29–30, 2001

Use of bispectral index for detection of partial cerebral hypoperfusion during cervical spine surgery: A case report

The BIS value may decrease by cerebral hypoperfusion. We report a case in which the BIS value suddenly decreased during cervical spine surgery, which led us to find cervical screws compressing the vertebral arteries. In a 79-year-old man undergoing cervical spine surgery, the BIS suddenly decreased from about 40 to 10-20, about 4 h after the start of surgery. Intraoperative 3-dementional computed tomography indicated that both the two tips of cervical screws inserted in the 6th cervical vertebra were within bilateral transverse foramens. These cervical screws were removed, and the BIS increased immediately. The cervical screws were re-inserted again thorough the same vertebra into the bilateral transverse foramens, and the BIS decreased immediately. Postoperatively, cerebral hypoperfusion due to compression of bilateral vertebral arteries by two cervical screws was identified. The BIS may be a useful to detect cerebral hypoperfusion due to compression of the vertebral artery by a cervical screw.

Near-infrared spectroscopy and processed electroencephalogram monitoring for predicting peri-operative stroke risk in cardiothoracic surgery: An observational cohort study

BACKGROUND

Stroke is a feared complication after cardiothoracic surgery, with an incidence of around 2 to 3%. Anaesthesia and postoperative sedation may obscure clinical symptoms of stroke and thus delay diagnosis and timely intervention.

OBJECTIVES

The objective was to assess the value of intra-operative neuromonitoring and blood pressure monitoring for predicting the occurrence of peri-operative stroke within 3 days after cardiothoracic surgery.

DESIGN

Single-centre retrospective observational cohort study.

SETTING

Academic tertiary care medical centre.

PATIENTS

All consecutive patients with cardiothoracic surgery and intra-operative neuromonitoring admitted postoperatively to the Intensive Care Unit (ICU) between 2008 and 2017.

MAIN OUTCOME MEASURES

The primary endpoint was the occurrence of any stroke confirmed by brain imaging within 3 days postcardiothoracic surgery. Areas under the curve (AUC) of intra-operative mean arterial pressure (MAP), cerebral oxygen saturation (ScO2) and bispectral index (BIS) below predefined thresholds were calculated, and the association with early stroke was tested using logistic regression analyses.

RESULTS

A total of 2454 patients admitted to the ICU after cardiothoracic surgery had complete intra-operative data for ScO2, BIS and MAP and were included in the analysis. In 58 patients (2.4%), a stroke was confirmed. In univariate analysis, a larger AUCMAP greater than 60 mmHg [odds ratio (OR) 1.43; 95% confidence interval (CI), 1.21 to 1.68) and larger AUCBIS<25 (OR 1.51; 95% CI, 1.24 to 1.83) were associated with the occurrence of postoperative stroke while ScO2 less than 50% or greater than 20% reduction from individual baseline was not (OR 0.91; 95% CI, 0.50 to 1.67). After multivariable analysis, AUCBIS<25 (OR 1.45; 95% CI, 1.12 to 1.87) and longer duration of MAP less than 60 mmHg (OR 1.52; 95% CI, 1.02 to 2.27) remained independently associated with stroke occurrence.

CONCLUSION

Cumulative intra-operative BIS values below 25 and longer duration of MAP below 60 mmHg were associated with the occurrence of peri-operative stroke within 3 days after cardiothoracic surgery. Prospective studies are warranted to evaluate a causal relationship between low BIS and stroke to establish whether avoiding intra-operative BIS values below 25 might reduce the incidence of peri-operative stroke.

Usefulness and Reliability of the Bispectral Index during Balanced Anesthesia for Neurovascular Surgery in New Zealand White Rabbits

Few data about the electroencephalogram and its calculated indices, such as the bispectral index (BIS), have been reported in rabbits. We aimed to evaluate whether a clinically stable anesthesia was mirrored by consistent and stable BIS values and to investigate the effects of modified cerebral blood supply, due to bilateral carotid clamping and re-opening, on BIS values. We also investigated the effects of fentanyl, as an antinociceptive drug, on the BIS. Sixty-eight rabbits undergoing general anesthesia for surgical creation of carotid bifurcation aneurysms were enrolled. The BIS values were recorded at nine selected time points (TPs) during each procedure and before and after fentanyl administration. The BIS values over time were compared with two-way repeated-measures analysis of variance followed by Tukey test, while the Wilcoxon signed rank test was performed to compare values at clamping and re-opening of the carotids as well as before and after fentanyl administration. The BIS values were significantly lower during anesthesia than at the end of anesthesia and at tracheal extubation; no significant differences were found among other TPs. Adequate depth of anesthesia was mirrored by consistent BIS values among rabbits, and alteration of cerebral blood supply did not modify BIS values, except once. Following fentanyl, BIS values did not change in a clinically relevant way.

Neuromonitoring and Neurocognitive Outcomes in Cardiac Surgery: A Narrative Review

Neurocognitive dysfunction after cardiac surgery can present with diverse clinical phenotypes, which include postoperative delirium, postoperative cognitive dysfunction, and stroke, and it presents a significant healthcare burden for both patients and providers. Neurologic monitoring during cardiac surgery includes several modalities assessing cerebral perfusion and oxygenation (near-infrared spectroscopy, transcranial Doppler and jugular venous bulb saturation monitoring) and those that measure cerebral function (processed and unprocessed electroencephalogram), reflecting an absence of a single, definitive neuromonitor. This narrative review briefly describes the technologic basis of these neuromonitoring modalities, before exploring their use in clinical practice, both as tools to predict neurocognitive dysfunction, and with a bundle of interventions designed to optimize cerebral oxygen supply, with the aim of reducing postoperative delirium and cognitive dysfunction following cardiac surgery.

Considerations for Reduction of Risk of Perioperative Stroke in Adult Patients Undergoing Cardiac and Thoracic Aortic Operations: A Scientific Statement From the American Heart Association

Perioperative stroke is one of the most severe and feared complications of cardiac surgery. Based on the timing of onset and detection, perioperative stroke can be classified as intraoperative or postoperative. The pathogenesis of perioperative stroke is multifactorial, which makes prediction and prevention challenging. However, information on its incidence, mechanisms, diagnosis, and treatment can be helpful in minimizing the perioperative neurological risk for individual patients. We herein provide suggestions on preoperative, intraoperative, and postoperative strategies aimed at reducing the risk of perioperative stroke and at improving the outcomes of patients who experience a perioperative stroke.

A Review of Bispectral Index Utility in Neurocritical Care Patients

Context: Bispectral Index (BIS) was introduced in 1960 to monitor the depth of anesthesia in the operating rooms. It has been recently used to monitor the sedation in the critically ill patients hospitalized in intensive care and neurocritical care units (NCCU). Evidence Acquisition: Patients in the NCCU, particularly those with prolonged mechanical ventilation require appropriate adjustments in the administration of sedative drugs. Similarly, those who require neuro protection with barbiturates need to be closely monitored in the depth of their coma. Results: BIS may be a useful tool in this situation, and it can also help shorten the duration of mechanical ventilation by determining the appropriate time to eliminate patients from mechanical ventilation. We conducted a literature search to evaluate the utility of BIS monitoring in the NCCU patients with subarachnoid hemorrhage, intracranial hemorrhage, coma, cerebral hypoxia, status epilepticus and traumatic brain injury. Conclusions: BIS monitoring may be a useful adjunct to take care of the patients. However, further studies with a larger population and better design are required to substantiate the role of BIS monitoring in the care of NCCU patients.

Bilateral bispectral index monitoring to detect cerebral hypoperfusion during carotid endarterectomy under general anesthesia

The bilateral use of bispectral index (BIS) monitoring in a 68-year-old male who underwent right carotid endarterectomy (CEA) under general anesthesia (GA) is described. During three episodes of right internal carotid artery cross-clamping intraoperatively, the right BIS value rose relative to the left within 1 min of clamping, followed by a return to baseline within 1-2 min of clamp release. Since unilateral BIS values can decrease or increase in response to cross-clamping, a significant difference in left and right BIS values may provide a simple and easily available method to detect cerebral hypoperfusion during CEA under GA.

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.

Ligation of the internal jugular vein increased regional cerebral oxygen saturation but decreased the bispectral index in a 72-year-old man: a case report

Regional cerebral oxygen saturation (rSO₂) and the bispectral index (BIS) are used to detect cerebral perfusion abnormalities. However, whether rSO₂ and BIS values change during ligation of the internal jugular vein (IJV) is unknown. We report a case in which BIS values were decreased, despite increased rSO₂ during ligation of the IJV. A 72-year-old man was diagnosed with metastasis of renal cancer to the thyroid associated with tumor embolism in the right IJV. Thyroidectomy with total laryngectomy was performed. After right IJV ligation, right rSO₂ was increased from 73 to 78 %, while the right BIS value was decreased from 40 to 27. Contralateral rSO₂ and BIS values were unchanged. Right rSO₂ and BIS values returned to pre-ligation values in 10 min. Ligation of the IJV might increase cerebral blood flow and ipsilateral rSO₂. Physicians should use BIS values with caution during IJV ligation because a sudden decrease in the BIS value is not always associated with cerebral hypoperfusion.

Bispectral index as a possible early marker of cerebral hypoperfusion

We report a case of unexplained transient ventricular fibrillation in a child with ventricular septal defect (VSD) scheduled for VSD closure. The bispectral index (BIS) values dropped within 15s of transient cardiac arrest and it showed recovery within 15 s of restoration of circulation. Monitoring BIS during surgery, especially cardiac surgeries may help identify periods of cerebral ischemia early.

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.

Regional anaesthesia for carotid endarterectomy

Summary Regional anaesthesia is a popular choice for patients undergoing carotid endarterectomy (CEA). Neurological function is easily assessed during carotid cross-clamping; haemodynamic control is predictable; and hospital stay is consistently shorter compared with general anaesthesia (GA). Despite these purported benefits, mortality and stroke rates associated with CEA remain around 5% for both regional anaesthesia and GA. Regional anaesthetic techniques for CEA have improved with improved methods of location of peripheral nerves including nerve stimulators and ultrasound together with a modification in the classification of cervical plexus blocks. There have also been improvements in local anaesthetic, sedative, and arterial pressure-controlling drugs in patients undergoing CEA, together with advances in the management of patients who develop neurological deficit after carotid cross-clamping. In the UK, published national guidelines now require the time between the patient's presenting neurological event and definitive treatment to 1 week or less. This has implications for the ability of vascular centres to provide specialized vascular anaesthetists familiar with regional anaesthetic techniques for CEA. Providing effective regional anaesthesia for CEA is an important component in the armamentarium of techniques for the vascular anaesthetist in 2014.

Neurophysiologic monitoring in neurosurgery

This article focuses on the application of neurophysiologic monitoring in uniquely neurosurgical procedures. Neurophysiologic monitoring provides functional testing and mapping to identify neural structures. Once identified, the functionality of the central and peripheral nervous system areas at risk for neurosurgical injury can be monitored. It discusses the use of motor-evoked potentials, sensory evoked potentials, electromyography and electroencephalography to assess neurologic change.

[EEG in intensive care unit: which indications, which material?]

There is a growing development of continuous EEG monitoring (cEEG) in the intensive care unit (ICU) management of neurological patients. Its main objective is the detection of epileptic seizures or status epilepticus because the sensitivity of standard short-duration EEG recording in the ICU is poor. The aim of monitoring is to allow rapid recognition and treatment of epileptic complications in order to decrease secondary insults to the brain and improve outcome. Several studies have demonstrated that a large proportion of patients has epileptic crisis after subarachnoid haemorrhage, stroke or brain trauma, without any clinical manifestation. The EEG feature has also demonstrated a prognosis value but its value for clinical management needs further studies. Another application of EEG in the ICU is monitoring depth of anaesthesia or barbiturate treatment. Due to artifacts contamination, this is possible only in deeply sedated of paralyzed patients. The impact or cEEG monitoring on clinical management and its indications have to be further defined.

Brain monitoring with electroencephalography and the electroencephalogram-derived bispectral index during cardiac surgery

Cardiac surgery presents particular challenges for the anesthesiologist. In addition to standard and advanced monitors typically used during cardiac surgery, anesthesiologists may consider monitoring the brain with raw or processed electroencephalography (EEG). There is strong evidence that a protocol incorporating the processed EEG bispectral index (BIS) decreases the incidence intraoperative awareness in comparison with standard practice. However, there is conflicting evidence that incorporating the BIS into cardiac anesthesia practice improves "fast-tracking," decreases anesthetic drug use, or detects cerebral ischemia. Recent research, including many cardiac surgical patients, shows that a protocol based on BIS monitoring is not superior to a protocol based on end-tidal anesthetic concentration monitoring in preventing awareness. There has been a resurgence of interest in the anesthesia literature in limited montage EEG monitoring, including nonproprietary processed indices. This has been accompanied by research showing that with structured training, anesthesiologists can glean useful information from the raw EEG trace. In this review, we discuss both the hypothesized benefits and limitations of BIS and frontal channel EEG monitoring in the cardiac surgical population.

Bispectral index variations in patients with neurological deficits during awake carotid endarterectomy

BACKGROUND AND OBJECTIVE

The bispectral index (BIS) is derived from the EEG and therefore may be useful to diagnose intraoperative cerebral ischaemia. This study was undertaken to investigate BIS changes in awake patients with and without neurological deficits during carotid endarterectomy under regional anaesthesia.

METHODS

Seventy consecutive carotid endarterectomies under regional anaesthesia were divided into two surgical groups: patients with and patients without neurological deficits. Patients' neurological status was evaluated and neurological deficits were compared with BIS values. Measurements were made at different surgical stages: baseline, after sedation, at the beginning of surgery, at preclamping, at the 3 min clamping test, during shunt insertion, at declamping, 15 min after declamping and at the end of surgery. We performed intergroup and intragroup comparisons of BIS values. A decrease in BIS of at least 10 associated with neurological deficits was taken as the cut-off point for the classification of patients with logistic regression models (crude and adjusted for potential confounders).

RESULTS

Thirteen patients (18.6% of the total) developed clinical cerebral ischaemia, though BIS values decreased in 10 of these patients (76.9%). The mean BIS values were 92.5+/-5.6 and 84.7+/-12.3 for patients without and with neurological deficits, respectively (P value<0.05). The odds ratios of a BIS decrease associated with neurological deficits were 8.5 (95% confidence interval 2.1-35.1) and 5.4 (95% confidence interval 1.2-24.3) adjusted for contralateral stenosis.

CONCLUSION

Our results describe a relationship between BIS reductions and neurological deficits during carotid surgery in awake patients.

Accidental cross-clamping of the superior vena cava: management and BIS evolution

The case of a 38-year old man with recurrent adenocarcinoma of the right lung and infiltration of the thoracic wall, who underwent a right pneumonectomy with thoracic wall resection, is described. Dissection of the right pulmonary hilous was extremely difficult due to the previous operations. The superior vena cava (SVC) was accidentally ligated, resulting in profound hypotension and increased venous pressure in the internal jugular vein. Immediate blood aspiration through a 8.5-French introducer sheath lowered the venous congestion. After the SVC was cross-clamped, the Bispectral Index (BIS) acutely decreased to 0 and remained low during the resuscitation. Over the next 5 hours, BIS was directly affected by mean arterial pressure. Four days postoperatively, the patient was neurologically intact.

Does bilateral bispectral index monitoring (BIS) detect the discrepancy of cerebral reperfusion during carotid endarterectomy?

The case of a 70 year-old man undergoing bilateral carotid endarterectomy (CEA), for whom alterations in his bispectral index (BIS) values were noted during general anesthesia, is presented. Prior to bypass of the internal carotid artery (ICA), there were no significant differences in bilateral BIS values. After bypass of the left ICA, the left BIS increased to approximately 60, while the right BIS remained at 40. Four months later, no such phenomenon was found during a right CEA. BIS is useful in detecting cerebral hypoperfusion during a lower limit of autoregulation. Attaching bilateral BIS monitors may indicate successful reperfusion of cerebral blood flow in CEA.

Bispectral index changes in carotid surgery

BACKGROUND

Intraoperative monitoring of cerebral ischemia with shunting during carotid endarterectomy (CEA) remains controversial. Our objective was to evaluate the sensitivity and specificity of BIS changes during carotid clamping in relation to shunted patients in awake CEA.

METHODS

Eighty CEAs under cervical block were included. There were two patient groups: with clinical signs of cerebral ischemia (shunted patients) and without signs of cerebral ischemia (nonshunted patients). Data were based on bispectral index (BIS) values and neurological monitoring at different surgery time points, with special attention paid during carotid clamping. BIS values were compared between shunted and nonshunted patients. Sensitivity and specificity, along with positive and negative predictive values of a percentage BIS value decrease during carotid clamping from baseline BIS values, were calculated in both patient groups.

RESULTS

Shunting was performed in 11 patients with cerebral ischemia at carotid clamping. Mean BIS values were 82.82+/-11.98 in shunted patients and 92.31+/-5.42 in nonshunted patients at carotid clamping (p<0.001). Relative decreased BIS values in relation to basal BIS values were 13.57% in shunted patients and 3.68% in nonshunted patients (p<0.05). The percentage decrease in BIS was 14%, sensitivity was 81.8% (95% CI 49.9-96.8), and specificity was 89.7% (95% CI 79.3-95.4).

CONCLUSION

BIS monitoring during carotid clamping is an easy, noninvasive method which correlates with cerebral ischemia in patients undergoing CEA. A decrease>or=14% from the basal BIS value presents a high negative predictive value, and ischemia is unlikely without a decrease. Nonetheless, a decrease may not always indicate cerebral ischemia with a low positive predictive value.

Simultaneous bilateral carotid endarterectomy under local anesthesia

A 75-year-old man with bilateral carotid stenosis and severe coronary artery disease underwent successful simultaneous bilateral carotid endarterectomy under local anesthesia. A few days later, coronary artery bypass grafting was performed with no complications.

Electrophysiologic monitoring in neurosurgery

Electrophysiologic techniques have become common in the neurosurgical operating room. This article reviews the methods used for mapping neural structures or monitoring during surgery. Mapping methods allow identification of target structures for surgery, or for identifying structures to allow avoidance or plot safe pathways to deeper structures. Monitoring methods allow for surgery on nearby structures to warn of encroachment, thereby reducing unwanted injury.

Carotid endarterectomy

Carotid endarterectomy (CEA) is performed to prevent embolic stroke in patients with atheromatous disease at the carotid bifurcation. There is now substantial evidence to support early operation in symptomatic patients, ideally within 2 weeks of the last neurological symptoms. Thus, the anaesthetist may be faced with a high risk patient in whom there has been limited time for preoperative preparation. The operation may be performed under local or general anaesthesia. The advantages and disadvantages of both are explored in this review. Carotid shunting may offer a degree of cerebral protection, but carries its own risks and has not been proved to reduce morbidity and mortality. The use of carotid shunts is based on clinical judgement, awake neurological monitoring, and the use of monitors of cerebral perfusion. There is no ideal monitor of cerebral perfusion in the patient receiving general anaesthesia. Both the intraoperative and postoperative periods may be witness to dramatic haemodynamic changes that may compromise the cerebral or myocardial circulations. In particular, postoperative hypotension may compromise both myocardial and cerebral perfusion, and severe hypertension can cause cerebral hyperperfusion. There is as yet limited evidence to guide the management of these problems. In summary, CEA can yield significant benefit, but those with the most to gain from the operation also present the greatest challenge to the anaesthetist.

Bispectral Index Profile During Carotid Cross Clamping

This study aimed at investigating the Bispectral Index (BIS) profile during carotid cross clamping (CXC). The study involved a pilot group of 10 patients undergoing routine carotid endarterectomy with shunt insertion under total intravenous anesthesia, and a study group of 26 additional patients. In all patients, rates of propofol and remifentanil providing a steady-state level of hypnosis (BIS: 40-60) were maintained constant throughout a recording period ranging from 3 minutes before CXC to shunt insertion. BIS was recorded throughout this period and the internal carotid backflow observed at the time of shunt insertion was graded as good, moderate, or poor. In addition, A-Line Autoregressive Index (AAI) and processed electroencephalogram (EEG) parameters were recorded in patients of the study group. All parameters were averaged over 1 minute before CXC, at CXC, 1, 2, and 3 minutes after CXC, and at shunt insertion. Statistical analysis was performed using chi2, Friedman, and Spearman correlation tests. For technical reasons, reliable AAI, BIS monitor-derived, and other processed EEG data were obtained in 24, 25, and 18 patients of the study group, respectively. During the first 3 minutes after CXC, BIS increased over 60 [68.8 (6.1)] in 47%, decreased below 40 [34.9 (4.4)] in 25%, and remained in the 40 to 60 range in 28% of all recruited patients. A BIS increase was more frequently observed in patients with moderate or poor than in those with good internal carotid backflow (78, 67, and 29%, respectively). It was significantly correlated to an increase in AAI and EEG amplitude, a decrease in EEG suppression ratio, and a shorter time between induction of anesthesia and CXC. A BIS decrease was significantly correlated to an increase in suppression ratio and a longer time between induction and CXC. In conclusion, during CXC under a constant level of intravenous anesthesia, BIS may increase, decrease, or remain unchanged. The paradoxical BIS increase could be related to borderline ischemia, a change in brain anesthetic agent concentration, or a change in the nociceptive-antinociceptive balance associated with a CXC-elicited painful stimulation. Caution should be used when interpreting BIS value during CXC.

Bispectral Index Monitoring of Unihemispheric Effects in Dolphins

When dolphins sleep, their electroencephalographic activity may change in only one cerebral hemisphere; i.e., the left and right brain hemispheres can take turns sleeping. We demonstrate that the bispectral index (BIS) monitor can detect interhemispheric asymmetry in the dolphin species Tursiops truncatus. Using two BIS sensors placed simultaneously over each side of the dolphin's head, we often, but not always, found significant differences between the two BIS values (e.g., left side 60 and right side 90) in non-medicated animals and in animals given propofol, atropine, and/or diazepam. Observations were each made over a period of approximately 3 h on dolphins resting out of the water. Unihemispheric effects may be inducible pharmacologically in dolphins. The dolphin, with its human-sized brain, may provide an animal model for study of unihemispheric effects in humans.