When the bispectral index (bis) can give false results

Effect of bispectral index on intra-operative awareness: A meta-analysis of randomized controlled studies

Background

Randomized controlled trials (RCTs) investigating the efficacy of bispectral index (BIS) to reduce intra-operative awareness (IOA) have reported conflicting results. The purpose of this meta-analysis is to consolidate results from RCTs to assess the efficacy of BIS in reducing IOA when compared to controls. Secondary outcomes included time to extubation, time to spontaneous and/or verbal eye opening, PACU discharge time, and utilization of inhaled anesthetics.

Methods

RCTs which reported on one of the primary and/or secondary outcomes were included. Literature search utilized keywords "randomized control trial" and "intraoperative awareness." Meta-analysis was performed using RevMan 5.

Results

Twenty-seven RCTs were included in the study with a total of 35,585 patients, with 18,146 patients in the BIS and 17,439 in the control group. Eighteen of 14,062 patients (0.12%) and 42 of 16,765 (0.25%) reported definite IOA in the BIS and control group, respectively, with no statistically significant difference. BIS was effective in reducing the time to spontaneous eye opening by an average of 1.3 minutes and the time to extubation by an average of 1.97 minutes. There was no difference in PACU discharge times among the groups. There was a significant decrease in consumption of sevoflurane but no difference in desflurane and propofol compared to the control group.

Conclusion

While BIS monitoring results in decreased incidence of intra-operative awareness by half, it was not statistically significant. BIS provides modest benefits with regard to reducing the time to extubation, the time to spontaneous eye opening, and consumption of sevoflurane.Level of evidence: I.

Unreported Source of Interference with the Bispectral Index During Liposuction: A Case Report

Incorrect bispectral index (BIS) values have been reported due to interference with this monitoring system. We report a case of a 46-year-old woman who underwent liposuction and breast lipofilling, where we observed a misinterpretation by the BIS algorithm that has not yet been reported. Concurrently with abdominal and thigh liposuction, an increase in the BIS value was observed. The importance of examining electroencephalogram (EEG) and density spectral array (DSA) readings during liposuction procedures is highlighted in this case report, extending our observations beyond just the numerical BIS value, which is not always reliable.

Comparative analysis of the effect of electromyogram to bispectral index and 95% spectral edge frequency under remimazolam and propofol anesthesia: a prospective, randomized, controlled clinical trial

Background

Bispectral index (BIS), an index used to monitor the depth of anesthesia, can be interfered with by the electromyogram (EMG) signal. The 95% spectral edge frequency (SEF95) also can reflect the sedation depth. Remimazolam in monitored anesthesia care results in higher BIS values than propofol, though in the same sedation level assessed by Modified Observers Assessment of Alertness and Sedation (MOAA/S). Our study aims to illustrate whether EMG is involved in remimazolam causing higher BIS value than propofol preliminarily and to explore the correlations among BIS, EMG, and SEF95 under propofol and remimazolam anesthesia.

Patients and methods

Twenty-eight patients were randomly divided into propofol (P) and remimazolam (RM) groups. Patients in the two groups received alfentanil 10 μg/kg, followed by propofol 2 mg/kg and remimazolam 0.15 mg/kg. Blood pressure (BP), heart rate (HR), and oxygen saturation (SpO2) were routinely monitored. The BIS, EMG, and SEF95 were obtained through BIS VISTATM. The primary outcomes were BIS, EMG, and the correlation between BIS and EMG in both groups. Other outcomes were SEF95, the correlation between BIS and SEF95, and the correlation between EMG and SEF95. And all the statistical and comparative analysis between these signals was conducted with SPSS 26.0 and GraphPad Prism 8.

Results

BIS values, EMG, and SEF95 were significantly higher in the RM group than in the P group (all p < 0.001). There was a strong positive correlation between BIS and EMG in the RM group (r = 0.416). Nevertheless, the BIS in the P group showed a weak negative correlation with EMG (r = -0.219). Both P (r = 0.787) and RM group (r = 0.559) had a reasonably significant correlation coefficient between BIS and SEF95. SEF95 almost did not correlate with EMG in the RM group (r = 0.101).

Conclusion

Bispectral index can be interfered with high EMG intensity under remimazolam anesthesia. However, EMG can hardly affect the accuracy of BIS under propofol anesthesia due to low EMG intensity and a weak negative correlation between EMG and BIS. Moreover, SEF95 may have a great application prospect in predicting the sedation condition of remimazolam.

Stimulation artefact on EEG trace with BIS monitoring during D-wave recording

The D-wave reflects the corticospinal fibre potentials and is frequently recorded intraoperatively for intramedullary spinal tumours to ensure maximum safe resection. A 38-year-old male had an intramedullary spinal cord tumour surgically removed while being monitored with D-wave from a single distal electrode technique. Total intravenous anaesthesia (TIVA) with propofol (without a muscle relaxant and with intermittent intravenous fentanyl boluses) was used for the maintenance of anaesthesia guided by processed electroencephalography (EEG) using a bispectral index (BIS^®) monitor. Regular spike artefacts were observed in the EEG signal recorded by the BIS® monitor during the application of the single-pulse transcranial electrical stimulus and were used as a visual indicator of stimulus delivery. Finally, we propose a novel method of confirming stimulus delivery during D-wave recording based on stimulation artefacts in the EEG signal recorded by the BIS® monitor.

Evaluation of Prognosis of Coma Patients With Acute Brain Injury by Electroencephalogram Bispectral Index Monitoring

BACKGROUND

The high mortality rate of comatose patients with traumatic brain injury is a prominent public health issue that negatively impacts patients and their families. Objective, reliable tools are needed to guide treatment decisions and prioritize resources.

OBJECTIVE

This study aimed to evaluate the prognostic value of the bispectral index (BIS) in comatose patients with severe brain injury.

METHODS

This was a retrospective cohort study of 84 patients with severe brain injury and Glasgow Coma Scale (GCS) scores of 8 and less treated from January 2015 to June 2017. Sedatives were withheld at least 24 hr before BIS scoring. The BIS value, GCS scores, and Full Outline of UnResponsiveness (FOUR) were monitored hourly for 48 hr. Based on the Glasgow Outcome Scale (GOS) score, the patients were divided into poor (GOS score: 1-2) and good prognosis groups (GOS score: 3-5). The correlation between BIS and prognosis was analyzed by logistic regression, and the receiver operating characteristic curves were plotted.

RESULTS

The mean (SD) of the BIS value: 54.63 (11.76), p = .000; and GCS score: 5.76 (1.87), p = .000, were higher in the good prognosis group than in the poor prognosis group. Lower BIS values and GCS scores were correlated with poorer prognosis. Based on the area under the curve of receiver operating characteristic curves, the optimal diagnostic cutoff value of the BIS was 43.6, and the associated sensitivity and specificity were 85.4% and 74.4%, respectively.

CONCLUSION

Taken together, our study indicates that BIS had good predictive value on prognosis. These findings suggested that BIS could be used to evaluate the severity and prognosis of severe brain injury.

Comparison of the Effects of Target-Controlled Infusion of Propofol and Sevoflurane as Maintenance of Anesthesia on Hemodynamic Profile in Kidney Transplantation

Background

Target-controlled infusion (TCI) propofol and sevoflurane are common agents for general anesthesia, including for kidney transplantation procedure. This study compared the effect of TCI propofol and sevoflurane on intraoperative hemodynamic profile in kidney transplant patients.

Methods

A single-blinded prospective study was performed in 46 kidney transplant recipients who were randomized into receiving TCI propofol or sevoflurane as anesthetics maintenance. Hemodynamic parameters such as mean arterial pressure (MAP), cardiac index (CI), stroke volume index (SVI), and systemic vascular resistance index (SVRI) were measured at baseline before induction, postintubation, first surgical incision, every 15 minutes after the first incision, reperfusion, and 15 minutes after reperfusion. Data were analyzed using unpaired t-test, paired t-test, and general linear model.

Results

Intraoperative MAP, CI, SVI, and SVRI changes were similar in both groups (p = 0.480, 0.216, 0.086, and 0.054). In comparison to the baseline value, TCI propofol and sevoflurane groups showed significant reductions of MAP at postintubation (p=0.010; p < 0.001) and during the first surgical incision (p=0.009; p < 0.001); significant reduction of CI at postintubation (p=0.003; p < 0.001) and during the first surgical incision (p < 0.001; p < 0.001); significant reduction of SVI at postintubation (p=0.013; p=0.008), during the first surgical incision (p=0.008; p=0.003), and 15 minutes after reperfusion (p=0.010; p=0.005); and significant increasing of SVRI during the first surgical incision (p=0.007; p=0.005). The TCI propofol group showed significantly lower SVRI compared to the sevoflurane group postintubation (p=0.029) and during the first surgical incision (p=0.026).

Conclusion

Intraoperative hemodynamic profile was similar between the TCI propofol and sevoflurane group during kidney transplant surgery. The TCI propofol group had higher CI and SVI but showed significantly lower SVRI as compared to the sevoflurane group. The incidence of postanesthesia agitation, postoperative outcome, and complication were not significantly different between the two groups.

Falsely high patient state index during cardiopulmonary bypass with intra-aortic balloon pumping: a case report

Background

The patient state index (PSI) is a parameter of a four-channel electroencephalography (EEG)-derived variable used to assess the depth of anesthesia. A PSI value of 25–50 indicates adequate state of hypnosis, and a value of 100 indicates a fully awake state. Due to reduced interference from electronic devices like electrocautery, falsely high intraoperative PSI values are rarely reported. However, this case report cautions about falsely high PSI during cardiopulmonary bypass (CPB) with intra-aortic balloon pumping (IABP).

Case presentation

A 68-year-old man was scheduled for coronary artery bypass graft surgery with IABP. General anesthesia was maintained using sevoflurane. Initial PSI was between 30 and 50 before CPB. Propofol was administered during CPB, and IABP provided pulsatile flow. IABP was stopped soon after the initiation of CPB, and the ascending aorta was partially clamped to anastomose the saphenous vein graft to the ascending aorta. The PSI value decreased drastically, but with resumption of IABP, the value increased to approximately 80, despite increasing the dose of anesthetics. Meanwhile, the EEG waveform was nearly flat. After discontinuing CPB, the PSI value returned to being extremely low. There was no evidence of intraoperative awareness or instrument trouble.

After reviewing the anesthesia record, the high PSI value was almost consistent with ongoing IABP during CPB. We suspect that the oscillation noise created by IABP during CPB erroneously influences the PSI algorithm, resulting in a falsely high PSI.

Conclusions

Anesthesiologists should note that adherence to pEEG-derived values without discretion may cause errors when monitoring the depth of anesthesia.

Proof of principle: Preoperative cognitive reserve and brain integrity predicts intra-individual variability in processed EEG (Bispectral Index Monitor) during general anesthesia

BACKGROUND

Preoperative cognitive reserve and brain integrity may explain commonly observed intraoperative fluctuations seen on a standard anesthesia depth monitor used ubiquitously in operating rooms throughout the nation. Neurophysiological variability indicates compromised regulation and organization of neural networks. Based on theories of neuronal integrity changes that accompany aging, we assessed the relative contribution of: 1) premorbid cognitive reserve, 2) current brain integrity (gray and white matter markers of neurodegenerative disease), and 3) current cognition (specifically domains of processing speed/working memory, episodic memory, and motor function) on intraoperative neurophysiological variability as measured from a common intraoperative tool, the Bispectral Index Monitor (BIS).

METHODS

This sub-study included participants from a parent study of non-demented older adults electing unilateral Total Knee Arthroplasty (TKA) with the same surgeon and anesthesia protocol, who also completed a preoperative neuropsychological assessment and preoperative 3T brain magnetic resonance imaging scan. Left frontal two-channel derived EEG via the BIS was acquired preoperatively (un-medicated and awake) and continuously intraoperatively with time from tourniquet up to tourniquet down. Data analyses used correlation and regression modeling.

RESULTS

Fifty-four participants met inclusion criteria for the sub-study. The mean (SD) age was 69.5 (7.4) years, 54% were male, 89% were white, and the mean (SD) American Society of Anesthesiologists score was 2.76 (0.47). We confirmed that brain integrity positively and significantly associated with each of the cognitive domains of interest. EEG intra-individual variability (squared deviation from the mean BIS value between tourniquet up and down) was significantly correlated with cognitive reserve (r = -.40, p = .003), brain integrity (r = -.37, p = .007), and a domain of processing speed/working memory (termed cognitive efficiency; r = -.31, p = .021). Hierarchical regression models that sequentially included age, propofol bolus dose, cognitive reserve, brain integrity, and cognitive efficiency found that intraoperative propofol bolus dose (p = .001), premorbid cognitive reserve (p = .008), and current brain integrity (p = .004) explained a significant portion of intraoperative intra-individual variability from the BIS monitor.

CONCLUSIONS

Older adults with higher premorbid reserve and less brain disease were more stable intraoperatively on a depth of anesthesia monitor. Researchers need to replicate findings within larger cohorts and other surgery types.

Minimum Alveolar Concentration of Desflurane for Maintaining BIS Below 50 in Children and Effect of Caudal Analgesia on it

Context:

Neuraxial techniques have sedative properties secondary to decreased inputs from sensory and motor afferents. We hypothesized that caudal analgesia decreases the requirement of desflurane as measured by bispectral index (BIS).

Aims:

This study aims to determine the minimum alveolar concentration (MAC) of desflurane for maintaining BIS below 50 (MACBIS₅₀) in children undergoing infraumbilical surgeries with laryngeal mask airway (LMA) and study the effect of caudal analgesia on the same.

Settings and Design:

This is prospective and observational study.

Subjects and Methods:

Thirty-nine American Society of Anesthesiologists physical status Classes I and II children in between 1 and 8 years of age undergoing elective infraumbilical surgery under general anesthesia were allocated randomly into two groups (Group C and Group D) after induction with sevoflurane and LMA insertion. In Group C, caudal block was performed with 0.75 mL/kg of 0.25% bupivacaine and BIS values were recorded after 10 min for 1 min at 10 s intervals. In Group D, BIS was recorded for desflurane for 1 min at 10 s intervals followed by a caudal block with the same dose.

Statistical Analysis Used:

Dixon up-down method with a step size of 0.5%, and probit analysis were used for analysis.

Results:

A total of 39 patients were enrolled. MAC of desflurane for maintaining MACBIS₅₀ was 5.57 (95% confidence interval [CI] 5.22–5.95) in Group D and 4.31 (95% CI 3.12–5.08) in Group C. The use of caudal anesthesia lowered the MAC of desflurane for maintaining MACBIS₅₀ in children by 22.36% (P < 0.001).

Conclusions:

The use of caudal analgesia significantly reduced MAC of desflurane for maintaining MACBIS₅₀ in children undergoing infraumbilical surgeries using LMA.

Anaesthesia and orphan disease: airway and anaesthetic management in Huntington's disease

We present a case that highlights the issues surrounding the delivery of a safe general anaesthetic to a patient with Huntington's disease (HD) and bulbar dysfunction. In the case of a 46-year-old patient undergoing laparoscopic percutaneous endoscopic gastrostomy tube insertion, we discuss the rationale behind our chosen method and anaesthetic agents as well as airway issues specific to HD. In a patient whose condition would not allow for an awake fibreoptic intubation, we opted for a modified rapid sequence induction. Special considerations were made with regard to muscle relaxation given the complications associated with inadequate paralysis and reversal in patients with HD. The technique we describe may also apply to other patient categories, such as patients with movement disorders, bulbar dysfunction and dementia.

Correlation Between Bispectral Index and Electrocorticographic Features During Epilepsy Surgery

Surgical resection guided by intraoperative electrocorticography (iECoG) has been in clinical use for many decades. The use of the bispectral index (BIS) for monitoring depth of anesthesia during different types of surgery, including epilepsy surgery, is increasing nowadays. The BIS is an EEG-derived variable indicating cortical electrical activity. However, the correlation between the BIS score and the iECoG score, with the purpose of optimizing the quality and time of the iECoG recordings in epilepsy surgery is unknown. The goal of this study was to evaluate the correlation between BIS values and iECoG parameters during the epilepsy surgery under anesthesia with propofol and fentanyl. This is a prospective study that included patients with epilepsy who underwent epilepsy surgery guided by BIS and iECoG (September 2008 to October 2013). Clinical, physiological, and sociodemographic characteristics are shown. We correlated the iECoG parameters (presence of burst suppressions [BS], suppression time [seconds], background frequency [Hz], and type of iECoG score by Mathern et al) with BIS values. We included 28 patients, 15/28 (53.5%) female, general mean age of 30.5 years (range 13-56 years). Patients underwent epilepsy surgery: 22/28 (79%) temporal and 6/28 (21%) extratemporal. We found a nonlinear polynomial cubic relationship between the mentioned variables noting that a BIS range of 40 to 60 gave the following results: iECoG BS periods <5 seconds, background frequency 10 to 17 Hz, and iECoG score 2 characterized by lack of >20-Hz background frequencies. No BS were observed with a BIS > 60. In conclusion BIS values and iECoG parameters during the epilepsy surgery under anesthesia with propofol and fentanyl have a nonlinear correlation. BS patterns were not found with a BIS > 60. These findings show that BIS is a nonlinear multidimensional measure, which possesses high variability with the iECoG parameters. BS patterns are not found with BIS > 60.

Clinical Applicability of Monitoring the Time Interval Between Anesthesia and Electroconvulsive Therapy

The anesthetic-electroconvulsive therapy (ECT) time interval (time interval elapsed from the beginning of anesthesia injection to the beginning of ECT stimulus) has been reported to have an important impact on seizure quality outcomes, because it is an indirect measure of the anesthetic plasma concentration when the ECT electrical stimulus is administered. We report the importance of the routine monitoring of this time interval in clinical settings, as an additional measure to interpret seizure quality outcomes at each ECT session, to further assist on ECT dosing decisions during the treatment course.

Comparison of FFT and marginal spectra of EEG using empirical mode decomposition to monitor anesthesia

BACKGROUND AND OBJECTIVE

Intraoperative awareness refers that patients can recall aspects of their surgery after being put under general anesthesia. This distressing complication causes affected patients to be conscious and probably feel pain, leading to emotional trauma or other sequelae. Monitoring and administrating the depth of anesthesia is necessary to prevent patients from awareness during a medical operation. In this paper, we analyzed the electroencephalograms (EEGs) of patients to characterize their anesthesia. The data set, "awareness" and "anesthesia" groups, each contained 558 samples, including patients who had undergone different types of surgeries.

METHODS

EEG signals acquired from patients in an aware state or under anesthesia were decomposed into a set of intrinsic mode functions (IMFs) through empirical mode decomposition (EMD). Fast Fourier transform (FFT) and Hilbert transform (HT) analyses were then performed on each IMF to determine the frequency spectra. The probability distributions of expected values of frequencies were generated for the same IMF in the two groups of patients. The corresponding statistical data, including analysis of variance tests, were also calculated. A receiver operating characteristic curve was used to identify optimal frequency value to discriminate between the two states of consciousness.

RESULTS

The frequencies of the IMFs for aware patients were found to be higher than those for anesthetized patients. The optimal frequency threshold by using FFT (or HT) for IMF 1 was 21.08 (or 25.00) Hz. IMF1 performed the highest with respect to the area under the curve (AUC) of 0.993 for FFT (or 0.989 for HT); hence it can be applied as a useful classifier to distinguish between fully anesthetized patients and aware patients.

CONCLUSIONS

This paper proposes a method for identifying whether patients' state of consciousness during a range of surgery types is "under anesthesia" or "aware." Our method involves using EEG to characterize the depth of anesthesia through two frequency analysis techniques. On the basis of our analyses, we conclude that the performance of IMF1 is satisfactory in distinguishing between patients' states of consciousness during surgery requiring general anesthesia.

Monitoring cerebral oxygenation and local field potential with a variation of isoflurane concentration in a rat model

We aimed to investigate experimentally how anesthetic levels affect cerebral metabolism measured by near-infrared spectroscopy (NIRS) and to identify a robust marker among NIRS parameters to discriminate various stages of anesthetic depth in rats under isoflurane anesthesia. In order to record the hemodynamic changes and local field potential (LFP) in the brain, fiber-optic cannulae and custom-made microelectrodes were implanted in the frontal cortex of the skull. The NIRS and LFP signals were continuously monitored before, during and after isoflurane anesthesia. As isoflurane concentration is reduced, the level of oxyhemoglobin and total hemoglobin concentrations of the frontal cortex decreased gradually, while deoxyhemoglobin increased. The reflectance ratio between 730nm and 850nm and burst suppression ratio (BSR) correspond similarly with the change of oxyhemoglobin during the variation of isoflurane concentration. These results suggest that NIRS signals in addition to EEG may provide a possibility of developing a new anesthetic depth index.

Hardin K. Inadequate Sedation During Therapeutic Paralysis: Use of Bispectral Index in Critically Ill Patients

Background

Patients receiving therapeutic paralysis may experience inadequate sedation due to intrinsic limitations of behavioral sedation assessment. Bispectral index (BIS™) provides an objective measure of sedation; however, the role of BIS™ is not well defined in intensive care unit (ICU) patients on neuromuscular blocking agents (NMBA).

Objective

The aim of this study was to delineate the relationship between BIS™ and level of sedation for critically ill patients during therapeutic paralysis.

Methods

This was a retrospective observational study conducted in ICU patients receiving continuous infusion NMBA and BIS™ monitoring. The primary endpoint was the correlation of BIS™ <60 during therapeutic paralysis with a Richmond Agitation Sedation Score (RASS) of −4 to −5 (i.e., deep or unarousable sedation) at the time of emergence from therapeutic paralysis.

Results

Thirty-one patients were included in the analysis. Three of these patients (9.6 %) were inadequately sedated upon emergence from paralysis; that is, restless or agitated (RASS +1 to +2). We did not observe a correlation between BIS™ and RASS upon emergence from paralysis (r = 0.27, p = 0.14). The sensitivity of BIS™ <60 in predicting deep sedation (RASS −5 to −4) was 100 % (95 % confidence interval [CI] 0–100) with a positive predictive value of 35.7 %. The sensitivity and positive predictive value of BIS™ <60 in predicting light sedation or deeper (RASS −5 to −2) was 92.9 % (95 %CI 83.3–100) and 92.9 %, respectively.

Conclusion

These results suggest that 1 in 10 critically ill patients receiving therapeutic paralysis may be inadequately sedated. BIS™ monitoring may serve as a useful adjunctive measure of sedation in critically ill patients receiving therapeutic paralysis.

Mechanisms underlying brain monitoring during anesthesia: limitations, possible improvements, and perspectives

Currently, anesthesiologists use clinical parameters to directly measure the depth of anesthesia (DoA). This clinical standard of monitoring is often combined with brain monitoring for better assessment of the hypnotic component of anesthesia. Brain monitoring devices provide indices allowing for an immediate assessment of the impact of anesthetics on consciousness. However, questions remain regarding the mechanisms underpinning these indices of hypnosis. By briefly describing current knowledge of the brain's electrical activity during general anesthesia, as well as the operating principles of DoA monitors, the aim of this work is to simplify our understanding of the mathematical processes that allow for translation of complex patterns of brain electrical activity into dimensionless indices. This is a challenging task because mathematical concepts appear remote from clinical practice. Moreover, most DoA algorithms are proprietary algorithms and the difficulty of exploring the inner workings of mathematical models represents an obstacle to accurate simplification. The limitations of current DoA monitors — and the possibility for improvement — as well as perspectives on brain monitoring derived from recent research on corticocortical connectivity and communication are also discussed.

The Anaesthetic-ECT Time Interval in Electroconvulsive Therapy Practice--Is It Time to Time?

BACKGROUND

Because most common intravenous anaesthetics used in ECT have anticonvulsant properties, their plasma-brain concentration at the time of seizure induction might affect seizure expression. The quality of ECT seizure expression has been repeatedly associated with efficacy outcomes. The time interval between the anaesthetic bolus injection and the ECT stimulus (anaesthetic-ECT time interval) will determine the anaesthetic plasma-brain concentration when the ECT stimulus is administered.

OBJECTIVE

The aim of this study was to examine the effect of the anaesthetic-ECT time interval on ECT seizure quality and duration.

METHODS

The anaesthetic-ECT time interval was recorded in 771 ECT sessions (84 patients). Right unilateral brief pulse ECT was applied. Anaesthesia given was propofol (1-2 mg/kg) and succinylcholine (0.5-1.0 mg/kg). Seizure quality indices (slow wave onset, amplitude, regularity, stereotypy and post-ictal suppression) and duration were rated through a structured rating scale by a single blinded trained rater. Linear Mixed Effects Models analysed the effect of the anaesthetic-ECT time interval on seizure quality indices, controlling for propofol dose (mg), ECT charge (mC), ECT session number, days between ECT, age (years), initial seizure threshold (mC) and concurrent medication.

RESULTS

Longer anaesthetic-ECT time intervals lead to significantly higher quality seizures (p < 0.001 for amplitude, regularity, stereotypy and post-ictal suppression).

CONCLUSIONS

These results suggest that the anaesthetic-ECT time interval is an important factor to consider in ECT practice. This time interval should be extended to as long as practically possible to facilitate the production of better quality seizures. Close collaboration between the anaesthetist and the psychiatrist is essential.

Continuous infusion of propofol in calves: bispectral index and hemodynamic effects

OBJECTIVE

To assess the bispectral index (BIS) and the hemodynamic effects of propofol administered by continuous infusion at different rates in calves.

STUDY DESIGN

Experimental crossover study.

ANIMALS

Eight intact male Dutch calves, aged 6-12 months and weighing 84-124 kg.

METHODS

The calves were anesthetized with propofol (5 mg kg(-1) ) intravenously (IV), and after endotracheal intubation, positioned in right lateral recumbency and allowed to breathe ambient air. Anesthesia was maintained by continuous infusion of propofol, administered IV with an infusion pump at 0.6 mg kg(-1)  minute(-1) (treatment G6) or 0.8 mg kg(-1)  minute(-1) IV (treatment G8), for 60 minutes. The eight animals were anesthetized twice, 1 week apart. The following hemodynamic variables and BIS were assessed before the induction of anesthesia (baseline) and 15, 30, 45, and 60 minutes after beginning the infusion of propofol: heart rate, systolic, diastolic and mean arterial pressures, cardiac output, mean pulmonary artery pressure, cardiac index, stroke index, pulmonary vascular resistance index, and systemic vascular resistance index, BIS, electromyography, and signal quality index.

RESULTS

The continuous infusions of propofol at different rates did not alter BIS variables during the infusion time between dose rates, and no clinically significant hemodynamic changes were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

A continuous infusion of propofol at 0.6 or 0.8 mg kg(-1)  minute(-1) caused minimal hemodynamic changes without clinical relevance in calves. BIS could not be reliably used to discriminate the anesthetic depth during the two propofol infusion rates.

Sedation assessment in a mobile intensive care unit: a prospective pilot-study on the relation of clinical sedation scales and the bispectral index

Introduction

The critically-ill undergoing inter-hospital transfers commonly receive sedatives in continuation of their therapeutic regime or to facilitate a safe transfer shielded from external stressors. While sedation assessment is well established in critical care in general, there is only little data available relating to the special conditions during patient transport and their effect on patient sedation levels. The aim of this prospective study was to investigate the feasibility and relationship of clinical sedation assessment (Richmond Agitation-Sedation Scale (RASS)) and objective physiological monitoring (bispectral index (BIS)) during patient transfers in our Mobile-ICU.

Methods

The levels of sedation of 30 pharmacologically sedated patients were evaluated at 12 to 17 distinct measurement points spread strategically over the course of a transfer by use of the RASS and BIS. To investigate the relation between the RASS and the BIS, Spearman’s squared rank correlation coefficient (ρ²) and the Kendall’s rank correlation coefficient (τ) were calculated. The diagnostic value of the BIS with respect to the RASS was investigated by its sensitivity and positive predictive value for possible patient awakening. Therefore, measurements were dichotomized considering a clinically sensible threshold of 80 for BIS-values and classifying RASS values being nonnegative.

Results

Spearman’s rank correlation resulted to ρ² = 0.431 (confidence interval (CI) = 0.341 to 0.513). The Kendall’s correlation coefficient was calculated as τ = 0.522 (CI = 0.459 to 0.576). Awakening of patients (RASS ≥0) was detected by a BIS value of 80 and above with a sensitivity of 0.97 (CI = 0.89 to 1.00) and a positive predictive value of 0.59 (CI = 0.45 to 0.71).

Conclusions

Our study demonstrates that the BIS-Monitor can be used for the assessment of sedation levels in the intricate environment of a Mobile-ICU, especially when well-established clinical scores as the RASS are impracticable. The use of BIS is highly sensitive in the detection of unwanted awakening of patients during transfers.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0615-9) contains supplementary material, which is available to authorized users.

[Usefulness of Bispectral Index (BIS) monitoring for early detection of cerebral hypoperfusions]

OBJECTIVES

The goal of the study was to assess whether clinically significant cerebral hypoperfusion in awake patients would be associated with some alterations in the values of the bispectral index (BIS) monitoring.

STUDY DESIGN

Observational study.

POPULATION AND METHODS

We monitored the BIS during endovascular carotid artery occlusion testing in awake patients.

RESULTS

Twenty-eight patients were included. Twenty-one adequately tolerated the procedure. Their BIS value remained stable throughout the procedure. Four patients had poor angiographic tolerance, but no clinical symptoms. Their BIS value slightly decreased during the test (minimal BIS: 83 [79-87]). Three patients had poor clinical and angiographic tolerance of the occlusion. They all experienced an immediate and dramatic decrease in their BIS value (minimal BIS: ipsilateral to clamping: 50 [45-60]; contralateral to clamping: 48 [45-52]). In all patients, the clinical symptoms and the BIS normalized after deflating the occlusion balloon.

CONCLUSION

In awake patients, the observed values of the BIS monitoring seem to be associated with clinically relevant cerebral hypoperfusion.

Interruption of bispectral index monitoring by nerve integrity monitoring during tympanoplasty -A case report-

We report that intraoperative NIM-2 monitoring devices can interfere with bispectral index monitoring. A 45-year-old male with chronic otits media underwent tympanolasty under general anesthesia with NIM-2 monitoring and bispectral index monitoring at our institution. And then, bispectral index monitoring was severely interrupted by facial nerve monitoring.

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.