Bispectral Values Research Articles

Bispectral Index Monitoring: Ability to Detect Deep Sedation during Endoscopy

Background: Clinical practice guidelines recommend monitoring the depth of anesthesia during endoscopic examination of the gastrointestinal tract using sedation scales, despite their subjective nature, while the use of the bispectral index, an objective measure, during sedation, remains controversial. The main objective of this study was to assess the ability of bispectral index monitoring to characterize the depth of anesthesia during endoscopy. Methods: We conducted a cross-sectional study to assess the performance of the bispectral index using data from a multicentre clinical trial with 180 patients undergoing scheduled colonoscopies. Sedation was monitored using the bispectral index and Ramsay Sedation Scale. Data on sedation were recorded at five-time points (t1 to t5) during the colonoscopy. Results: Bispectral values were significantly associated with Ramsay scores (rho, -0.73; p < 0.0001). In regression analysis, each unit increase in bispectral value was associated with a reduction in the risk of a high Ramsay score (> 3) at all points (OR 0.922; 95% CI: 0.865–0.979; p < 0.0001 at t1). Receiver operating characteristic curve analysis found areas under the curve of 0.8272 for a bispectral index cut-off for deep sedation of 69.76 (sensitivity, 95.35%; negative predictive value, 97.53%) when reaching the colic flexure (t2) and 0.8399 for a cut-off of 69.29 (sensitivity, 96.15%; negative predictive value, 98.81%) at the end of the colonoscopy (t5). Conclusion: Bispectral index monitoring enables objective real-time reliable assessment of sedation. It enables easy continuous monitoring with a very good performance for detecting deep sedation and correlates with a clinical scale routinely used in endoscopic procedures.

The prediction of postoperative delirium with the preoperative bispectral index in older aged patients: a cohort study

BackgroundPostoperative delirium (POD) is the most common postoperative complication in elderly patients, especially in older aged patients (aged 75 years or over). The development of electroencephalography analysis could provide indicators for early detection, intervention, and evaluation. If there are pathophysiological changes in the brain, the BIS value will also change accordingly. In this study, we investigated the predictive value of the preoperative bispectral (BIS) index in POD for patients aged over 75 years.MethodsIn this prospective study, patients (≥ 75 years) undergoing elective non-neurosurgery and non-cardiac surgery under general anesthesia were included (n = 308). Informed consent was obtained from all involved patients. Before the operation and during the first 5 postoperative days, delirium was assessed with the confusion assessment method by trained researchers twice every day. Thereafter, the preoperative bedside BIS of each patient was dynamically acquired by the BIS VISTA monitoring system and the BIS monitoring of electrodes. A series of evaluation scales were assessed before and after surgery. A preoperative predictive score was generated according to the results of multivariable logistic regression. The receiver operating characteristic curves were drawn and the area under the curves was estimated to evaluate the perioperative diagnostic values of BIS and preoperative predictive score for POD. The specificity, sensitivity, positive predictive value (PPV), and negative predictive (NPV) value were calculated.ResultsDelirium occurred in 50 of 308 (16.2%) patients. The median BIS of delirious patients was 86.7 (interquartile range [IQR] 80.0–94.0), lower than that of the non-delirious 91.9 (IQR 89.7–95.4, P < 0.001). According to the ROC curve of the BIS index, the optimal cut-off value was 84, with a sensitivity of 48%, specificity of 87%, PPV 43%, NPV 89% for forecasting POD and the area under curves was 0.67. While integrating BIS, mini-mental state examination, anemia, activities of daily living, and blood urea nitrogen, the model had a sensitivity of 78%, specificity of 74%, PPV of 0.37%, and NPV of 95% for forecasting POD, and the area under curves was 0.83.ConclusionsPreoperative bedside BIS in delirium patients was lower than that in non-delirium patients when undergoing non-neurosurgery and non-cardiac surgery in patients aged over 75. The model of integrating BIS, mini-mental state examination, anemia, activities of daily living, and blood urea nitrogen is a promising tool for predicting postoperative delirium in patients aged over 75.

Effect of combined intraoperative use of the Nociception Level (NOL) and bispectral (BIS) indexes on desflurane administration

BackgroundCurrently, nociception monitors are not part of standard anaesthesia care. We investigated whether combined intraoperative nociception (NOL index) and anaesthesia (BIS index) monitoring during general anaesthesia would reduce anaesthetics consumption and enhance intraoperative safety and postoperative recovery when compared to standard of care monitoring (SOC). MethodsIn this randomised study, we included 60 patients undergoing colonic surgery under desflurane/remifentanil anaesthesia and epidural analgesia. Patients received either standard monitoring or combined BIS + NOL index monitoring. In the monitored group, remifentanil infusion was titrated to achieve a NOL index below 20. Desflurane was adjusted to BIS values (45–55). In the SOC group, remifentanil and desflurane were titrated on vital signs and MAC. The primary outcome was intraoperative desflurane consumption. ResultsFifty-five patients were analysed. Desflurane administration was reduced in the monitored group from 0.25 ± 0.05 to 0.20 ± 0.06 mL kg−1 h−1 (p < 0.001). The cumulative time with a BIS under 40 was significantly higher in the SOC group with a median time of 12.6 min (95% CI: 0.6–80.0) versus 2.0 min (95% CI: 0.3–5.83) (p = 0.023). Time for extubation was significantly shorter in the monitored group: 4.4 min (95% CI: 2.4–4.9) versus 6.28 min (95% IC: 5.0–8.2) (p = 0.003). We observed no differences in remifentanil or phenylephrine requirements during anaesthesia or in postoperative outcome measures, such as postoperative pain, opioid consumption, neurocognitive recovery. ConclusionCombined intraoperative monitoring of anaesthesia and nociception during colonic surgery resulted in less desflurane consumption and quicker extubation time compared to standard clinical care monitoring.

The synergistic effect of dexmedetomidine on propofol for paediatric deep sedation: A randomised trial.

Propofol and dexmedetomidine are used separately, and sometimes together, for paediatric deep sedation. Although their combination has been described in adults, the effect of dexmedetomidine as a potential synergist in children has not been studied before. The primary objective was to compare the propofol requirements of children who receive propofol alone with those who receive it in combination with dexmedetomidine for deep sedation for upper and lower endoscopic gastrointestinal procedures. This was a prospective, open-label, randomised study comparing patients who received propofol alone (group P) with those who received dexmedetomidine and propofol (group DP). The depth of sedation was titrated to a target bispectral (BIS) index. A Gastroenterology Procedure Unit at a single, tertiary care academic medical centre from April 2018 until December 2019. Eligible patients were scheduled for upper endoscopy, lower endoscopy or both. A total of 39 patients were enrolled (20 DP) and (19 P). Patients in Group DP received dexmedetomidine 0.5 μg kg-1 administered over 1 min followed by an infusion of 0.15 μg kg-1 h-1. In both groups, intravenous propofol was given in bolus increments titrated to a BIS index of 40 to 50 and then a continuous infusion of propofol to maintain BIS at 40 to 50. The primary outcome measure was propofol requirement in each group. Secondary outcome measures were time to achieve the targeted sedation depth, time to achieve an Aldrete recovery score of 9, duration of sedation, mean BIS values, adverse events, 'PAED' scores and time to discharge from the postanaesthesia care unit (PACU). The median (range) total dose of propofol was 0.23 (0.10 to 0.50) mg kg-1 min-1 in group DP and 0.40 (0.20 to 0.50) mg kg-1 min-1 in group P (P = 0.0004). Time of discharge from the PACU was 60 (20 to 121) min in group DP and 63 (46 to 91) min in group P (P = 0.0409). The combination of dexmedetomidine and propofol for paediatric procedural sedation achieved a significant reduction in median propofol dose and a slightly shorter median time to discharge from PACU. Large-scale studies may determine whether this reduction decreases the risk of significant adverse events. ClinicalTrials.gov identifier NCT02952222.

Remifentanil Alleviates Propofol-Induced Burst Suppression without Affecting Bispectral Index in Female Patients: A Randomized Controlled Trial.

The bispectral index is affected by various factors, such as noxious stimuli and other drugs, such as muscle relaxants. The burst suppression ratio from bispectral index monitoring is correlated with electroencephalographic burst suppression, which is associated with deep anesthesia, metabolic disorders, and brain injury. We assessed patients undergoing total intravenous anesthesia and examined the effects of remifentanil on the bispectral index, burst suppression ratio, and hemodynamic changes immediately after loss of consciousness with propofol. Seventy American Society of Anesthesiologists physical status class I and II Korean female patients scheduled for general anesthesia were administered propofol with an effect-site concentration of 5 μg/mL, using a target-controlled infusion (TCI). After losing consciousness, patients received either saline or remifentanil at an effect-site concentration of 5 ng/mL for 10 min. During this period, we recorded the bispectral index values, including burst suppression ratio, blood pressure, and heart rate. With remifentanil infusion, burst suppression ratios were lower (p < 0.01) but bispectral values were not different. The burst suppression ratio was significantly different at 6, 7, 8, and 10 min after remifentanil infusion (p < 0.05). In female patients with propofol-induced unconsciousness, remifentanil alleviated the burst suppression ratio without affecting the bispectral value.

An advanced bispectrum features for EEG-based motor imagery classification

Motor imagery (MI)-related brain activities can be effectively described by frequency analysis. Bispectrum is developed to overcome the drawback of power spectrum that the estimation of power spectrum discards the phase relationship among frequency components. However, the widely used bispectral features extraction method adds up all bispectral values as one feature, which could lead to the loss of effective information and increase of the sensitivity to non-linear and non-Gaussian noises. Thus, the representative bispectral features extraction method may be inefficient for MI classification. In addition, recent research suggests that the variations of EEG signals could provide more useful underlying information of event-related brain responses. This paper presents an advanced variations based bispectral feature extraction method to improve the performance of MI classification. The proposed method calculates the variations of MI-related EEG signals as input to bispectrum estimation. Besides, a new segmented bispectral sum features are developed to reduce the influence of non-linear and non-Gaussian noises and emphasize the valuable information for MI classification. The dataset collected in our laboratory and BCI Competition IV dataset 2b were adopted to validate the proposed method. The results indicate that the proposed method outperforms the power spectrum based methods and the representative bispectral features based methods. Moreover, compared to other state-of-the-art works, our approach also achieves the greater performance for MI classification.

Anesthetic requirements measured by bilateral bispectral analysis and femoral blockade in total knee arthroplasty

A continuous peripheral nerve blockade has proved benefits on reducing postoperative morphine consumption; the combination of a femoral blockade and general anesthesia on reducing intraoperative anesthetic requirements has not been studied. The objective of this study was to determine the relevance of timing in the performance of femoral block to intraoperative anesthetic requirements during general anesthesia for total knee arthroplasty. A single-center, prospective cohort study on patients scheduled for total knee arthroplasty, were sequentially allocated to receive 20mL of 2% mepivacaine throughout a femoral catheter, prior to anesthesia induction (Preoperative) or when skin closure started (Postoperative). An algorithm based on bispectral values guided intraoperative anesthetic management. Postoperative analgesia was done with an elastomeric pump of levobupivacaine 0.125% connected to the femoral catheter and complemented with morphine patient control analgesia for 48hours. The Kruskall Wallis and the chi-square tests were used to compare variables. Statistical significance was set at p<0.05. There were 94 patients, 47 preoperative and 47 postoperative. Lower fentanyl and sevoflurane were needed intraoperatively in the Preoperative group; median values and range: 250 (100-600) vs 450 (200-600)μg and 21 (12-48) vs 32 (18-67)mL p=0.001, respectively. There were no differences in the median verbal numeric rating scale values 4 (0-10) vs 3 (0-10); and in median morphine consumption 9 (2-73) vs 8 (0-63)mg postoperatively. A preoperative femoral blockade is useful in decreasing anesthetic requirements in total knee arthroplasty surgery but no added effect in the postoperative analgesic control.

Awareness during anaesthesia for surgery requiring evoked potential monitoring: A pilot study

Abstract Background: Evoked potential monitoring such as somatosensory-evoked potential (SSEP) or motor-evoked potential (MEP) monitoring during surgical procedures in proximity to the spinal cord requires minimising the minimum alveolar concentrations (MACs) below the anaesthetic concentrations normally required (1 MAC) to prevent interference in amplitude and latency of evoked potentials. This could result in awareness. Our primary objective was to determine the incidence of awareness while administering low MAC inhalational anaesthetics for these unique procedures. The secondary objective was to assess the adequacy of our anaesthetic technique from neurophysiologist’s perspective. Methods: In this prospective observational pilot study, 61 American Society of Anesthesiologists 1 and 2 patients undergoing spinal surgery for whom intraoperative evoked potential monitoring was performed were included; during the maintenance phase, 0.7–0.8 MAC of isoflurane was targeted. We evaluated the intraoperative depth of anaesthesia using a bispectral (BIS) index monitor as well as the patients response to surgical stimulus (PRST) scoring system. Post-operatively, a modified Bruce questionnaire was used to verify awareness. The adequacy of evoked potential readings was also assessed. Results: Of the 61 patients, no patient had explicit awareness. Intraoperatively, 19 of 61 patients had a BIS value of above sixty at least once, during surgery. There was no correlation with PRST scoring and BIS during surgery. Fifty-four out of 61 patient’s evoked potential readings were deemed ‘good’ or ‘fair’ for the conduct of electrophysiological monitoring. Conclusions: This pilot study demonstrates that administering low MAC inhalational anaesthetics to facilitate evoked potential monitoring does not result in explicit awareness. However, larger studies are needed to verify this. The conduct of SSEP electrophysiological monitoring was satisfactory with the use of this anaesthetic technique. However, the conduct of MEP monitoring was satisfactory, only in patients with Nurick Grade 1 and 2. The MEP response was poor in patients with Nurick Grade 4 and 5.

Anesthetic requirements measured by bilateral bispectral analysis and femoral blockade in total knee arthroplasty

Background and objectivesA continuous peripheral nerve blockade has proved benefits on reducing postoperative morphine consumption; the combination of a femoral blockade and general anesthesia on reducing intraoperative anesthetic requirements has not been studied. The objective of this study was to determine the relevance of timing in the performance of femoral block to intraoperative anesthetic requirements during general anesthesia for total knee arthroplasty. MethodsA single-center, prospective cohort study on patients scheduled for total knee arthroplasty, were sequentially allocated to receive 20mL of 2% mepivacaine throughout a femoral catheter, prior to anesthesia induction (Preoperative) or when skin closure started (Postoperative). An algorithm based on bispectral values guided intraoperative anesthetic management. Postoperative analgesia was done with an elastomeric pump of levobupivacaine 0.125% connected to the femoral catheter and complemented with morphine patient control analgesia for 48hours. The Kruskall Wallis and the chi-square tests were used to compare variables. Statistical significance was set at p<0.05. ResultsThere were 94 patients, 47 preoperative and 47 postoperative. Lower fentanyl and sevoflurane were needed intraoperatively in the Preoperative group; median values and range: 250 (100–600) vs 450 (200–600)μg and 21 (12–48) vs 32 (18–67)mL p=0.001, respectively. There were no differences in the median verbal numeric rating scale values 4 (0–10) vs 3 (0–10); and in median morphine consumption 9 (2–73) vs 8 (0–63)mg postoperatively. ConclusionsA preoperative femoral blockade is useful in decreasing anesthetic requirements in total knee arthroplasty surgery but no added effect in the postoperative analgesic control.

Comment on "Depth of Anesthesia as a Risk Factor for Perioperative Morbidity".

Petsiti and colleagues recent study on causal relationship between depth of anesthesia and perioperative morbidity [1] is an attractive opportunity to discuss a significant topic: what do we know about Deep Hypnotic Status (DHS) during general anesthesia (GA) and how can we recognize it? In truth, though significant steps have been taken by neuroscience and the knowledge of pharmacodynamics has been fine-tuned, we do not have a comprehensive view of what really happens to the brain during GA. The real problem is driving the anesthesia in a middle earth, furthest from both the burst suppression and sudden emergencies. Thus, if we cannot define the exact anesthesia level of our patient, how can we establish a correlation between DHS and postoperative complications and morbidity? While the authors correctly cited previous studies on the topic, nevertheless we meet Sigl [2] among the authors of one of these references. It is not a big surprise for the scholars of brain monitoring because he was, along with Chamoun, the first to describe the bispectral (BIS) technology in 1994 [3]. It is questionable whether BIS monitor exactly expresses the depth of anesthesia (DOA). However, it may be impossible to measure the real DOA by the simple method accepted by all anesthesiologists. Thus, BIS monitor is regarded as the most reliable and clinically available monitoring for the DOA, although its efficacy is controversial [4]. An anesthesia status not sufficiently deep may cause events of AA; however according to Petsiti et al. a deep hypnotic time (DHT) is a new significant factor associated with postoperative outcome [1]. Petsiti et al. defined DHT as the cumulative period of BIS index values < 45 [1], in line with the previous observations of Lindholm et al. [5]. While single data are not indicative of the anesthesia status, the variable time adds more power to the BIS value. This is the most important issue of the paper by Petsiti et al. because it shows the efficacy of DHT as a risk factor for perioperative mortality, even if the BIS monitoring system is questionable [1]. BIS monitor was the first electroencephalography- (EEG-) based DOA monitor. It is the most widely used system to assess the monitoring of DOA; nevertheless during the last 15–20 years a number of EEG-based technologies have become commercially available. Although several algorithms have been used for patenting brain monitors and many indices are used as references for monitoring the DOA at the moment, there is no device to assess the exact level of anesthesia. Jensen and colleagues have long studied level of consciousness during GA. They published on the detrended fluctuation analysis of EEG, proponing several indexes in order to characterize the patient state (awake, sedated, and anesthetized states) [6]. Nevertheless, as stated by them, these indices are able to detect the loss of consciousness but not to assess the exact level of anesthesia. In the meantime, others have proposed complex algorithms combining EEG analysis and no EEG parameters. Schneider et al. [7] studied a combination of standard monitoring, EEG parameters, and patient and drug information demonstrating that it is possible to separate the different anesthetic levels. However, their pattern is a complex analysis with a late construction which is difficult to apply in order to immediately recognize intraoperative awakening, in particular under neuromuscular blockade. They concluded that “additional studies are required to validate results of the current study.” Recently, the authors of the Michigan Awareness Control Study [8] concluded that they were not able to find an alert threshold for both anesthetic drugs and BIS values and there is the necessity for an individualized anesthetic strategy. Fortunately, as we are writing the progress of science does not stop. Thus, we are witnessing a rapid evolution of the brain monitoring EEG-based techniques. The studies of Boly et al. [9] on the spectral EEG changes after propofol administration are very important, and Purdon et al. [10] published their fascinating research, explaining that EEG pattern (and its changing) is indicative in real time of the patient transaction from consciousness to the anesthesia status. We hope that these technologies are perfected and soon on a large scale distributed to permanently solve the AA problem and cut down the postoperative complications due to DHT. At the same time the attempts as those of Petsiti are much appreciated.

A study of the effect of caudal epidural block on bispectral index targeted propofol requirement in children: A comparative study.

Caudal epidural block is one of the most commonly performed neuraxial block techniques with reliable peri-operative and post-operative analgesia in pediatric patients. In our randomized, prospective, double-blinded, open level, parallel group study, we have established the effect of caudal epidural block on maintenance requirement of intravenous (IV) propofol in targeted bispectral (BIS) monitored patients.Context:Neuraxial anesthesia exhibits sedative properties that may reduce the requirement for general anesthesia. TIVA with propofol has been administered as an established method of maintaining general anesthesia in children. Caudal analgesia being a type of neuraxial block, also seems to reduce the requirement of sedative hypnotics in pediatric patients. Numerous studies show that for patients, administered with caudal epidural block, they require reduced intra-operative volatile inhalation anesthetics. In the present study, we have established the anesthetic sparing effect of Caudal Epidural Analgesia in children undergoing infra-umbilical surgical procedure and calculated the efficacy of propofol-infusion in maintaining adequate depth of anesthesia.Aims:(1) To study and compare the dose requirements of propofol using caudal epidural analgesia. (2) To calculate the efficacy of propofol as maintenance anesthetic agent in both groups and to compare hemodynamic stability of patients in both the techniques.Settings and Design:In our study, after administering general anesthesia to pediatric patients, we have administered caudal analgesia and IV analgesia to monitor the requirement of intra-operative propofol infusion using BIS monitor with a target value of 40-60 in both groups.Materials and Methods:82 patients (aged between 3 and 6 years) have been selected undergoing infra-umbilical surgery and randomly allocated into two groups containing 41 patients in each group. Both the groups group B and group A then intubated with glycopyrrolate, 2 mg/kg injection fentanyl, propofol till loss of verbal contact and atracurium at the rate of 0.5 mg/kg and group B has been administered caudal epidural blockade with 1 ml/kg 0.2% ropivacaine. Propofol infusion at the rate of 10 mg/kg/h is given as maintenance. BIS value has been recorded throughout and propofol requirement at the end of surgery has been calculated.Statistical Analysis Used:Numerical variables between groups have been analyzed using the Student's t-test and the Mann-Whitney U-test as applicable. Categorical variables have been analyzed using the Pearson's Chi-square test. P < 0.05 is considered statistically significant.Results:Consumption of propofol at the start of operation in the group A is 2.9 ± 0.17 and group B is 2.91 ± 0.17, which is not statistically significant (P > 0.05), whereas at the end of the operation in the group A is 11.33 ± 0.17 and group B is 7.83 ± 0.63, which is statistically significant (P < 0.05). Incidence of adverse effects is statistically insignificant between the two groups. The time for administration of rescue analgesic is 2.1 ± 0.88 in group A and 6.5 ± 0.17 in group B, which is statistically significant due to caudal analgesia.Conclusions:We conclude that in BIS-monitored patients (3-6 years) with infra-umbilical surgeries have shown a reduction in consumption of IV propofol due to caudal epidural blockade.

The ability of bispectral-guided management compared to routine monitoring for reflecting awareness rate in patients undergoing abdominal surgery.

Background:Awareness during general anesthesia in different types of surgery is an important described adverse event. Bispectral (BIS) monitoring is one of the recent techniques proposed to monitor the depth of anesthesia.Objectives:The present study tested the hypothesis that the awareness rate and changes in hemodynamic parameters within anesthesia would be lower in patients allocated to BIS-guided management than those allocated to routine monitoring.Materials and MethodsIn total, 333 adult patients with the American Society of Anesthesiologists (ASA) physical status I-III, aged between 18 and 65 years scheduled for elective abdominal surgery under general anesthesia were included in this randomized double-blind placebo controlled trial. Patients were randomly allocated to BIS monitoring (n = 163) or routine monitoring (n = 170). BIS values and hemodynamic parameters including systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and SPO2 were marked before induction (control value), after intubation and laryngoscopy, at intubation, after incision, and also during the operation every 15 minutes until extubation.Results:The overall incidence of awareness in the BIS and routine monitoring groups were 5.5% and 4.1%, which was not significantly different. There were no significant differences in hemodynamic indices including SBP, DBP, HR, and SPO2 before induction of anesthesia between the two groups. These between-group differences in the studied indices remained insignificant at different time points after anesthesia induction as well as post ICU hospitalization. Furthermore, the trend of changes in hemodynamic parameters was comparable in the two groups.Conclusions:BIS-guided management may not be superior to routine monitoring protocols to prevent awareness as well as hemodynamic changes during general anesthesia in patients undergoing abdominal surgeries.

Bispectral index in predicting the prognosis of patients with coma in intensive care unit.

The bispectral (BIS) index is a processed electroencephalogram (EEG) parameter with extensive validation and demonstrated clinical utility. The study aimed to investigate the correlation between the BIS index and the prognosis of patients with coma in the ICU. A total of 208 patients with coma in the ICU were enrolled in this study. According to the BIS value, the patients were divided into four groups: group I, BIS value 0 to 20; group II, BIS value 21 to 40; group III, BIS value 41 to 60; and group IV, BIS value greater than 60. The difference in BIS values with the differences in prognosis of patients with coma was compared between the four groups, and the prognosis of patients with coma was stratified into consciousness, coma, vegetative state, and brain death. Subsequently, the best cut-off score of BIS values calculated for determining the correlation between BIS value and mental state was proposed. There are no significant differences in the age and APACHE II scores between the four groups (P>0.05). An inverse correlation was observed between BIS value and mental state (r= -0.749, P=0.00). According to the ROC curve, as BIS value was greater than 42.5, there were higher sensitivity and specificity in conscious-coma patients. BIS value is correlated with the prognosis of patients with coma in ICU, and BIS value can be a useful marker for estimating the prognosis of comatose patients.

Post-Transplant Assessment of Consciousness in Acute-on-Chronic Liver Failure Patients Undergoing Liver Transplantation Using Bispectral Index Monitoring

PurposeDeterioration of consciousness is a critical situation for liver transplantation (OLT) recipients. The bispectral (BIS) index based on electroencephalographic parameters, is primarily used to monitor the depth of unconsciousness. The present study sought to assess the usefulness of posttransplant BIS index to monitor acute-on-chronic liver failure patients. MethodsThis 1-year retrospective study of 28 adult patients with acute-on-chronic liver failure was performed from July 2011 to June 2012, using post-transplant BIS monitoring. ResultsThe mean patient age was 51 ± 8 years. Their mean pretransplant Child-Turcotte-Pugh score was 12.3 ± 1.4, and the mean Model for End-stage Liver Disease score, 36.4 ± 5.9. After OLT, the mean initial Glasgow Coma Scale (GCS) score and BIS index were 3.4 ± 1.7 and 43.5 ± 9.1, respectively. After 6 hours the mean GCS and BIS values rose to 8.6 ± 4.0 and 52.4 ± 10.3 and after 12 hours to 9.7 ± 3.4 and 61.3 ± 15.7 respectively. Eye opening in response to a voice occurred at a mean of 8.9 ± 6.7 hours after arrival in the intensive care unit regardless of graft function. The mean GCS and BIS values were 10.6 ± 2.8 and 69.1 ± 13.5, respectively. The endotracheal tube was removed after a median of 140 hours; 9 patients required a tracheostomy. Among them 2 died within the first 3 months after OLT. ConclusionsBIS monitoring is a noninvasive, simple, easy-to-interpret method to measure consciousness among patients intubated with an endotracheal tube.

Bispectral-based methods for clustering time series

Distinguishing among linear and nonlinear time series or between nonlinear time series generated by different underlying processes is challenging, as second-order properties are generally insufficient for the task. Different nonlinear processes have different nonconstant bispectral signatures, whereas the bispectral density function of a Gaussian or linear time series is constant. Based on this, we propose a procedure to distinguish among various nonlinear time series and between nonlinear and linear time series through application of a hierarchical clustering algorithm based on distance measures computed from the square modulus of the estimated normalized bispectra. We find that clustering using a distance measure computed by averaging the ratio of normalized bispectral periodogram ordinates over the intersection of the principle domain of each pair of time series provides good performance, subject to trimming of extreme bispectral values prior to taking the ratios. Additionally, we show through simulation studies that the distance procedure performs better than a significance test that we derive. Moreover, it is robust with respect to the choice of smoothing parameter in estimating the bispectrum. As an example, we apply the method to a set of time series of intensities of gamma-ray bursts, some of which exhibit nonlinear behavior; this enables us to identify gamma-ray bursts that may be emanating from the same type of astral event.

The Bispectrum as a Source of Phase-Sensitive Invariants for Fourier Descriptors: A Group-Theoretic Approach

This paper develops the theory behind the bispectrum, a concept that is well established in statistical signal processing but not, until recently, extended to computer vision as a source of frequency-domain invariants. Recent papers on using the bispectrum in vision show good results when the bispectrum is applied to spherical harmonic models of three-dimensional (3-D) shapes, in particular by improving discrimination over previously-proposed magnitude invariants, and also by allowing detection of neutral pose in human activity detection. The bispectrum has also been formulated for vector spherical harmonics, which have been used in medical imaging for 3-D anatomical modeling. In a paper published in this journal, Smach et al. use duality theory to establish the completeness of second-order invariants which, as shown here, are the same as the bispectrum. This paper unifies earlier works of various researchers by deriving the bispectrum formula for all compact groups. It also provides a constructive algorithm for recovering functions from their bispectral values on SO(3). The main theoretical result shows that the bispectrum serves as a complete source of invariants for homogeneous spaces of compact groups, including such important domains as the sphere S 2.

Hemodynamic Profile of Target-Controlled Spinal Anesthesia Compared With 2 Target-Controlled General Anesthesia Techniques in Elderly Patients With Cardiac Comorbidities

The impact of anesthesia techniques in patients experiencing hip fracture is controversial. This study compares the effects on blood pressure of 3 anesthesia techniques that are considered safe for the elderly. Forty-five patients older than 75 years, with American Society of Anesthesiologists physical status III or IV, with cardiac comorbidities, and undergoing surgery for hip fracture, were randomized to receive continuous spinal anesthesia (CSA), propofol target-controlled infusion (TCI), or sevoflurane (SEVO). In CSA patients, a T10 metameric level target was achieved by titration of 2.5 mg of bupivacaine boluses. In patients on TCI and SEVO, a bispectral value target of around 50 guided the concentration of propofol or sevoflurane. Analgesia in the TCI and SEVO groups was provided with remifentanil. Hypotension was defined as a 30% decrease in mean arterial pressure and was treated with an intravenous bolus of ephedrine. The number of hypotension episodes was lower in the CSA group: 0 (range, 0-6) versus 11.5 (range, 1-25) in the TCI group and 10 (range, 1-23) in the SEVO group (P < 0.001). Both TCI and SEVO patients needed more ephedrine compared with CSA patients (30.5 [15.5], 26 [23], and 1.5 [2.5] mg, respectively, P < 0.001). The maximal decrease in mean arterial pressure was lower in the CSA group (26% [17%]) compared with that in the TCI group (47% [8%]) and the SEVO group (46% [12%]; P < 0.001). In elderly patients, spinal anesthesia using titrated doses of bupivacaine provided better blood pressure stability than propofol or sevoflurane anesthesia.

Changes in EEG and Bispectral Index in Children during Inhalation Anesthesia

Objective: to estimate bispectral (BIS) index and electroencephalographic (EEG) changes during anesthesia with halothane, sevoflurane, and a successive combination of sevoflurane and isoflurane, by taking into account age. Subjects and methods. Sixty children aged 3 to 17 years, who had undergone elective surgery, were randomized to 3 groups of 20 children each: 1) halothane anesthesia; 2) sevoflurane anesthesia; and 3) a successive combination of sevoflurane and isoflurane. A 1:1 oxygen-nitrous oxide mixture was used for anesthesia in all the groups. EEG (using a 6-channel computer-assisted encephalograph) and bispectral index (XP version) was continuously recorded throughout the anesthesia, except the transition to isoflurane in Group 3. Results. In the halothane group, EEG displayed a gradual reduction in basic rhythm, an increase in slow activity with the rhythm being recovered on emergence. The BIS index changed from 96—99 to 19—36 with a spike of up to 80—87 on emergence. In Groups 2 and 3 where the induction of anesthesia used sevoflurane, EEG recorded a pointed а-rhythm, increased amplitude, and rhythm synchronization. The BIS value changed from 96—99 to 19—37. In Group 2, it was 30 to 40 on anesthesia maintenance and up to 82—87 on emergence. In Group 3, the isofluorane anesthesia stage changed EEC patterns towards rhythm synchronization and gave rise to slow fluctuations in all leads. The BIS index was 30—39 on anesthesia maintenance and 80—86 on emergence. Conclusion. EEC and BIS index monitoring values corresponded to the clinical course and depth of anesthesia. The comparison of the clinical data of the course of anesthesia and the values of EEG and BIS monitoring could lead to the conclusion that BIS technology might be of informative value in children. Key words: inhalation anesthesia, electroencephalography, BIS monitoring, isoflurane, sevoflurane, halothane.

Predicted effect-site concentration of propofol and sufentanil for gynecological laparoscopic surgery

this study was to estimate the predicted effect-site concentration of propofol administered by a target-controlled infusion (TCI) for maintenance of anesthesia based on the bispectral (BIS) index as a measure of hypnosis in laparoscopic surgery. one-hundred and sixty unpremedicated patients undergoing gynecologic laparoscopy were assigned randomly to receive one of the target effect-site concentrations of propofol 2.0, 2.5, 3.0, 3.5 and 4.0 microg/ml during TCI with propofol and sufentanil. The dose-response relationship of propofol for the maintenance of adequate anesthesia based on BIS, movement and hemodynamic response was investigated using a fixed effect-site concentration of sufentanil (0.2 ng/ml). The BIS values, hemodynamic variables, time course during emergence and intraoperative awareness were also assessed. the predicted effect-site propofol concentrations for adequate anesthesia at the skin incision in 50% (EC(50) ) and 95% (EC(95) ) of patients undergoing gynecologic laparoscopy were 2.2 and 3.7 microg/ml, respectively. The predicted propofol EC(50) and EC(95) to maintain adequate anesthesia in these patients were 2.6 microg/ml (95% CI 2.3-2.7 microg/ml) and 3.6 microg/ml (95% CI 3.3-4.0 microg/ml), respectively. The BIS values, effect-site concentration of propofol, hemodynamic data and time course during emergence and post-operative adverse events were comparable in each group. There were no reports of intraoperative awareness in the post-anesthetic care unit. based on the anesthetic depth assessed by the clinical signs and BIS monitoring, the predicted effect-site propofol concentrations for the maintenance of anesthesia in patients undergoing gynecologic laparoscopy were similar in those administered adequate anesthesia at the skin incision during TCI.

Differential effects of hyperventilation on cerebral blood flow velocity after tourniquet deflation during sevoflurane, isoflurane, or propofol anesthesia

The purpose of this study was to compare the degree of increase in middle cerebral artery (MCA) blood flow velocity after tourniquet deflation when modulating hyperventilation during orthopedic surgery under sevoflurane, isoflurane, or propofol anesthesia. Twenty-four patients undergoing elective orthopedic surgery were randomly divided into sevoflurane, isoflurane, and propofol groups. Anesthesia was maintained with sevoflurane, isoflurane, or propofol administration with 33% oxygen and 67% nitrous oxide at anesthetic drug concentrations adequate to maintain bispectral values between 45 and 50. A 2.0-MHz transcranial Doppler probe was attached to the patient's head at the temporal window, and mean blood flow velocity in the MCA (V (mca)) was continuously measured. The extremity was exsanguinated with an Esmarch bandage, and the pneumatic tourniquet was inflated to a pressure of 450 mmHg. Arterial blood pressure, heart rate, V (mca) and arterial blood gases were measured every minute for 10 min after release of the tourniquet in all three groups. Immediately after tourniquet release, the patients' respiratory rates were increased to tightly maintain end-tidal carbon dioxide (PetCO(2)) at 35 mmHg. No change in partial pressure of carbon dioxide in arterial blood (PaCO(2)) was observed pre- and posttourniquet deflation in any of the three groups. Increase in V (mca) in the isoflurane group was greater than that in the other two groups after tourniquet deflation. In addition, during the study period, no difference in V (mca) after tourniquet deflation was observed between the propofol and sevoflurane groups. Hyperventilation could prevent an increase in V (mca) in the propofol and sevoflurane groups after tourniquet deflation. However, hyperventilation could not prevent an increase in V (mca) in the isoflurane group.