Validation of the index of consciousness during sevoflurane and remifentanil anaesthesia: a comparison with the bispectral index and the cerebral state index

EEG spectral slope: A reliable indicator for continuous evaluation of consciousness levels during propofol anesthesia

The level of consciousness undergoes continuous alterations during anesthesia. Prior to the onset of propofol-induced complete unconsciousness, degraded levels of behavioral responsiveness can be observed. However, a reliable index to monitor altered consciousness levels during anesthesia has not been sufficiently investigated. In this study, we obtained 60-channel EEG data from 24 healthy participants during an ultra-slow propofol infusion protocol starting with an initial concentration of 1 μg/ml and a stepwise increase of 0.2 μg/ml in concentration. Consecutive auditory stimuli were delivered every 5 to 6 s, and the response time to the stimuli was used to assess the responsiveness levels. We calculated the spectral slope in a time-resolved manner by extracting 5-second EEG segments at each auditory stimulus and estimated their correlation with the corresponding response time. Our results demonstrated that during slow propofol infusion, the response time to external stimuli increased, while the EEG spectral slope, fitted at 15-45 Hz, became steeper, and a significant negative correlation was observed between them. Moreover, the spectral slope further steepened at deeper anesthetic levels and became flatter during anesthesia recovery. We verified these findings using an external dataset. Additionally, we found that the spectral slope of frontal electrodes over the prefrontal lobe had the best performance in predicting the response time. Overall, this study used a time-resolved analysis to suggest that the EEG spectral slope could reliably track continuously altered consciousness levels during propofol anesthesia. Furthermore, the frontal spectral slope may be a promising index for clinical monitoring of anesthesia depth.

Effects of qCON and qNOX-guided general anaesthesia management on patient opioid use and prognosis: a study protocol

INTRODUCTION

The adverse effects of general anaesthetic drugs (especially opioids) cannot be ignored. However, current nociceptive-monitoring techniques still lack consistency in guiding the use of opioids. This trial will study the demand for opioid use and patient prognosis in qCON and qNOX-guided general anaesthesia management.

METHODS AND ANALYSIS

This prospective, randomised, controlled trial will randomly recruit 124 patients undergoing general anaesthesia for non-cardiac surgery in equal numbers to either the qCON or BIS group. The qCON group will adjust intraoperative propofol and remifentanil dosage according to qCON and qNOX values, while the BIS group will adjust according to BIS values and haemodynamic fluctuations. The differences between the two groups will be observed in remifentanil dosing and prognosis. The primary outcome will be intraoperative remifentanil use. Secondary outcomes will include propofol consumption; the predictive ability of BIS, qCON and qNOX on conscious responses, noxious stimulus and body movements; and changes in cognitive function at 90 days postoperatively.

ETHICS AND DISSEMINATION

This study involves human participants and was approved by the Ethics Committee of the Tianjin Medical University General Hospital (IRB2022-YX-075-01). Participants gave informed consent to participate in the study before taking part. The study results will be published in peer-reviewed journals and presented at relevant academic conferences.

TRIAL REGISTRATION NUMBER

ChiCTR2200059877.

Usefulness of bispectral index and patient state index during sevoflurane anesthesia in children: A prospective observational study

Cortical electroencephalography-based devices are used to monitor the depth of anesthesia. In this study, we evaluated the values of bispectral index (BIS) and patient state index (PSI) during sevoflurane anesthesia in children. The ability/accuracy of BIS and PSI to predict the maintenance and recovery state of anesthesia was evaluated based on prediction probability (Pk) values and the secondary outcomes were agreement and correlation of 2 monitors. Fifty children (3-12 years old) were enrolled and the patients received sevoflurane anesthesia with remifentanil followed by propofol administration. Before the induction of anesthesia, BIS and PSI sensors were simultaneously placed on the forehead, and data were collected until the end of anesthesia. Maintenance state was defined as the period following intubation until the cessation of sevoflurane, while recovery state was defined as the period following the cessation of sevoflurane until awake. Pk, agreement or correlation of BIS and PSI in different anesthesia state were calculated. Anesthesia reduced mean BIS and PSI values. Pk of BIS (95% confidential interval [CI]: 0.78-0.91) and PSI (95% CI: 0.82-0.91) for anesthesia were 0.85 and 0.87, respectively. Agreement was 0.79 for recovery state and 0.73 for maintenance state. Pk values were comparable for BIS and PSI. Agreement between BIS and PSI measurements in the same state was relatively good. Therefore, these monitors are appropriate for monitoring for different state of anesthesia in pediatric population.

Evaluation of Anesthetic Specific EEG Dynamics during State Transitions between Loss and Return of Responsiveness

Purpose: electroencephalographic (EEG) information is used to monitor the level of cortical depression of a patient undergoing surgical intervention under general anesthesia. The dynamic state transitions into and out of anesthetic-induced loss and return of responsiveness (LOR, ROR) present a possibility to evaluate the dynamics of the EEG induced by different substances. We evaluated changes in the EEG power spectrum during anesthesia emergence for three different anesthetic regimens. We also assessed the possible impact of these changes on processed EEG parameters such as the permutation entropy (PeEn) and the cerebral state index (CSI). Methods: we analyzed the EEG from 45 patients, equally assigned to three groups. All patients were induced with propofol and the groups differed by the maintenance anesthetic regimen, i.e., sevoflurane, isoflurane, or propofol. We evaluated the EEG and parameter dynamics during LOR and ROR. For the emergence period, we focused on possible differences in the EEG dynamics in the different groups. Results: depending on the substance, the EEG emergence patterns showed significant differences that led to a substance-specific early activation of higher frequencies as indicated by the “wake” CSI values that occurred minutes before ROR in the inhalational anesthetic groups. Conclusion: our results highlight substance-specific differences in the emergence from anesthesia that can influence the EEG-based monitoring that probably have to be considered in order to improve neuromonitoring during general anesthesia.

Depth of Anesthesia Monitoring

The electroencephalogram (EEG) can be analyzed in its raw form for characteristic drug-induced patterns of change or summarized using mathematical parameters as a processed electroencephalogram (pEEG). In this article we aim to summarize the contemporary literature pertaining to the commonly available pEEG monitors including the effects of commonly used anesthetic drugs on the EEG and pEEG parameters, pEEG monitor pitfalls, and the clinical implications of pEEG monitoring for anesthesia, pediatrics, and intensive care.

Comparison of Bispectral Index and Patient State Index values according to recovery from moderate neuromuscular block under steady-state total intravenous anesthesia

There were insufficient researches of the comparison between Bispectral Index (BIS) and Patient State Index (PSI) values during the recovery of moderate NMB. We investigated the response of these indices during neuromuscular blockade (NMB) reversal by sugammadex under steady-state total intravenous anesthesia (TIVA) using propofol/remifentanil. In this prospective, observational study, patients undergoing laparoscopic cholecystectomy were enrolled. At the end of surgery, after confirming that train-of-four (TOF) count as 1 or 2, we maintained a steady state (BIS value of 40-50). After administration of 2 mg kg^-1 sugammadex, BIS, PSI, and electromyography (EMG) signal values were recorded at one-minute intervals for 10 min. The primary outcome was the difference between the changes in BIS and PSI from baseline to a TOF ratio (TOFR) of 90 after sugammadex administration in steady-state TIVA. A total of 48 patients completed this trial. There was no significant difference between the changes in BIS and PSI values from baseline to TOFR 90 (- 0.333 ± 4.955 vs. - 0.188 ± 4.616; 95% confidence interval [CI] - 2.095 to 1.803; p = 0.882). Both BIS-EMG and PSI-EMG values at baseline and TOFR 90 were not statistically different (95% CI - 0.550 to 1.092; p = 0.510, 95% CI - 1.569 to 0.527; p = 0.322, respectively). No patient experienced any complications. Changes in BIS and PSI values after NMB reversal during steady-state TIVA were not significantly different. Both BIS and PSI provide trustworthy values for monitoring anesthetic depth during NMB reversal under TIVA.Trial Registration: This study was registered in the Clinical Trial Registry of Korea ( https://cris.nih.go.kr : KCT 0003805).

The Raw and Processed Electroencephalogram as a Monitoring and Diagnostic Tool

In this narrative review, different aspects of electroencephalogram (EEG) monitoring during anesthesia are approached, with a special focus on cardiothoracic and vascular anesthesia, from the basic principles to more sophisticated diagnosis and monitoring utilities. The available processed EEG-derived indexes of the depth of the hypnotic component of anesthesia have well-defined limitations and usefulness. They prevent intraoperative awareness with recall in specific patient populations and under a specific anesthetic regimen. They prevent intraoperative overdose, and they shorten recovery times. They also help to avoid lengthy intraoperative periods of suppression activity, which are known to be deleterious in terms of outcome. Other than those available indexes, the huge amount of information contained in the EEG currently is being used only partially. Several other areas of interest regarding EEG during anesthesia have emerged in terms of anesthesia mechanisms elucidation, nociception monitoring, and diagnosis or prevention of brain insults.

Time delay of the qCON monitor and its performance during state transitions

We investigated the performance of the qCON index regarding its time delay for sudden changes in the anesthetic level as well as to separate responsiveness from unresponsiveness during loss and return of responsiveness (LOR and ROR). For evaluation of the time delay, we replayed relevant EEG episodes to the qCON to simulate sudden changes between the states (i) awake/sedation, (ii) adequate anesthesia, or (iii) suppression. We also replayed EEG from 40 patients during LOR and ROR to evaluate the qCON’s ability to separate responsiveness from unresponsiveness. The time delays depended on the type of transition. The delays for the important transition between awake/sedation and adequate anesthesia were 21(5) s from awake/sedation to adequate anesthesia and 26(5) s in the other direction. The performance of the qCON to separate responsiveness from unresponsiveness depended on signal quality, the investigation window, i.e. ± 30 s or ± 60 s around LOR/ROR, and the specific transition being tested. AUC was 0.63–0.90 for LOR and 0.61–0.79 for ROR. Time delay and performance during state transitions of the qCON were similar to other monitoring systems such as bispectral index. The better performance of qCON during LOR than ROR probably reflects the sudden change in EEG activity during LOR and the more heterogeneous EEG during ROR.

Use of Multiple EEG Features and Artificial Neural Network to Monitor the Depth of Anesthesia

The electroencephalogram (EEG) can reflect brain activity and contains abundant information of different anesthetic states of the brain. It has been widely used for monitoring depth of anesthesia (DoA). In this study, we propose a method that combines multiple EEG-based features with artificial neural network (ANN) to assess the DoA. Multiple EEG-based features can express the states of the brain more comprehensively during anesthesia. First, four parameters including permutation entropy, 95% spectral edge frequency, BetaRatio and SynchFastSlow were extracted from the EEG signal. Then, the four parameters were set as the inputs to an ANN which used bispectral index (BIS) as the reference output. 16 patient datasets during propofol anesthesia were used to evaluate this method. The results indicated that the accuracies of detecting each state were 86.4% (awake), 73.6% (light anesthesia), 84.4% (general anesthesia), and 14% (deep anesthesia). The correlation coefficient between BIS and the index of this method was 0.892 (p<0.001). The results showed that the proposed method could well distinguish between awake and other anesthesia states. This method is promising and feasible for a monitoring system to assess the DoA.

Neuromonitoring in the elderly

PURPOSE OF REVIEW

To summarize recent recommendations on intraoperative electroencephalogram (EEG) neuromonitoring in the elderly aimed at the prevention of postoperative delirium and long-term neurocognitive decline. We discuss recent perioperative EEG investigations relating to aging and cognitive dysfunction, and their implications on intraoperative EEG neuromonitoring in elderly patients.

RECENT FINDINGS

The incidence of postoperative delirium in elderly can be reduced by monitoring depth of anesthesia, using an index number (0-100) derived from processed frontal EEG readings. The recently published European Society of Anaesthesiology guideline on postoperative delirium in elderly now recommends guiding general anesthesia with such indices (Level A). However, intraoperative EEG signatures are heavily influenced by age, cognitive function, and choice of anesthetic agents. Detailed spectral EEG analysis and research on EEG-based functional connectivity provide new insights into the pathophysiology of neuronal excitability, which is seen in elderly patients with postoperative delirium.

SUMMARY

Anesthesiologists should become acquainted with intraoperative EEG signatures and their relation to age, anesthetic agents, and the risk of postoperative cognitive complications. A working knowledge would allow an optimized and individualized provision of general anesthesia for the elderly.

Pharmacokinetic and pharmacodynamic interactions in anaesthesia. A review of current knowledge and how it can be used to optimize anaesthetic drug administration

This review describes the basics of pharmacokinetic and pharmacodynamic drug interactions and methodological points of particular interest when designing drug interaction studies. It also provides an overview of the available literature concerning interactions, with emphasis on graphic representation of interactions using isoboles and response surface models. It gives examples on how to transform this knowledge into clinically and educationally applicable (bedside) tools.

Effects of small-dose remifentanil combined with index of consciousness monitoring on gastroscopic polypectomy: a prospective, randomized, single-blinded trial

BACKGROUND

With the development of painless diagnosis and treatment, remifentanil, a synthetic opioid agonist, is increasingly used in gastroscopy for its rapid, short-term, and potent analgesic effect. However, the dosage of remifentanil used in endoscopy is unclear. Index of consciousness (IOC) is a new anesthesia depth-monitoring indicator that can be divided into index of consciousness 1 (IOC₁) and index of consciousness 2 (IOC₂); IOC₁ is used for estimating a patient's sedation state, whereas IOC₂ reflects analgesic depth. We hypothesized that combining with IOC₁ and IOC₂ monitoring may be helpful to identify an optimal remifentanil dosage in gastroscopic polypectomy.

METHODS

One hundred twenty patients scheduled for gastroscopic polypectomy were enrolled and were randomly assigned to remifentanil 2 ng/mL (group R2), 4 ng/mL (group R4), or 6 ng/mL (group R6), and 40 cases were in each group. During the anesthesia period, remifentanil was kept at the initial given concentration but propofol was adjusted according to IOC₁. The primary outcomes were the dosage of propofol and remifentanil. The secondary outcomes were the variety of IOC₁ and IOC₂, patients' awakening time, and peri-operative adverse reactions such as hypotension, hypertension, bradycardia, tachycardia, body movements, hypoxemia, therapy interruption, nausea, vomiting, aspiration, and intra-operative awareness.

RESULTS

With the increasing dosage of remifentanil, the propofol dosage and patients' awakening time decreased significantly, the morbidity of hypertension and body movements also declined, but the incidence of hypotension, bradycardia, and hypoxemia rose. In group R2, the value of IOC₂ remained above 50 during the treatment. However, IOC₂ dropped to below 30 at the beginning of the gastroscopy in group R6, and there was statistical difference in hypoxemia between groups R2 and R6 (P <0.05).

CONCLUSIONS

With the help of IOC monitoring, we found that a target concentration of remifentanil 4 ng/mL is comparatively ideal in patients under gastroscopic polypectomy.

TRIAL REGISTRATION

Chinese Clinical Trial Register: ChiCTR-OOD-16009489 , on October 19, 2016.

Effects of indexes of consciousness (IoC1 and IoC2) monitoring on remifentanil dosage in modified radical mastectomy: a randomized trial

Background

This study investigated the effects of indexes of consciousness (IoC1 and IoC2) monitoring on remifentanil dosage.

Methods

In this randomized, single-blinded, prospective study, 120 patients undergoing unilateral modified radical mastectomy were randomly assigned to the treatment group (T group, n = 60) or control group (C group, n = 60). In the T group, patients received both IoC1 (sedation) and IoC2 (analgesia) monitoring, and remifentanil dosages were adjusted by anesthetists according to IoC2. In the C group, remifentanil dosages were adjusted based on the anesthetists’ judgment according to the patients’ vital signs. Remifentanil dose, adjustment frequency, infusion duration, intraoperative adverse events, and quality of anesthetic recovery were compared between the two groups. The primary outcome was the dose of remifentanil.

Results

Compared with the C group, mean remifentanil dosage was significantly higher in the T group (3.8 ± 1.9 versus 3.2 ± 1.2 μg kg^-1 h^-1, P < 0.05) during the anesthetic period, as was the adjustment frequency of target-controlled infusion (2.9 ± 1.9 versus 2.0 ± 1.2 times/surgery, P < 0.05), but there was no difference in infusion duration. Voluntary eye opening, extubation time, and recovery score were not significantly different between the two groups (P > 0.05). Total adverse events were significantly reduced in the T group (P < 0.05).

Conclusions

IoC1-targeted propofol dosing does not seem to be significantly different to hemodynamic-based monitoring, whereas IoC2 monitoring can increase remifentanil dosage during modified radical mastectomy, but the anesthetic process is more controllable and total adverse events are reduced, which improves the controllability of anesthesia.

Trial registration

Trial registration number: ChiCTR-TRC-13004101, registered on 27 November 2013.

Computational Depth of Anesthesia via Multiple Vital Signs Based on Artificial Neural Networks

This study evaluated the depth of anesthesia (DoA) index using artificial neural networks (ANN) which is performed as the modeling technique. Totally 63-patient data is addressed, for both modeling and testing of 17 and 46 patients, respectively. The empirical mode decomposition (EMD) is utilized to purify between the electroencephalography (EEG) signal and the noise. The filtered EEG signal is subsequently extracted to achieve a sample entropy index by every 5-second signal. Then, it is combined with other mean values of vital signs, that is, electromyography (EMG), heart rate (HR), pulse, systolic blood pressure (SBP), diastolic blood pressure (DBP), and signal quality index (SQI) to evaluate the DoA index as the input. The 5 doctor scores are averaged to obtain an output index. The mean absolute error (MAE) is utilized as the performance evaluation. 10-fold cross-validation is performed in order to generalize the model. The ANN model is compared with the bispectral index (BIS). The results show that the ANN is able to produce lower MAE than BIS. For the correlation coefficient, ANN also has higher value than BIS tested on the 46-patient testing data. Sensitivity analysis and cross-validation method are applied in advance. The results state that EMG has the most effecting parameter, significantly.

The effect of modified ultrafiltration duration on pulmonary functions and hemodynamics in newborns and infants following arterial switch operation*

OBJECTIVES

Modified ultrafiltration is used to ameliorate the deleterious effects of cardiopulmonary bypass in pediatric cardiac surgery patients. The ideal duration of modified ultrafiltration has not been established yet. We investigated the effects of extended duration of modified ultrafiltration on pulmonary functions and hemodynamics in the early postoperative period in newborns and infants who had transposition of great arteries operations.

DESIGN

Single-center prospective randomized study.

SETTING

Pediatric cardiac surgery operating room and ICU.

PATIENTS

Sixty newborns and infants who had been scheduled to undergo transposition of great arteries operation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Modified ultrafiltration was applied to all patients following the termination of cardiopulmonary bypass (for 10, 15, and 20 min in groups 1, 2, and 3, respectively). Pulmonary compliance, gas exchange capacity, hemodynamic measurements, inotropic support, blood loss, transfusion requirements, hematocrit level, and duration of ventilatory support were measured after intubation, at termination of cardiopulmonary bypass, at the end of modified ultrafiltration, and in the 1st, 6th, 12th, and 24th hours after admission to ICU. The amount of fluid removed by modified ultrafiltration in groups 2 and 3 was larger than that of group 1 (p < 0.01). Systolic blood pressure was significantly increased at the end of modified ultrafiltration in group 3 compared to groups 1 and 2 (p < 0.05). Hematocrit levels were significantly increased at the end of modified ultrafiltration in groups 2 and 3 compared to group 1 (p < 0.01). Therefore, RBCs were transfused less after modified ultrafiltration in groups 2 and 3 compared to group 1 (p < 0.05). Static and dynamic compliance, oxygen index, and ventilation index had improved similarly in all three groups at the end of modified ultrafiltration (p > 0.05) CONCLUSIONS:: Modified ultrafiltration acutely improved pulmonary compliance and gas exchange in all groups. Increased hematocrit and blood pressure levels were also observed in the longer modified ultrafiltration group. However, extended duration of modified ultrafiltration did not have a significant impact on duration of intubation or the stay in ICU.

Health worker exposure risk during inhalation sedation with sevoflurane using the (AnaConDa®) anaesthetic conserving device

INTRODUCTION AND OBJECTIVE

Occupational exposure to sevoflurane should not exceed 2 ppm. During inhalation sedation with sevoflurane using the anaesthetic conserving device (AnaConDa(®)) in the post-anaesthesia care unit, waste gases can be reduced by gas extraction systems or scavenging devices such as CONTRAfluran™. However, the efficacy of these methods has not been clearly established. To determine the safest scenario for healthcare workers during inhalation sedation with sevoflurane in the post-surgical intensive care unit.

MATERIALS AND METHODS

An experimental study on occupational exposure was conducted in a post-cardiothoracic care unit during March-August 2009. The measurements were performed in four post-cardiac surgery sedated adults in post-surgical intensive care unit and four nurses at the bedside, and at four points: scenario A, inhalation sedation without gas extraction system or contrafluran as a reference scenario; scenario B, applying a gas extraction system to the ventilator; scenario C, using contrafluran; and scenario 0, performing intravenous isolation sedation. Sevoflurane concentrations were measured in the nurses' breathing area during patient care, and at 1.5 and 8 m from the ventilator using diffusive passive monitor badges.

RESULTS

All badges corresponding to the nurses' breathing area were below 2 ppm. Levels of sevoflurane detected using prevention systems were lower than that in the control situation. Only one determination over 2 ppm was found, corresponding to the monitor placed nearest the gas outlet of the ventilator in scenario A. Trace concentrations of sevoflurane were found in scenario 0 during intravenous sedation.

CONCLUSIONS

Administration of sevoflurane through the AnaConDa(®) system during inhalation sedation in post-surgical intensive care units is safe for healthcare workers, but gas extraction systems or scavenging systems, such as CONTRAfluran™ should be used to reduce occupational exposure as much as possible.

Anesthesia management with single injection paravertebral block for aorta coarctation in infant

BACKGROUND

Thoracotomy causes severe pain in the postoperative period. Perioperative thoracic paravertebral block reduces pain score and may improve outcome after pediatric cardiac surgery. This prospective study was designed for the efficacy and duration of a single level, single injection ultrasound-guided thoracic paravertebral block (TPVB) for fifteen infants undergoing aortic coarctation repair.

METHODS

After approval of the ethical committee and the relatives of the patients, 15 infants who had undergone thoracotomy were enrolled in the study. The patients received 0.5 ml·kg(-1) a bolus 0.25% bupivacaine with epinephrine 1 : 200 000 at T5-6 level after standard general anesthesia induction. Anesthesia depth with Index of Consciousness (IOC) and tissue oxygen saturation with cerebral (rSO2-C) and somatic thoracodorsal (rSO2-S) were monitored. Intraoperative hemodynamic and postoperative hemodynamic and pain scores were evaluated for 24 h after surgery. Face, Legs, Activity, Cry, Consolability (FLACC) score was utilized to measure postoperative pain in the intensive care unit. Rescue 0.05 mg·kg(-1) IV morphine was applied to patients in whom FLACC was >3.

RESULTS

The median age of the patients was 4.5 (1-11) months, and the median intraoperative endtidal isoflurane concentration was 0.6% (0.3-0.8). The amount of remifentanil used intraoperatively was 4.5 (2.5-14) μg·kg(-) (1) ·h(-1). Intraoperative heart rate and blood pressure values significantly decreased compared with values detected at 5th, 10th, and 15th min after TPVB application, after incision prior and after cross-clamp (P < 0.01). The median time of first dose of morphine application after block was 320 (185-430) min. The median morphine consumption in 24 h was 0.16 (0.09-0.4) mg·kg(-1). The median length of postoperative intensive care unit and in-hospital stay times was 23 (1-67) h and 4 (1-10) days, respectively.

CONCLUSION

We believe that TPVB, as part of a balanced anesthetic and analgesic regime, provides effective pain relief in patients undergoing aortic coarctation repair.

Monitoring of anesthetic depth during surgical correction of acquired valvular disorders: single center, randomized trial

OBJECTIVE

The authors' primary objective was to test the hypothesis that Cerebral State Index (CSI)-guided control of anesthetic depth might reduce the consumption of anesthetics and shorten the duration of ICU and hospital stays after surgical correction of combined valve disorders.

DESIGN

Single center, randomized trial.

SETTING

City Hospital Number 1 of Arkhangelsk, Russian Federation.

PARTICIPANTS

Fifty adult patients with combined valve disorders requiring surgical correction.

INTERVENTIONS

The patients were randomized into 2 groups. In the CSI group, anesthetic depth was monitored, and the rate of infusion of propofol was titrated to maintain the depth of anesthesia corresponding to a CSI of 40-60. In the control group, the depth of anesthesia was monitored clinically, and the dosage of propofol was administered according to the recommendations of the manufacturer.

MEASUREMENTS AND MAIN RESULTS

All patients received standard perioperative monitoring. Consumption of anesthetics and length of ICU and hospital stays were recorded. Preoperative patient characteristics did not differ significantly between the groups. In the CSI group, average intraoperative doses of midazolam and propofol were reduced by 41% and 19%, respectively (p<0.01). Maintenance of anesthesia guided by CSI shortened the time until fit for ICU discharge by 50% and reduced the lengths of ICU and postoperative hospital stays by 35% and 25%, respectively (p< 0.05).

CONCLUSIONS

Monitoring of anesthetic depth reduces the requirements for midazolam and propofol, resulting in a faster recovery and a shorter postoperative ICU and hospital stay after surgical correction of combined valve disorders.

Evolution of electroencephalogram signal analysis techniques during anesthesia

Biosignal analysis is one of the most important topics that researchers have tried to develop during the last century to understand numerous human diseases. Electroencephalograms (EEGs) are one of the techniques which provides an electrical representation of biosignals that reflect changes in the activity of the human brain. Monitoring the levels of anesthesia is a very important subject, which has been proposed to avoid both patient awareness caused by inadequate dosage of anesthetic drugs and excessive use of anesthesia during surgery. This article reviews the bases of these techniques and their development within the last decades and provides a synopsis of the relevant methodologies and algorithms that are used to analyze EEG signals. In addition, it aims to present some of the physiological background of the EEG signal, developments in EEG signal processing, and the effective methods used to remove various types of noise. This review will hopefully increase efforts to develop methods that use EEG signals for determining and classifying the depth of anesthesia with a high data rate to produce a flexible and reliable detection device.

Electroencephalogram signatures of loss and recovery of consciousness from propofol

Unconsciousness is a fundamental component of general anesthesia (GA), but anesthesiologists have no reliable ways to be certain that a patient is unconscious. To develop EEG signatures that track loss and recovery of consciousness under GA, we recorded high-density EEGs in humans during gradual induction of and emergence from unconsciousness with propofol. The subjects executed an auditory task at 4-s intervals consisting of interleaved verbal and click stimuli to identify loss and recovery of consciousness. During induction, subjects lost responsiveness to the less salient clicks before losing responsiveness to the more salient verbal stimuli; during emergence they recovered responsiveness to the verbal stimuli before recovering responsiveness to the clicks. The median frequency and bandwidth of the frontal EEG power tracked the probability of response to the verbal stimuli during the transitions in consciousness. Loss of consciousness was marked simultaneously by an increase in low-frequency EEG power (<1 Hz), the loss of spatially coherent occipital alpha oscillations (8-12 Hz), and the appearance of spatially coherent frontal alpha oscillations. These dynamics reversed with recovery of consciousness. The low-frequency phase modulated alpha amplitude in two distinct patterns. During profound unconsciousness, alpha amplitudes were maximal at low-frequency peaks, whereas during the transition into and out of unconsciousness, alpha amplitudes were maximal at low-frequency nadirs. This latter phase-amplitude relationship predicted recovery of consciousness. Our results provide insights into the mechanisms of propofol-induced unconsciousness, establish EEG signatures of this brain state that track transitions in consciousness precisely, and suggest strategies for monitoring the brain activity of patients receiving GA.

Parameter selection in permutation entropy for an electroencephalographic measure of isoflurane anesthetic drug effect

The permutation entropy (PE) of the electroencephalographic (EEG) signals has been proposed as a robust measure of anesthetic drug effect. The calculation of PE involves the somewhat arbitrary selection of embedding dimension (m) and lag (τ) parameters. Previous studies of PE include the analysis of EEG signals under sevoflurane or propofol anesthesia, where different parameter settings were determined using a number of different criteria. In this study we choose parameter values based on the quantitative performance, to quantify the effect of a wide range of concentrations of isoflurane on the EEG. We analyzed a set of previously published EEG data, obtained from 29 patients who underwent elective abdominal surgery under isoflurane general anesthesia combined with epidural anesthesia. PE indices using a range of different parameter settings (m = 3-7, τ = 1-5) were calculated. These indices were evaluated as regards: the correlation coefficient (r) with isoflurane end-tidal concentration, the relationship with isoflurane effect-site concentration assessed by the coefficient of determination (R (2)) of the pharmacokinetic-pharmacodynamic models, and the prediction probability (PK). The embedding dimension (m) and lag (τ) have significant effect on the r values (Two-way repeated-measures ANOVA, p < 0.001). The proposed new permutation entropy index (NPEI) [a combination of PE(m = 3, τ = 2) and PE(m = 3, τ = 3)] performed best among all the parameter combinations, with r = 0.89(0.83-0.94), R (2) = 0.82(0.76-0.87), and PK = 0.80 (0.76-0.85). Further comparison with previously suggested PE measures, as well as other unrelated EEG measures, indicates the superiority of the NPEI. The PE can be utilized to indicate the dynamical changes of EEG signals under isoflurane anesthesia. In this study, the NPEI measure that combines the PE with m = 3, τ = 2 and that with m = 3, τ = 3 is optimal.

Assessment of unconsciousness in pigs during exposure to nitrogen and carbon dioxide mixtures

The aim of this study was to assess unconsciousness in pigs during and after the exposure to gas mixtures of 70% nitrogen (N(2)) and 30% carbon dioxide (CO(2)) (70N30C), 80% N(2) and 20% CO(2) (80N20C) and 85% N(2) and 15% CO(2) (85N15C) compared with 90% CO(2) in air (90C) by means of the Index of Consciousness(®)(IoC), their behaviour and the absence of brain stem reflexes. The experiment included three trials of 24 pigs divided into four groups according to the number of treatments. Half of the group was exposed for a short time and the other half for a long time (3 and 5 min for the N(2)/CO(2) mixtures exposure and 2 and 3 min in 90C exposure, respectively). During exposure, the IoC and the electroencephalography suppression rate (ESR) were assessed, as well as the time to onset and percentage of gasping, loss of balance, vocalizations, muscular excitation and gagging. At the end of the exposure, the corneal reflex, rhythmic breathing and sensitivity to pain were each assessed at 10 s intervals for 5 min. Brain activity decreased significantly (P < 0.05) 37.60 s after the start of the exposure to 90% CO(2), which was significantly earlier than in 70N30C, 80N20C and 85N15C exposure, (45.18 s, 46.92 s and 43.27 s, respectively). Before brain activity decreased, all pigs experienced gasping and loss of balance and a 98% muscular excitation. The duration of the muscular excitation was longer in animals exposed to 70N30C, 80N20C and 85N15C than 90C (P < 0.01). After a long exposure time, all animals exposed to 90C died, whereas the 30.4% of animals exposed to N(2)/CO(2) gas mixtures survived. Pigs exposed to 85N15C recovered corneal reflex and sensitivity to pain significantly earlier than when exposed to 90C. Exposure to 90C causes a higher aversive reaction but a quicker loss of consciousness than N(2)/CO(2) gas mixtures. Exposure to N(2)/CO(2) gas mixtures causes a lower percentage of deaths and an earlier recovery of the brain stem activity than 90C, whereas the time to recover the cortical activity is similar. In conclusion, the inhalation of N(2)/CO(2) gas mixtures reduces the aversion compared with high concentrations of CO(2); however, the period of exposure for inducing unconsciousness may be longer in N(2)/CO(2) gas mixtures, and the signs of recovery appear earlier, compared to CO(2).

Auto-mutual information function of the EEG as a measure of depth of anesthesia

Monitoring the depth of anesthesia (DOA) is necessary in order to decrease the incident of awareness in anesthesia and to prevent delays in the recovery phase. In the last decades a number of noninvasive methods have been proposed for the analysis of the electroencephalogram (EEG) for monitoring DOA. The objective of this work was to apply auto mutual information function (AMIF) to EEGs of patients under anesthesia in order to find variables able to characterize the following 4 states: awake, sedated, anesthetized and burst suppression episodes. The results show that the single and combined AMIF parameters were able to correctly classify the states in the range 72.2%-94.1% and 61.1%-100%, respectively.

Monitoring the depth of anaesthesia

One of the current challenges in medicine is monitoring the patients’ depth of general anaesthesia (DGA). Accurate assessment of the depth of anaesthesia contributes to tailoring drug administration to the individual patient, thus preventing awareness or excessive anaesthetic depth and improving patients’ outcomes. In the past decade, there has been a significant increase in the number of studies on the development, comparison and validation of commercial devices that estimate the DGA by analyzing electrical activity of the brain (i.e., evoked potentials or brain waves). In this paper we review the most frequently used sensors and mathematical methods for monitoring the DGA, their validation in clinical practice and discuss the central question of whether these approaches can, compared to other conventional methods, reduce the risk of patient awareness during surgical procedures.

Recent advance in patient monitoring

Recent advance in technology has developed a lot of new aspects of clinical monitoring. We can monitor sedation levels during anesthesia using various electroencephalographic (EEG) indices, while it is still not useful for anesthesia depth monitoring. Some attempts are made to monitor the changes in sympathetic nerve activity as one of the indicators of stress, pain/analgesia, or anesthesia. To know the balance of sympathetic and parasympathetic activity, heart rate or blood pressure variability is investigated. For trend of cardiac output, low invasive monitors have been investigated. Improvement of ultrasound enables us to see cardiac structure and function continuously and clearer, increases success rate and decreases complication of central venous puncture and various kinds of nerve blocks. Without inserting an arterial catheter, trends of arterial oxygen tension or carbon dioxide tension can be monitored. Indirect visualization of the airway decreases difficult intubation and makes it easier to teach tracheal intubation. The changes in blood volume can be speculated non-invasively. Cerebral perfusion and metabolism are not ordinary monitored yet, but some studies show their usefulness in management of critically ill. This review introduces recent advances in various monitors used in anesthesia and critical care including some studies of the author, especially focused on EEG and cardiac output. However, the most important is that these new monitors are not almighty but should be used adequately in a limited situation where their meaning is confirmed.

Depth of anesthesia

PURPOSE OF REVIEW

The present review article provides a summary of the recent literature evaluating the technology for monitoring depth of anesthesia and patient outcomes associated with its use.

RECENT FINDINGS

The tentative and controversial findings of a 2006 study suggesting a correlation of mortality with lower intraoperative bispectral index scores were reproduced in a more recent study, but the correlation could be accounted for by controlling for patient comorbidities, particularly malignancy. In a large trial involving patients at high risk for awareness, general anesthesia with volatile agents guided by bispectral index monitoring was associated with a low incidence of awareness, but no more so than the use of alarms for limits on volatile agent concentration. Studies comparing both emerging and more established brain function monitors suggest that, in spite of their different algorithms for processing and filtering electromyographic signal, many monitors are affected by the use of neuromuscular blocking agents. Recent evidence is consistent with previous studies that describe a nonlinear model for the dose-response of EEG parameters to increasing concentration of anesthetic agents with a dosing plateau response over a clinically relevant dose range.

SUMMARY

The goal of precisely dosed general anesthesia guided by brain monitoring remains elusive.

Processed electroencephalogram in depth of anesthesia monitoring

PURPOSE OF REVIEW

We critically review the principles underlying processed electroencephalogram (EEG) monitors and recent studies validating their use in monitoring anesthetic depth.

RECENT FINDINGS

Depth of anesthesia is a theoretical construct to conceptualize anesthetic effects on the central nervous system as discrete or continuous phases or states. Clinical signs for assessing anesthetic depth are currently being supplemented by brain monitors. Their use may help to prevent insufficient anesthesia, which can lead to intraoperative awareness with recall, as well as anesthetic overdose, which may be associated with adverse events. Commercial and open-source brain monitoring indices are computed from frequency, entropy, or information theoretic analysis of the spontaneous or evoked EEG. These techniques are undergoing refinement to determine the best method for titrating anesthetics. Future depth-of-anesthesia monitors will benefit from current work aimed at correlating anesthetic effects to alterations in specific neural circuits.

SUMMARY

Current processed EEG monitors are limited by their calibration range and the interpatient variability in their dose-response curves. The next generation of depth-of-anesthesia monitors will require a greater understanding of the transformations of cortical and subcortical activity into EEG signals, the effects of anesthetics at a systems level, and the neural correlates of consciousness.

Index of consciousness and bispectral index values are interchangeable during normotension and hypotension but not during non pulsatile flow state during cardiac surgical procedures: a prospective study

OBJECTIVES

Awareness under anesthesia is an avoidable complication during general anesthesia. Anesthetic depth monitors assist anesthesiologists in providing appropriate levels of anesthesia. Index of consciousness monitoring is a recently introduced monitor in the array of anesthesia depth monitors. The objective of this study was to assess the interchangeability of bispectral index, which is already in clinical use and the recently introduced index of consciousness techniques. The other objective was to assess this interchangeability during normotension, hypotension and during pulseless state in patients undergoing coronary artery bypass graft surgery. This study is a prospective observational study, conducted in a tertiary referral hospital.

MEASUREMENTS AND MAIN RESULTS

Fifteen cardiac surgical patients undergoing off pump and conventional coronary artery bypass under cardiopulmonary bypass participated in the study. Bispectral index and index of consciousness monitoring were carried out simultaneously during various stages of consciousness, and assessed for interchangeability. Bland Altman plotting and 'mountain plot' were used to assess the interchangeability. Eleven in the cohort underwent off pump and the rest (n = 4) conventional coronary artery bypass surgery under cardiopulmonary bypass. A set of 887 data were obtained during the study period. The data were classified as those obtained during normotension, hypotension and pulseless state during cardiopulmonary bypass.

RESULTS

732 sets of data were obtained during normotension, 84 during hypotension and 71 during cardiopulmonary bypass. Overall interchangeability was good, suggested by low bias (0.96), high precision (0.54), r value of 0.7 and P value of <0.0001. It was found that the data obtained during normotension was also interchangeable, suggested by low bias (0.8), high precision (0.54) and r value of 0.7. The data obtained during hypotension was not as highly interchangeable as during normotension-bias 0.4, precision 1.66 and r value of 0.7. The analysis of value during cardiopulmonary bypass suggested non interchangeability (bias 3.87, precision 3.05, r value 0.3 and P value = 0.0067.

CONCLUSIONS

The bispectral index and index of consciousness values may be interchangeable. The interchangeability is better appreciated during normotension and hypotension but not during non pulsatile state of cardiopulmonary bypass.