Intrapatient Reproducibility of the BISxp® Monitor

Response of the GE Entropy™ monitor to neuromuscular block in awake volunteers

BACKGROUND

The GE Entropy™ monitor analyses the frontal electroencephalogram (EEG) and generates two indices intended to represent the degree of anaesthetic drug effect on the brain. It is frequently used in the context of neuromuscular block. We have shown that a similar device, the Bispectral Index monitor (BIS), does not generate correct values in awake volunteers when neuromuscular blocking drugs are administered.

METHODS

We replayed the EEGs recorded during awake paralysis from the original study to an Entropy monitor via a calibrated electronic playback system. Each EEG was replayed 30 times to evaluate the consistency of the Entropy output.

RESULTS

Both State Entropy and Response Entropy decreased during periods of neuromuscular block to values consistent with anaesthesia, despite there being no change in conscious state (State Entropy <60 in eight of nine rocuronium trials and nine of 10 suxamethonium trials). Entropy values did not return to pre-test levels until after the return of movement. Entropy did not generate exactly the same results when the same EEG was replayed multiple times, which is primarily because of a cyclical state within the Entropy system itself.

CONCLUSIONS

The GE Entropy™ monitor requires muscle activity to generate correct values in an awake subject. It could therefore be unreliable at detecting awareness in patients who have been given neuromuscular blocking drugs. In addition, Entropy does not generate the same result each time it is presented with the same EEG.

Accuracy of BIS monitoring using a novel interface device connecting conventional needle-electrodes and BIS sensors during frontal neurosurgical procedures

Background

Bispectral index (BIS) monitoring is a widely used non-invasive method to monitor the depth of anesthesia. However, in the event of surgeries requiring a frontal approach, placement of the electrode may be impossible at the designated area to achieve a proper BIS measurement.

Methods

We developed an investigational interface device to connect needle-electrodes to BIS sensors. The safety and clinical performance were investigated in patients who underwent surgery. Direct BIS values from a disposable BIS electrode and indirect values via the interface device were simultaneously recorded from the same areas of electrode placement in a single patient. The agreement between the direct and indirect BIS values was statistically analyzed.

Results

The interface device with a silver electrode demonstrated sufficient electric conduction to transmit electroencephalogram signals. The overall BIS curves were similar to those of direct BIS monitoring. Direct and indirect BIS values from 18 patients were statistically analyzed using a linear mixed model and a significant concordance was confirmed (indirect BIS = 7.0405 + 0.8286 * direct BIS, p<0.0001). Most observed data (2582/2787 data points, 92.64%) had BIS unit differences of 10 or less.

Conclusions

The interface device provides an opportunity for intraoperative BIS monitoring of patients, whose clinical situation does not permit the placement of conventional adhesive sensors at the standard location.

Propofol-Bispectral Index (BIS) Electroencephalography (EEG) Pharmacokinetic-Pharmacodynamic Model in Patients With Post-Cerebral Hemorrhage Hydrocephalus

Background. Titrating hypnotic agents for patients who suffer from a cerebral insult is a challenging task. To date there is no real gold standard to precisely quantify electroencephalography (EEG) response in a fashion that could be utilized for patients with post-cerebral hemorrhage hydrocephaly. While we must administer "as per usual" analgesics for noxious stimuli, we have to administer the hypnotic agents more "sparingly" due to lack of objective monitoring. Methods. We compared 15 adult post-cerebral hemorrhage hydrocephalus patients undergoing ventriculo-peritoneal shunt placement with 15 controls matched for gender and approximate age. We set propofol target controlled infusion estimated plasma concentrations (C_p) to gradually reach 4 µg/mL over 4 minutes. To precisely quantify post-cerebral hemorrhage mental dysfunction, we used electronically retrieved bispectral index (BIS) and propofol C_p data points to create individual inhibitory monophasic mathematical model for each patient that incorporates an independent hysteresis "lag" function. Results. In post-cerebral hemorrhage patients C_p-BIS curve, C₅₀ (propofol concentration associated with inhibitory 50% BIS response) cutoff point was significantly shifted to the left by 39%. Whereas before infusion and at stable propofol 4 µg/mL aneurismal surgical sides ipsilateral (75 ± 13, 25 ± 9) and contralateral (73 ± 15, 27 ± 9) mean ± SD BIS values were significantly lower than ipsilateral (95 ± 3, 46 ± 12) and contralateral (94 ± 3, 46 ± 12) matched controls. Conclusions. Using BIS as surrogate marker of propofol hypnotic effect, BIS monitoring in patients with post-cerebral hemorrhage hydrocephaly showed a pattern of change and trend that was similar albeit 39% significantly lower than subjects without.

Comparative evaluation of the bispectral index (BIS) and BISpro during propofol anaesthesia

OBJECTIVE

To compare the accuracy, correlation and agreement between the bispectral index (BIS) and BISpro during propofol anaesthesia.

METHODS

The BIS, BISpro, heart rate, target-concentration of propofol and Observer's Assessment of Alertness and Sedation (OAA/S) score were recorded every 30 s in female patients scheduled for hysteroscopic surgery. Propofol anaesthesia was induced by an initial target-controlled concentration (1.0 μg/ml) followed by a stepwise increase (0.5 μg/ml) until the patient was unresponsive. Spearman's correlation coefficient and prediction probability were calculated for the association between sedation levels and the above parameters. The ability of investigated parameters to distinguish between OAA/S scores was analysed. Bland-Altman analysis was used to compare the agreement between BIS and BISpro. The BIS and BISpro cut-off values for lost response were also determined.

RESULTS

Out of 30 patients in total, a high correlation was found between BIS and BISpro, and both correlated well with OAA/S score. Only BIS was able to distinguish all investigated OAA/S states accurately, but the ability to predict OAA/S score 5 to loss of response was comparable between BIS and BISpro. The calculated cut-off values were 68 for BIS and 70 for BISpro.

CONCLUSION

BISpro and BIS are reliable monitors of general anaesthesia during sedation.Trial registration number: Chinese Clinical Trial Registry (URL: www.chictr.org.cn): ChiCTR1900024037 (retrospectively registered).

Variations in Values of State, Response Entropy and Haemodynamic Parameters Associated with Development of Different Epileptiform Patterns during Volatile Induction of General Anaesthesia with Two Different Anaesthetic Regimens Using Sevoflurane in Comparison with Intravenous Induct: A Comparative Study

BACKGROUND AND OBJECTIVES

Raw electroencephalographic (EEG) signals are rarely used to monitor the depth of volatile induction of general anaesthesia (VIGA) with sevoflurane, even though EEG-based indices may show aberrant values. We aimed to identify whether response (RE) and state entropy (SE) variations reliably reflect the actual depth of general anaesthesia in the presence of different types of epileptiform patterns (EPs) in EEGs during induction of general anaesthesia.

MATERIALS AND METHODS

A randomized, prospective clinical study was performed with 60 patients receiving VIGA using sevoflurane with the increasing concentrations (group VIMA) or the vital capacity (group VCRII) technique or an intravenous single dose of propofol (group PROP). Facial electromyography (fEMG), fraction of inspired sevoflurane (FiAA), fraction of expired sevoflurane (FeAA), minimal alveolar concentration (MAC) of sevoflurane, RE and SE, and standard electroencephalographic evaluations were performed in these patients.

RESULTS

In contrast to periodic epileptiform discharges, erroneous SE and RE values in the patients' EEGs were associated with the presence of polyspikes (PS) and rhythmic polyspikes (PSR), which were more likely to indicate toxic depth rather than false emergence from anaesthesia with no changes in the FiAA, FeAA, and MAC of sevoflurane.

CONCLUSION

Calculated RE and SE values may be misleading during VIGA when EPs are present in patients' EEGs. During VIGA with sevoflurane, we recommend monitoring raw EEG data in scientific studies to correlate it with potentially erroneous RE and SE values and the end-tidal concentration of sevoflurane in everyday clinical practice, when monitoring raw EEG is not available, because they can mislead anaesthesiologists to reduce sevoflurane levels in the ventilation gas and result in unintentional true emergence from anaesthesia. Further studies are required to investigate the behaviour of EEG-based indices during rapid changes in sevoflurane concentrations at different stages of VIGA and the influence of polyspikes and rhythmic polyspikes on the transformation of EEG signals into a digital form.

Obimon: An open-source device enabling group measurement of electrodermal activity

Electrodermal activity (EDA) provides the means to gauge the activity of the sympathetic nervous system. Assessment of EDA for research purposes requires measurement systems that are sensitive to small changes in arousal in the full measurement range, collecting, storing, and monitoring data. The objective behind designing a new open-source device was to be able to measure EDA simultaneously on many subjects, monitoring their activity in real time remotely and collecting high precision data suitable for analyses. To assure feasibility of simultaneous measurements on multiple subjects, the devices must be compact and wearable, without compromising data quality. Experiments were carried out using synchronized devices in group and single subject environments. Validity of EDA measurements of Obimon was demonstrated compared to a reference system (Nexus) during a breathing exercise, a short movie, and while exposed to loud computer-generated tones, using Pearson correlation, Passing-Bablok regression, and Bland-Altman analysis. Seamless management of several Obimons and real-time visualization of EDA via Android phone/tablet application from a large number of participants was demonstrated. Based on analyses of the data collected, we conclude that the Obimon device presented here is a valid and feasible tool for collecting EDA in single or multisubject environments.

Influence of electrocautery-induced electromagnetic interference on quantitative electroencephalographic monitoring of hypnosis during general anesthesia: comparison between the ADMS® and the BIS VISTATM

Background

Hypnosis monitors analyze small-amplitude electrical signals transmitted from the brain that could be exposed to the electromagnetic field that occurs around the body during electrocautery (ECT). We investigated the influence of ECT on hypnosis monitoring during anesthesia.

Methods

We simultaneously monitored BIS and uCON during 50 gynecologic oncology surgeries. During the episodes of ECT, we compared the absolute difference (a-Diff) between the baseline index and the most deviated index after ECT over either 30–60 s (ECT30–60) or more than 60 s (ECT > 60) between the monitors. We also investigated the bias and the limits of agreement between the monitors.

Results

Between the two monitors, the a-Diff of ECT30–60 was 1.4 ± 1.1 for the BIS, which was significantly greater than 0.6 ± 0.9 for the uCON (P = 0.003), and the a-Diff of ECT > 60 was 16.5 ± 8.2 for the BIS, which was also significantly greater than 1.4 ± 1.3 for uCON (P < 0.001). The intra-monitor index differences showed that the BIS during ECT > 60 was significantly greater than that during ECT30–60 (P < 0.001), but the uCON showed no significant difference between ECT30–60 and ECT > 60 (P = 0.056). The estimated bias between the monitors was 6.3 ± 9.8 and 95% limits agreement was –12.3 to 25.0.

Conclusions

Prolonged ECT intervention might lead to spurious estimations of quantitative EEG indexes. Therefore, hypnosis should be clinically assessed in combination with scrutinized judgment of relevant clinical symptoms and signs for hypnosis.

Neurally adjusted ventilatory assist feasibility during anaesthesia: A randomised crossover study of two anaesthetics in a large animal model

BACKGROUND

Spontaneous breathing during mechanical ventilation improves gas exchange by redistribution of ventilation to dependent lung regions. Neurally adjusted ventilatory assist (NAVA) supports spontaneous breathing in proportion to the electrical activity of the diaphragm (EAdi). NAVA has never been used in the operating room and no studies have systematically addressed the influence of different anaesthetic drugs on EAdi.

OBJECTIVES

The aim of this study was to test the feasibility of NAVA under sedation and anaesthesia with two commonly used anaesthetics, sevoflurane and propofol, with and without remifentanil, and to study their effects on EAdi and breathing mechanics.

DESIGN

A crossover study with factorial design of NAVA during sedation and anaesthesia in pigs.

SETTING

University basic science laboratory in Uppsala, Sweden, from March 2009 to February 2011.

ANIMALS

Nine juvenile pigs were used for the experiment.

INTERVENTIONS

The lungs were ventilated using NAVA while the animals were sedated and anaesthetised with continuous low-dose ketamine combined with sevoflurane and propofol, with and without remifentanil.

MAIN OUTCOME MEASURES

During the last 5 min of each study period (total eight steps) EAdi, breathing pattern, blood gas analysis, neuromechanical efficiency (NME) and neuroventilatory efficiency (NVE) during NAVA were determined.

RESULTS

EAdi was preserved and normoventilation was reached with both sevoflurane and propofol during sedation as well as anaesthesia. Tidal volume (Vt) was significantly lower with sevoflurane anaesthesia than with propofol. NME was significantly higher with sevoflurane than with propofol during anaesthesia with and without remifentanil. NVE was significantly higher with sevoflurane than with propofol during sedation and anaesthesia.

CONCLUSION

NAVA is feasible during ketamine-propofol and ketamine-sevoflurane anaesthesia in pigs. Sevoflurane promotes lower Vt, and affects NME and NVE less than propofol. Our data warrant studies of NAVA in humans undergoing anaesthesia.

Differences between state entropy and bispectral index during analysis of identical electroencephalogram signals: a comparison with two randomised anaesthetic techniques

BACKGROUND

It is claimed that bispectral index (BIS) and state entropy reflect an identical clinical spectrum, the hypnotic component of anaesthesia. So far, it is not known to what extent different devices display similar index values while processing identical electroencephalogram (EEG) signals.

OBJECTIVE

To compare BIS and state entropy during analysis of identical EEG data. Inspection of raw EEG input to detect potential causes of erroneous index calculation.

DESIGN

Offline re-analysis of EEG data from a randomised, single-centre controlled trial using the Entropy Module and an Aspect A-2000 monitor.

SETTING

Klinikum rechts der Isar, Technische Universität München, Munich.

PATIENTS

Forty adult patients undergoing elective surgery under general anaesthesia.

INTERVENTIONS

Blocked randomisation of 20 patients per anaesthetic group (sevoflurane/remifentanil or propofol/remifentanil). Isolated forearm technique for differentiation between consciousness and unconsciousness.

MAIN OUTCOME MEASURES

Prediction probability (PK) of state entropy to discriminate consciousness from unconsciousness. Correlation and agreement between state entropy and BIS from deep to light hypnosis. Analysis of raw EEG compared with index values that are in conflict with clinical examination, with frequency measures (frequency bands/Spectral Edge Frequency 95) and visual inspection for physiological EEG patterns (e.g. beta or delta arousal), pathophysiological features such as high-frequency signals (electromyogram/high-frequency EEG or eye fluttering/saccades), different types of electro-oculogram or epileptiform EEG and technical artefacts.

RESULTS

PK of state entropy was 0.80 and of BIS 0.84; correlation coefficient of state entropy with BIS 0.78. Nine percent BIS and 14% state entropy values disagreed with clinical examination. Highest incidence of disagreement occurred after state transitions, in particular for state entropy after loss of consciousness during sevoflurane anaesthesia. EEG sequences which led to false 'conscious' index values often showed high-frequency signals and eye blinks. High-frequency EEG/electromyogram signals were pooled because a separation into EEG and fast electro-oculogram, for example eye fluttering or saccades, on the basis of a single EEG channel may not be very reliable. These signals led to higher Spectral Edge Frequency 95 and ratio of relative beta and gamma band power than EEG signals, indicating adequate unconscious classification. The frequency of other artefacts that were assignable, for example technical artefacts, movement artefacts, was negligible and they were excluded from analysis.

CONCLUSION

High-frequency signals and eye blinks may account for index values that falsely indicate consciousness. Compared with BIS, state entropy showed more false classifications of the clinical state at transition between consciousness and unconsciousness.

Chaos analysis of EEG during isoflurane-induced loss of righting in rats

It has long been known that electroencephalogram (EEG) signals generate chaotic strange attractors and the shape of these attractors correlate with depth of anesthesia. We applied chaos analysis to frontal cortical and hippocampal micro-EEG signals from implanted microelectrodes (layer 4 and CA1, respectively). Rats were taken to and from loss of righting reflex (LORR) with isoflurane and behavioral measures were compared to attractor shape. Resting EEG signals at LORR differed markedly from awake signals, more similar to slow wave sleep signals, and easily discerned in raw recordings (high amplitude slow waves), and in fast Fourier transform analysis (FFT; increased delta power), in good agreement with previous studies. EEG activation stimulated by turning rats on their side, to test righting, produced signals quite similar to awake resting state EEG signals. That is, the high amplitude slow wave activity changed to low amplitude fast activity that lasted for several seconds, before returning to slow wave activity. This occurred regardless of whether the rat was able to right itself, or not. Testing paw pinch and tail clamp responses produced similar EEG activations, even from deep anesthesia when burst suppression dominated the spontaneous EEG. Chaotic attractor shape was far better at discerning between these awake-like signals, at loss of responses, than was FFT analysis. Comparisons are provided between FFT and chaos analysis of EEG during awake walking, slow wave sleep, and isoflurane-induced effects at several depths of anesthesia. Attractors readily discriminated between natural sleep and isoflurane-induced “delta” activity. Chaotic attractor shapes changed gradually through the transition from awake to LORR, indicating that this was not an on/off like transition, but rather a point along a continuum of brain states.

Monitoring hypnotic effect and nociception with two EEG-derived indices, qCON and qNOX, during general anaesthesia

BACKGROUND

The objective of the present study was to validate the qCON index of hypnotic effect and the qNOX index of nociception. Both indices are derived from the frontal electroencephalogram (EEG) and implemented in the qCON 2000 monitor (Quantium Medical, Barcelona, Spain).

METHODS

The study was approved by the local ethics committee, including data from 60 patients scheduled for ambulatory surgery undergoing general anaesthesia with propofol and remifentanil, using TCI. The Bis (Covidien, Boulder, CO, USA) was recorded simultaneously with the qCON. Loss of eyelash reflex [loss of consciousness (LOC)] was recorded, and prediction probability for Bis and qCON was calculated. Movement as a response to noxious stimulation [laryngeal mask airway (LMA) insertion, laryngoscopy and tracheal intubation] was registered. The correlation coefficient between qCON and Bis was calculated. The patients were divided into movers/non-movers as a response to noxious stimulation. A paired t-test was used to assess significant difference for qCON and qNOX for movers/non-movers.

RESULTS

The prediction probability (Pk) and the standard error (SE) for qCON and Bis for detecting LOC was 0.92 (0.02) and 0.94 (0.02) respectively (t-test, no significant difference). The R between qCON and Bis was 0.85. During the general anaesthesia (Ce propofol > 2 μg/ml, Ce remifentanil > 2 ng/ml), the mean value and standard deviation (SD) for qCON was 45 (8), while for qNOX it was 40 (6). The qNOX pre-stimuli values were significantly different (P < 0.05) for movers/non-movers as a response to LMA insertion [62.5 (24.0) vs. 45.5 (24.1)], tracheal intubation [58.7 (21.8) vs. 41.4 (20.9)], laryngoscopy [54.1 (21.4) vs. 41.0 (20.8)]. There were no significant differences in remifentanil or propofol effect-site concentrations for movers vs. non-movers.

CONCLUSION

The qCON was able to reliably detect LOC during general anaesthesia with propofol and remifentanil. The qNOX showed significant overlap between movers and non-movers, but it was able to predict whether or not the patient would move as a response to noxious stimulation, although the anaesthetic concentrations were similar.

Impact of right-handedness on anaesthetic sensitivity, intra-operative awareness and postoperative mortality

Anatomical, neurological and behavioural research has suggested differences between the brains of right- and non-right-handed individuals, including differences in brain structure, electroencephalogram patterns, explicit memory and sleep architecture. Some studies have also found decreased longevity in left-handed individuals. We therefore aimed to determine whether handedness independently affects the relationship between volatile anaesthetic concentration and the bispectral index, the incidence of definite or possible intra-operative awareness with explicit recall, or postoperative mortality. We studied 5585 patients in this secondary analysis of data collected in a multicentre clinical trial. There were 4992 (89.4%) right-handed and 593 (10.6%) non-right-handed patients. Handedness was not associated with (a) an alteration in anaesthetic sensitivity in terms of the relationship between the bispectral index and volatile anaesthetic concentration (estimated effect on the regression relationship -0.52 parallel shift; 95% CI -1.27 to 0.23, p = 0.17); (b) the incidence of intra-operative awareness with 26/4992 (0.52%) right-handed vs 1/593 (0.17%) non-right-handed (difference = 0.35%; 95% CI -0.45 to 0.63%; p = 0.35); or (c) postoperative mortality rates (90-day relative risk for non-right-handedness 1.19, 95% CI 0.76-1.86; p = 0.45). Thus, no change in anaesthetic management is indicated for non-right-handed patients.

Asymmetry of Bispectral Index (BIS) in severe brain-injured patients treated by barbiturates with unilateral or diffuse brain injury

OBJECTIVE

Bispectral index (BIS) may be used in traumatic brain-injured patients (TBI) with intractable intracranial hypertension to adjust barbiturate infusion but it is obtained through a unilateral frontal electrode. The objective of this study was to evaluate differences in BIS between hemispheres in two groups: unilateral frontal (UFI) and diffuse (DI) injured.

PATIENTS AND METHODS

Prospective monocenter observational study in 24 TBI treated with barbiturates: 13 UFI and 11 DI. Simultaneous BIS and EEG was recorded for 1h. Goal of monitoring was a left BIS between 5 and 15. Biases in BIS were considered as clinically relevant if greater than 5. Differences in biases were interpreted from both statistical (Mann-Whitney test) and clinical points of view.

RESULTS

Mean BIS in the two hemispheres remained in the same monitoring range. There were statistic and clinical differences in some values in the two groups of patients (15% of bias greater than I5I in UFI group and 10% in DI group). BIS monitoring allowed the adequate number of bursts/minutes to be predicted in 18 patients and did not detect an overdosage in 2.

CONCLUSIONS

While asymmetric BIS values in TBI patients occur whatever the kind of injury, they were not found to be clinically relevant in most of these heavily sedated patients. Asymmetrical BIS monitoring might be sufficient to monitor barbiturate infusion in TBI provided that the concordance between BIS and EEG is regularly checked.

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.

NREM sleep staging using WAV(CNS) index

OBJECTIVE

Visual scoring of 30-s epochs of sleep data is not always adequate to show the dynamic structure of sleep in sufficient details. It is also prone to considerable inter- and intra-rater variability. Moreover, it involves considerable training and experience, and is very tedious, time-consuming, labor-intensive and costly. Hence, automatic sleep staging is needed to overcome these limitations. Since naturally occurring NREM sleep and anesthesia have been reported to possess various underlying neurophysiological similarities, EEG-based depth-of-anesthesia monitors have started to penetrate into sleep research. This study investigates the ability of WAV(CNS) index (as implemented in NeuroSENSE depth-of-anesthesia monitor) to detect NREM sleep stages and wake state for full overnight PSG data.

METHODS

Full overnight PSG sleep data, obtained from 24 adolescents, was scored by a registered PSG technologist for different sleep stages. Retrospective analysis was performed on a single frontal channel using the WAV(CNS) algorithm. Non-parametric descriptive statistics were used to examine the relationship between WAV(CNS) index and sleep stages.

RESULTS

A strong correlation (ρ = 0.9458) was found between the WAV(CNS) index and NREM sleep stages, with WAV(CNS) index values decreasing with increasing sleep stages. Moreover, there was no significant overlap between different NREM sleep stages as classified by the WAV(CNS) index, which was able to significantly differentiate (P < 0.001) between all pairs of Awake and different NREM stages.

CONCLUSIONS

This study demonstrates that changes in the depth of natural NREM sleep are reflected sensitively by changes in the WAV(CNS) index. Hence, WAV(CNS) index may serve as an automatic real-time indicator of depth of natural sleep with high temporal resolution, and can possibly be of great use for automated sleep staging in routine/postoperative somnographic studies.

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.

Correlation and agreement between the bispectral index vs. state entropy during hypothermic cardio-pulmonary bypass

BACKGROUND

The bispectral index (BIS) and spectral entropy enable monitoring the depth of anaesthesia. Mild hypothermia has been shown to affect the ability of electroencephalography monitors to reflect the anaesthetic drug effect. The purpose of this study was to investigate the effect of hypothermia during a cardio-pulmonary bypass on the correlation and agreement between the BIS and entropy variables compared with normothermic conditions.

METHODS

This prospective clinical study included coronary artery bypass grafting patients (n=25) evaluating correlation and agreement (Bland-Altman analysis) between the BIS and both spectral and response entropy during a hypothermic cardio-pulmonary bypass (31-34 degrees C) compared with nomothermic conditions (34-37.5 degrees C). Anaesthesia was maintained with propofol and sufentanil and adjusted clinically, while the anaesthetist was blinded to the monitors.

RESULTS

The BIS and entropy values decreased during cooling (P<0.05), but the decrease was more pronounced for entropy variables compared with BIS (P<0.05). The correlation coefficients (bias+/-SD; percentage error) between the BIS vs. spectral state entropy and response entropy were r(2)=0.56 (1+/-11; 42%) and r(2)=0.58 (-2+/-11; 43%) under normothermic conditions, and r(2)=0.17 (10+/-12; 77%) and r(2)=0.18 (9+/-11; 68%) under hypothermic conditions, respectively. Bias was significantly increased under hypothermic conditions (P<0.001 vs. normothermia).

CONCLUSION

Acceptable agreement was observed between the BIS and entropy variables under normothermic but not under hypothermic conditions. The BIS and entropy variables may therefore not be interchangeable during a hypothermic cardio-pulmonary bypass.

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

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

When the bispectral index (bis) can give false results

BACKGROUND AND OBJECTIVES

The bispectral index (BIS) is a multifactorial parameter derived from the electroencephalogram (EEG), which allows monitoring of the hypnotic component of anesthesia. It was obtained from the algorithm based on the analysis of a large number of EEGs from volunteers and patients undergoing sedation and general anesthesia with different anesthetic agents. The use of BIS to monitor the depth of anesthesia reduces the incidence of intraoperative awakening and recall, among other benefits. The objective of this review was to present clinical situations in which the BIS gives false results, either elevated or decreased, due to conditions related to the patient or anesthetic actions unforeseen when the algorithm was elaborated.

CONTENTS

The bispectral index can be altered and influenced in different clinical situations in which abnormal EEG patterns are present; the effects of different anesthetics and other drugs not included when the algorithm was elaborated; interference from electrical equipment; as well as peculiarities of the monitor.

CONCLUSIONS

Although the BIS algorithm underwent several changes since its first version, the anesthesiologist should be aware of situations that cause false BIS readings to avoid complications, may it be secondary to anesthetic overdose or underdosing, which might cause intraoperative awakening and recall.

Same-patient reproducibility of state entropy: a comparison of simultaneous bilateral measurements during general anesthesia

BACKGROUND

State Entropy (SE) is an index of anesthetic depth similar to Bispectral Index (BIS). Both indices use a single-channel electroencephalogram, recorded from a unilaterally applied electrode on the forehead, as their input. Intrapatient reproducibility of BIS was questioned in a recent study in which simultaneous measurements from two electrodes applied to the same patient showed conflicting anesthetic depths. Our purpose was to determine whether SE results are similarly reproducible, even though their computation uses a different algorithm than BIS. In this study, we investigated the reproducibility of SE measurements simultaneously obtained from bilaterally applied electrodes in the same patient.

METHODS

Entropy electrodes were applied bilaterally on 21 patients under general inhaled anesthesia. Simultaneous SE measurements from both electrodes were recorded every 10 s from each patient. Data were analyzed with Bland-Altman statistics.

RESULTS

We obtained 14,379 pairs of SE measurements. Four percent of the individual measurements suggested conflicting anesthetic depth along with a numeric difference more than 10 points. Bias was not clinically significant (-0.3). Ninety-five percent limits of agreement were -11.7 and +11.6.

CONCLUSIONS

SE showed a clinically significant degree of disagreement when probes were applied on both sides of the forehead in the same patient. Bland-Altman statistics showed better same-patient reproducibility in SE than did a similar study on BIS. Nevertheless, 4% of the simultaneously measured pairs of SE suggested different anesthetic depths and differed by more than 10 points. Caution is advised when using SE as a clinical index of anesthetic depth.

Bispectral Index Monitoring of Unihemispheric Effects in Dolphins

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

Anesthesia techniques in complex spine surgery

The safe performance of complex spine surgery requires the close collaboration of the anesthesiology and surgical teams. The avoidance of medical and anesthetic complications depends on the appropriate preoperative medical evaluation, patient positioning, selection and administration of anesthetic agents, management of intraoperative fluid status, emergence from anesthesia, and administration of postoperative analgesia.

Cerebral state index: comparison between pairwise registrations from the left and the right sides of the brain

BACKGROUND

Lateralization of cerebral blood flow and EEG activity is known to vary during cognition, sleep and waking. In spite of this, electrode placement for the cerebral state index (CSI) monitor is not specified to a particular side of the brain. This study is designed to determine if pairwise registrations differ for CSI measured simultaneously from the left or right sides of the brain.

METHODS

In total, 25 ASA I-II patients undergoing elective day surgery under general anaesthesia were recruited. Pairwise recordings were made every minute from two CSI monitors (Cerebral State Monitor, Danmeter A/S; Odense, Denmark) connected to the left and the right side of the head. Sedation was graded according to the observer's assessment of alertness/sedation rating scale and correlated with CSI.

RESULTS

A large overlap of indices, of similar magnitude, for each side of the brain was seen between different levels of sedation. The agreement between pairwise registrations was high, correlation between the 584 CSI pairs of recordings left/right was r(2)=0.92.

CONCLUSIONS

Despite known lateralization of the EEC, this study found a very high correlation in CSI derived simultaneously from the left and right sides of the brain by two independent monitors.