Estimating anesthetic depth by electroencephalography during anesthetic induction and intubation in patients undergoing cardiac surgery

Association between intraoperative pulmonary artery pressure and cardiovascular complications after off-pump coronary artery bypass surgery: a single-center observational study

BACKGROUND

The impact of intraoperative pulmonary hemodynamics on prognosis after off-pump coronary artery bypass (OPCAB) surgery remains unknown. In this study, we examined the association between intraoperative vital signs and the development of major adverse cardiovascular events (MACE) during hospitalization or within 30 days postoperatively.

METHODS

This retrospective study analyzed data from a university hospital. The study cohort comprised consecutive patients who underwent isolated OPCAB surgery between November 2013 and July 2021. We calculated the mean and coefficient of variation of vital signs obtained from the intra-arterial catheter, pulmonary artery catheter, and pulse oximeter. The optimal cut-off was defined as the receiver operating characteristic curve (ROC) with the largest Youden index (Youden index = sensitivity + specificity - 1). Multivariate logistic regression analysis ROC curves were used to adjust all baseline characteristics that yielded P values of < 0.05.

RESULTS

In total, 508 patients who underwent OPCAB surgery were analyzed. The mean patient age was 70.0 ± 9.7 years, and 399 (79%) were male. There were no patients with confirmed or suspected preoperative pulmonary hypertension. Postoperative MACE occurred in 32 patients (heart failure in 16, ischemic stroke in 16). The mean pulmonary artery pressure (PAP) was significantly higher in patients with than without MACE (19.3 ± 3.0 vs. 16.7 ± 3.4 mmHg, respectively; absolute difference, 2.6 mmHg; 95% confidence interval, 1.5 to 3.8). The area under the ROC curve of PAP for the prediction of MACE was 0.726 (95% confidence interval, 0.645 to 0.808). The optimal mean PAP cut-off was 18.8 mmHg, with a specificity of 75.8% and sensitivity of 62.5% for predicting MACE. After multivariate adjustments, high PAP remained an independent risk factor for MACE.

CONCLUSIONS

Our findings provide the first evidence that intraoperative borderline pulmonary hypertension may affect the prognosis of patients undergoing OPCAB surgery. Future large-scale prospective studies are needed to verify the present findings.

Anaesthetic interventions for prevention of awareness during surgery

BACKGROUND

General anaesthesia is usually associated with unconsciousness. 'Awareness' is when patients have postoperative recall of events or experiences during surgery. 'Wakefulness' is when patients become conscious during surgery, but have no postoperative recollection of the period of consciousness.

OBJECTIVES

To evaluate the efficacy of two types of anaesthetic interventions in reducing clinically significant awareness:- anaesthetic drug regimens; and- intraoperative anaesthetic depth monitors.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, ISSUE 4 2016); PubMed from 1950 to April 2016; MEDLINE from 1950 to April 2016; and Embase from 1980 to April 2016. We contacted experts to identify additional studies. We performed a handsearch of the citations in the review. We did not search trial registries.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of either anaesthetic regimens or anaesthetic depth monitors. We excluded volunteer studies, studies of patients prior to skin incision, intensive care unit studies, and studies that only randomized different word presentations for memory tests (not anaesthetic interventions).Anaesthetic drug regimens included studies of induction or maintenance, or both. Anaesthetic depth monitors included the Bispectral Index monitor, M-Entropy, Narcotrend monitor, cerebral function monitor, cerebral state monitor, patient state index, and lower oesophageal contractility monitor. The use of anaesthetic depth monitors allows the titration of anaesthetic drugs to maintain unconsciousness.

DATA COLLECTION AND ANALYSIS

At least two authors independently scanned abstracts, extracted data from the studies, and evaluated studies for risk of bias. We made attempts to contact all authors for additional clarification. We performed meta-analysis statistics in packages of the R language.

MAIN RESULTS

We included 160 studies with 54,109 enrolled participants; 53,713 participants started the studies and 50,034 completed the studies or data analysis (or both). We could not use 115 RCTs in meta-analytic comparisons because they had zero awareness events. We did not merge 27 of the remaining 45 studies because they had excessive clinical and methodological heterogeneity. We pooled the remaining 18 eligible RCTs in meta-analysis. There are 10 studies awaiting classification which we will process when we update the review.The meta-analyses included 18 trials with 36,034 participants. In the analysis of anaesthetic depth monitoring (either Bispectral Index or M-entropy) versus standard clinical and electronic monitoring, there were nine trials with 34,744 participants. The overall event rate was 0.5%. The effect favoured neither anaesthetic depth monitoring nor standard clinical and electronic monitoring, with little precision in the odds ratio (OR) estimate (OR 0.98, 95% confidence interval (CI) 0.59 to 1.62).In a five-study subset of Bispectral Index monitoring versus standard clinical and electronic monitoring, with 34,181 participants, 503 participants gave awareness reports to a blinded, expert panel who adjudicated or judged the outcome for each patient after reviewing the questionnaires: no awareness, possible awareness, or definite awareness. Experts judged 351 patient awareness reports to have no awareness, 87 to have possible awareness, and 65 to have definite awareness. The effect size favoured neither Bispectral Index monitoring nor standard clinical and electronic monitoring, with little precision in the OR estimate for the combination of definite and possible awareness (OR 0.96, 95% CI 0.35 to 2.65). The effect size favoured Bispectral Index monitoring for definite awareness, but with little precision in the OR estimate (OR 0.60, 95% CI 0.13 to 2.75).We performed three smaller meta-analyses of anaesthetic drugs. There were nine studies with 1290 participants. Wakefulness was reduced by ketamine and etomidate compared to thiopental. Wakefulness was more frequent than awareness. Benzodiazepines reduces awareness compared to thiopental, ketamine, and placebo., Also, higher doses of inhaled anaesthetics versus lower doses reduced the risk of awareness.We graded the quality of the evidence as low or very low in the 'Summary of findings' tables for the five comparisons.Most of the secondary outcomes in this review were not reported in the included RCTs.

AUTHORS' CONCLUSIONS

Anaesthetic depth monitors may have similar effects to standard clinical and electrical monitoring on the risk of awareness during surgery. In older studies comparing anaesthetics in a smaller portion of the patient sample, wakefulness occurred more frequently than awareness. Use of etomidate and ketamine lowered the risk of wakefulness compared to thiopental. Benzodiazepines compared to thiopental and ketamine, or higher doses of inhaled anaesthetics versus lower doses, reduced the risk of awareness.

Using EEG to monitor anesthesia drug effects during surgery

The use of processed electroencephalography (EEG) using a simple frontal lead system has been made available for assessing the impact of anesthetic medications during surgery. This review discusses the basic principles behind these devices. The foundations of anesthesia monitoring rest on the observations of Guedel with ether that the depth of anesthesia relates to the cortical, brainstem and spinal effects of the anesthetic agents. Anesthesiologists strive to have a patient who is immobile, is unconscious, is hemodynamically stable and who has no intraoperative awareness or recall. These anesthetic management principles apply today, despite the absence of ether from the available anesthetic medications. The use of the EEG as a supplement to the usual monitoring techniques rests on the observation that anesthetic medications all alter the synaptic function which produces the EEG. Frontal EEG can be viewed as a surrogate for the drug effects on the entire central nervous system (CNS). Using mathematical processing techniques, commercial EEG devices create an index usually between 0 and 100 to characterize this drug effect. Critical aspects of memory formation occur in the frontal lobes making EEG monitoring in this area a possible method to assess risk of recall. Integration of processed EEG monitoring into anesthetic management is evolving and its ability to characterize all of the anesthetic effects on the CNS (in particular awareness and recall) and improve decision making is under study.

An effective correlation dimension and burst suppression ratio of the EEG in rat. Correlation with sevoflurane induced anaesthetic depth

BACKGROUND AND OBJECTIVE

Anaesthesiologists need parameters that measure the depth of anaesthesia. In the context of this need, the present study investigated in rats how two variables from the electroencephalogram, the burst suppression ratio and effective correlation dimension correlated with a measure of anaesthetic depth as measured in the strength of a noxious withdrawal reflex.

METHODS

Eight rats were exposed to different inspiratory concentrations of sevoflurane, each rat in two separate experiments. In the first experiment, spontaneously breathing animals could move freely and no painful stimuli were applied. In the second experiment, in mechanically ventilated restrained anaesthetized rats, the withdrawal reflex was measured every 80 s. In both experiments the electroencephalogram was continuously recorded. The concentration in the effector compartment was estimated using a first order two compartment model. Correlation dimension was computed following the Grassberger/Procaccia/Takens approach with optimized parameter settings to achieve maximum sensitivity to anaesthetic drug effects and enable real-time computation. The Hill, equation was fitted to the data, describing the effect as a function of sevoflurane concentration.

RESULTS

Good correlations of Depth of Anaesthesia with correlation dimension as well as burst suppression ratio were established in both types of experiments. Arousal by noxious stimuli decreased burst suppression ratio and increased correlation dimension. The effective sevoflurane concentration associated with 50% of the maximum effect (C50) was higher in experiment II (stimulation) than in experiment I (no stimulation): i.e. for correlation dimension 2.18% vs. 0.60% and for burst suppression ratio 3.07% vs. 1.73%. The slope factors were: gammaCD = 4.15 vs. gammaCD = 1.73 and gammaBSR = 5.2 vs. gammaBSR = 5.4. Correlation dimension and burst suppression ratio both correlated with the strength of the withdrawal reflex with correlation coefficients of 0.46 and 0.66 respectively (P < 0.001).

CONCLUSIONS

Both correlation dimension and burst suppression ratio are related to anaesthetic depth and are affected by noxious stimuli. The relationship between anaesthetic depth and burst suppression ratio is confirmed and the potential of correlation dimension is demonstrated.

Comparison of spontaneous frontal EMG, EEG power spectrum and bispectral index to monitor propofol drug effect and emergence

BACKGROUND

The aim of this study was to investigate the accuracy of frontal spontaneous electromyography (SEMG) and EEG spectral edge frequency (SEF 95%), median frequency (MF), relative delta power (RDELTA) and bispectral index (BIS) in monitoring loss of and return of consciousness and hypnotic drug effect during propofol administration at different calculated plasma target concentrations.

METHODS

Propofol was administered by using a target-controlled infusion at different propofol steady-state concentrations. All variables were measured simultaneously at specific calculated concentrations and endpoints.

RESULTS

Loss of consciousness was accurately monitored by BIS, SEMG and SEF 95%, and propofol drug effect by BIS only. Return of consciousness was predicted by BIS, MF and SEF 95%. Due to the biphasic EEG pattern of propofol and the lack of reproducible data at specific propofol concentrations, the clinical usefulness of SEF 95%, MF and RDELTA was very limited. SEMG was useful to detect loss and return of consciousness, but without predictive value.

CONCLUSIONS

The BIS might be an accurate measure to monitor depth of anaesthesia and hypnotic drug effect. Other neurophysiologic measures have limited value to monitor depth of anaesthesia and hypnotic drug effect.

Design of a recognition system to predict movement during anesthesia

The need for a reliable method of predicting movement during anesthesia has existed since the introduction of anesthesia. This paper proposes a recognition system, based on the autoregressive (AR) modeling and neural network analysis of the electroencephalograph (EEG) signals, to predict movement following surgical stimulation. The input to the neural network will be the AR parameters, the hemodynamic parameters blood pressure (BP) and heart rate (HR), and the anesthetic concentration in terms of the minimum alveolar concentration (MAC). The output will be the prediction of movement. Design of the system and results from the preliminary tests on dogs are presented in this paper. The experiments were carried out on 13 dogs at different levels of halothane. Movement prediction was tested by monitoring the response to tail clamping, which is considered to be a supramaximal stimulus in dogs. The EEG data obtained prior to tail clamping was processed using a tenth-order AR model and the parameters obtained were used as input to a three-layer perceptron feedforward neural network. Using only AR parameters the network was able to correctly classify subsequent movement in 85% of the cases as compared to 65% when only hemodynamic parameters were used as the input to the network. When both the measures were combined, the recognition rate rose to greater than 92%. When the anesthetic concentration was added as an input the network could be considerably simplified without sacrificing classification accuracy. This recognition system shows the feasibility of using the EEG signals for movement during anesthesia.

Monitoring depth of anaesthesia

In clinical practice, indirect and non-specific signs are used for monitoring anaesthetic adequacy. These include haemodynamic, respiratory, muscular and autonomic signs. These measures do not indicate adequacy of anaesthesia in a reliable manner. Many attempts have been made to find a more accurate monitor. Direct monitoring of anaesthetic effect should be possible by EEG measurement. EEG information can be reduced, condensed and simplified, leading to single numbers (spectral edge frequency and median frequency). These methods appear insufficient for assessing anaesthetic adequacy. The bispectral index, derived from bispectral analysis of the EEG, is a very promising tool for measuring adequacy of anaesthesia. An alternative approach is to monitor evoked potentials. Middle latency auditory evoked potentials may be helpful in assessing anaesthetic adequacy. Both techniques need further validation.

A multicenter study of bispectral electroencephalogram analysis for monitoring anesthetic effect

Bispectral analysis (BIS) of the electroencephalogram (EEG) has been shown in retrospective studies to predict whether patients will move in response to skin incision. This prospective multicenter study was designed to evaluate the real-time utility of BIS in predicting movement response to skin incision using a variety of general anesthetic techniques. Three hundred patients from seven study sites received an anesthetic regimen expected to give an approximately 50% movement response at skin incision. EEG was continuously recorded via an Aspect B-500 monitor and BIS was calculated in real time from bilateral frontocentral channels displayed on the monitor. Half of the patients were randomized to a treatment group in which anesthetic drug doses were increased to produce a lower BIS. In the control group, BIS was recorded, but no action taken on the data displayed. A determination of movement in response to skin incision was made in the 2 min succeeding incision. Retrospective pharmacodynamic modeling was performed using STANPUMP to estimate effect-site concentrations of intravenously administered anesthetics. BIS values were significantly higher in the control group (66 +/- 19) versus the BIS-guided group, in which additional anesthesia was administered to produce a lower BIS (51 +/- 19). The movement response rate was significantly higher in the control group at 43% compared with 13% in the BIS-guided group, but response rates were low at sites which used larger doses of opioids. Logistic regression analysis showed that BIS, estimated opioid effect-site concentrations, and heart rate (in that order) were the best predictors of movement at skin incision. This study demonstrates that dosing anesthetic drugs to lower BIS values achieves a lower probability of movement in response to surgical stimulation. BIS is a significant predictor of patient response to incision, but the utility of the BIS depends on the anesthetic technique being used. When drugs such as propofol or isoflurane are used as the primary anesthetic, changes in BIS correlate with the probability of response to skin incision. When opioid analgesics are used, the correlation to patient movement becomes much less significant, so that patients with apparently "light" EEG profiles may not move or otherwise respond to incision. Therefore, the adjunctive use of opioid analgesics confounds the use of BIS as a measure of anesthetic adequacy when movement response to skin incision is used as the primary end point.

Comparison of isoflurane and desflurane anesthetic depth using burst suppression of the electroencephalogram in neurosurgical patients

We compared the anesthetic effects of desflurane and isoflurane using percent burst suppression of the electroencephalogram (EEG) as an end-point in 10 neurosurgical patients. The EEG was recorded from frontal leads and processed variables were analyzed as a function of increasing isoflurane and desflurane concentration with age and baseline delta EEG power (0.5-3.75 Hz) as independent variables. Isoflurane and desflurane (0.5, 1.0, 1.5, 2.0 minimum alveolar anesthetic concentration [MAC]) were incrementally administered until the EEG was quiesecent at least 40% of the time. Both anesthetics were evaluated separately in each patient. By analysis of variance, isoflurane and desflurane produced dose-related increments in burst suppression which were significantly affected by the age and baseline delta EEG of the patient. When isoflurane and desflurane were equated by MAC and adjusted for age, they produced statistically similar patterns of EEG burst suppression. Within subjects, a high degree of correlation was observed for percent burst suppression between equipotent levels of isoflurane and desflurane (r = 0.85; P < 0.05). Patients with baseline delta EEG power less than 80% of total power showed increases in delta EEG and decreases in median frequency with isoflurane and desflurane. Patients with baseline delta EEG power > 80% of total power produced no change in EEG frequency with increasing anesthesia but revealed a greater sensitivity to the development of burst suppression. These results show that isoflurane and desflurane produce similar EEG suppression in neurosurgical patients. If the EEG is initially slow, further slowing cannot be used to assess anesthetic depth.

Prediction of movement using bispectral electroencephalographic analysis during propofol/alfentanil or isoflurane/alfentanil anesthesia

Conventional electroencephalographic (EEG) analysis techniques do not use the phase information from the Fourier analysis. This study used a new technique of EEG analysis, bispectral analysis, which measures interfrequency phase relationships in the EEG. Using a reference database, and a process of multivariate discriminant analysis, we developed a univariate bispectral variable, the bispectral index (BIS). This study was designed to test the efficacy of BIS in predicting movement to incision during either an isoflurane/alfentanil anesthetic or a propofol/alfentanil anesthetic technique. Fifty consenting patients were randomized to two groups; one received isoflurane/alfentanil and the other, propofol/alfentanil for anesthesia. EEG was recorded using a microcomputer system and the data were analyzed off-line. Hemodynamic variables were also recorded. After skin incision, each patient was observed carefully for 2 min to detect purposeful movement. A significant difference was found between the BIS values for movers versus nonmovers within each of the two treatment groups (P < or = 0.002). However, isoflurane/alfentanil nonmovers could not be distinguished from propofol/alfentanil movers (P < or = 0.180), suggesting a treatment group effect independent of response classification. Preincision hemodynamic variables did not predict patient movement in response to skin incision. These findings suggest the possibility that different anesthetics have different effects on BIS, and thus BIS may not be independent of the anesthetic. Interfrequency phase coupling, a nonlinear feature of the EEG which is measured with bispectral analysis, may contain clinically useful information for the assessment of anesthetic adequacy. In this study, BIS was a better predictor of patient response than other currently available variables including hemodynamic status.

EEG bispectrum predicts movement during thiopental/isoflurane anesthesia

OBJECTIVE

The objective of our study was to test the efficacy of the bispectral index (BIS) compared with spectral edge frequency (SEF), relative delta power, median frequency, and a combined univariate power spectral derivative in predicting movement to incision during isoflurane/oxygen anesthesia.

METHODS

A total of 42 consenting patients were assigned to 3 groups, isoflurane 0.75, 1.0, and 1.25 minimal alveolar concentration (MAC). Anesthesia was induced with thiopental and maintained with the appropriate end-tidal concentration of isoflurane. The electroencephalogram (EEG) was recorded using a microcomputer system, and data were analyzed off-line. The EEG during the 2 min before incision was analyzed. Following skin incision, each patient was carefully observed for 60 sec to detect occurrence of purposeful movement.

RESULTS

For all groups combined, there was a statistically significant difference for BIS (p < 0.0001) and also for relative delta power (p < 0.016) between movers and nonmovers. There was a statistically significant difference between movers and nonmovers at 1.25 MAC isoflurane for BIS (p < 0.01). There were no other significant differences for any other EEG variable at any concentration of isoflurane. No EEG variable showed a relationship to isoflurane concentration.

CONCLUSIONS

When bispectral analysis of the EEG was used to develop a retrospectively determined index, there was an association of the index with movement. Thus, it may be a useful predictor of whether patients will move in response to skin incision during anesthesia with isoflurane/oxygen.

Time-frequency spectral representation of the EEG as an aid in the detection of depth of anesthesia

A time-frequency spectral representation (TFSR) has been used to study the nonstationary information in the EEG as an aid in determining the anesthetic depth. This paper uses a TFSR with an exponential weighting function for the purpose. Raw EEG data were collected form 10 mongrel dogs at various levels of halothane anesthesia. Depth of anesthesia was tested by observing the response to tail clamping, which is considered a supramaximal stimulus in dogs. A positive response was graded as awake (depth 0), and a negative response was graded as asleep (depth 1). The EEG obtained during a period of 30 sec tail clamp was processed into TFSRs. It was observed that at depth 0, the spectrum becomes localized in time and frequency. The percentage of energy in the delta (1-3.5 Hz) and theta (3.5-7.5 Hz) frequency bands increased. At depth 1, the spectrum remained unchanged throughout the period of tail clamp. The performance of the TFSR in detecting the patient's awareness was also compared with the power spectrum. It was concluded that under certain anesthetic conditions, the TFSR is superior to the power spectrum.

Assessment of depth of general anesthesia. Observations on processed EEG and spectral edge frequency

The daily use of muscle relaxants and the lack of correlation between the hemodynamic behavior and stages of general anesthesia represent the main obstacles in defining the level of cortical activity depression by the anesthetic drugs. Since classical EEG is cumbersome in the operating room, and demands special knowledge, computerized methods of EEG wave analysis have more or less replaced the 'raw' display of the electrical activity of CNS. The paper describes the place of spectral edge frequency (SEF), one of the parameters obtained by processing the EEG waves, in the list of variables which could be monitored during general anesthesia. Besides, our preliminary observations on a combination of mean blood pressure variations and SEF value are presented. In fact, we designed a hypothetical matrix of those two parameters, which seems to be a useful tool for guiding the general anesthesia. SEF kept in a pre-established range (usually 8-12 Hz) seems to be linked with a more evident hemo-dynamic stability. Some data also suggested that a stable SEF on that range contributed to a higher degree of immediate postoperative analgesia after Cesarean section. The limits of SEF oblige the scientists to go on looking for other monitored parameters, to be studied in correlation with processed EEG. Further studies are needed, in order to improve the anesthesiologist's capabilities to define correctly the stage of general anesthesia.

Human brain measures of clinical pain: a review. I. Topographic mappings

A comprehensive paper (Parts I and II) has been developed to review the cerebral measures employed in studying the brain neurophysiological activities of clinical pain. Part I focuses on the electro-, magnetic-physiological assessment of clinical pain, and Part II concerns the anatomico-, chemical-physiological assessment of clinical pain. In Part I, these measures include the qualitative inspection of the conventional electroencephalogram, quantitative assessment of brain electrical spectral activity through cortical power spectrum density and coherence analyses, and quantitative averaging of cortical electrical or magnetic activities using brain evoked potentials. The mapping and measurement of these electrical activities and magnetic fields are results of recent advent in computer technology and advanced algorithms. Promises and limitations of these topographic measures in understanding pain in the brain are stated. The next article (Part II) of this paper will review tomographic imaging of pain-related brain activities in regional cerebral flow, the scanning of gross and fine brain structures by computerized axial tomography or magnetic resonance imaging, and the imaging and measurement of brain metabolic changes, energy uptake, and receptor bindings through positron emission tomography or single-photon emission computerized tomography. Molecular chemical transformation by the nuclear magnetic resonance analysis of tissue changes and analgesic-receptor interactions will also be noted.

Application of semilinear canonical correlation to the measurement of opioid drug effect

To examine the relationship between the electroencephalograph (EEG) and plasma opioid concentration, one would like to collapse the high-dimensional EEG signal into a univariate quantity. Such a simplification of the EEG is desirable because a univariate quantity can be modeled using standard nonlinear regression techniques, and because most of the information in the EEG is redundant or unrelated to drug concentration. In previous studies of the EEG response to opioids, the manner in which a univariate component was extracted from the EEG was ad hoc. In this paper, this extraction was performed optimally using a new statistical technique, semilinear canonical correlation. Data from 15 patients who received an intravenous infusion of the semisynthetic opioid alfentanil were analyzed. The components of the EEG that were nearly maximally correlated with plasma drug concentration were found, based on a standard pharmacokinetic-pharmacodynamic model. Two new EEG components were produced from the powers in the frequency spectrum of the EEG: a weighted sum of the logarithms of the powers, and a weighted sum of the powers expressed as percentages of the total power. These components both had a median R2 of 0.84, compared to median R2s ranging from 0.37 to 0.83 for five commonly used ad hoc EEG components. The new components also had less variability in R2 between subjects.