Narcotrend, bispectral index, and classical electroencephalogram variables during emergence from propofol/remifentanil anesthesia

Effects of isoflurane, remifentanil and dexmedetomidine on selected EEG parameters derived from a Narcotrend Monitor before and after nociceptive stimulation at different MAC multiples in cats

Background

The aim of this prospective and complete cross-over study was to evaluate the effects of isoflurane, remifentanil and dexmedetomidine on EEG parameters derived from the Narcotrend® Monitor before and after nociceptive stimulation at different isoflurane MAC (minimal alveolar concentration) multiples. Seven adult European Domestic Short Hair cats were used. Each cat went through 3 experimental treatments. Group I received isoflurane, group IR received isoflurane and a constant rate infusion (CRI) of remifentanil (18 μg/kg/h IV), and group ID received isoflurane and a CRI of dexmedetomidine (3 μg/kg/h IV). The isoflurane MAC in each group was determined via supramaximal electrical stimulation. The EEG parameters were derived by a Narcotrend Monitor at specific time points before and after nociceptive stimulation at 0.75, 1.0 and 1.5 MAC.

The depth of anaesthesia was also assessed by a clinical score.

Results

The mean MAC sparing effects in group IR and group ID were 9.8 and 55.2%, respectively. The best correlation of EEG and MAC multiples was found for the Narcotrend Index (NI) in group I (r = − 0.67). The NI was also able to differentiate between 0.75 MAC and 1.5 MAC in group IR. Spectral edge frequency had a lower correlation with MAC multiples in group I (r = − 0.62) but was able to differentiate between 0.75 MAC and 1.5 MAC in groups I and IR, and between 1.0 MAC and 1.5 MAC in group IR. Narcotrend Index, SEF 95 and MF increased significantly after nociceptive stimulation at 1.0 MAC in group I, and SEF 95 increased significantly at 0.75 MAC in group ID. The clinical score correlated closer than any of the EEG parameters with MAC in all groups, with highest correlation values in group I (r = − 0.89). Noxious stimulation led to a significant increase of the clinical score at 0.75 MAC and 1.0 MAC in group I.

Conclusions

The EEG parameters derived from the Narcotrend Monitor show correlation to isoflurane MAC multiples in cats, but the anaesthetic protocol and especially the addition of dexmedetomidine have great influence on the reliability. The Narcotrend Monitor can be used as an additional tool to assess anesthetic depth in cats.

Variation of bispectral index in children aged 1-12 years under propofol anesthesia: an observational study

Background

The use of the bispectral index (BIS) is widespread in pediatric anesthesia, but few studies have attempted to perform a detailed evaluation of how BIS varies according to age in children under propofol anesthesia. This prospective study aimed to explore the exact relationship between BIS value and the age of 1- to 12-year-old children under propofol anesthesia.

Methods

This study enrolled 165 children (1 < yr. ≤ 12), scheduled for surgery under anesthesia, and divided them into 11 age groups. Of the 165 participants, 157 completed the study protocol. All patients were anesthetized with propofol for over 30 s. An observation period of 4 min followed. BIS values were recorded at 0 (immediately after propofol injection), 30, 40, 50, 60, 90, 120, 180, and 240 s after the injection. BIS values at each time point corresponding to the 11 age groups were compared using repeated measures ANOVA.

Results

BIS values significantly differed among the nine time points (p < 0.01) as well as among the different age groups (p < 0.01) after propofol administration. Post-hoc Bonferroni tests showed a difference in BIS values between groups 1–4 (1 < yr. ≤ 5) and groups 5–11(5 < yr. ≤ 12). BIS values were lower in the latter than in the former, from 50 to 240 s. The minimum BIS values in group 1 < yr. ≤ 5 and in group 5 < yr. ≤ 12 were recorded at 60 s as 49 ± 17 and 35 ± 14, respectively.

Conclusions

During propofol anesthesia, the BIS values were closely related to age, which can be divided into two groups: 1 < yr. ≤ 5 and 5 < yr. ≤ 12. BIS values of the older age group were lower than those of the younger age group at the same time points.

Trial registration

Registration number: chictr-roc-16008630. Registered on 12 June 2016. Retrospectively registered.

Sedative depth on neurological outcomes in a juvenile rat model of cardiopulmonary resuscitation

The guidelines for cardiopulmonary resuscitation (CPR) in pediatric advanced life support suggest that midazolam is the preferred agent for sedation in patients with mild hypothermia, whereas children with cardiac arrest (CA) are at a crucial stage regarding their immature nervous system. Studies have shown that midazolam may have a detrimental effect on the developmental of the pediatric nervous system. Our previous study found that midazolam induced neuronal damage after CPR in young rats. It is speculated that: midazolam causes the potential injury of neurons by inhibiting mitochondrial autophagy expression and is an important factor for the poor prognosis in children after successful CPR. This project intends to adopt the modified asphyxiant CPR model in juvenile rats. Survival rate, neurological function and histopathological changes were evaluated to determine the protective effects of appropriate sedation depth on cerebral ischemia-reperfusion injury in juvenile rats after CPR. Combined with cell biology and molecular biology related technologies, the mechanism by which the mitochondrial pinkl-parkin signaling pathway induces autophagy to inhibit neuronal apoptosis may be key factor in the protective effects of sedation depth on the brain. The aim of this study is to provide experimental evidence and elucidate the mechanisms of improvement of cerebral ischemia-reperfusion injury by sedation depth in children after successful CPR and to lay a theoretical and experimental basis for clinical treatment.

Equipment failure of intravenous syringe pump detected by increase in Narcotrend stage: A case report

RATIONALE

Awareness is the recovery of consciousness during general anesthesia. It occurs when patients under general anesthesia receive inadequate anesthetic medications to maintain unconsciousness during surgery. Equipment failure is a common cause of intraoperative awareness.

PATIENT CONCERNS

A 16-year-old boy, 85 kg in weight, was admitted to our hospital for thyroglossal cystectomy under general anesthesia. Six minutes after the intubation, we noted that the Narcotrend index indicated a condition of light anesthesia and the patient was observed to be in tears.

DIAGNOSIS

Improper positioning of the syringe fixing clamp on the CP700TCI infusion pump caused equipment failure and light anesthesia.

INTERVENTIONS

Bolus of 50 mg propofol and 2 mg midazolam were administered manually by syringe, and inhalation of 2% sevoflurane was supplemented. Infusion pump was replaced.

OUTCOMES

The Narcotrend index of the patient returned to state of deep anesthesia following manual administration of the anesthetic medications. Following the surgery, the patient had an uneventful recovery, and did not present with evidence of awareness.

LESSONS

Users of the CP700TCI syringe pump should pay attention to the position of the syringe fixing clamp. Anesthesiologists should check all the equipment according to a defined checklist prior to anesthesia. Narcotrend monitor could help to detect light anesthesia and prevent potential awareness.

Clinical Use of a Multivariate Electroencephalogram (Narcotrend) for Assessment of Anesthetic Depth in Horses during Isoflurane-Xylazine Anesthesia

Objective

To investigate the use of the Narcotrend electroencephalogram (EEG) monitor for the assessment of anesthetic depth in horses undergoing xylazine balanced isoflurane anesthesia.

Study design

Blinded experimental study.

Animals

Seven healthy warm-blooded horses, aged 10.6 ± 5.9 years, weighing 535 ± 55 kg.

Methods

Horses were anesthetized for a terminal surgical trial with xylazine, thiopentone, and guaiphenesin for induction and isoflurane and xylazine continuous rate infusion for maintenance. After surgery, an EEG was recorded and processed by the Narcotrend monitor. It displays an index [Narcotrend index (NI)] between 0 and 100, which is supposed to indicate anesthetic depth. This index was recorded and correlated with eight different end tidal (ET) isoflurane concentrations between 0.8 and 2.2 vol%. In addition, anesthetic depth was numerically scored based on common clinical signs with a score of 1 (plane “too deep”) to 4 (plane “too light”). After testing for normal distribution, both clinical scores and NI were correlated with different ET isoflurane concentrations using Spearman rank correlation.

Results

Correlation of NI with ET isoflurane concentrations was poor (r_s = 0.24). The NI ranged between maximal 48 and minimal 13 in the horses. The clinical scores decreased with increasing ET isoflurane concentrations (r_s = 0.80). They ranged from 1 to 4 in different horses at the concentrations investigated.

Conclusion

In this study, the NI did not seem to be useful for assessment of anesthetic depth in horses receiving isoflurane anesthesia balanced with a xylazine constant rate infusion.

Comparison of the Effect of Anesthesia With Midazolam-Fentanyl Versus Propofol-Remifentanil on Bispectral Index in Patients Undergoing Coronary Artery Bypass Graft

The aim of this study was to compare the effect of anesthesia with midazolam-fentanyl versus propofol-remifentanil on the BIS (bispectral index) in patients undergoing coronary artery bypass grafting (CABG). Sixty-four patients undergoing CABG were randomly assigned to one of two study groups: midazolam-fentanyl (MF, N= 32) or propofol-remifentanil (PR, N= 32). The BIS was measured before induction of anesthesia, five minutes after induction of anesthesia, at skin incision, sternotomy, pericardiotomy, aorta cannulation, onset of cardiopulmonary bypass, during rewarming, five minutes after separation from cardiopulmonary bypass, at thorax closure, and at the end of the surgery. There were no significant differences between the two groups with regard to age and gender. The difference in mean BIS between the two groups was significant (P < 0.05) at all times, except before induction, five minutes after induction, at skin incision and on rewarming. Changes in the BIS were lower in the PR group than in the MF group. Both techniques can provide adequate anesthesia in patients undergoing CABG. However, the probability of awareness during anesthesia is lower with propofol-remifentanil than with midazolam-fentanyl.

Dose requirement and complications of diluted and undiluted propofol for deep sedation in endoscopic retrograde cholangiopancreatography

BACKGROUND

In general, the dose requirement and complications of propofol are lower when used in the diluted form than in the undiluted form. The aim of this study was to determine the dose requirement and complications of diluted and undiluted propofol for deep sedation in endoscopic retrograde cholangiopancreatography.

METHODS

Eighty-six patients were randomly assigned to either group D (diluted propofol) or U (undiluted propofol). All patients were sedated with 0.02-0.03 mg/kg midazolam (total dose ≤2 mg for age <70 years and 1 mg for age ≥70) and 0.5-1 μg/kg fentanyl (total dose ≤75 μg for age <70 and ≤50 μg for age ≥70). Patients in group U (42) were sedated with standard undiluted propofol (10 mg/mL). Patients in group D (44) were sedated with diluted propofol (5 mg/mL). All patients in both groups were monitored for the depth of sedation using the Narcotrend system. The primary outcome variable was the total dose of propofol used during the procedure. The secondary outcome variables were complications during and immediately after the procedure, and recovery time.

RESULTS

All endoscopies were completed successfully. Mean propofol doses per body weight and per body weight per hour in groups D and U were 3.0 mg/kg, 6.2 mg/kg per hour and 4.7 mg/kg, 8.0 mg/kg per hour, respectively. The mean dose of propofol, expressed as total dose, dose/kg or dose/kg per hour and the recovery time were not significantly different between the two groups. Sedation-related adverse events during and immediately after the procedure were higher in group U (42.9%) than in group D (18.2%) (P=0.013).

CONCLUSIONS

Propofol requirement and recovery time in the diluted and undiluted propofol groups were comparable. However, the sedation-related hypotension was significantly lower in the diluted group than the undiluted group.

Use of cerebral state index to predict long-term unconsciousness in patients after elective craniotomy with delay recovery

Background

The major difficulty in postoperative care in patients after craniotomy is to distinguish the intracranial deficits from the residual effect of general anesthesia. In present study, we used cerebral state index (CSI) monitoring in patients after craniotomy with delayed recovery, and evaluated the prediction probability of CSI for long-term postoperative unconsciousness.

Methods

We enrolled 57 consecutive adult patients admitted to neurosurgical intensive care unit (NICU) after elective craniotomy with delayed recovery. CSI was continuously monitored for 6 hours after admission. Patient's level of consciousness was followed up for 24 hours. According to whether obeyed verbal command, patients were divided into awaken group and non-awaken group. CSI values were compared between the two groups. Prediction probability (P_K) was calculated to determine the probability of CSI in predicting unconsciousness 24 hours after operation.

Results

In awaken group (n = 51), CSI increased significantly after the 2nd NICU admitted hour (P < 0.05). At each time point, CSI values in awaken group were significantly higher than those in non-awaken group (n = 6) (P < 0.05). The values of P_K (SE) for CSI in the first 6 admitted hours ranged from 0.94 (0.06) to 0.99 (0.02).

Conclusions

In patients after craniotomy with delayed recovery, CSI monitoring in early postoperative hours had high prediction probability for long-term unconsciousness. CSI monitoring may be a reliable objective method to predict level of consciousness after elective craniotomy.

[Measurement of the depth of anaesthesia]

One of the most important mandates of the anaesthesiologist is to control the depth of anaesthesia. An unsolved problem is that a straight definition of the depth of anaesthesia does not exist. Concerning this it is rational to separate hypnosis from analgesia, from muscle relaxation and from block of cardiovascular reactions. Clinical surrogate parameters such as blood pressure and heart rate are not well-suited for a valid statement about the depth of hypnosis. To answer this question the brain has become the focus of interest as the target of anaesthesia. It is possible to visualize the brain's electrical activity from anelectroencephalogram (EEG). The validity of the spontaneous EEG as an anesthetic depth monitor is limited by the multiphasic activity, especially when anaesthesia is induced (excitation) and in deep anaesthesia (burst suppression). Recently, various commercial monitoring systems have been introduced to solve this problem. These monitoring systems use different interpretations of the EEG or auditory-evoked potentials (AEP). These derived and calculated variables have no pure physiological basis. For that reason a profound knowledge of the algorithms and a validation of the monitoring systems is an indispensable prerequisite prior to their routine clinical use. For the currently available monitoring systems various studies have been reported. At this time it is important to know that the actual available monitors can only value the sedation and not the other components of anaesthesia. For example, they cannot predict if a patient will react to a painful stimulus or not. In the future it would be desirable to develop parameters which allow an estimate of the other components of anaesthesia in addition to the presently available monitoring systems to estimate sedation and muscle relaxation. These could be sensoric-evoked potentials to estimate analgesia and AEPs for the detection of awareness.

Electroencephalographic Narcotrend Index monitoring during procedural sedation and analgesia in children

BACKGROUND

The electroencephalographic Narcotrend Index (NI) may potentially help to titrate sedative medication during diagnostic and therapeutic procedures in children.

METHODS

With local ethics committee approval and informed parental consent, 31 patients, aged 8.9 +/- 4.3 years, scheduled for elective upper gastrointestinal endoscopy were enrolled in this prospective, double-blinded observational study. Initially, patients received a single dose of intravenous piritramide 0.1 mg x kg(-1), followed by propofol 2 mg x kg(-1) and, if necessary, additional propofol doses (0.5 mg x kg(-1)) to achieve and maintain a level of deep sedation throughout the procedure. Sedation was assessed by the University of Michigan Sedation Scale (UMSS). We investigated the relationship between depth of sedation, and the NI, and the classical EEG parameters (cEEG), total EEG power (Power), spectral edge (SEF) and median frequency, and relative power in the beta, alpha, theta and delta bands. The performance of the NI and cEEG parameters was evaluated by prediction probability (P(K)), receiver operating characteristic (ROC) and Spearman rank order correlation analysis.

RESULTS

Mean P(K) values for NI (0.88) vs UMSS were higher than for the other cEEG parameters, except for Power (0.82) and SEF(0.81). Spearman correlation analysis revealed superiority of the NI over all cEEG parameters. The area under the curve for the NI was 0.93, which was superior to all other EEG parameters beside Power (0.86) and relative power in alpha (0.82).

CONCLUSIONS

The results of this study suggest that the NI may be an objective nondisruptive tool for assessment of hypnotic depth in children under propofol-induced procedural sedation.

Variation of bispectral index under TIVA with propofol in a paediatric population

BACKGROUND

In this prospective observational study, we aim to explore the relationship between age and bispectral index (BIS) values at different plasma concentrations of propofol.

METHODS

Fifty children aged from 3 to 15 yr were included. Anaesthesia was induced using a target-controlled infusion of propofol with the Kataria pharmacokinetic model together with a bolus of remifentanil followed by a continuous infusion rate at 0.2 microg kg(-1) min(-1). Target plasma propofol concentration was initially stabilized to 6 microg ml(-1) and continued for 6 min. The target was then decreased and stabilized to 4 microg ml(-1) and then to 2 microg ml(-1). BIS values, plasma propofol concentration, and EEG were continuously recorded. In order to explore the relationship between variations in propofol concentration and the EEG bispectrum, we used a multiple correspondence analysis (MCA). Results are shown in median (range).

RESULTS

We found no statistical difference between BIS values with propofol 6 microg ml(-1) [23 (12-40)] and 4 microg ml(-1) [28 (9-67)]. At 2 microg ml(-1), BIS was significantly different [52 (24-71)], but a significant correlation between the age of children and BIS values was found (r2=0.66; P<0.01). There was little change in children's position between 6 and 4 microg ml(-1) in the structure model of the MCA. From 4 to 2 microg ml(-1), the position of children moved only on axis 2.

CONCLUSIONS

These results showed the difficulty to interpret BIS values because of the absence of significant change for higher plasma propofol concentration variation or because of the link with age for the lower plasma concentration.

Effect of age and sedative agent on the accuracy of bispectral index in detecting depth of sedation in children

OBJECTIVE

This study evaluated age- and sedative agent-related differences in bispectral index across observed sedation levels in a large sample of children < 18 years of age.

PATIENTS AND METHODS

With institutional review board approval and waiver of consent, data from 4 independently conducted studies were combined in a secondary analysis of 3373 observations from 248 children aged 1 month to 18 years. In these studies, bispectral index values of sedated children were recorded in a blinded fashion, and sedation depth was scored using the University of Michigan Sedation Scale (UMSS). Bispectral index was evaluated across UMSS scores for several age groups and during use of each sedative agent (with/without opioids).

RESULTS

There was a moderate inverse correlation between bispectral index and UMSS for all age groups. There were significant differences in bispectral index across UMSS and between each sedation level except UMSS 3 to 4 in all the age groups and UMSS 0 to 1 in infants. The mean bispectral index and the cutoff values on the receiver-operating-characteristic curve for mild, moderate, and deep sedation were significantly lower in infants < or = 6 months compared with older children at each sedation level. Bispectral index was reasonably sensitive and specific in differentiating mild (UMSS 0-1) from deeper (UMSS 3-4) levels of sedation but poorly differentiated between moderate and deep levels of sedation in all age groups. There was a moderate correlation between bispectral index and UMSS during the use of chloral hydrate, pentobarbital, propofol, and midazolam but poor correlation during ketamine or opioid use. Bispectral index values were significantly lower during deep sedation with propofol and pentobarbital compared with midazolam and chloral hydrate.

CONCLUSIONS

Our findings suggest that, although bispectral index may differentiate light from deep sedation in most children, bispectral index must be interpreted cautiously in sedated children, with particular consideration given to patient age and use of sedative agents.

Pharmakokinetische/pharmakodynamische Modelle für Inhalationsanästhetika

Pharmacokinetic models can be differentiated into two groups: physiological-based models and empirical models. Traditionally the pharmacokinetics of volatile anaesthetics are described using physiological-based models together with the respective tissue-blood distribution coefficients. The compartments of the empirical model have no anatomical equivalents and are merely the product of the mathematical procedure for parameter estimation. The end expiratory concentration of volatile anaesthetics is approximately equal to the arterial concentration and, therefore, the description of the transition between plasma and effect site for volatile anaesthetics plays a central role. The most important parameter here is the k(e0) value which is a time constant and describes the time delay for the transition from the central compartment to the calculated effect compartment. The k(e0) values for sevoflurane and isoflurane are the same but the concentration balance between the end-tidal concentration and the effect compartment occurs twice as quickly with desflurane. In clinical practice volatile anaesthetics are normally combined with N(2)O and/or opioids. This results in an additive interaction between volatile anaesthetics and N(2)O but a synergistic interaction of volatile anaesthetics with opioids. However, there are relatively few investigations on the interactions between the clinically widely used combination of volatile anaesthetics, N(2)O and opioids.

Depth of Anesthesia Monitoring

Depth-of-anesthesia monitoring with EEG or EEG combined with mLAER is becoming widely used in anesthesia practice. Evidence shows that this monitoring improves outcome by reducing the incidence of intra-operative awareness while reducing the average amount of anesthesia that is administered, resulting in faster wake-up and recovery, and perhaps reduced nausea and vomiting. As with any monitoring device, there are limitations in the use of the monitors and the anesthesiologist must be able to interpret the data accordingly. The limitations include the following. The currently available monitoring algorithms do not account for all anesthetic drugs, including ketamine, nitrous oxide and halothane. EMG and other high-frequency electrical artifacts are common and interfere with EEG interpretation. Data processing time produces a lag in the computation of the depth-of-anesthesia monitoring index. Frequently the EEG effects of anesthetic drugs are not good predictors of movement in response to a surgical stimulus because the main site of action for anesthetic drugs to prevent movement is the spinal cord. The use of depth-of-anesthesia monitoring in children is not as well understood as in adults. Several monitoring devices are commercially available. The BIS monitor is the most thoroughly studied and most widely used, but the amount of information about other monitors is growing. In the future, depth-of-anesthesia monitoring will probably help in further refining and better understanding the process of administering anesthesia.

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.

The Narcotrend monitor

The Narcotrend (MonitorTechnik, Bad Bramstedt, Germany) is an EEG monitor designed to measure the depth of anaesthesia. It has been developed at the University Medical School of Hannover, Germany, has been commercially available for 5 years and has meanwhile received US Food and Drug Administration approval. The Narcotrend algorithm is based on pattern recognition of the raw electroencephalogram (EEG) and classifies the EEG traces into different stages from A (awake) to F (increasing burst suppression down to electrical silence). The newest Narcotrend software version includes a dimensionless Narcotrend index from 100 (awake) to 0 (electrical silence). The raw EEG signal can be recorded by standard electrocardiogram electrodes for single- and double-channel registration. The Narcotrend monitor provides a vast amount of information: the actual Narcotrend stage and index, the trend ('cerebrogram'), the raw EEG signal and a power spectrum and several derived EEG parameters. Multiple clinical and validation studies are available for the Narcotrend monitor, including comparisons with the BIS monitor (Aspect Medical Systems, Natick, USA).

Does Using the Bispectral Index (BIS) During Craniotomy Affect the Quality of Recovery?

One of the aims of neuroanesthesia is to provide early postoperative recovery and neurologic examination in patients undergoing supratentorial surgery. Our aim was to investigate the role of using the bispectral index (BIS) in recovery from anesthesia and altering drug administration in patients undergoing craniotomy. Fifty American Society of Anesthesiologists' (ASA) physical status I-II patients undergoing craniotomy were included in the study. The patients were randomly divided into two groups, and all patients received standard induction drugs, and 0.8%-1.5% sevoflurane was used for maintenance of anesthesia. In the BIS-guided group, the concentration of sevoflurane was titrated to maintain BIS at 40-60. In the control group, the anesthesiologist was blind to BIS, and the concentration of sevoflurane was changed according to the patients' hemodynamic changes. The hemodynamic data, BIS values, and sevoflurane concentrations were recorded every 15 minutes. In addition, the BIS value was recorded by the primary anesthetist in the BIS-guided group and by another independent anesthetist in the control group. At the end of the study, recovery criteria and Aldrete recovery scores were recorded every 15 minutes. Neurologic assessments were performed when the Aldrete score was 9-10. BIS values were higher, and sevoflurane concentrations (P < 0.05) and total doses of fentanyl (P < 0.01) were lower, in the BIS-guided group. Times to first spontaneous breathing, eye opening, and extubation (P = 0.035, P = 0.001, and P = 0.0001, respectively) were significantly shorter in the BIS-guided group. Time to an Aldrete score of 9-10 and adequate neurologic assessment were similar between the groups. In conclusion, BIS monitoring by supratentorial craniotomy under general anesthesia reduced the maintenance anesthetic concentration and narcotic drug usage and lowered the recovery times from general anesthesia.

Different Conditions That Could Result in the Bispectral Index Indicating an Incorrect Hypnotic State

Since its introduction in 1996, the Bispectral Index (BIS) has gained increasing popularity in daily anesthesia practice. However, numerous reports have been appearing in the literature of paradoxical BIS changes and inaccurate readings. The purpose of this review is to assess the utility of BIS monitoring through examining the various published reports of all BIS values not coinciding with a clinically judged sedative-hypnotic state, whether arising from an underlying pathophysiology of electroencephalographic (EEG) cerebral function or because of shortcomings in the performance and design of the BIS monitor. High electromyographic activity and electric device interference could create subtle artifact signal pollution without their necessarily being displayed as artifacts. This would be misinterpreted by the BIS algorithm as EEG activity and assigned a spuriously increased BIS value. Numerous clinical conditions that have a direct effect on EEG cerebral function could also directly influence the BIS value.

Narcotrend or Bispectral Index Monitoring During Desflurane-Remifentanil Anesthesia: A Comparison with a Standard Practice Protocol

Bispectral Index (BIS) (Aspect Medical Systems, Newton, MA) and Narcotrend (MonitorTechnik, Bad Bramstedt, Germany) are monitoring devices that were, as others, designed to assess the depth of anesthesia. Meanwhile, a number of studies indicate that with total IV anesthesia, BIS and Narcotrend have comparable effects on drug consumption and recovery times whereas comparative clinical data for volatile anesthetics are still missing. Therefore, we designed the present prospective, randomized, and double-blinded study to compare the effects of BIS and Narcotrend monitoring during desflurane-remifentanil anesthesia and versus a standard anesthetic practice protocol. One-hundred-twenty adult patients scheduled for minor orthopedic surgery were randomized to receive a desflurane-remifentanil anesthetic controlled either by Narcotrend or by BIS or solely by clinical variables. Anesthesia was induced with 0.4 microg x kg(-1) x min(-1) remifentanil and 2 mg/kg propofol. After tracheal intubation, remifentanil was infused at a constant rate of 0.2 microg x kg(-1) x min(-1) whereas desflurane in 1.5 L/min O(2)/air was adjusted according to clinical variables or the following target values: during maintenance of anesthesia to a value of "D(0)" (Narcotrend) or "50" (BIS), 15 min before the end of surgery to "C(1)" (Narcotrend) or "60" (BIS), whereas in the standard protocol group, desflurane was controlled according to clinical variables, e.g., heart rate, arterial blood pressure, movements. Recovery times and desflurane consumption were recorded by a blinded investigator. The desflurane vaporizer was weighed before and after anesthesia and consumption per minute was calculated. Data are mean +/- sd. The groups were comparable for demographic data, duration of anesthesia, and mean remifentanil dosages. Compared with standard practice, patients with Narcotrend or BIS monitoring needed significantly less desflurane (standard practice 443 +/- 71 mg/min, Narcotrend 374 +/- 124 mg/min, BIS monitoring 416 +/- 99 mg/min desflurane [both P < 0.05]). However, recovery times were not significantly different between the groups, e.g., opening of eyes 4.7 +/- 2.2 versus 3.7 +/- 2.0 versus 4.2 +/- 2.1 min. During desflurane-remifentanil anesthesia, Narcotrend and BIS monitoring seem to be equally effective compared with standard anesthetic practice: BIS and Narcotrend allow for a small reduction of desflurane consumption whereas recovery times are only slightly reduced.

IMPLICATIONS

Monitoring the electroencephalogram with Narcotrend or Bispectral Index during desflurane-remifentanil anesthesia only slightly reduces recovery times when compared with a standard practice protocol.

Impact of patient age on propofol consumption during propofol-remifentanil anaesthesia

BACKGROUND

This study was designed to investigate the impact of patient age on propofol consumption and recovery time using a propofol-remifentanil anaesthetic standardized with Narcotrend EEG monitoring. The Narcotrend is a monitor for measuring the depth of anaesthesia based upon a six-letter classification from A (awake) to F (increasing burst suppression) including 14 substages.

METHODS

In 200 patients scheduled for minor orthopaedic surgery Narcotrend EEG electrodes were positioned on the patient's forehead as recommended by the manufacturer. Anaesthesia was induced with remifentanil 0.4 microg kg(-1) min(-1) and 2 mg kg(-1) propofol. Immediately after intubation remifentanil was reduced to a constant rate of 0.2 microg kg(-1) min(-1) whereas a propofol infusion was now started at 3 mg kg(-1) h(-1) and then adjusted accordingly to achieve a target Narcotrend stages of D(0-2) indicating general anaesthesia. At the end of surgery the propofol and remifentanil infusions were stopped without tapering, the time to unstimulated opening of eyes was determined, and the propofol consumption (given as mg kg(-1) h(-1)) was calculated from the total amount of infused propofol but without the induction bolus, from the actual body weight and the duration of propofol infusion. Furthermore, a linear regression analysis was applied for propofol consumption vs. age.

RESULTS

The ages of the patients studied ranged from 16 to 83 yr old and patients were classified as ASA I-III. Propofol consumption significantly decreased with the patients' age: 30 yr of age or below the propofol consumption was calculated as 5.9 +/- 1.7 mg kg(-1) h(-1), for 31-50 yr as 5.4 +/- 1.8 mg kg(-1) h(-1), for 51-70 yr as 4.5 +/- 1.7 mg kg(-1) h(-1) and above 70 yr as 3.5 +/- 1.4 mg kg(-1) h(-1). Linear regression analysis revealed propofol (mg kg(-1) h(-1)) = 9.136 - (0.0597 x age (yr)); R = 0.53. Concomitantly, the recovery time to opening of eyes increased with the patients' age: < or = 30 yr, 7.4 +/- 3.7 min; 31-50 yr, 9.5 +/- 4.0 min; 51-70 yr, 9.8 +/- 4.1 min; and > or = 71 yr, 14.9 +/- 12.1 min.

CONCLUSIONS

We conclude that with Narcotrend guidance, mean propofol consumption and recovery times are age dependent. However, as a result of large inter-individual variability, age per se does not allow a prediction of individual propofol need or recovery time.

The correlation of the Narcotrend Index and classical electroencephalographic parameters with endtidal desflurane concentrations and hemodynamic parameters in different age groups

BACKGROUND

The Narcotrend Index (NI) for assessment of depth of anesthesia by analysis of the electroencephalogram (EEG), is potentially a pharmacodynamic measure of the effects of desflurane on the brain.

METHODS

In this prospective study of 30 pediatric and adult patients (group 1: 3-6 years, n = 10; group 2: > 6 < 12 years; group 3: 12-40 years), undergoing ophthalmological surgery, we investigated the pharmacodynamic relationship between nonsteady state endtidal desflurane concentrations (eT(Des)), NI, classical EEG parameters (cEEG), heart rate (HR) and mean arterial pressure (MAP). The performance of the Narcotrend for differentiation between consciousness and unconsciousness was evaluated using prediction probability (P(K)).

RESULTS

Spearman correlation analysis showed significant negative correlations (P < 0.001) between eT(Des) and NI (group 1: r = -0.93, group 2: r = -0.86, group 3: r = -0.66). Correlations between eT(Des) and MAP or HR were either only weak negative (r < -0.5) or not significant. Desflurane EC(50) (eT(Des) with half maximal effect on NI) was 7.18% for group 1, 7.34% for group 2, and 4.15% for group 3 (P < 0.001 Vs groups 1 and 2). Overall awake NI values (96.7 +/- 1.4) were significantly higher (P < 0.001) than at the moment of loss of consciousness (58.3 +/- 17.5), with no overlap (P(K) 1.0), whereas P(K) values for cEEG, MAP and HR were all <0.85.

CONCLUSIONS

The pharmacodynamic relationship between eT(Des) and NI is age dependent with a significantly higher EC(50) in children than in adolescents and adults. The NI appears to be superior to cEEG, MAP and HR in differentiating consciousness from unconsciousness.

SNAP index and Bispectral index during different states of propofol/remifentanil anaesthesia

The accuracy of the new SNAP index with the Bispectral index (BIS) to distinguish different states of propofol/remifentanil anaesthesia was compared in 19 female patients who were undergoing minor gynaecological surgery. Comparisons of the SNAP index, BIS, spectral edge frequency, mean arterial blood pressure and heart rate were performed. The ability of all parameters to distinguish between the steps of anaesthesia -awake vs. loss of response, awake vs. anaesthesia, anaesthesia vs. first reaction and anaesthesia vs. extubation - were analysed with the prediction probability. The prediction probability to differentiate between two interesting nuances of anaesthetic states -loss of response vs. first reaction - was calculated. Only the BIS showed no overlap between the investigated steps of anaesthesia. Both the SNAP index and BIS failed to differentiate the nuances of anaesthesia. The SNAP index and BIS were superior to mean arterial blood pressure and heart rate and spectral edge frequency in distinguishing between different steps of anaesthesia with propofol and remifentanil and provided useful additional information.

Comparability of Narcotrend index and bispectral index during propofol anaesthesia

BACKGROUND

The dimensionless Narcotrend (NCT) index (MonitorTechnik, Germany, version 4.0), from 100 (awake) to 0, is a new index based on electroencephalogram pattern recognition. Transferring guidelines for titrating the Bispectral Index (BIS, Aspect Medical Systems, USA, version XP) to the NCT index depends on their comparability. We compared the relationship between BIS and NCT values during propofol anaesthesia.

METHODS

Eighteen adult patients about to have radical prostatectomy were investigated. An epidural catheter was placed in the lumbar space and electrodes for BIS and NCT were applied as recommended by the manufacturers. After i.v. fentanyl 0.1 mg, anaesthesia was induced with a propofol infusion. After intubation, patients received bupivacaine 0.5% 15 ml via the epidural catheter. Forty-five minutes after induction, the propofol concentration was increased to substantial burst suppression pattern and then decreased. This was done twice in each patient, and BIS and Narcotrend values were recorded at intervals of 5 s. The efficacy of NCT and BIS in predicting consciousness vs unconsciousness was evaluated using the prediction probability (P(K)).

RESULTS

We collected 38 629 artefact-free data pairs of BIS and NCT values from the respective 5-s epochs. Because of artefacts, another 5008 epochs had been excluded from data analysis (3855 epochs for the NCT index alone, 245 epochs for the BIS alone and 908 epochs for both indices). Mean (sd) values in awake patients were 94 (6) for Narcotrend and 91 (8) for BIS. With loss of the eyelash reflex, both values were significantly reduced, to 72 (9) for NCT (P<0.001) and to 77 (11) for the BIS index (P<0.001). The PK value for loss of eyelash reflex was similar for BIS (0.95) and NCT (0.93). Decreasing BIS values coincided with decreasing NCT values. A sigmoid model [NCT index=52.8+26.8/(1+exp(-(BIS-78.3)/4.8))(0.4); r=0.52] described the correlation between BIS and NCT index in a BIS range between 100 and 50. For BIS values lower than 50, a second sigmoid model with a correlation of r=0.83 was applied [NCT index=6.6+45.3/(1+exp(-(BIS-29.8)/2.4)) (0.6) r=0.83]. The relationship between burst suppression ratio (BSR) and NCT index was best described by the following sigmoid model: NCT index=265/(1+exp((-BSR+108)/-49); r=0.73.

CONCLUSIONS

We found a sufficient correlation between BIS and NCT index, but deviations from the line of identity in some ranges require attention. Therefore, a simple 1:1 transfer from BIS to NCT values is not adequate. Our results might serve as a blueprint for the rational translation of BIS into NCT values.

Comparative evaluation of Narcotrend, Bispectral Index, and classical electroencephalographic variables during induction, maintenance, and emergence of a propofol/remifentanil anesthesia

In the present study, we sought to compare the abilities of Narcotrend (NT) with the Bispectral Index (BIS) electroencephalographic system to monitor depth of consciousness immediately before induction of anesthesia until extubation during a standardized anesthetic. We investigated 26 patients undergoing laminectomy. Investigated states of anesthesia were: awake, loss of response, loss of eyelash reflex, steady-state anesthesia, first reaction, and extubation during emergence. NT, BIS, spectral edge frequency, median frequency, relative power in delta, theta, alpha, beta, and hemodynamics were recorded simultaneously. The ability of all variables to distinguish between awake versus loss of response, awake versus loss of eyelash reflex, awake versus steady-state anesthesia, steady-state anesthesia versus first reaction and extubation were analyzed with the prediction probability. Effects of remifentanil during propofol infusion were investigated with Friedman's and post hoc with Wilcoxon's test. Only NT and BIS were able to distinguish all investigated states accurately with a prediction probability >0.95. After start of remifentanil infusion, only hemodynamics changed statistically significantly (P < 0.05). NT and BIS are more reliable indicators for the assessment of anesthetic states than classical electroencephalographic variables and hemodynamics, whereas the analgesic potency of depth of anesthesia could not be detected by NT and BIS.

IMPLICATIONS

The modern electroencephalographic monitoring systems Narcotrend and Bispectral Index are more reliable indicators for the assessment of anesthetic states than classical electroencephalographic and hemodynamic variables to predict anesthetic conditions from before induction of anesthesia until extubation during a standardized anesthetic regime with propofol and remifentanil. The analgesic potency of depth of anesthesia could not be detected by Narcotrend and Bispectral Index.

Prediction of depth of sedation and anaesthesia by the Narcotrend EEG monitor

BACKGROUND

The Narcotrend (Monitor Technik, Bad Bramstedt, Germany) assesses sedation by automatic classification of EEG signals, using a scale first used for visual evaluation of the EEG. Limited information is available on its value, and only a few studies of the method exist. We set out to study the performance of the Narcotrend during propofol sedation.

METHODS

In 23 ASA I-II patients, aged 18-65 yr, about to have general anaesthesia, we induced anaesthesia in steps using a target-controlled infusion of propofol. After equilibration for 8 min at each predicted propofol concentration (0.5, 1.0, 2.0, 3.0 and 4.0 microg x ml(-1)), sedation was assessed clinically with the modified Observer's Assessment of Alertness/Sedation Scale and the Narcotrend stage was noted. The prediction performance of the Narcotrend was assessed with the prediction probability P(K). A P(K) value of 1.0 means an exact prediction on every occasion, while a P(K) of 0.5 is no better than a 50:50 chance of being correct.

RESULTS

In 12 women and 11 men (age 42 (sd 11) yr), a total of 138 measurements were made; 129 were analysed and nine were of poor signal quality. The prediction probability for the corresponding level of sedation was P(K)=0.92 (se 0.01); for the different target concentrations of propofol it was P(K) = 0.91 (se 0.01).

CONCLUSIONS

The Narcotrend can monitor sedation with propofol. Other sedatives, anaesthetics and opioids should be used to test this monitor.

Narcotrend index versus bispectral index as electroencephalogram measures of anesthetic drug effect during propofol anesthesia

The Narcotrend monitor (MonitorTechnik, Bad Bramstedt, Germany) performs an automatic analysis of the electroencephalogram (EEG) during anesthesia based on a visual assessment of the raw EEG. Its newest software version 4.0 includes a dimensionless index that, similar to the bispectral index (BIS), ranges from 100 (awake) to 0. We compared the performance of Narcotrend index and BIS as EEG measures of anesthetic drug effect during propofol anesthesia. Eighteen adult patients scheduled for radical prostatectomy were investigated. An epidural catheter was placed in the lumbar space and electrodes for BIS (version XP; Aspect Medical Systems, Natick, MA) and Narcotrend were positioned as recommended by the manufacturers. Narcotrend index, BIS values, and propofol plasma and effect site concentrations as parallelly simulated by Rugloop software (Department of Anesthesia, Ghent University, Belgium) were automatically recorded in intervals of 5 s. Induction of anesthesia consisted of a fentanyl bolus and a propofol infusion. After endotracheal intubation, patients received 15 mL bupivacaine 0.5% epidurally, and 45 min later propofol dosages were subsequently increased and decreased twice. Simulated propofol effect site concentrations ranged from 2.0 +/- 0.4 microg/mL (smallest) to 6.3 +/- 1.3 microg/mL (largest) during these subsequent increases and decreases of propofol. In terms of prediction probability (P(K)) the performance of the Narcotrend index (P(K) = 0.88 +/- 0.03) to predict propofol effect site concentrations was comparable to the BIS (P(K) = 0.85 +/- 0.04). Using the respective EEG index as a measure of drug effect the mean k(e0) was calculated as 0.20 +/- 0.05 min(-1) for Narcotrend index and 0.16 +/- 0.07 min(-1) for BIS. In the observed propofol concentration range Narcotrend index detected differences in EEG dynamics as well as BIS.

IMPLICATIONS

This study in 18 adult patients undergoing radical prostatectomy describes the relationship between Narcotrend index and bispectral index versus predicted propofol effect compartment concentrations. In terms of prediction probability, the performance of the Narcotrend index and the bispectral index to predict propofol effect site concentrations was comparable.

Changes in cortical electrical activity during induction of anaesthesia with thiopental/fentanyl and tracheal intubation: a quantitative electroencephalographic analysis

BACKGROUND

There are regional differences in the effects of anaesthetics agents and perioperative stimuli on the EEG. We studied the topography of the EEG during induction of anaesthesia and intubation in patients receiving thiopental and fentanyl to document regional electrical brain activity.

METHODS

EEG was recorded in 25 patients in the awake state, after pre-medication, during induction, at loss of consciousness and after intubation. Eight bipolar recordings were made and the relative power of the frequency bands delta, theta, alpha, and beta were used (after z-score transformation for age) to measure changes in regional EEG activity.

RESULTS

Noxious stimulation during tracheal intubation partially reversed the slowing of the EEG caused by anaesthesia. During induction of anaesthesia alpha activity was most reduced in temporal and occipital regions. The most prominent EEG changes after intubation were an increase in alpha and a decrease in delta power (P<0.001). The largest changes were in the frontal and temporal leads for alpha and in the frontal and central leads for delta. Heart rate and arterial pressure remained constant during intubation.

CONCLUSIONS

Changes in alpha and delta power were identified as the most sensitive EEG measures of regional changes in electrical brain activity during anaesthesia and noxious stimulation.