A multicenter study of bispectral electroencephalogram analysis for monitoring anesthetic effect

Comparison of Dexmedetomidine Versus Fentanyl-Based Anesthetic Protocols Under Patient State Index Guidance in Patients Undergoing Elective Neurosurgical Procedures with Intraoperative Neurophysiological Monitoring

Objectives The study was designed to elucidate the effects of dexmedetomidine as an anesthetic adjunct to propofol in total intravenous anesthesia (TIVA) on anesthetic dose reduction, the quality of intraoperative neurophysiological monitoring (IONM) recordings, analgesic requirements, and recovery parameters in patients undergoing neurosurgical procedures with neurophysiological monitoring. Methods A total of 54 patients for elective neurosurgical procedures with IONM were randomized to group D (dexmedetomidine) and group F (fentanyl). A loading dose of the study drug of 1µg/kg followed by 0.5 µg/kg/h infusion was used in two groups. Propofol-based TIVA with a Schneider target-controlled infusion model was used for induction and maintenance with effect site concentration of 4-5 and 2.5-4 µg/mL, respectively, titrated to a Patient State Index (PSI) of 25-40. Baseline IONM recordings were obtained after induction. The mean propofol consumption, number of patient movements, quality of IONM recordings, number of fentanyl boluses, hemodynamic characteristics, and recovery parameters were recorded. Results The mean propofol consumption was significantly lower in group D when compared to group F (101.4 ± 13.5 µg/kg/min vs 148.0 ± 29.8 µg/kg/min). Baseline IONM recordings were acquired in all patients without any difficulty. The two groups were comparable with respect to the number of additional boluses of fentanyl, patient movements, and recovery characteristics. Conclusion Dexmedetomidine as an adjuvant to propofol in TIVA reduces the requirement of the latter, without affecting the IONM recordings. The addition of dexmedetomidine also ensures stable hemodynamics and decreases the requirement of opioids with similar recovery characteristics.

Effects of Dexmedetomidine Combined with Intravenous Anesthesia on Oxidative Stress Index, Postoperative Sleep Quality, and Brain Function in HICH Patients

To investigate the effects of dexmedetomidine combined with intravenous anesthesia on oxidative emergency indicators, postoperative sleep quality, and brain function in patients with hypertensive cerebral hemorrhage (HICH), a total of 285 HICH patients admitted to our hospital from February 2020 to February 2021 were selected. The combined anesthesia group (n = 142) and the control group (n = 143) were established by the random number table method. The control group received conventional intravenous anesthesia, and the combined anesthesia group received dexmedetomidine combined intravenous anesthesia. Two groups of patients before and after operation was observed vital signs, oxidative stress index difference, comparing each time, the change of the two groups of brain function index, adverse reactions occurred between observation group, and the postoperative period of Pittsburgh Sleep Quality Index Scale (PSQI) score as a result, the Pearson correlation coefficient analysis of oxidative stress level and the correlation of HICH patients sleep quality. After operation, the mean arterial pressure (MAP) and heart rate (HR) of patients in both groups decreased significantly. The MAP level in the combined anesthesia group significantly increased compared to the control group, and the HR level decreased significantly than the control group (all P < 0.05). The levels of TNF-α, IL-6 and MDA in both groups increased significantly on day 7 after operation compared with before operation, but the indexes in the combined anesthesia group significantly decreased compared with the control group (P < 0.05). The level of superoxide dismutase (SOD) in both groups significantly decreased compared to that before operation, and the index value in combined anesthesia group significantly increased compared to that in the control group (P < 0.05). After surgery, the levels of central nerve specific protein (S100-β) and neuron specific enolase (NSE) in 2 groups increased with time, and the indexes in the combined anesthesia group significantly decreased compared to the control group (all P < 0.05). The incidence of adr in combined anesthesia group decreased significantly than that in control group (P < 0.05). After surgery, PSQI scores of the two groups showed a downward trend with time extension, and scores of the combined anesthesia group decreased significantly than those of the control group at 24 h, 48 h and 7 d after surgery (all P < 0.05). Pearson's correlation coefficient was used to analyze that TNF-α, IL-6, and MDA levels were positively correlated with PSQI score, while SOD level was negatively correlated with PSQI score (all P < 0.05). Dexmedetomidine combined with intravenous anesthesia can significantly improve the vital signs and oxidative stress response of HICH patients, effectively reduce the risk of adverse reactions, have little impact on the brain function of patients, and can improve the postoperative sleep quality of patients. This operation is worthy of clinical application. In addition, this study further analyzed the influence mechanism of postoperative sleep quality in patients with HICH and showed that TNF-α, IL-6, MDA, and SOD were all correlated with sleep quality in patients with HICH, suggesting that follow-up detection of these indicators has positive significance in improving the prognosis of patients.

Intraoperative hand strength as an indicator of consciousness during awake craniotomy: a prospective, observational study

Awake craniotomy enables mapping and monitoring of brain functions. For successful procedures, rapid awakening and the precise evaluation of consciousness are required. A prospective, observational study conducted to test whether intraoperative hand strength could be a sensitive indicator of consciousness during the awake phase of awake craniotomy. Twenty-three patients who underwent awake craniotomy were included. Subtle changes of the level of consciousness were assessed by the Japan Coma Scale (JCS). The associations of hand strength on the unaffected side with the predicted plasma concentration (Cp) of propofol, the bispectral index (BIS), and the JCS were analyzed. Hand strength relative to the preoperative maximum hand strength on the unaffected side showed significant correlations with the Cp of propofol (ρ =  − 0.219, p = 0.007), the BIS (ρ = 0.259, p = 0.002), and the JCS (τ =  − 0.508, p = 0.001). Receiver operating characteristic curve analysis for discriminating JCS 0–1 and JCS ≥ 2 demonstrated that the area under the curve was 0.76 for hand strength, 0.78 for Cp of propofol, and 0.66 for BIS. With a cutoff value of 75% for hand strength, the sensitivity was 0.76, and the specificity was 0.67. These data demonstrated that hand strength is a useful indicator for assessing the intraoperative level of consciousness during awake craniotomy.

Effects of various methods of dexmedetomidine administration for sedation in elderly patients undergoing spinal anesthesia: a randomized controlled study

Background

The purpose of this study was to investigate the degree of sedation and the incidence of adverse effects resulting from various methods of administering the initial dose followed by continuous infusion of dexmedetomidine (DEX) for sedation in elderly patients undergoing spinal anesthesia.

Methods

In total, 72 patients aged over 65 years who were to be administered spinal anesthesia were randomly allocated into three groups. The initial doses were injected to the groups as follows: group DD, DEX 0.5 μg/kg for 10 min; group MD, midazolam 0.02 mg/kg; and group D, no initial dose. This was followed immediately by infusing a maintenance dose of DEX 0.5 μg/kg/h to all groups.

Results

The Bispectral index (BIS) in the D group was significantly higher than in the other two groups. There were no significant differences in the Ramsay sedation scale (RSS) among the groups. The RSS 3 level was reached in 10 min from the start of sedation in MD and DD groups and in 20 min from the start of sedation in D group. Neither bradycardia nor hypotension was observed in any of the groups.

Conclusions

Patients in all three groups reached the RSS 3 sedating-effect level. However, the group that received continuous infusion only without the initial dose showed higher BIS than the other two groups and reached the RSS 3 later. No adverse events were observed in any of the groups.

Age progression from vicenarians (20-29 year) to nonagenarians (90-99 year) among a population pharmacokinetic/pharmacodynamic (PopPk-PD) covariate analysis of propofol-bispectral index (BIS) electroencephalography

BACKGROUND

Pharmacokinetic/pharmacodynamic (PK/PD) modeling has made an enormous contribution to intravenous anesthesia. Because of their altered physiological, pharmacological and pathological aspects, titrating general anesthesia in the elderly is a challenging task.

METHODS

Eighty patients were consecutively enrolled divided by decades from vicenarians (20-29 year) to nonagenarians (90-99 year) into eight groups. Using target controlled infusion (TCI) and electroencephalographic (EEG)-derived bispectral index (BIS) we set propofol plasma concentration (C_p) to gradually reach 3.5 μg mL^-1 over 3.5-min. In each patient, we constructed a PK/PD model and conducted a population PK/PD (PopPK-PD) covariate analysis.

RESULTS

Age was significant covariate for baseline BIS effect (E₀), inhibitory propofol concentration at 50% BIS decline (IC₅₀) and maximum BIS decline (E_max). First-order rate constant K_e0 of 0.47 min^-1 in vicenarians (20-29 year) gradually increased with age-progression to 1.85 min^-1 in nonagenarians (90-99 year). Simulation modelling showed that clinically recommended C_p of 3.5 μg mL^-1 for 20-29 year BIS 50 should be reduced to 3.0 for 30-49 year, 2.5 for 50-69 year and 2.0 for 80-89 year.

CONCLUSION

We quantified and graded EEG-BIS age-progression among different age groups divided by decades. We demonstrated deeper BIS values with decades' age progression. Our data has important implications for propofol dosing. The practical information for physicians in their daily clinical practice is using propofol C_p of 3.5 μg mL^-1 might not yield BIS value of 50 in elderly patients. Our simulations showed that the recommended regimen of C_p 3.5 μg mL^-1 for 20-29 year should be gradually decreased to 2.0 μg mL^-1 for 80-89 year.

CLINICAL TRIAL REGISTRY NUMBERS

European Community Clinical Trials Database EudraCT (http://eudract.emea.eu) initial trial registration number: 2011-002847-81, and subsequently registered at www.clinicaltrials.gov; trial registration number: NCT02585284. Xijing Hospital of Fourth Military Medical University ethics committee approval number 20110707-4.

Efficacy of the bispectral index and Observer's Assessment of Alertness/Sedation Scale in monitoring sedation during spinal anesthesia: A randomized clinical trial

OBJECTIVE

The bispectral index (BIS) has been used to monitor sedation during spinal anesthesia. We evaluated the correlation between BIS and the Observer's Assessment of Alertness/Sedation Scale (OAA/S) in patients sedated with dexmedetomidine, propofol, or midazolam.

METHODS

This prospective, randomized study included 46 patients scheduled for knee arthroplasty under spinal anesthesia with sedation. The patients were randomized to receive sedation with dexmedetomidine (n = 15), propofol (n = 15), or midazolam (n = 16). Correlation between BIS and OAA/S was assessed during sedation in the three groups.

RESULTS

A linear correlation was observed between BIS and OAA/S, and there was no significant difference in BIS score between the groups during mild to moderate sedation status (OAA/S 3-5). During deep sedation (OAA/S 1-2), the BIS score in the midazolam group was significantly higher than that in the propofol and dexmedetomidine groups (74.4 ± 11.9 vs 67.7 ±  9.5 vs 62.6 ± 12.2).

CONCLUSIONS

BIS values differed at the same level of sedation between different sedative agents. Objective sedation scores should therefore be used in combination with BIS values for the assessment of sedation levels during spinal anesthesia.

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.

Use of the Bispectral Index to Predict Eye Position of Children during General Anesthesia

Purpose

To assess the relationship between eye position and anesthesia depth using the bispectral index (BIS) value, a parameter derived from electroencephalography data.

Methods

We investigated the relationship between BIS value and eye position in 32 children who underwent surgery for epiblepharon under general anesthesia. BIS values were recorded continuously throughout the procedure (from induction to awakening). Eye positions were video-recorded and analyzed after surgery. The vertical position of each eye was scored according to its height in relation to the medial canthus. An eye position in which the upper eyelid covered one-third of the cornea was defined as a significant ocular elevation.

Results

The BIS value correlated inversely with the end-tidal concentration of each anesthetic agent, whereas it correlated positively with the eye elevation score (eye position = 0.014 × BIS + 0.699, p = 0.011). The mean eye position score was significantly greater in patients whose BIS values were over 65. Eleven patients (34.4%) had significant ocular elevation; their mean concurrent BIS value was 61.6. Two of these patients had elevation during surgery and 9 had elevation during emergence from anesthesia.

Conclusions

We found that high BIS values were correlated with low levels of anesthetic concentration and high eye position, suggesting that BIS monitoring may be useful for predicting eye position during anesthesia. Particular attention must be given to eye position during ophthalmic surgery. Anesthesia depth can be maintained by assuring that the BIS value remains below 65.

Bispectral Index in Poisoning Cases with Multi-drug Ingestion: A Predictable Role for Early Endotracheal Intubation

Objective:

Bispectral index (BIS) is one of the several methods used to monitor the depth of anesthesia. Poisoning with ingestion of different drugs is one of the most common poisonings that have different clinical signs from drowsiness to coma. This study was performed to compare the BIS index number in poisoned patients with multi drugs ingestion with or without the need for endotracheal intubation.

Methods:

This cross-sectional study was performed on poisoned patients with ingestion of different drugs referring to Clinical Toxicology Department of Noor University Hospital, Isfahan, Iran. The clinical signs and symptoms and the vital signs at the admission time were measured, and the required therapies were given. The endotracheal intubation was done for patients who had the indication of intubation. BIS was monitored and compared for all patients with or without a need for intubation on the admission time and time of endotracheal intubation. Obtained data were analyzed by SPSS software.

Findings:

At the admission time, the mean (standard error [SE]) BIS index value for poisoned patients who needed endotracheal intubation was 66.47 ± 2.57 in comparison with 85.21 ± 1.47 for patients who did not need intubation (P < 0.001). The results of receiver operating characteristic curve (mean ± SE) showed the discrimination was excellent for BIS (0.899 ± 0.04; 95% confidence interval: 0.81–0.98) (P < 0.0001). BIS <79.5 had the sensitivity 88% and specificity 87% for endotracheal intubation.

Conclusion:

BIS is an appropriate index for prediction of the need to intubation in poisoned patients with ingestion of different drugs.

The EC90 of remifentanil for blunting cardiovascular responses to head fixation for neurosurgery under total intravenous anesthesia with propofol and remifentanil based on bispectral index monitoring: estimation with the biased coin up-and-down sequential method

Background

Head fixation can induce hemodynamic instability. Remifentanil is commonly used with propofol for total intravenous anesthesia (TIVA) during neurosurgery. This study investigated the 90% effective concentration (EC₉₀) of remifentanil for blunting of cardiovascular responses to head fixation during neurosurgery via bispectral index (BIS) monitoring.

Methods

Fifty patients undergoing neurosurgery requiring head fixation were enrolled. This study was performed using the biased coin up-and-down design sequential method (BCD). After tracheal intubation, the effect-site target concentration (Ce) of remifentanil was adjusted to achieve hemodynamic stability and reset to the level preoperatively assigned to each patient, according to the BCD method, approximately 10 min before head fixation. Baseline hemodynamic values were recorded before head fixation. An ineffective response was defined as a case with a > 20% increase in hemodynamic values from baseline. Otherwise, the response was determined to be effective. The EC₉₀ of remifentanil was calculated as a modified isotonic estimator.

Results

Forty-three patients completed this study. The EC₉₀ of remifentanil for blunting cardiovascular responses to head fixation was estimated to be 6.48 ng/mL (95% CI, 5.94–6.83 ng/mL).

Conclusions

Adjustment of the Ce of remifentanil to approximately 6.5 ng/mL before head fixation could prevent noxious cardiovascular responses in 90% of neurosurgical ASA I-II patients aged 20 to 65 years old during propofol target-controlled infusion titrated to maintain BIS between 40 and 50.

Trial registration

ClinicalTrials.gov Identifier NCT01489137, retrospectively registered 5 December 2011.

Effect of Intravenous Magnesium Sulfate on the Minimum Alveolar Concentrations of Desflurane Using Bispectral Index Monitoring: A Prospective Randomized Double-blind Controlled Study

BACKGROUND

Magnesium sulfate has been implicated to influence the minimum alveolar concentration (MAC) of various volatile anesthetics, but its effect on desflurane remains unanswered so far.

AIM

To study the effect of perioperative intravenous magnesium sulfate on MAC of desflurane using bispectral index (BIS) monitoring.

SETTINGS

Operating room of a tertiary care hospital.

DESIGN

A prospective, randomized, controlled, double-blind clinical trial.

METHODS

Sixty American Society of Anesthesiologists Physical Status I/II patients aged 18-65 years and scheduled for breast conservative surgeries were randomized into three groups of 20 each. Control group (Group 1) was administered 100 ml normal saline (NS) as bolus followed by NS infusion. Magnesium (Mg) was administered as bolus of 40 mg/kg in 100 ml NS followed by NS infusion in Group 2 and as bolus of 40 mg/kg followed by infusion of 10 mg/kg/h of Mg in NS in Group 3. Anesthesia was induced with propofol, fentanyl, and atracurium. Dial setting of desflurane was adjusted to target a BIS of 45-55. Time from cessation of desflurane to beginning of spontaneous movement, time taken to respond to verbal commands, time of extubation, and time taken to reach BIS value of 70 were recorded.

STATISTICAL ANALYSIS

Statistics was done using SPSS program using ANOVA and the Chi-square test for variables and a P < 0.05 was taken to indicate a significant difference.

RESULTS

No significant difference was present in MAC, end-tidal desflurane, and cumulative consumption of morphine. Recovery was similar in Group 2 and Group 3, but time to eye opening (P = 0.011), time to respond to verbal commands (P < 0.001), and time to extubate (P < 0.001) were significantly delayed when compared with patients in Group 1. Hemodynamic changes were comparable among three groups.

CONCLUSIONS

From this study, we conclude that MACs of desflurane using BIS as a guide remains unaffected by perioperative infusion of magnesium sulfate.

Changes in the Bispectral Index in Response to Loss of Consciousness and No Somatic Movement to Nociceptive Stimuli in Elderly Patients

Background:

Bispectral index (BIS) is considered very useful to guide anesthesia care in elderly patients, but its use is controversial for the evaluation of the adequacy of analgesia. This study compared the BIS changes in response to loss of consciousness (LOC) and loss of somatic response (LOS) to nociceptive stimuli between elderly and young patients receiving intravenous target-controlled infusion (TCI) of propofol and remifentanil.

Methods:

This study was performed on 52 elderly patients (aged 65–78 years) and 52 young patients (aged 25–58 years), American Society of Anesthesiologists physical status I or II. Anesthesia was induced with propofol administered by TCI. A standardized noxious electrical stimulus (transcutaneous electrical nerve stimulation, [TENS]) was applied (50 Hz, 80 mA, 0.25 ms pulses for 4 s) to the ulnar nerve at increasing remifentanil predicted effective-site concentration (Ce) until patients lost somatic response to TENS. Changes in awake, prestimulus, poststimulus BIS, heart rate, mean arterial pressure, pulse oxygen saturation, predicted plasma concentration, Ce of propofol, and remifentanil at both LOC and LOS clinical points were investigated.

Results:

BIS_LOC in elderly group was higher than that in young patient group (65.4 ± 9.7 vs. 57.6 ± 12.3) (t = 21.58, P < 0.0001) after TCI propofol, and the propofol Ce at LOC was 1.6 ± 0.3 μg/ml in elderly patients, which was significantly lower than that in young patients (2.3 ± 0.5 μg/ml) (t = 7.474, P < 0.0001). As nociceptive stimulation induced BIS to increase, the mean of BIS maximum values after TENS was significantly higher than that before TENS in both age groups (t = 8.902 and t = 8.019, P < 0.0001). With increasing Ce of remifentanil until patients lost somatic response to TENS, BIS_LOS was the same as the BIS_LOC in elderly patients (65.6 ± 10.7 vs. 65.4 ± 9.7), and there were no marked differences between elderly and young patient groups in BIS_awake, BIS_LOS, and Ce of remifentanil required for LOS.

Conclusion:

In elderly patients, BIS can be used as an indicator for hypnotic-analgesic balance and be helpful to guide the optimal administration of propofol and remifentanil individually.

Trial Registration:

CTRI Reg. No: ChiCTR-OOC-14005629; http://www.chictr.org.cn/showproj.aspx?proj=9875.

Effect of nitrous oxide on bispectral index values at equi-minimum alveolar concentrations of sevoflurane and desflurane

BACKGROUND AND AIMS

Bispectral index (BIS) values may be anaesthetic agent-specific, depending on their ability to suppress the electroencephalogram (EEG) signals. We carried out a prospective, randomised clinical trial to study the effect of nitrous oxide (N₂O) on the BIS values at an equi-minimum alveolar concentration (MAC) of sevoflurane and desflurane.

METHODS

Sixty adult patients undergoing spine surgery were randomised into two groups; Group S (sevoflurane; n = 30) and Group D (desflurane; n = 30) for the maintenance of anaesthesia in oxygen and air or oxygen and N₂O mixture (FiO₂-0.4) (Stage 1). BIS and fraction of inspired and end-tidal concentration of agents were noted at 1.0 MAC. In Stage 2, air or N₂O was discontinued and the other carrier gas was introduced. At steady state of this carrier gas, values were again noted as in Stage 1. Statistical analysis was performed using two-way analysis of variance followed by Bonferroni correction, and Student's t-test for paired data. P<0.05 was considered statistically significant.

RESULTS

With air-oxygen as the carrier gas, sevoflurane and desflurane resulted in comparable BIS values (P = 0.44). With addition of 60% N₂O, there was a significant increase in BIS values at 1.0 MAC for both the agents. Furthermore, higher BIS values were observed with sevoflurane compared to desflurane (P = 0.01).

CONCLUSION

Sevoflurane and desflurane at equi-MAC concentration exert similar effect on BIS values when used with air-oxygen. N₂O results in higher BIS values; this effect is more pronounced in combination with sevoflurane.

Spectral Gini Index for Quantifying the Depth of Consciousness

We propose indices that describe the depth of consciousness (DOC) based on electroencephalograms (EEGs) acquired during anesthesia. The spectral Gini index (SpG) is a novel index utilizing the inequality in the powers of the EEG spectral components; a similar index is the binarized spectral Gini index (BSpG), which has low computational complexity. A set of EEG data from 15 subjects was obtained during the induction and recovery periods of general anesthesia with propofol. The efficacy of the indices as indicators of the DOC was demonstrated by examining Spearman's correlation coefficients between the indices and the effect-site concentration of propofol. A higher correlation was observed for SpG and BSpG (0.633 and 0.770, resp., p < 0.001) compared to the conventional indices. These results show that the proposed indices can achieve a reliable quantification of the DOC with simplified calculations.

Sedation for Percutaneous Endoscopic Lumbar Discectomy

Although anesthetic requirements for minimally invasive neurosurgical techniques have been described in detail and applied successfully since the early 2000s, most of the literature on this subject has dealt with cranial cases that were operated on in the supine or sitting positions. However, spinal surgery has also used minimally invasive techniques that were performed in prone position for more than 30 years to date. Although procedures in both these neurosurgical techniques require the patient to be awake for a certain period of time, the main surgical difference with minimally invasive spinal surgery is that the patients are in the prone position, which may result in increased requirement of airway management because of deep sedation. In addition, although minimally invasive spinal surgery progresses slowly and different techniques are used with no agreement on the terminology used to describe these techniques thus far, the anesthetist needs to understand the surgical and anesthetic requirements for each type of intervention in order to take necessary precautions. This paper reviews the literature on this topic and discusses the anesthetic necessities for percutaneous endoscopic laser surgery.

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 equi-minimum alveolar concentration of sevoflurane and isoflurane on bispectral index values during both wash in and wash out phases: A prospective randomised study

BACKGROUND AND AIMS

At equal minimum alveolar concentration (MAC), volatile agents may produce different bispectral index (BIS) values especially at low BIS levels when the effect is volatile agent specific. The present study was performed to compare the BIS values produced by sevoflurane and isoflurane at equal MAC and thereby assessing which is a better hypnotic agent.

METHODS

Sixty American Society of Anaesthesiologists I and II patients undergoing elective mastoidectomy were divided into groups receiving either isoflurane or sevoflurane, and at equi-MAC. BIS value was measured during both wash in and wash out phase, keeping other parameters same. Statistical analysis was performed using the Friedman two-way analysis and Mann-Whitney U-test. A P < 0.05 was considered significant.

RESULTS

BIS value was significantly lower with sevoflurane at all MAC values as compared to isoflurane, except in the beginning and at MAC awake. However, both the drugs proved to be cardiostable.

CONCLUSION

At equi-MAC sevoflurane produces lower BIS values during wash in as well as wash out phase as compared to isoflurane, reflecting probably an agent specific effect and a deficiency in BIS algorithm for certain agents and their interplay.

Effect of sevoflurane concentration on visual evoked potentials with pattern stimulation in dogs

The purpose of this study was to investigate the effects of sevoflurane concentration on canine visual evoked potentials with pattern stimulation (P-VEPs). Six clinically normal laboratory-beagle dogs were used. The minimum alveolar concentration (MAC) of sevoflurane was detected from all subjects by tail clamp method. The refractive power of the right eyes of all subjects was corrected to −2 diopters after skiascopy. For P-VEP recording, the recording and reference electrode were positioned at inion and nasion, respectively, and the earth electrode was positioned on the inner surface. To grasp the state of CNS suppression objectively, the bispectral index (BIS) value was used. The stimulus pattern size and distance for VEP recording were constant, 50.3 arc-min and 50 cm, respectively. P-VEPs and BIS values were recorded under sevoflurane in oxygen inhalational anesthesia at 0.5, 1.0, 1.5, 2.0, 2.5 and 2.75 sevoflurane MAC. For analysis of P-VEP, the P100 implicit time and N75-P100 amplitude were estimated. P-VEPs were detected at 0.5 to 1.5 MAC in all dogs, and disappeared at 2.0 MAC in four dogs and at 2.5 and 2.75 MAC in one dog each. The BIS value decreased with increasing sevoflurane MAC, and burst suppression began to appear from 1.5 MAC. There was no significant change in P100 implicit time and N75-P100 amplitude with any concentration of sevoflurane. At concentrations around 1.5 MAC, which are used routinely to immobilize dogs, sevoflurane showed no effect on P-VEP.

The use of the bispectral index in the detection of pain in mechanically ventilated adults in the intensive care unit: a review of the literature

The bispectral index is a technique that involves assessing brain activity (through electroencephalography as well as electromyography), and has been proposed to be useful for the detection of pain among patients who are unable to communicate verbally. This review aimed to clarify whether the bispectral index is an appropriate tool to assess pain in the intensive care unit.

BACKGROUND:

Pain assessment is an immense challenge for clinicians, especially in the context of the intensive care unit, where the patient is often unable to communicate verbally. Several methods of pain assessment have been proposed to assess pain in this environment. These include both behavioural observation scales and evaluation of physiological measurements such as heart rate and blood pressure. Although numerous validation studies pertaining to behavioural observation scales have been published, several limitations associated with using these measures for pain assessment remain. Over the past few years, researchers have been interested in the use of the bispectral index monitoring system as a proxy for the evaluation of encephalography readings to assess the level of anesthesia and, potentially, analgesia.

OBJECTIVES:

To synthesize the main studies exploring the use of the bispectral index monitoring system for pain assessment, to guide future research in adults under sedation in the intensive care unit.

METHOD:

The EMBASE, Medline, CINAHL and PsycINFO databases were searched for studies published between 1996 and 2013 that evaluated the use of the bispectral index in assessing pain.

RESULTS:

Most studies conclude that nociceptive stimulation causes a significant increase in the bispectral index and revealed the importance of controlling certain confounding variables such as the level of sedation.

DISCUSSION:

Further studies are needed to clearly demonstrate the relationship between nociceptive stimuli and the bispectral index, as well as the specificity of the bispectral index in detecting pain.

Bispectral index for improving anaesthetic delivery and postoperative recovery

BACKGROUND

The use of clinical signs may not be reliable in measuring the hypnotic component of anaesthesia. The use of bispectral index (BIS) to guide the dose of anaesthetic may have certain advantages over clinical signs. This is the second update of a review originally published in 2007.

OBJECTIVES

The primary objective of this review focused on whether the incorporation of BIS into the standard practice for management of anaesthesia can reduce the risk of intraoperative awareness, consumption of anaesthetic agents, recovery time and total cost of anaesthesia in surgical patients undergoing general anaesthesia.

SEARCH METHODS

In this updated version, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 1), MEDLINE (1990 to 31 January 2013), EMBASE (1990 to 31 January 2013) and reference lists of articles. Previously, we searched to May 2009.

SELECTION CRITERIA

We included randomized controlled trials comparing BIS with standard practice criteria for titration of anaesthetic agents.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality, extracted data and analysed the data. We contacted study authors for further details.

MAIN RESULTS

We included 36 trials. In studies using clinical signs as standard practice, the results demonstrated a significant effect of the BIS-guided anaesthesia in reducing the risk of intraoperative awareness among surgical patients at high risk for awareness (7761 participants; odds ratio (OR) 0.24, 95% confidence interval (CI) 0.12 to 0.48). This effect was not demonstrated in studies using end tidal anaesthetic gas (ETAG) monitoring as standard practice (26,530 participants; OR 1.13, 95% CI 0.56 to 2.26). BIS-guided anaesthesia reduced the requirement for propofol by 1.32 mg/kg/hr (672 participants; 95% CI -1.91 to -0.73) and for volatile anaesthetics (desflurane, sevoflurane, isoflurane) by 0.65 minimal alveolar concentration equivalents (MAC) (95% CI -1.01 to -0.28) in 985 participants. Irrespective of the anaesthetics used, BIS reduced the following recovery times: time for eye opening (2557 participants; by 1.93 min, 95% CI -2.70 to -1.16), response to verbal command (777 participants; by 2.73 min, 95% CI -3.92 to -1.54), time to extubation (1501 participants; by 2.62 min, 95% CI -3.46 to -1.78), and time to orientation (373 participants; by 3.06 min, 95% CI -3.63 to -2.50). BIS shortened the duration of postanaesthesia care unit stay by 6.75 min (1953 participants; 95% CI -11.20 to -2.31) but did not significantly reduce the time to home readiness (329 participants; -7.01 min, 95% CI -30.11 to 16.09).

AUTHORS' CONCLUSIONS

BIS-guided anaesthesia can reduce the risk of intraoperative awareness in surgical patients at high risk for awareness in comparison to using clinical signs as a guide for anaesthetic depth. BIS-guided anaesthesia and ETAG-guided anaesthesia may be equivalent in protection against intraoperative awareness but the evidence for this is inconclusive. In addition, anaesthesia guided by BIS kept within the recommended range improves anaesthetic delivery and postoperative recovery from relatively deep anaesthesia.

Cardiorespiratory and antinociceptive effects of two different doses of lidocaine administered to horses during a constant intravenous infusion of xylazine and ketamine

BACKGROUND

This study investigated the antinociceptive effects of a constant rate infusion (CRI) of lidocaine during xylazine and ketamine anesthesia in horses and aimed to correlate these effects with cardiorespiratory variables, bispectral index (BIS) and plasma lidocaine concentrations. Six adult crossbred mares weighing 320-400 kg were anesthetized on three different occasions. Sedation was performed with xylazine (0.75 mg/kg IV) and anesthetic induction with guaifenesin (75 mg/kg IV) and ketamine (2 mg/kg IV). Anesthesia was maintained with 37.5 μg/kg/min of xylazine and 87.5 μg/kg/min of ketamine both administered intravenously for 75 min. The three treatments consisted of: lidocaine (loading dose: 5 mg/kg, CRI: 100 μg/kg/min; THL); lidocaine (loading dose: 2.5 mg/kg; CRI: 50 μg/kg/min: TLL); and saline (TS); all given 15 min after induction and maintained for 1 h. Antinociception was measured by response to electrical stimulation and bispectral index (BIS) was recorded during anesthesia. Parametric and non-parametric data were compared using ANOVA followed by Student-Newman-Keuls and Friedman tests, respectively.

RESULTS

Plasma lidocaine concentrations peaked at the end of lidocaine loading dose and was greater in THL (9.61 ± 2.75 μg/mL) vs TLL (4.50 ± 3.34 μg/mL). Electrical noxious stimulation caused purposeful movement in all horses from TS, but no response in THL. The BIS was decreased in THL only and was less when compared to the other treatments throughout anesthesia. Blood pressure, PaO2 and PaCO2 increased and heart rate (HR), respiratory rate (RR), pH, total plasma protein and temperature decreased during anesthesia in all treatments. PaCO2 and HR were greater and RR and pH less in THL compared to TLL and TS at 30 min during anesthesia. All recoveries were considered excellent. Time to standing was longer after THL (60 ± 20 min) than following TLL and TS (32 ± 17 and 30 ± 15 min, respectively).

CONCLUSIONS

At the highest dose administered (THL) lidocaine CRI during xylazine/ketamine anesthesia decreased BIS and motor response to noxious stimulation, and prolonged recovery time without significant added cardiorespiratory depression.

Dose sparing of induction dose of propofol by fentanyl and butorphanol: A comparison based on entropy analysis

Background:

The induction dose of propofol is reduced with concomitant use of opioids as a result of a possible synergistic action.

Aim and Objectives:

The present study compared the effect of fentanyl and two doses of butorphanol pre-treatment on the induction dose of propofol, with specific emphasis on entropy.

Methods:

Three groups of 40 patients each, of the American Society of Anaesthesiologistsphysical status I and II, were randomized to receive fentanyl 2 μg/kg (Group F), butorphanol 20 μg/kg (Group B 20) or 40 μg/kg (Group B 40) as pre-treatment. Five minutes later, the degree of sedation was assessed by the observer's assessment of alertness scale (OAA/S). Induction of anesthesia was done with propofol (30 mg/10 s) till the loss of response to verbal commands. Thereafter, rocuronium 1 mg/kg was administered and endotracheal intubation was performed 2 min later. OAA/S, propofol induction dose, heart rate, blood pressure, oxygen saturation and entropy (response and state) were compared in the three groups.

Statistical Analysis:

Data was analyzed using ANOVA test with posthoc significance, Kruskal–Wallis test, Chi-square test and Fischer exact test. A P<0.05 was considered as significant.

Results:

The induction dose of propofol (mg/kg) was observed to be 1.1±0.50 in Group F, 1.05±0.35 in Group B 20 and 1.18±0.41 in Group B40. Induction with propofol occurred at higher entropy values on pre-treatment with both fentanyl as well as butorphanol. Hemodynamic variables were comparable in all the three groups.

Conclusion:

Butorphanol 20 μg/kg and 40 μg/kg reduce the induction requirement of propofol, comparable to that of fentanyl 2 μg/kg, and confer hemodynamic stability at induction and intubation.

Clinical Decision Support and Closed-Loop Control for Cardiopulmonary Management and Intensive Care Unit Sedation Using Expert Systems

Patients in the intensive care unit (ICU) who require mechanical ventilation due to acute respiratory failure also frequently require the administration of sedative agents. The need for sedation arises both from patient anxiety due to the loss of personal control and the unfamiliar and intrusive environment of the ICU, and also due to pain or other variants of noxious stimuli. While physicians select the agent(s) used for sedation and cardiovascular function, the actual administration of these agents is the responsibility of the nursing staff. If clinical decision support systems and closed-loop control systems could be developed for critical care monitoring and lifesaving interventions as well as the administration of sedation and cardiopulmonary management, the ICU nurse could be released from the intense monitoring of sedation, allowing her/him to focus on other critical tasks. One particularly attractive strategy is to utilize the knowledge and experience of skilled clinicians, capturing explicitly the rules expert clinicians use to decide on how to titrate drug doses depending on the level of sedation. In this paper, we extend the deterministic rule-based expert system for cardiopulmonary management and ICU sedation framework presented in [1] to a stochastic setting by using probability theory to quantify uncertainty and hence deal with more realistic clinical situations.

Effect of flumazenil on recovery from anesthesia and the bispectral index after sevoflurane/fentanyl general anesthesia in unpremedicated patients

Background

Benzodiazepines have a hypnotic/sedative effect through the inhibitory action of γ-aminobutyric acid type A receptor. Flumazenil antagonizes these effects via competitive inhibition, so it has been used to reverse the effect of benzodiazepines. Recently, flumazenil has been reported to expedite recovery from propofol/remifentanil and sevoflurane/remifentanil anesthesia without benzodiazepines. Endogenous benzodiazepine ligands (endozepines) were isolated in several tissues of individuals who had not received benzodiazepines.

Methods

Forty-five healthy unpremedicated patients were randomly allocated to either flumazenil or a control groups. Each patient received either a single dose of 0.3 mg of flumazenil (n = 24) or placebo (n = 21). After drug administration, various recovery parameters and bispectral index (BIS) values in the flumazenil and control groups were compared.

Results

Mean time to spontaneous respiration, eye opening on verbal command, hand squeezing on verbal command, extubation and time to date of birth recollection were significantly shorter in the flumazenil group than in the control group (P = 0.004, 0.007, 0.005, 0.042, and 0.016, respectively). The BIS value was significantly higher in flumazenil group than in the control group beginning 6 min after flumazenil administration.

Conclusions

Administration of a single dose of 0.3 mg of flumazenil to healthy, unpremedicated patients at the end of sevoflurane/fentanyl anesthesia without benzodiazepines resulted in earlier emergence from anesthesia and an increase in the BIS value. This may indicate that flumazenil could have an antagonistic effect on sevoflurane or an analeptic effect through endozepine-dependent mechanisms.

Perioperative care following complex laryngotracheal reconstruction in infants and children

Laryngotracheal reconstruction (LTR) involves surgical correction of a stenotic airway with cartilage interpositional grafting, followed by either placement of a tracheostomy and an intraluminal stent (two-stage LTR) or placement of an endotracheal tube with postoperative sedation and mechanical ventilation for an extended period of time (singlestage LTR). With single-stage repair, there may be several perioperative challenges including the provision of adequate sedation, avoidance of the development of tolerance to sedative and analgesia agents, the need to use neuromuscular blocking agents, the maintenance of adequate pulmonary toilet to avoid perioperative nosocomial infections, and optimization of postoperative respiratory function to facilitate successful tracheal extubation. We review the perioperative management of these patients, discuss the challenges during the postoperative period, and propose recommendations for the prevention of reversible causes of extubation failure in this article. Optimization to ensure a timely tracheal extubation and successful weaning of mechanical ventilator, remains the primary key to success in these surgeries as extubation failure or the need for prolonged postoperative mechanical ventilation can lead to failure of the graft site, the need for prolonged Pediatric Intensive Care Unit care, and in some cases, the need for a tracheostomy to maintain an adequate airway.

Bispectral index monitoring (BIS) as a guide for intubation without neuromuscular blockade in office-based pediatric general anesthesia: a retrospective evaluation

The Bispectral Index System is a useful guide for timing of adequate intubation conditions in office-based pediatric general anesthesia without neuromuscular blockade. As the number of cases in the office-based setting increase, many clinicians opt to intubate patients without neuromuscular blockade to avoid airway complications associated with skeletal muscle relaxation. Conventionally, this technique is conducted using the traditional monitoring criteria of vital signs, end-tidal inhalation agents, as well as anesthesiologist timing and knowledge of the pharmacodynamics of the anesthetic agent to help determine the proper depth of anesthesia for adequate intubating conditions. This study retrospectively assesses the use of the Bispectral Index System (BIS) as a guide for timing of nonparalytic tracheal intubation in pediatric office-based general anesthesia. Anesthetic records for 168 children, American Society of Anesthesiology physical status I and II, and ranging in age from 18 months to 17 years were retrospectively analyzed. Intubation outcomes were based on 6 preset criteria to reflect the adequacy of the technique. The mean BIS value during the time of intubation was 34.7. There were no complications encountered. A BIS mean value of 34.7 provided adequate intubation conditions without muscle relaxation in office-based pediatric anesthesia without complications.

Detection of nonlinear interactions of EEG alpha waves in the brain by a new coherence measure and its application to epilepsy and anti-epileptic drug therapy

EEG and field potential rhythms established in the cortex and thalamus may accommodate the propagation of seizures. This article describes the interaction between thalamus and cortex during pentylenetetrazol (PTZ) seizures in rats with and without prior treatment with ethosuximide (ESM), a well-known antiepileptic drug (AED) that raises the threshold for seizures, was given before PTZ. The AED was given before PTZ convulsant administration. We track this thalamo-cortical association with a novel measure we have called the cross-bicoherence gain, or BISCOH. This quantity allows us to measure the spectral coherence in a purely higher order spectralmethodology. BISCOH is able to track the formation of nonlinearities at specific frequencies in the recorded EEG. BISCOH showed a strong increase in low alpha wave harmonic generationat 10 and 12.5 Hz after ESM treatment (p < 0.02 and p < 0.007, respectively). Conventional coherence failed to show distinctive and significant changes in thalamo-cortical coupling after ESM treatment at those frequencies and instead showed changes at 5 Hz. This rise in cortical rhythms is evidence of harmonic generation or new frequency formation in the thalamo-cortical system withAED therapy. BISCOH could become a powerful tool in unraveling changes in coherence due to neuroelectric modulation resulting from drug treatment or electrical stimulation.

SNAP II versus BIS VISTA monitor comparison during general anesthesia

INTRODUCTION

Effectively monitoring the level of consciousness during general anesthesia is clinically beneficial to both the patient and the physician. An electroencephalogram (EEG)-based level-of-consciousness monitor can help minimize intraoperative awareness as well as the effects of over-sedation. In this study, we compared the SNAP II (Stryker Instruments, Kalamazoo, MI USA) and BIS VISTA (Aspect Medical Systems, Newton, MA USA) monitors' primary metrics (SI and BIS, respectively) in terms of correlation, agreement and responsiveness to return to preoperative baseline in surgical cases involving general anesthesia.

METHODS

With institutional approval and written informed consent, 33 patients received general anesthesia with isoflurane while undergoing abdominal surgery. We attached both the SNAP II and BIS VISTA electrodes to each patient. We collected data from each monitor simultaneously and continuously, beginning just prior to induction and ending after extubation. Each monitor's level-of-consciousness index is a unit less metric that ranges from 0 to 100, with 100 indicating full consciousness. We performed a Bland-Altman and parameter difference analyses on the data. We calculated the time it took for each monitor to return to preoperative baseline level following cessation of anesthesia. We established an equivalence between the two indices over their entire range for our particular clinical scenario.

RESULT

The indices were correlated (r = 0.736, P < 0.0001, N = 3,706 data point pairs). There was an overall difference between the two indices (median = 16.0, 25th/75th%ile = 10.0/21.1) with BIS lower than SI. A 40-60 BIS range (the typical target range during general anesthesia) was approximately equivalent to a 54-74 SI range. In all 33 subjects, SI reached baseline before BIS at the end of the case (median = 3.3 min, 25th/75th%ile = 1.6 min/8.2 min versus median = 8.9 min, 25th/75th = 3.7 min/14.5 min, P = 0.0200), even though both metrics were equal at the beginning of the case.

DISCUSSION

Although the SI and BIS both can assess a patient's level of consciousness and are correlated, they are not in agreement with each other numerically and therefore are not interchangeable. It is difficult to assess each monitor's true responsiveness to acute changes in consciousness level from our study design. The differences between the metrics we observed in this study are most likely due to differences in signal processing methodologies, EEG frequencies employed and signal filtering utilized in the monitors.

Prospective study comparing skin impedance with EEG parameters during the induction of anaesthesia with fentanyl and etomidate

Objective

Sympathetic stimulation leads to a change in electrical skin impedance. So far it is unclear whether this effect can be used to measure the effects of anaesthetics during general anaesthesia. The aim of this prospective study is to determine the electrical skin impedance during induction of anaesthesia for coronary artery bypass surgery with fentanyl and etomidate.

Methods

The electrical skin impedance was measured with the help of an electro-sympathicograph (ESG). In 47 patients scheduled for elective cardiac surgery, anaesthesia was induced with intravenous fentanyl 10 μg/kg and etomidate 0.3 mg/kg. During induction, the ESG (Electrosympathicograph), BIS (Bispectral IndeX), BP (arterial blood pressure) and HR (heart rate) values of each patient were recorded every 20 seconds. The observation period from administration of fentanyl to intubation for surgery lasted 4 min.

Results

The ESG recorded significant changes in the electrical skin impedance after administration of fentanyl and etomidate(p < 0.05). During induction of anaesthesia, significant changes of BIS, HR and blood pressure were observed as well (p < 0.05).

Conclusions

The electrical skin impedance measurement may be used to monitor the effects of anesthetics during general anaesthesia.

Remifentanil versus fentanyl compared in a target-controlled infusion of propofol anesthesia: quality of anesthesia and recovery profile

PURPOSE

The aim of the present study was to compare the clinical properties of fentanyl versus remifentanil in a target-controlled infusion (TCI) of propofol anesthesia regimen with bispectral index (BIS) monitoring.

METHODS

Forty consenting patients scheduled for elective septorhinoplasty were prospectively studied as one of two groups: fentanyl (group F) or remifentanil (group R). After loading boluses of fentanyl 3 microg kg(-1) or remifentanil 1 microg kg(-1) were administered, the continuous infusion of fentanyl or remifentanil was started at a rate of 0.03 or 0.15 microg kg(-1) min(-1), respectively. Propofol infusion was then commenced with a 3 microg ml(-1) effect site concentration (Ce) by means of a TCI device. The Ce propofol was adjusted to keep BIS at 50 +/- 10.

RESULTS

The general mean value of propofol Ce for group F and group R was 4.0 and 3.5 microg ml(-1), respectively. As to the recovery profile, the eye opening time (mean, 6.7 vs. 4.6 min), extubation time (mean, 7.3 vs. 4.7 min), and orientation time (mean, 7.6 vs. 4.9 min) were found to be significantly longer in group F than in group R.

CONCLUSION

We concluded that in propofol-based TCI anesthesia under BIS supervision for septorhinoplasty operations, remifentanil was better than fentanyl, especially with respect to emergence from total intravenous anesthesia (TIVA). Furthermore, the durations of anesthesia and operation were rather short, which indicates that fentanyl can be safely used.

Anesthesia in adult cardiac surgery without maintenance of muscle relaxants: a randomized clinical trial

There may be no need for muscle paralysis during cardiac surgery when adequate anesthesia is provided. We studied intra- and post-operative conditions during cardiac surgery without maintenance muscle relaxant therapy. Eighty adult patients who were candidates for elective coronary artery bypass graft surgery were randomly allocated into two groups. In the noMR or study group (noMR group; n = 40) only an intubation dose of cisatracurium (0.15 mg kg(-1)) was administrated, as opposed to the control group (MR group; n = 40), who had a continuous infusion added to the intubation dose. The anesthesia level was maintained at a Bispectral score of 40-50 using a propofol infusion. A remifentanil infusion was titrated to control patient hemodynamic response. During surgery, any minor (fine body or respiratory muscle movements) or major (coarse body movements or bucking/caught) movements were recorded. Postoperatively, analgesia was provided by remifentanil. The surgical condition was classified into three states: good (no movement), acceptable (minor movements), or poor (major movements). Anesthesia, surgery and postoperative characteristics were compared between the two groups. Statistical analysis was performed in only 78 patients (noMR = 38, MR = 40). The demographic and preoperative characteristics of the two groups were comparable. Intra-operative propofol consumption was the same, but significantly more remifentanil was used in the noMR group (p = 0.001). Post-operative characteristics and complication rates did not differ between the two groups. There were no movements in the MR group patients, while in the noMR group one patient had major movement and three had minor movements. We concluded that omitting maintenance muscle relaxants in adult cardiac surgery or eliminating residual muscle paralysis at the end of the surgery without improving early outcome can increase patient intra-operative movement risk.

[Depth of anaesthesia during intubation: comparison between propofol and thiopentone]

In order to study the depth of anaesthesia during endotracheal intubation, 30 patients received either thiopentone or propofol for anaesthesia induction. The BIS value as a parameter for the depth of anaesthesia and the rate pressure product (RPP) were acquired online. Patients who received thiopentone for anaesthesia induction showed significantly higher BIS values at the moment of intubation and reached BIS values >60 significantly more frequently than patients receiving propofol. The RPP in the propofol group lay significantly below that of the thiopentone patients. For all patients there was an mean increase in BIS values of 8 index points and an increase in the RPP. Therefore, BIS values around 50 should be achieved before intubation in order to avoid the critical BIS value for awareness of >60 despite the increase caused by the intubation procedure. Within 24 h of intubation all patients were interviewed for possible signs of awareness. None of the patients was able to remember the intubation or reported other experiences that indicated an unconscious awareness. Nevertheless, the progress of BIS values in a standardized intubation as performed in the normal clinical routine, shows that the use of thiopentone for initiating anaesthesia results in a very flat level of anaesthesia during intubation. The risk for patients to experience awareness should therefore, not be underestimated. Therefore, when using thiopentone it is recommended to also use a rapid acting muscle relaxant or to select a high ED95 to compensate for the flat level of anaesthesia. Alternatively, repetetive boluses of the hypnotic shortly before intubation should be considered or to revert to propofol. The dosage and pharmacokinetics of the analgesic should also be taken into consideration because an insufficient analgesia leads to a faster flattening of the depth of anaesthesia.

Neural network adaptive output feedback control for intensive care unit sedation and intraoperative anesthesia

The potential applications of neural adaptive control for pharmacology, in general, and anesthesia and critical care unit medicine, in particular, are clearly apparent. Specifically, monitoring and controlling the depth of anesthesia in surgery is of particular importance. Nonnegative and compartmental models provide a broad framework for biological and physiological systems, including clinical pharmacology, and are well suited for developing models for closed-loop control of drug administration. In this paper, we develop a neural adaptive output feedback control framework for nonlinear uncertain nonnegative and compartmental systems with nonnegative control inputs. The proposed framework is Lyapunov-based and guarantees ultimate boundedness of the error signals. In addition, the neural adaptive controller guarantees that the physical system states remain in the nonnegative orthant of the state space. Finally, the proposed approach is used to control the infusion of the anesthetic drug propofol for maintaining a desired constant level of depth of anesthesia for noncardiac surgery.

Comparing Entropy and the Bispectral Index with the Ramsay Score in Sedated ICU Patients

OBJECTIVE

ENTROPY is a new anesthetic depth monitor based on the analysis of the EEG signal. Our aim has been to evaluate sedation of intubated surgical critically ill patients by means of the Ramsay sedation score, the Bispectral index and ENTROPY, and to analyse the correlation between these variables.

METHODS

Sedation was evaluated every 15 min for a 1 h period in 50 non-paralysed postoperative critically ill, intubated patients, enrolled over a 6 month period. A 5 min steady-state period was allowed before each assessment. Both the Bispectral index and the Entropy parameters Response Entropy (RE) and State Entropy (SE), were collected before assessing the Ramsay scale.

RESULTS

Mean values for SE, RE and BIS were 53 +/- 27, 60 +/- 30, and 62 +/- 24 respectively. The median value for the Ramsay was 6 (range 1-6). Significant correlation was found between the four variables (SE-BIS: r = 0.79, p < 0.001; RE-BIS: r = 0.80, p < 0.001; SE-Ramsay: rho = -0.71, p < 0.001, RE-Ramsay: rho = -0.72, p < 0.001; BIS-Ramsay: rho = -0.78, p < 0.001; RE-SE: r = 0.98, p < 0.001). An overlap of BIS and Entropy values for every Ramsay score value between 4-6 was found.

CONCLUSIONS

ENTROPY, BIS and Ramsay score values correlate significantly in sedated postoperative ICU patients. ENTROPY does not appear superior to BIS for the assessment of sedation in this context.

Propofol versus alfentanil to prevent movement responses during uterine curettage

BACKGROUND

Propofol anaesthesia is frequently associated with movement responses in non-paralysed patients. Opioids decrease the probability of movement during noxious stimulation. Heart rate variability and frontal electromyography (EMG), which are related to subcortical functions, may be more closely related than surface electroencephalography (EEG) to movement responses to noxious stimulation.

METHODS

Eighty-two patients scheduled for uterine dilatation and curettage were randomized to receive at the first intra-operative movement either a supplemental alfentanil bolus, 0.5 mg intravenously, or a supplemental propofol bolus, 0.7 mg/kg intravenously. The incidences of recurring movement during the procedure were compared between the two groups. The associations of a measure of heart rate variability (Anemon index), heart rate, EMG and two EEG variables with movement responses were evaluated.

RESULTS

The incidences of recurring movement were 73% and 38% in the alfentanil and propofol groups, respectively [difference, 35%; 95% confidence interval, 9-56%; P= 0.014 between the groups). The Anemon index, heart rate, EMG and surface EEG variables displayed mainly reactive associations with movement responses.

CONCLUSION

During uterine curettage under propofol-alfentanil-nitrous oxide anaesthesia, a propofol bolus of 0.7 mg/kg was more effective in preventing the recurrence of movement responses than an alfentanil bolus of 0.5 mg. Several physiological variables may be used to track significant arousal reactions, but not to predict them.

Monitoring depth of anesthesia

Devices which monitor some aspect of anesthetic drug effects have evolved in the past few years into imperfect, but very useful, clinical tools. With appropriate respect for their limitations these monitors can be used to reduce anesthetic drug utilization and turnover time. The intriguing hypothesis that such monitors will reduce the risk of intraoperative awareness is currently under test.

Spectral frequency index monitoring during propofol-remifentanil and propofol-alfentanil total intravenous anaesthesia

BACKGROUND

The aim of this study was to evaluate the usefulness of spectral frequency index (SFx) monitoring to assess the depth of anaesthesia during propofol-opioid total intravenous anaesthesia (TIVA).

METHODS

Thirty-three patients scheduled for laparoscopic cholecystectomy under propofol TIVA were prospectively and randomly allocated to receive either remifentanil (bolus of 1.0 microg/kg, followed by continuous infusion from 0.25 to 0.05 microg/kg/min) [n = 18] or alfentanil (bolus of 10 microg/kg, followed by continuous infusion from 2.0 to 0.5 microg/kg/min) [n = 15]. EEG activity was monitored to achieve the desired depth of anaesthesia, and intravenous propofol was titrated to keep the SFx at 70-80%. The remifentanil and alfentanil groups were compared in relation to the plasma propofol concentration required for an adequate level of hypnosis during maintenance of anaesthesia, Pearson correlation coefficient for the relationship between the plasma propofol concentration and SFx values, recovery parameters, and recall of events during anaesthesia.

RESULTS

The study groups were comparable with regard to demographic characteristics, type and duration of surgery, and time to resumption of spontaneous ventilation. No evidence of explicit recall was noted. The mean plasma propofol concentration required for an adequate level of hypnosis during maintenance of anaesthesia was significantly higher in the alfentanil group (3.20 microg/mL) compared with the remifentanil group (2.17 microg/L) [p < 0.05]. In both groups, the Pearson correlation coefficient test showed a linear correlation between SFx values and propofol concentration in the studied propofol concentration range. The mean time to orientation for name and place was significantly shorter (p < 0.05), the mean propofol concentration at orientation for name and place and at the resumption of spontaneous ventilation timepoints was significantly lower (both p < 0.01), and the mean SFx value at resumption of spontaneous ventilation timepoint was significantly higher (p < 0.01) in the remifentanil group.

CONCLUSIONS

As SFx is linearly related to plasma propofol concentration, this index may be used to measure anaesthetic effect during propofol anaesthesia. The results of this clinical trial are consistent with a previous computer-simulated opioid-propofol model with regard to intraoperative and recovery variables, although the recovery occurred at different propofol concentration and SFx values.

Analyzing effects of sodium pentobarbital on hemodynamic responses by using a graphic control system

The maintenance of adequate anesthesia is very important for animal studies. This goal could be achieved if the pharmacokinetics of the anesthetic is known and a well-controlled instrument system is used. To this end, a graphic control system is developed to study the effects of sodium pentobarbital on anesthesia. Hemodynamic signals such as mean blood pressure, pulse pressure, heart rate were analyzed and used as index for quantitative evaluating the level of anesthesia. Factors that could affect the anesthesia, e.g. body weight (BW) of the rat and the concentration of pentobarbital were used as independent variables to examine the survival time (dependent variable) for an overdosage anesthesia. The relationship among the BW, the drug concentration, and the survival time before death were formulated. As most physiological system have shown, the empirical relationship is exponential in nature. This implies that the mechanism is highly nonlinear and it is complicated by the buffering characteristics of life. Hence, a precision feedback control system seems to be necessary for a well-controlled anesthesia.

EEG signal processing in anesthesia-using wavelet-based informational tools

A new tool of wavelet entropy (WE) is applied to characterize the dynamical properties of EEGs for purpose of evaluating the depth of anesthesia (DOA). 31 cases are analysed with WE, and the result shows the WE measure for EEGs can distinguish awake and asleep state in anesthesia with a high accuracy of 95%. Compared with C(n) complexity, the WE demonstrates the same good performance, and needs shorter data length for analysis. These remind that WE is a potential quantifier of DOA.

Beat-by-beat cardiovascular index to predict unexpected intraoperative movement in anesthetized unparalyzed patients: a retrospective analysis

OBJECTIVE

Unexpected intraoperative movement may be detrimental during delicate surgery. This study tested retrospectively an algorithm based on beat-by-beat circulatory variables (incorporated into a Cardiovascular depth of anesthesia index: CARDEAN in relationship to unexpected movement, and compared its performance to that of the electroencephalogram (EEG)-derived index: BIS-XP 4.0.

METHODS

40 ASA I or II patients presenting for knee surgery had EEG (BIS XP 4.0), beat-by-beat (Finapres) finger non-invasive blood pressure (BP), conventional brachial BP and electrocardiogram (EKG) monitors attached. Anesthesia was induced and maintained with propofol and remifentanil. Before incision, the propofol concentration was set to maintain BIS < 60. From incision to emergence, the anesthesiologist was denied access to BIS or Finapres. Anesthesia adjustment was titrated at the discretion of the anesthesiologist according to conventional signs only: brachial BP, EKG, eyelash reflex, movement. Occurrences of movement and eye signs (divergence of eyeballs, tears, corneal reflex, eyelash reflex) were observed. The CARDEAN algorithm was written retrospectively and tested vs. BIS.

RESULTS

11 movements occurred in 8 patients. CARDEAN > 60 predicted movement in 30% of the cases, 15 to 274 s before movement (sensitivity: 100%, specificity: 95%; relative operating curve ROC = 0.98; prediction probability pk = 0.98). BIS > 60 predicted movement in 19% of cases (sensitivity: 64%; specificity: 94%, ROC: 0.85, pk: 0.85).

CONCLUSION

Retrospectively, a cardiovascular index predicted unexpected intraoperative movements. Prospective validation is needed.

Safe removal of LMA in children - at what BIS?

BACKGROUND

Removal of an LMA without producing untoward complications has remained a matter of concern to all anesthesiologists; more so in pediatric practice where the margin of safety is narrow. Most work on LMA in adults supports its removal following return of airway reflexes. The situation regarding its removal in children is, however, less clear.

METHODS

We conducted a randomized, prospective study to compare incidence of airway complications after removal of the LMA at deep or awake planes in 120 children, ASA I or II, aged 1-8 years and to objectively determine the most appropriate Bispectral index (BIS) to allow safe removal of an LMA in children. They were studied in two groups of 60 and depth of anesthesia (whether awake-Gp A or deep-Gp D) for LMA removal was decided by random distribution from sealed envelopes. BIS was recorded continuously for all the patients until 2 min after removal of LMA.

RESULTS

Mean SpO2 after removal of LMA was 93% Gp A and 98% in Gp D. The mean duration of surgery in Gp A was 53.9 +/- 10 and in Gp D 46.7 +/- 4 min. PESev at removal in Gp A was 0.20 +/- 0.16 and in Gp D was 0.59 +/- 0.1. BIS median in Gp A was 79 with a maximum of 86 and minimum of 66. In Gp D BIS, median was 60 with maximum of 76 and minimum of 58. The number of patients with airway complications in awake removal group was 21 (35%) and in deep removal group was 4 (6.6%).

CONCLUSIONS

Bispectral index scoring should prove a useful adjunct to the present monitoring and can be used to achieve smoother emergence conditions. We suggest that LMA removal should be attempted in children when a BIS value of approximately 60 is reached.

The effect of addition of nitrous oxide to a sevoflurane anesthetic on BIS, PSI, and entropy

OBJECTIVE

N(2)O is a commonly used anesthetic that has amnestic and analgesic properties. Recently, devices that estimate depth of consciousness have been introduced in an attempt to better titrate anesthesia, however the effect of N(2)O on these monitors is unclear.

METHODS

General anesthesia was induced and titrated to maintain normal blood pressure and pulse in healthy adults. Data were collected in three 10 minute intervals (Sevo, Sevo + N(2)O, Sevo). In Phase A, sevoflurane concentration was held constant during the N(2)O trial in 60 subjects monitored with either BIS, PSI, or Entropy. In Phase B, sevoflurane concentration was reduced as N(2)O was added, maintaining a constant overall "MAC" in 20 subjects monitored concurrently with BIS and Entropy. Sample size for both phases was designed to detect a 10 unit change in measure of processed EEG with alpha = .05 and statistical power = .80.

RESULTS

In Phase A, supplementing sevoflurane with > 65% N(2)O increased MAC from 1.3 +/- 0.05 to 2.2 +/- 0.10, but did not significantly alter BIS nor PSI (p-value for differential MAC is < 0.05). Entropy, however, dropped significantly, with a change in state entropy (SE) from 31.1 +/- 7.3 to 18.9 +/- 3.7 and a corresponding rise when N(2)O was discontinued. In Phase B, supplementing sevoflurane with > 65% N(2)O with a concomitant reduction in sevoflurane resulted in an increase in both BIS (from 34 +/- 5 to 53.9 +/- 11.5) and SE (from 32 +/- 8.2 to 55.4 +/- 21.3).

CONCLUSION

Supplementing sevoflurane with > 65% N(2)O did not result in a significant change in either BIS or PSI when sevoflurane concentration was kept constant. Entropy, however, significantly decreased as anesthetic depth increased. When sevoflurane concentration was reduced during N(2)O administration, both BIS and Entropy rose despite maintenance of anesthetic depth, indicating a variable concentration effect between volatiles and N(2)O.

The impact of age on bispectral index values and EEG bispectrum during anaesthesia with desflurane and halothane in children

BACKGROUND

The relationship between end-tidal sevoflurane concentration, bispectral index (BIS) and the EEG bispectrum in children appears to be age dependent. The aim of this study was to quantify the BIS values at 1 MAC (minimum alveolar concentration) for desflurane and halothane, and explore the relationship with age for these anaesthetic agents in children.

METHODS

ECG, EEG and BIS were recorded continuously in 90 children aged 6-170 months requiring anaesthesia for elective surgery. Fifty children were anaesthetized with desflurane, and 40 children with halothane. Recordings were performed through to a steady state of 2 MAC, and thereafter at 1 and 0.5 MAC, respectively. The bispectrum of the EEG was estimated using MATLAB(c) software. A multiple correspondence analysis (MCA) was used.

RESULTS

At a steady state of 1 MAC, BIS values were significantly higher with halothane 62 (43-80) than desflurane 34 (18-64). BIS values were significantly correlated with age in both groups: DES (r(2)=0.57; P<0.01) and HALO (r(2)=0.48; P<0.01). Changes in position in the structured model of the MCA (dependent on the pattern of the EEG bispectrum) were different for the two volatile anaesthetic agents.

CONCLUSIONS

In children, BIS values are linked to age irrespective of the volatile anaesthetic agent used. The difference in BIS values for different agents at the same MAC can be explained by the specific effect on the EEG bispectrum induced by each anaesthetic agent, bringing into question the ability of the EEG bispectrum to accurately determine the depth of anaesthesia.

Comparison of the EEG-based SNAP index and the Bispectral (BIS) index during sevoflurane-nitrous oxide anaesthesia

The BIS monitor (Aspect Medical Inc, Newton, USA) was the first electroencephalogram (EEG)-based monitor of the hypnotic effect reflected by a dimensionless figure ranging from 100 (awake state) to 0 (flat line EEG). Its widespread use makes it the most-studied and the best-known among same intended devices. Its algorithm processes low-frequency EEG oscillations in order to provide the Bispectral index. A BIS index ranging from 40 to 60 has been established as the proper for surgical performance. The BIS monitor permits a closer approach to the hypnotic component of anaesthesia beyond clinical signs and may reduce the probability of intraoperative awareness; therefore, it has become a recommended monitoring tool in routine practice. The SNAP monitor (Nicolet Biomedical, Madison WI, USA) is also intended for monitoring the hypnotic effect of anaesthetics, which is in turn displayed as an index ranging from 100 to 0, with 100 meaning a fully awake state and 0 meaning no brain activity. The algorithm of the SNAP monitor is featured by its additional processing of ultra-high EEG frequencies, which seem to be involved in the formation of consciousness. The use of these frequencies would theoretically improve responsiveness during increased brain activity. We studied its behaviour patterns and capability to monitor the hypnotic effect induced by sevoflurane-nitrous oxide by comparison with the BIS index. Seventy patients ASA I-III were induced with propofol, fentanyl and rocuronium, and maintained with sevoflurane-N(2)O. BIS and SNAP indices were simultaneously recorded before induction, after intubation, after incision, at the following 10, 30 and 50 minutes, awakening and extubation time points, together with heart rate and blood pressure. The Pearson correlation was R(2) = 0.68 (p < .05). The Bland and Altman test showed a bias of 14.3 for SNAP index values with respect to BIS index values. We concluded that the SNAP index correlates with variations in the hypnotic effect induced by sevoflurane-nitrous oxide anaesthesia when compared with the BIS index. In this context, a SNAP index ranging from 58 to 70 would be equivalent to the BIS index range 40 to 60 and, therefore, the accurate for surgical performance.

Cerebral monitoring in the operating room and the intensive care unit: an introductory for the clinician and a guide for the novice wanting to open a window to the brain. Part I: The electroencephalogram

While there is an increasing body of knowledge in regard to central nervous system function and/or the mode of action of centrally active agents on neuronal function, little is done to develop new techniques on how to measure such changes. Also, monitoring of the cardiovascular system in the past has made extensive progress especially when it comes to evaluate the failing heart. In contrast monitoring of the central nervous system is only done in rare cases where operative procedures likely impede nervous function integrity. Since in the past decade the aging population undergoing operation has rise considerably, the risk of cerebral malperfusion or minute signs of degradation of the aging central nervous system (CNS) to anesthetics and agents being used in the operation room (OR) or the intensive care unit (ICU), needs continuous monitoring of an organ which presents the highest vulnerability and is likely to deteriorate faster than the cardiovascular system. In spite the rapid improvement in technology regarding the electroencephalogram (EEG) and evoked potential monitoring, physicians still are reluctant to use a technology on a routine base, which will give them insight information into brain function and activity. Such "windows to the brain" now not just are reserved to specialists working in the area of neurology and/or psychiatry. More so, cerebral monitoring is getting an integrated part in the overall therapy in patients undergoing operation or who need ventilatory support in the ICU as it effects the well-being and the outcome. The present book therefore, is intended for the practitioners who work with the patient, guide the clinician in his decision making and outlining those situations where cerebral monitoring presents an integrated part in the diagnosis and therapy of patient care. Without going too much into the technical details, representative cases underline the potential use of cerebral monitoring in the underlying clinical situation where either the patient presents borderline perfusion of the CNS, undergoes vascular surgery, or where monitoring of cerebral function in the intensive care in a head trauma patients is an integrated part in therapy. The book therefore is meant for all those clinicians who have to deal with the CNS in a day-to-day situation. This may be the anesthesiologist, the surgeon, the intensive care therapist, the nurse anesthetist as well as all other medical personal involved in intensive care therapy. The aim of the book therefore is to outline the possibilities, the limitations, and the options for therapy when the windows to the brain are opened, how to interpret the data in the light of other physiological parameters and aid the user in the technical details of how to avoid artifacts in recording which may have an impact on final decision making. Therefore, emphasis is placed on the electrode placement, artifact and electrical noise reduction, as well as data interpretation so that cerebral function diagnosis can be made on reliable grounds. The following serves as an introduction to and as a reference guide for Cerebral Monitoring in the OR and the ICU: Gives complete coverage of EEG power spectra analysis. Describes in detail the EEG machines available to be used in the OR and ICU setting. Describes in detail the major features of EEG power spectra and evoked potential measurements, including amplifiers, filter setting and microprocessor algorithm for data reduction. Gives suggestions for assessing and improving signal quality, including noise and artifact rejection, which usually are encountered in the operation room and the intensive care unit, both of which can be considered as electrically contaminated. Gives examples of EEG power spectra and evoked potential monitoring related to different types of anesthesia, in coma, after head trauma, and for the detection of ischemic events. In addition, gives complete coverage of those machines being available for the OR and the ICU, including a list of parameters regarding latency and amplitude in evoked potential As an introductory, recommendations are given for the novice to start cerebral monitoring and guide the beginner in setting up cerebral monitoring in the clinical environment.

Dopamine-dependent non-linear correlation between subthalamic rhythms in Parkinson's disease

The basic information architecture in the basal ganglia circuit is under debate. Whereas anatomical studies quantify extensive convergence/divergence patterns in the circuit, suggesting an information sharing scheme, neurophysiological studies report an absence of linear correlation between single neurones in normal animals, suggesting a segregated parallel processing scheme. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys and in parkinsonian patients single neurones become linearly correlated, thus leading to a loss of segregation between neurones. Here we propose a possible integrative solution to this debate, by extending the concept of functional segregation from the cellular level to the network level. To this end, we recorded local field potentials (LFPs) from electrodes implanted for deep brain stimulation (DBS) in the subthalamic nucleus (STN) of parkinsonian patients. By applying bispectral analysis, we found that in the absence of dopamine stimulation STN LFP rhythms became non-linearly correlated, thus leading to a loss of segregation between rhythms. Non-linear correlation was particularly consistent between the low-beta rhythm (13-20 Hz) and the high-beta rhythm (20-35 Hz). Levodopa administration significantly decreased these non-linear correlations, therefore increasing segregation between rhythms. These results suggest that the extensive convergence/divergence in the basal ganglia circuit is physiologically necessary to sustain LFP rhythms distributed in large ensembles of neurones, but is not sufficient to induce correlated firing between neurone pairs. Conversely, loss of dopamine generates pathological linear correlation between neurone pairs, alters the patterns within LFP rhythms, and induces non-linear correlation between LFP rhythms operating at different frequencies. The pathophysiology of information processing in the human basal ganglia therefore involves not only activities of individual rhythms, but also interactions between rhythms.

Comparison of electrophysiologic monitors with clinical assessment of level of sedation

OBJECTIVE

To assess the correlation between 2 clinical sedation scales and 2 electroencephalographic (EEG)-based monitors used during surgical procedures that required mild to moderate sedation.

PATIENTS AND METHODS

Patients scheduled for elective surgery participated in this Institutional review board-approved study from March 2003 to February 2004. Level of sedation was determined both clinically using the Ramsay and the Observer's Assessment of Alertness/Sedation scales and with 2 EEG measures (the Bispectral Index version XP [BIS XP] or the Patient State Analyzer [PSA 4000]). Correlation between these 2 measures of sedation were tested using nonparametric statistical tests.

RESULTS

The BIS XP monitor was used in 26 patients, and the PSA 4000 monitor was used in 24 patients. The Ramsay and Observer's Assessment of Alertness/Sedation scores correlated with each other (r = -0.96; P < .001) and with both the BIS XP (r = -0.89 and r = 0.91, respectively; P < .001) and the PSA 4000 (r = -0.80 and r = 0.80, respectively; P < .001) values. However, this correlation was strongest only at the extremes. Between the BIS XP and PSA 4000 values of 61 and 80, the clinical sedation scores varied greatly.

CONCLUSION

On the basis of our results, these EEG-based monitors cannot reliably distinguish between light and deep sedation.

Auricular Acupuncture for Pain Relief after Ambulatory Knee Arthroscopy-A Pilot Study

Auricular acupuncture (AA) is effective in treating various pain conditions, but there have been no analyses of AA for the treatment of pain after ambulatory knee surgery. We assessed the range of analgesic requirements under AA after ambulatory knee arthroscopy. Twenty patients randomly received a true AA procedure (Lung, Shenmen and Knee points) or sham procedure (three non-acupuncture points on the auricular helix) before ambulatory knee arthroscopy. Permanent press AA needles were retained in situ for one day after surgery. Post-operative pain was treated with non-steroidal anti-inflammatory ibuprofen, and weak oral opioid tramadol was used for rescue analgesic medication. The quantity of post-operative analgesics and pain intensity were used to assess the effect of AA. The incidence of analgesia-related side effects, time to discharge from the anesthesia recovery room, heart rate and blood pressure were also recorded. Ibuprofen consumption after surgery in the AA group was lower than in the control group: median 500 versus 800 mg, P = 0.043. Pain intensity on a 100 mm visual analogue scale for pain measurement and other parameters were similar in both groups. Thus AA might be useful in reducing the post-operative analgesic requirement after ambulatory knee arthroscopy.

Modeling the effects of anesthesia on the electroencephalogram

Changes to the electroencephalogram (EEG) observed during general anesthesia are modeled with a physiological mean field theory of electrocortical activity. To this end a parametrization of the postsynaptic impulse response is introduced which takes into account pharmacological effects of anesthetic agents on neuronal ligand-gated ionic channels. Parameter sets for this improved theory are then identified which respect known anatomical constraints and predict mean firing rates and power spectra typically encountered in human subjects. Through parallelized simulations of the eight nonlinear, two-dimensional partial differential equations on a grid representing an entire human cortex, it is demonstrated that linear approximations are sufficient for the prediction of a range of quantitative EEG variables. More than 70,000 plausible parameter sets are finally selected and subjected to a simulated induction with the stereotypical inhaled general anesthetic isoflurane. Thereby 86 parameter sets are identified that exhibit a strong "biphasic" rise in total power, a feature often observed in experiments. A sensitivity study suggests that this "biphasic" behavior is distinguishable even at low agent concentrations. Finally, our results are briefly compared with previous work by other groups and an outlook on future fits to experimental data is provided.