BIS-guided Anesthesia Research Articles

Preserved Memory Function during Bispectral Index–guided Anesthesia with Sevoflurane for Major Orthopedic Surgery

Memory function under anesthesia is undesired but may arise from light hypnosis as well as stress-enhanced learning during surgery. The bispectral index (BIS, Aspect Medical Systems, Norwood, MA) is a monitor of hypnotic state that can help to avoid light hypnosis (i.e., BIS above 60). This study tested the hypothesis that BIS-guided anesthesia maintaining BIS 50-60 reduces the likelihood of memory function under anesthesia. After obtaining informed consent, 128 patients scheduled for joint replacement surgery under general anesthesia with sevoflurane were randomly assigned to BIS-guided anesthesia, titrating drugs to BIS 50-60 (BIS group), or a standard practice group in which BIS was recorded but did not guide drug administration. After induction, all patients were repeatedly played a list of 15 words. After recovery from anesthesia, all were interviewed about recall and completed a recognition memory test containing the presented words (targets, 33.3%) and new words (distractors). Preoperatively, patients filled out a stress questionnaire (Spielberger State-Trait Anxiety Inventory). BIS values above 60 were recorded in both groups, but no patient recalled the presented words postoperatively. Only patients in the BIS group selected targets more often than distractors (37.1% vs. 31.5% hit rate, P = 0.001). Target hit rates correlated poorly to stress scores (P > 0.9), but were associated with the amount of fentanyl received preoperatively (P = 0.01) and pain management technique (P < 0.01). BIS titration to BIS 50-60 does not necessarily curb memory function under anesthesia when BIS values higher than 60 occur. Preoperative analgesia attenuated the likelihood of memory function under anesthesia.

Anesthesia Awareness and the Bispectral Index

Awareness during anesthesia is a serious complication with potential long-term psychological consequences. Use of the bispectral index (BIS), developed from a processed electroencephalogram, has been reported to decrease the incidence of anesthesia awareness when the BIS value is maintained below 60. In this trial, we sought to determine whether a BIS-based protocol is better than a protocol based on a measurement of end-tidal anesthetic gas (ETAG) for decreasing anesthesia awareness in patients at high risk for this complication. We randomly assigned 2000 patients to BIS-guided anesthesia (target BIS range, 40 to 60) or ETAG-guided anesthesia (target ETAG range, 0.7 to 1.3 minimum alveolar concentration [MAC]). Postoperatively, patients were assessed for anesthesia awareness at three intervals (0 to 24 hours, 24 to 72 hours, and 30 days after extubation). We assessed 967 and 974 patients from the BIS and ETAG groups, respectively. Two cases of definite anesthesia awareness occurred in each group (absolute difference, 0%; 95% confidence interval [CI], -0.56 to 0.57%). The BIS value was greater than 60 in one case of definite anesthesia awareness, and the ETAG concentrations were less than 0.7 MAC in three cases. For all patients, the mean (+/-SD) time-averaged ETAG concentration was 0.81+/-0.25 MAC in the BIS group and 0.82+/-0.23 MAC in the ETAG group (P=0.10; 95% CI for the difference between the BIS and ETAG groups, -0.04 to 0.01 MAC). We did not reproduce the results of previous studies that reported a lower incidence of anesthesia awareness with BIS monitoring, and the use of the BIS protocol was not associated with reduced administration of volatile anesthetic gases. Anesthesia awareness occurred even when BIS values and ETAG concentrations were within the target ranges. Our findings do not support routine BIS monitoring as part of standard practice. (ClinicalTrials.gov number, NCT00281489 [ClinicalTrials.gov].).

Bispectral Index-Guided General Anesthesia in Combination with Thoracic Epidural Analgesia Reduces Recovery Time in Fast-Track Colon Surgery: Retracted

The impact of bispectral index (BIS)-guided general anesthesia on recovery from general anesthesia has been evaluated in different patient populations. The benefit of using BIS has been inconsistent. We designed this study to examine the value of BIS-guided anesthesia in a fast-track setting where the goal is rapid recovery. Forty-four patients undergoing open colon resection were randomly assigned to receive either BIS-guided (BIS group, n = 22) or clinically guided (standard care group, n = 22) total IV anesthesia with propofol after placing a thoracic epidural catheter. Duration of postanesthesia care unit stay, time to tracheal extubation, direct drug cost, the incidence of hemodynamic abnormalities, ability of ambulation on the day of surgery, and patient satisfaction with anesthetic management were assessed. In the BIS-guided group, tracheal extubation was achieved significantly earlier (7.6 vs. 15.4 min, P < 0.01) and the postanesthesia care unit stay was significantly shorter (51 vs. 85 min, P < 0.01). Total anesthetic drug cost was reduced by 23% and the incidence of hypotension requiring treatment was significantly lower in the BIS group. Early ambulation, patient satisfaction, and incidence of adverse events were not significantly different between the groups. BIS-guided IV anesthesia in combination with thoracic epidural analgesia facilitates rapid recovery and reduces the overall cost of care in patients undergoing fast-track colon surgery.

Bispectral index-guided desflurane and propofol anesthesia in ambulatory arthroscopy: comparison of recovery and discharge profiles

In this prospective, randomized study we compared the recovery profiles of bispectral index (BIS)-guided anesthesia regimens with desflurane or propofol in ambulatory arthroscopy. Fifty ASA I-II adult patients who underwent knee arthroscopy were randomized to receive desflurane (D) or propofol (P) infusion accompanied by remifentanil and nitrous oxide during maintenance, titrated to maintain a bispectral index value between 50 and 60. Initial awakening, fast-track eligibility, and home readiness as well as intraoperative hemodynamics, were compared. The groups did not differ with respect to demographics, duration of operation, or intraoperative vital signs. Although the times for initial awakening parameters were shorter in group D, the differences between the groups were not significant. The time needed for the White fast-track score to reach 12 was shorter in group P than group D (9 +/- 3.5 min vs 12.5 +/- 5.3 min). However, home readiness did not differ significantly between the groups. Desflurane is an alternative to propofol for BIS-guided ambulatory anesthesia. Using desflurane in combination with opioid analgesics blunted its rapid emergence characteristics, and the higher frequency of emetic symptoms with desflurane diminished the success of its fast-track eligibility.

Bispectral index in pediatrics: fashion or a new tool?

The bispectral index (BIS, Aspect Medical Systems, Inc. Newton, MA) is becoming the gold standard for assessing depth of anesthesia in adult patients. Indeed, BIS values are highly correlated with the concentration of hypnotic drugs such as propofol or sevoflurane (1–8). The BIS is derived from a large database of EEG traces obtained in adult patients under various conditions of anesthesia (9). This database is regularly updated and the corresponding software is changed accordingly. The calculation of BIS is kept secret, but the elements included into the algorithm are known. Basically, the value displayed takes into account the frequency of EEG signal (the proportion of rapid to slow waves decreases with increasing hypnotic concentration), the synchronization of the waveforms (from virtually no synchronization in awake patient to higher degree of synchronization with increasing depth of anesthesia), and the percentage of burst suppression (the latter being observed at very deep level of anesthesia). The BIS is displayed as a dimensionless number between 0 (deep anesthesia) and 100 (awake), with 40–60 being suitable for surgical anesthesia (10). The BIS has well-known limitations. First, the BIS is more or less insensitive to narcotics, thus it reflects the hypnotic state which is only one component of anesthesia. Therefore it is not surprising that the specificity of BIS for predicting the response to noxious stimuli (such as surgical incision or laryngoscopy) under balanced anesthesia is low. Second, the BIS algorithm was validated mainly against propofol or volatile agents currently in use (isoflurane, desflurane and sevoflurane). BIS values are not correlated with ketamine plasma concentrations and are much higher at a given MAC values of halothane compared with sevoflurane (11). The latter drawbacks are not surprising as EEG traces obtained with these agents are very different from those integrated in the database (i.e. propofol and more recent volatile agents) (12–14). The BIS monitor was developed to assess depth of anesthesia and to decrease the incidence of awareness. The latter objective is achieved (15). Indeed, the B-Aware randomized controlled trial demonstrated that BISguided anesthesia reduces the risk of awareness in at-risk adult surgical patients undergoing relaxant general anesthesia. Other potential benefits in adults include decreased drug consumption, decreased postoperative incidence of nausea and vomiting (16) and quicker recovery time compared with non BIS-guided anesthesia (17). Having said that, one can understand easily that the BIS was conceived as an adult tool, not a pediatric one. Thus, the preliminary questions are: does it work in pediatric patients and if the answer is positive, what could be the interest of this device in pediatric patients? As indicated above, the BIS is only derived from adult EEG traces while EEG traces in young children differ from adult traces. Roughly, from infancy to adulthood, the amplitude of EEG decreases and dominant frequency increases (in other words, EEG becomes composed of faster waves of smaller amplitude with increasing age). However, the effects of anesthetic agents on EEG tracings are comparable throughout life. BIS values recorded in pediatric patients are inversely correlated with endtidal sevoflurane (18–20) and isoflurane concentrations (21) as in adults. BIS values are better Correspondence to: Pr Isabelle Murat, Service d’Anesthesie-Reanimation, Hopital d’enfants Armand Trousseau, 26 avenue du Dr Arnold Netter, 75571 Paris cedex 12, France (email: isabelle. murat@trs.aphp.fr). Pediatric Anesthesia 2005 15: 177–180 doi:10.1111/j.1460-9592.2004.01564.x

Electroencephalographic Monitoring Should Not Provide Risks of Intraoperative Memory Because of Aspired Faster Emergence and Reduction of Drug Consumptions: In Reply

We thank Dr. Bischoff et al. for their interest in our study on Narcotrend (MonitorTechnik, Bad Bramstedt, Germany) and Bispectral Index® (BIS®; Aspect Medical Systems Inc., Newton, MA) monitoring used for guidance of propofol titration during propofol–remifen tanil anesthesia. 1The results of our study indicate that compared with standard practice, patients with Narcotrend or BIS monitoring needed significantly less propofol, opened their eyes earlier, and were extubated sooner.Bischoff et al. now discuss the possibility of an increased risk of memory function resulting in potential awareness if electroencephalographic monitoring is used to optimize recovery times and drug consumption. They do so especially in view of our study design, which included a lightening of anesthesia during the last 15 min before the end of surgery to a target value of C1for Narcotrend or 60 for BIS®.Now, three questions must be discussed: First, should electroencephalographic monitoring in principle be used to fast track anesthesia; second, does monitoring of the depth of anesthesia result in an increased risk of awareness; and third, is it adequate to lighten anesthesia at the end of surgery?First, electroencephalographic monitoring is a valuable tool to fast-track anesthesia. Several studies, including ours, 1–3have shown that monitoring the depth of anesthesia clearly reduces the guesswork regarding how much of the anesthetic is necessary for the individual patient. Thus, this monitoring allows for individual titration of anesthesia, resulting in a reduction of drug consumption and recovery times.Second, Myles et al. 4have now brought some light to the discussion about the impact of electroencephalographic monitoring on the risk of awareness. In their investigation, 1,227 patients were randomly assigned to a BIS-guided anesthetic protocol with BIS target values of 40–60, and 1,238 patients received “routine care,” with no electroencephalographic monitoring information available. With this study design, Myles et al. observed 2 cases of awareness in the BIS® group and 11 in the standard practice group (P &lt; 0.022). Therefore, BIS-guided anesthesia reduced the risk of awareness by 82% and was also associated with a decreased time to eye opening.Third, lightening of anesthesia at the end of surgery has been standard of care for many years without electroencephalographic monitoring. In particular, in our study, we used target values of 60 for BIS® (being within the study range of Myles et al. ) and C1for the Narcotrend. In a previous investigation, BIS values of 60 were matched to Narcotrend stages of C1, 5and therefore, these results were used as target values for the guidance of propofol titration in our investigation.In conclusion, we are convinced that it is possible to optimize recovery times, reduce drug consumption, and have a lower risk of awareness by using electroencephalographic monitoring during general anesthesia.

EMERGENCE AND RECOVERY FROM BIS-GUIDED ADMINISTRATION OF ANESTHESIA

S499 INTRODUCTION: Remifentanil, a short-acting opioid has been shown to reduce the amount of co-administered hypnotic required. [1] Bispectral index (BIS), a processed EEG variable, correlates with the level of hypnosis during anesthesia. [2,3] BIS levels under 60 are required to obtain adequate hypnosis during surgical procedures. [4,5] This study compares emergence and recovery from BIS-guided anesthesia with remifentanil with either isoflurane or propofol. METHODS: After HIC approval, 76 consenting patients were randomized to two groups, one receiving remifentanil and isoflurane (ISO), the other remifentanil and propofol (PRO). In both groups, anesthesia was induced with propofol and remifentanil. Hemodynamic responses were used to titrate remifentanil infusion rates, maintaining MAP and heart rate within a 20% range compared with awake baseline. BIS was used to titrate ISO/PRO, maintaining BIS between 45 and 60. Thirty minutes before end of surgery 0.15 mg/kg morphine was administered for postoperative pain control. 15 min. before end of surgery anesthetics were reduced to keep BIS between 60 and 75. At the end of surgery, remifentanil and anesthetic agents were discontinued. Patients were observed for return of spontaneous and adequate respiration, return of consciousness and extubation. Postanesthetic assessment was performed using a modified Aldrete-score (0-10). [6] A score of 9 was needed for discharge. Statistical analysis was performed using Chi square and repeated t-testing (Bonferoni-Holms adjusted). RESULTS: Demographic data showed no significant differences between the groups (Table 1). Surgical duration was significantly shorter with isoflurane (94 +/- 40 min) than with propofol (121 +/- 53 min).Table 1: Demographic dataRecovery data were calculated from end of drugs' administration to return of spontaneous respiration (spont resp), adequate respiration (adeq resp), consciousness (ROC), extubation (EXT) and and full recovery (REC). (Table 2)Table 2: Recovery times (min)Mean remifentanil infusion rate was significantly lower (p<0.001) with ISO (0.18 +/- 0.06 [micro sign]g/kg/min) than with PRO (0.31 +/- 0.20 [micro sign]g/kg/min). Average isoflurane endtidal concentration was 0.66 +/- 0.13 %, propofol infusion rate 123 +/- 48 [micro sign]g/kg/min. CONCLUSIONS: BIS-guided anesthesia with remifentanil in combination with both isoflurane or propofol has comparably short recovery times. At comparable hypnotic levels, controlled by BIS, hemodynamic control requires higher doses of remifentanil with propofol, than with isoflurane.

A Multicenter Study of Bispectral Electroencephalogram Analysis for Monitoring Anesthetic Effect

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