Auditory Evoked Potential Index Research Articles

The Impact of Acoustic Stimulation on the AEP Monitor/2 Derived Composite Auditory Evoked Potential Index Under Awake and Anesthetized Conditions

The AEP Monitor/2 features an auditory evoked potential (AEP) and electroencephalogram (EEG)-derived hybrid index of the patient's hypnotic state. The composite AEP index (AAI) is preferably calculated from the AEP, but in case of low signal quality it is based entirely on the spontaneous EEG. We investigated the impact of auditory input on the AAI in 16 patients with correctly positioned headphones for acoustic stimulation and headphones disconnected from the patient's ears under awake and anesthetized conditions. The AAI and the Narcotrend Index (NI), another EEG-based measure of hypnotic depth, were recorded simultaneously. AAI values under awake and anesthetized conditions were higher with correctly positioned headphones than with headphones disconnected from the patient's ears (P < 0.05) but remained within the range indicating the patient's actual hypnotic state as given by the manufacturer of the monitor. Under awake conditions with correctly positioned headphones we observed frequent fluctuations between AEP-derived and EEG-derived AAI, whereas with headphones disconnected from the patient's ears the AAI calculation was completely EEG based. Acoustic stimulation had no impact on the Narcotrend Index. Although relevant misinterpretations of the patient's hypnotic state as a consequence of a turnover from AEP-derived to EEG-derived AAI values should not occur, an improved harmonization of the two methods of indexing would be desirable. The AEP Monitor/2 generates an Index (AAITM) indicating the patient's hypnotic state by analyzing either auditory evoked potentials (AEP) or spontaneous electroencephalographic (EEG) activity. We demonstrate that, though significantly different under AEP-derived or EEG-derived conditions, AAI values remain within the range indicating the patient's actual hypnotic state as given by the manufacturer of the device.

A Comparison of Bispectral Index and Rapidly Extracted Auditory Evoked Potentials Index Responses to Noxious Stimulation During Sevoflurane Anesthesia

A Comparison of Bispectral Index and Rapidly Extracted Auditory Evoked Potentials Index Responses to Noxious Stimulation During Sevoflurane Anesthesia

Evaluation of Auditory Evoked Potential and Bispectral Index in Patient-Controlled Sedation with Propofol

Background: The auditory evoked potential (AEP) index and bispectral (BIS) index have been proposed as methods to measure the depth of sedation. A prospective study was designed to assess the performance of both these methods for measuring the depth of sedation induced by propofol patient-controlled sedation (PCS) under spinal anesthesia. Methods: Forty ASA I and II adult patients under spinal anesthesia using 0.5% hyperbaric bupivacaine were studied. Group 1 (10mg bolus, 30 mg loading) and Group 2 (20 mg bolus, 60 mg loading) received propofol and maintained PCS with 1min lockout interval and 100 mg/hr continuous infusion. AEP, BIS and Observer's assessment of alertness/sedation (OAA/S) scale were monitored during the operation. Results: AEP and BIS decreased and increased following the changes on the patient's OAA/S scores and correlated with sedation significantly. There were no significant difference in mean AEP index (group 1; 13.4 8.4, group 2; 8.9 6.2), BIS index (group 1; 76.2 9.7, group 2; 71.2 9.8), and OAA/S scale (group 1; 3.8 1.3, group 2; 3.2 1.5) between the groups. Incidence of perioperative respiratory depression was significantly higher in group 2 (25%) than group 1 (5%), and incidence of involuntary movement was significantly higher in group 1 (20%) than group 2 (5%) (P

Performance of the rapidly extracted auditory evoked potentials index to detect the recovery and loss of wakefulness in anesthetized and paralyzed patients.

The rapidly extracted auditory evoked potentials index (A-lineTM ARX Index or AAI) has been proposed as a method to measure the depth of anesthesia. A prospective study was designed to assess the performance of AAI to detect the recovery and loss of wakefulness in anesthetized and paralyzed patients. Fourteen adult patients undergoing elective surgery were anesthetized with propofol 1.5 mg kg-1, vecuronium 0.1 mg kg-1 and further propofol 1.0 mg kg-1. Wakefulness was measured by the ability of the patient to respond to command using the isolated forearm technique (IFT). After the patient responded, propofol was infused at 10 mg kg-1. h-1 until wakefulness (responsiveness) was lost. The AAI was recorded continuously throughout the study and analyzed off-line. The AAI showed a significant difference between the values registered during, 30 s before and 30 s after the recovery, and also between 30 s before and 30 s after the loss of wakefulness. The prediction probability (Pk) values for AAI were 0.786 and 0.864 during the transitions from unresponsiveness to responsiveness and from responsiveness to unresponsiveness. The area under the receiver operating characteristic curve for the responsive and unresponsive values was 0.926 (SE 0.002, 95% CI 0.922-0.931), and the AAI values of approximately 5%, 50% and 95% predicted probability of wakefulness were 19, 29 and 39, respectively. The AAI may be a good predictor of recovery and loss of wakefulness for anesthetized and paralyzed patients.

Relationship between bispectral index, auditory evoked potential index and effect-site EC50 for propofol at two clinical end-points

Many anaesthetists are deterred from using total i.v. anaesthesia because of uncertainty over the concentration of propofol required to prevent awareness. We predicted blood and effect-site concentrations of propofol at two clinical end-points: loss of consciousness and no response to a painful stimulus. Forty unpremedicated Caucasian patients were anaesthetized with i.v. propofol delivered by a Diprifusor target-controlled infusion (TCI). Bispectral index (BIS) and auditory evoked potential index (AEPex) were measured and blood and effect-site propofol concentrations were predicted. Logistic regression was used to estimate population values for predicted blood and effect-site propofol concentrations at the clinical end-points and to correlate these with BIS and AEPex. The effect-site EC(50) at loss of consciousness was 2.8 micro m ml(-1) with an EC(05) and an EC(95) of 1.5 and 4.1 micro m ml(-1), respectively. The predicted EC(50) when there was no response to a tetanic stimulus was 5.2 micro m ml(-1) with an EC(05) and an EC(95) of 3.1 and 7.2 micro m ml(-1), respectively. Unconsciousness and lack of response to a painful stimulus occur within a defined range of effect-site concentrations, predicted by Diprifusor TCI software.

Comparison of Changes in Bispectral Index and Auditory Evoked Potential Index during Endotracheal Intubation

Background: Depth of anesthesia monitoring needs a consistent and reliable measure in close to real time. The aim of this study was to compare auditory evoked potential (AEP) as determined using the autoregressive model with exogenous input (ARX-mode1) versus the bispectral index (BIS) by conventional averaging. The hypothesis of the present study was that since the ARX-mode1 extracts AEP faster than BIS, the former should be able to detect changes during the brief, intense stimulus of endotracheal intubation. Methods: Forty ASA physical status I or II patients scheduled for orthopaedic surgery were randomly assigned to 2 groups (group 1; BIS and group 2; AEP). Anesthesia was induced with target-controlled infusions of propofol. After the effect-site concentration of propofol was reached at 4l/ml, vecuronium 0.1 mg/kg was administered. The trachea was intubated 3 min after the administration of vecuronium. AAI and BIS were compared during endotracheal intubation. Results: During endotracheal intubation, the ARX-extracted AEP Index showed a significant increase (P

Auditory Evoked Potential Index (AAI) and Bispectral IndexTM (BISTM) during Induction of Anesthesia with Propofol and Remifentanil

Auditory Evoked Potential Index (AAI) and Bispectral IndexTM (BISTM) during Induction of Anesthesia with Propofol and Remifentanil

Changes in the rapidly extracted auditory evoked potentials index and the bispectral index during sedation induced by propofol or midazolam under epidural block

The bispectral index (BIS) and the rapidly extracted auditory evoked potentials index (A-line ARX Index or AAI) have been proposed as methods to measure the depth of sedation. A prospective study was designed to assess the performance of both these methods for measuring the depth of sedation induced by propofol or midazolam under epidural block. Thirty-two ASA I and II adult patients undergoing elective gynaecological surgery under low-thoracolumbar epidural block were studied. Eighteen patients received propofol (Group P: 20 mg bolus every 3 min) and 14 received midazolam (Group M: 0.5 mg bolus every 5 min) until an observer's assessment of alertness/sedation (OAA/S) scale score of 1 was achieved. AAI and BIS were monitored for different OAA/S scores. AAI and BIS decreased and increased following the changes on the patients' OAA/S scores and correlated with sedation significantly. During the onset phase, the coefficients of Spearman's rank correlation for AAI and BIS were respectively 0.958 and 0.898 (P < 0.001) for Group P, and 0.973 and 0.945 (P < 0.001) for Group M. During the recovery phase in Group P, the coefficients were respectively 0.946 and 0.702 (P < 0.001). Linear regression analysis showed that both AAI and BIS were linearly related to the OAA/S scores. The coefficients of Spearman's rank correlation and linear regression for AAI were all greater than those for BIS (P < 0.05). Both AAI and BIS correlated well with the depth of sedation induced by propofol or midazolam under epidural block. AAI may be more valuable when monitoring depth of sedation.

Gateway Ballroom 102, 10/17/00 9: 00 AM-12: 30 PM (JS) Comparison of the BIS and the Auditory Evoked Potentials Index (AAI) during Propofol Anesthesia for Cardiac Surgery

<b>Gateway Ballroom 102, 10/17/00 9: 00 AM-12: 30 PM (JS) Comparison of the BIS and the Auditory Evoked Potentials Index (AAI) during Propofol Anesthesia for Cardiac Surgery</b>

The Performance of Electroencephalogram Bispectral Index and Auditory Evoked Potential Index to Predict Loss of Consciousness During Propofol Infusion

The bispectral index (BIS) of the electroencephalogram and middle latency auditory evoked potentials are likely candidates to measure the level of unconsciousness and, thus, may improve the early recovery profile. We prospectively investigated the predictive performance of both measures to distinguish between the conscious and unconscious state. Twelve patients undergoing lower limb orthopedic surgery during regional anesthesia additionally received propofol by target-controlled infusion for sedation. The electroencephalogram BIS and the auditory evoked potential index (AEPi), a mathematical derivative of the morphology of the auditory evoked potential waveform, were recorded simultaneously in all patients during repeated transitions from consciousness to unconsciousness. Logistic regression procedures, receiver operating characteristic analysis, and sensitivity and specificity were used to compare predictive ability of both indices. In the logistic regression models, both the BIS and AEPi were significant predictors of unconsciousness (P < 0.0001). The area under the receiver operating characteristic curve for discrete descending index threshold values was apparently, but not significantly (P > 0.05), larger for the AEPi (0.968) than for the BIS (0.922), indicating a trend of better discriminatory performance. We conclude that both the BIS and AEPi are reliable means for monitoring the level of unconsciousness during propofol infusion. However, AEPi proved to offer more discriminatory power in the individual patient. Both the bispectral index of the electroencephalogram and the auditory evoked potentials index are good predictors of the level of sedation and unconsciousness during propofol infusion. However, the auditory evoked potentials index offers better discriminatory power in describing the transition from the conscious to the unconscious state in the individual patient.

The Performance of Electroencephalogram Bispectral Index and Auditory Evoked Potential Index to Predict Loss of Consciousness During Propofol Infusion

The bispectral index (BIS) of the electroencephalogram and middle latency auditory evoked potentials are likely candidates to measure the level of unconsciousness and, thus, may improve the early recovery profile. We prospectively investigated the predictive performance of both measures to distinguish between the conscious and unconscious state. Twelve patients undergoing lower limb orthopedic surgery during regional anesthesia additionally received propofol by target-controlled infusion for sedation. The electroencephalogram BIS and the auditory evoked potential index (AEPi), a mathematical derivative of the morphology of the auditory evoked potential waveform, were recorded simultaneously in all patients during repeated transitions from consciousness to unconsciousness. Logistic regression procedures, receiver operating characteristic analysis, and sensitivity and specificity were used to compare predictive ability of both indices. In the logistic regression models, both the BIS and AEPi were significant predictors of unconsciousness (P < 0.0001). The area under the receiver operating characteristic curve for discrete descending index threshold values was apparently, but not significantly (P > 0.05), larger for the AEPi (0.968) than for the BIS (0.922), indicating a trend of better discriminatory performance. We conclude that both the BIS and AEPi are reliable means for monitoring the level of unconsciousness during propofol infusion. However, AEPi proved to offer more discriminatory power in the individual patient. Implications Both the bispectral index of the electroencephalogram and the auditory evoked potentials index are good predictors of the level of sedation and unconsciousness during propofol infusion. However, the auditory evoked potentials index offers better discriminatory power in describing the transition from the conscious to the unconscious state in the individual patient.

Prediction of movement at laryngeal mask airway insertion: comparison of auditory evoked potential index, bispectral index, spectral edge frequency and median frequency

We have studied 46 patients to compare the efficacy of the auditory evoked potential (AEP) index, bispectral index (BIS), 95% spectral edge frequency (SEF) and median frequency (MF) in predicting movement in response to insertion of the laryngeal mask airway (LMA). Anaesthesia was induced with target-controlled infusions of propofol and alfentanil. After loss of eyelash reflex and adequate jaw relaxation, the LMA was inserted without the assistance of a laryngoscope or neuromuscular blocker. Patients who showed any visible spontaneous muscle movement within 1 min of LMA insertion were defined as movers. Values in movers and non-movers at 30 s before LMA insertion were analysed. Only AEP index discriminated between movers and non-movers with a prediction probability of 0.872. BIS, SEF and MF could not predict movement at LMA insertion. AEP index was the most reliable predictor of movement in response to LMA insertion.

Analysis of the EEG bispectrum, auditory evoked potentials and the EEG power spectrum during repeated transitions from consciousness to unconsciousness

We have compared the auditory evoked potential (AEP) index (a numerical index derived from the AEP), 95% spectral edge frequency (SEF), median frequency (MF) and the bispectral index (BIS) during alternating periods of consciousness and unconsciousness produced by target-controlled infusions of propofol. We studied 12 patients undergoing hip or knee replacement under spinal anaesthesia. During periods of consciousness and unconsciousness, respective mean values for the four measurements were: AEP index, 60.8 (SD 13.7) and 37.6 (6.5); BIS, 85.1 (8.2) and 66.8 (10.5); SEF, 24.2 (2.2) and 18.7 (2.1); and MF, 10.9 (3.3) and 8.8 (2.0). Threshold values with a specificity of 100% for a state of unconsciousness were: AEP index, 37 (sensitivity 52%); BIS, 55 (sensitivity 15%); and SEF, 16.0 (sensitivity 9%). There was no recorded value for MF that was 100% specific for unconsciousness. Of the four measurements, only AEP index demonstrated a significant difference (P < 0.05) between all mean values 1 min before recovery of consciousness and all mean values 1 min after recovery of consciousness. Our findings suggest that of the four electrophysiological variables, AEP index was best at distinguishing the transition from unconsciousness to consciousness.