Auditory Evoked Potential Index Research Articles

Processed electroencephalogram and evoked potential techniques for amelioration of postoperative delirium and cognitive dysfunction following non-cardiac and non-neurosurgical procedures in adults.

Postoperative delirium (POD) and postoperative cognitive dysfunction (POCD) may complicate a patient's postoperative recovery in several ways. Monitoring of processed electroencephalogram (EEG) or evoked potential (EP) indices may prevent or minimize POD and POCD, probably through optimization of anaesthetic doses. To assess whether the use of processed EEG or auditory evoked potential (AEP) indices (bispectral index (BIS), narcotrend index, cerebral state index, state entropy and response entropy, patient state index, index of consciousness, A-line autoregressive index, and auditory evoked potentials (AEP index)) as guides to anaesthetic delivery can reduce the risk of POD and POCD in non-cardiac surgical or non-neurosurgical adult patients undergoing general anaesthesia compared with standard practice where only clinical signs are used. We searched CENTRAL, MEDLINE, Embase and clinical trial registry databases up to 28 March 2017. We updated this search in February 2018, but these results have not been incorporated in the review. We included randomized or quasi-randomized controlled trials comparing any method of processed EEG or evoked potential techniques (entropy, BIS, AEP etc.) against a control group where clinical signs were used to guide doses of anaesthetics in adults aged 18 years or over undergoing general anaesthesia for non-cardiac or non-neurosurgical elective operations. We used the standard methodological procedures expected by Cochrane. Our primary outcomes were: occurrence of POD; and occurrence of POCD. Secondary outcomes included: all-cause mortality; any postoperative complications; and postoperative length of stay. We used GRADE to assess the quality of evidence for each outcome. We included six randomized controlled trials (RCTs) with 2929 participants comparing processed EEG or EP indices-guided anaesthesia with clinical signs-guided anaesthesia. There are five ongoing studies and one study awaiting classification.Anaesthesia administration guided by the indices from a processed EEG (bispectral index) probably reduces the risk of POD within seven days after surgery with risk ratio (RR) of 0.71 (95% CI 0.59 to 0.85; number needed to treat for an additional beneficial outcome (NNTB) of 17, 95% CI 11 to 34; 2197 participants; 3 RCTs; moderate quality of evidence). Three trials also showed the lower rate of POCD at 12 weeks after surgery (RR 0.71, 95% CI 0.53 to 0.96; NNTB 38, 95% CI 21 to 289; 2051 participants; moderate-quality evidence), but it is uncertain whether processed EEG indices reduce POCD at one week (RR 0.84, 95% CI 0.69 to 1.02; 3 trials; 1989 participants; moderate-quality evidence), and at 52 weeks (RR 0.30, 95% CI 0.05 to 1.80; 1 trial; 59 participants; very low quality of evidence). There may be little or no effect on all-cause mortality (RR 1.01, 95% CI 0.62 to 1.64; 1 trial; 1155 participants; low-quality evidence). One trial suggested a lower risk of any postoperative complications with processed EEG (RR 0.51, 95% CI 0.37 to 0.71; 902 participants, moderate-quality evidence). There may be little or no effect on reduced postoperative length of stay (mean difference -0.2 days, 95% CI -2.02 to 1.62; 1155 participants; low-quality evidence). There is moderate-quality evidence that optimized anaesthesia guided by processed EEG indices could reduce the risk of postoperative delirium in patients aged 60 years or over undergoing non-cardiac surgical and non-neurosurgical procedures. We found moderate-quality evidence that postoperative cognitive dysfunction at three months could be reduced in these patients. The effect on POCD at one week and over one year after surgery is uncertain. There are no data available for patients under 60 years. Further blinded randomized controlled trials are needed to elucidate strategies for the amelioration of postoperative delirium and postoperative cognitive dysfunction, and their consequences such as dementia (including Alzheimer's disease (AD)) in both non-elderly (below 60 years) and elderly (60 years or over) adult patients. The one study awaiting classification and five ongoing studies may alter the conclusions of the review once assessed.

Intraoperative auditory evoked potential recordings are more reliable at signal detection from different sensor sites on the forehead compared to bispectral index.

Bispectral index (BIS) and auditory evoked potential (AEP) monitoring require the attachment of forehead sensors, posing difficulties when the surgical field involves the forehead. This study analyzed the relationship between BIS values and AEP indices from different sites on the head to establish alternative sensor locations for AEP recording. Thirty patients scheduled for elective surgery under sevoflurane anesthesia were randomly assigned to the forehead, nose or mandible groups (n=10 patients per group). AEP sensors were placed at the assigned position for each group and BIS sensors were placed on the forehead. BIS value and AEP index were simultaneously recorded from induction until emergence from general anesthesia. Relationships between BIS values and AEP indices were analyzed using a regression method and compared between groups using Pearson's correlation coefficients. Square regression models better expressed the relationships than linear models in all groups. The z-transformed coefficient in the forehead group was the same as the nose group (p=0.24) and significantly different in the mandible group (p=0.0046). These findings suggest that AEPs can be accurately recorded from sensors placed on the nose. Nasal AEP might be useful for monitoring electrical activity in the brain during surgeries involving the forehead.

Middle latency auditory-evoked potential index monitoring of cerebral function to predict functional outcome after emergency craniotomy in patients with brain damage.

BackgroundAt present, no satisfactory reports on the monitoring of cerebral function to predict functional outcomes after brain damage such as traumatic brain injury (TBI) and stroke. The middle latency auditory-evoked potential index (MLAEPi) monitor (aepEX plus®, Audiomex, UK) is a mobile MLAEP monitor measuring the degree of consciousness that is represented by numerical values. Hence, we hypothesized that MLAEPi predicts neurological outcome after emergency craniotomy among patients with disturbance of consciousness (DOC), which was caused by brain damage.MethodsThe afore-mentioned patients who underwent emergency craniotomy within 12 h of brain damage and were subsequently monitored using MLAEPi were enrolled in this study. DOC was defined as an initial Glasgow Coma Scale score < 8. MLAEPi was measured for 14 days after craniotomy. Neurological outcome was evaluated before discharge using a cerebral performance category (CPC) score and classified into three groups: favorable outcome group for a CPC score of 1 or 2, unfavorable outcome group for a score of 3 or 4, and brain dead (BD) group for a score of 5.ResultsThirty-two patients were included in this study (17 with TBIs and 15 with acute stroke). Regarding outcome, 10 patients had a favorable outcome, 15 had an unfavorable outcome, and 7 were pronounced BD. MLAEPi was observed to be significantly higher on day 5 than that observed immediately after craniotomy in cases of favorable or unfavorable outcome (63 ± 3.5 vs. 36 ± 2.5 in favorable outcome; 63 ± 3.5 vs. 34 ± 1.8 in unfavorable outcome). MLAEPi was significantly lower in BD patients than in those with a favorable or unfavorable outcome on day 3 (24 ± 4.2 in BD vs. 52 ± 5.2 and 45 ± 2.7 in favorable and unfavorable outcome, respectively) and after day 4. MLAEPi was significantly higher in patients with a favorable outcome than in those with a favorable or unfavorable outcome after day 6 (68 ± 2.3 in favorable outcome vs. 48 ± 2.3 in unfavorable outcome).ConclusionWe believe that MLAEPi satisfactorily denotes cerebral function and predicts outcomes after emergency craniotomy in patients with DOC, which was caused by acute brain damage.

Accuracy of different methods in monitoring depth of sedation induced by propofol: a comparison between BIS, NI, IoC and AAI

Objective To compare the accuracy of bispectral index(BIS), Narcotrend index(NI), index of consciousness(IoC)versus auditory evoked potential index(AAI)in monitoring the depth of sedation induced by propofol. Methods Sixty ASA physical status Ⅰ or Ⅱ patients of both sexes, aged 41-64 yr, with body mass index 20-30 kg/m2, scheduled for elective surgeries under general anesthesia, were enrolled in the study.Propofol was given by target-controlled infusion(TCI)with the initial target effect-site concentration(Ce)of 0.8 μg/ml using Marsh pharmacokinetic model, and then the Ce of propofol was increased by 0.1 μg/ml, and OAA/S was performed.Before TCI of propofol, the values of BIS, NI, IoC and AAI were recorded, and at the same time the value of OAA/S score was 5.During TCI of propofol, when OAA/S score reached 4, 3, 2 and 1 in turn, the Ce of propofol was recorded, the sequence for determination of the values of BIS, NI, IoC and AAI was determined using a random number table, and the values were then recorded for 5 s after the values were stable and then averaged.The parameters for vital signs were maintained within the normal range.Pearson correlation of BIS, NI, IoC and AAI values with Ce of propofol was analyzed. Results The correlation coefficients of BIS, NI, IoC and AAI values with the Ce of propofol were rBIS-Ce=-0.829, rNI-Ce=-0.886, rIoC-Ce=-0.881 and rAAI-Ce=-0.791, respectively.There was no significant difference between rBIS-Ce, rNI-Ce, rIoC-Ce and rAAI-Ce. Conclusion There are no significant differences in the accuracy of BIS, NI, IoC or AAI in monitoring the depth of sedation induced by propofol in middle-aged patients with non-noxious stimuli. Key words: Monitoring, physiologic; Electroencephalography; Evoked potentials, auditory; Conscious sedation; Propofol; Narcotrend; Index of consciousness

The Effect of Music on Preventing Intraoperative Awareness in Pediatric Patients Undergoing Open-Heart Surgery

AbstractUse of music has the potential to positively affect patient perception during of surgical treatment. Intraoperative awareness is the most frustrating complication in patient undergoing surgery under general anesthesia. Study Design was Quasi-experimental research design. Three tools were used to conduct this study namily: Preoperative assessment tool, intraoperative assessment tool and postoperative assessment tool. Method: In a prospective, randomized double blind study, patients were randomized into two equal groups; In C group (n = 25) patients acted as the control and did not listening to music, while in music group (n = 25) patients listening to music. In both groups, auditory evoked potentials index electrodes connected before induction of anesthesia at operative room to detect depth of anesthesia and occurrence of awareness. An interview with the patients and their parents to evaluate occurrence of awareness by using a semi-structured in-depth questionnaire. The main results: The results of the current study revealed that there was statistically significant decrease in occurrence of awareness in music group versus the control group (P value =0.000***). Conclusion: The application of music was highly effective in reducing awareness.

AAI-guided anaesthesia is associated with lower incidence of 24-h MMSE < 25 and may impact the IL-6 response

IntroductionTrauma stress and neuro-inflammation caused by surgery/anaesthesia releases cytokines. This study analysed impact of Auditory Evoked Potential Index (AAI) depth-of-anaesthesia titration on the early plasma IL-6 release after eye surgery under general anaesthesia. MethodThis is a subgroup analysis of a prospective randomized study on the effect of auditory evoked potential guided anaesthesia for eye surgery. Plasma IL-6 levels taken before, 5 and 24 h after end of surgery from 450 patients undergoing elective ophthalmic surgery under desflurane anaesthesia were analysed. Minimal mental state examination (MMSE) was also tested at 24-h. ResultsIL- 6 increased significantly at both 5 and further at 24 h after surgery (3.2, 4.5 and 5.1 base-line, 5 and 24-h respectively), the IL-6 increase showed different patterns between the 2 groups; IL-6 was significantly increased in the control group of patients between preoperative baseline and 24 h after surgery (p = 0.008) also between 5 h and 24 h, (p = 0.006) after surgery while the AAI-group had only minor non-significant changes. The 18 patients that showed a 24-h MMSE score less than 25 had a significant higher 24-h IL-6 compared to the 390 patients with a MMSE score > 24 (p = 0.002). ConclusionThe IL-6 increase after surgery was less pronounced in patients where anaesthesia was titrated by AAI compared to anaesthesia adjusted on clinical signs only. IL-6 were also found to be higher in patients with a MMSE < 25 at 24-h. Further studies are warranted evaluating the role of depth of anaesthesia monitoring on the risk for early cognitive impairment and neuro-inflammation. Trial registrationClinicaltrials.gov identifier: NA/study were conducted between January 2005–April 2008.

Monitoring sedation for bronchoscopy in mechanically ventilated patients by using the Ramsay sedation scale versus auditory-evoked potentials

BackgroundAppropriate sedation benefits patients by reducing the stress response, but it requires an appropriate method of assessment to adjust the dosage of sedatives. The aim of this study was to compare the difference in the sedation of mechanically ventilated patients undergoing flexible bronchoscopy (FB) monitored by auditory-evoked potentials (AEPs) or the Ramsay sedation scale (RSS).MethodsIn a prospective, randomized, controlled study, all patients who underwent FB with propofol sedation were monitored and their sedation adjusted. During FB, one group was monitored by AEP and another group was monitored by RSS. The propofol dosage was adjusted by the nursing staff during examination to maintain the Alaris AEP index (AAI) value between 25 and 40 in the AEP group and the RSS at 5 or 6 in the RSS group. Before FB and during FB, the AAI, heart rate (HR), and mean arterial pressure (MAP) were recorded every 5 min. The percentages of time at the sedation target and the propofol dosages were calculated.ResultsNineteen patients received AEP monitoring and 18 patients received RSS monitoring. The percentage of time at the sedation target during FB was significantly higher in the AEP monitoring group (51.3%; interquartile range [IQR], 47.0–63.5%) than in the RSS group (15.4%; IQR, 9.5–23.4%), (P < 0.001). During FB, the RSS group had a significantly higher AAI (P = 0.011), HR (P < 0.001), and MAP (P < 0.001) than the AEP group.ConclusionsIn mechanically ventilated patients undergoing FB, AEP monitoring resulted in less variation in AAI, HR, and MAP, and a higher percentage of time at the sedation target than RSS monitoring.Trial registrationClinicalTrials.gov NCT01448811.

Middle latency auditory-evoked potential index for predicting the degree of consciousness of comatose patients in EDs

IntroductionDigitized assessment of the degree of consciousness is a universal challenge in emergency departments (EDs) and intensive care units (ICUs). The middle latency auditory-evoked potential index (MLAEPi) monitor aepEX plus (Audiomex, Glasgow, Scotland, UK) is the first mobile middle latency auditory-evoked potential monitor. We speculated that the initial MLAEPi determined on arrival at EDs could indicate cerebral function and predict the degree of consciousness of comatose patients. MethodsWe used MLAEPi-related data from 50 comatose patients with disturbance of consciousness (DOC), 50 patients with cardiopulmonary arrest (CPA), and 50 healthy volunteers (control). Comatose patients were defined as those with an initial Glasgow Coma Scale score of 8 or less. The CPA group consisted of patients who arrived at EDs without restoration of spontaneous circulation. Among the patients with DOC who underwent sedation at EDs, the change in the MLAEPi was evaluated between arrival at the ED and ICU admission. ResultsThe initial MLAEPi was significantly lower in the DOC group than in the control group but significantly higher in the DOC group than in the CPA group. Among the comatose patients, the receiver operating characteristic curve for the initial MLAEPi showed an area under the curve of 0.93 (P < .01) for the DOC group. Thirty patients with DOC underwent sedation at EDs, and the initial MLAEPi was significantly higher than those at other periods during emergency care. ConclusionThe MLAEPi (simple numerical value) may be used to evaluate the degree of consciousness in comatose patients while performing emergency care in EDs.

Initial middle latency auditory evoked potentials index helps to predict resuscitated outcomes in patients with cardiac arrest

IntroductionWe speculated that initial middle latency auditory evoked potentials index (MLAEPi) can indicate cerebral function and predict the restoration of spontaneous circulation (ROSC), postresuscitation survival or of neurologic outcomes among patients with cardiac arrest. MethodsThis prospective study included 61 patients with cardiac arrest who received basic life support and did not achieve ROSC until arrival at the emergency center between September 2010 and September 2011. All patients were then administered advanced cardiac life support at the emergency department. Initial MLAEPi was immediately measured using an MLAEP monitor (aepEX plus; Audiomex, Glasgow, Scotland, UK) during the first cycle of advanced cardiac life support. Prediction of the ROSC, survival, and good outcome were investigated. ResultsSixteen patients achieved ROSC (ROSC group), and 45 did not achieve ROSC at the scene (non-ROSC group). The initial MLAEPi was significantly higher in the ROSC than in the non-ROSC group (33 vs 28, P < .01). Four survivors in the ROSC group were classified as good outcomes (Cerebral Performance Category 1 and 2). Initial MLAEPi in survivors were significantly higher than that in nonsurvivors (43 vs 29, P < .01). The receiver operating characteristic curves for the initial MLAEPi with area under the curves was 0.75 (95% confidence interval [CI], 0.62-0.88; P < .01) for ROSC, 0.94 (95% CI, 0.88-1.00; P < 0.01) for survival, and 0.96 (95% CI, 0.89-1.03; P < .01) for a good outcome, respectively. ConclusionsInitial MLAEPi represented by simple numerical values upon presentation at emergency facilities could predict ROSC, survival, and neurologic outcomes among patients with cardiac arrest.

Accuracy of auditory evoked potential index in monitoring depth of sevoflurane anesthesia in infants

Objective To evaluate the accuracy of auditory evoked potential index （AAI） in monitoring the depth of sevoflurane anesthesia in infants. Methods Fifty ASA Ⅰ or Ⅱ pediatric patients, aged 1-3 yr, scheduled for elective surgery under general anesthesia, were enrolled in this study. Anesthesia was induced with propofol, cisatracurium and remifentanil. The patients were tracheal intubated and mechanically ventilated. PET CO2 was maintained at 35-45 mm Hg. Anesthesia was maintained with inhalation of sevoflurane. Fresh gas flow was first set at 6 L/min for 15 min and then reduced to 3 L/min. The end-tidal sevoflurane concentration （CETSeV） was maintained at 2.5% , 2.8% , 3.0% , 3.5% , 3.7% and 4.0% . Each C_ET SeV was maintained for 3 min. AAI was continuously monitored before induction of anesthesia, after induction, immediately before sevoflurane in- halation, and at the 6 CET Sev. Results AAI was negatively correlated with CET Sev （ r = - 0. 872, P 〈 0.01 ） . Conclusion AAI can accurately reflect the depth of sevoflurane anesthesia in infants. Key words: Evoked potentials, auditory ; Monitoring, intraoperative ; Child ; Anesthetics, inhalation

Composite-, plain-auditory evoked potentials index and bispectral index to measure the effects of sevoflurane

The composite auditory evoked potentials index (cAAI) uses both cortical electroencephalogram (EEG) and response to auditory stimuli, while the bispectral index (BIS) uses only the cortical EEG and auditory evoked potentials index (AAI) uses only response to auditory stimuli. We expected that the cAAI was more useful to monitor anesthetic effect of sevoflurane than the BIS and AAI. The present study compared the changes of cAAI, AAI, and BIS in different sevoflurane concentration. Forty-five adult patients were anesthetized with sevoflurane in 50 % nitrous oxide. AAI (AEP version 1.4), cAAI (AEP version 1.6), and BIS (A-2000) were compared (each 15 patients in AAI, cAAI, and BIS groups) before induction, just before and after intubation, at 10 min since sevoflurane was set to 1.0, 1.5 and 2.0 %, and after extubation. All three indices decreased significantly before intubation. The cAAI was significantly higher than the AAI at sevoflurane 1.0 and 1.5 %. The AAI and BIS were significantly lower at sevoflurane 2.0 % than those at sevoflurane 1.0 %, but the cAAI did not. The cAAI had the largest and AAI had the smallest inter-individual variation. In sevoflurane-nitrous oxide anesthesia, cAAI was inferior to AAI and BIS to discriminate different anesthetic effect. The cAAI had larger inter-individual variation than the AAI and BIS.

Composite auditory evoked potentials index is not a good indicator of depth of anesthesia in propofol-fentanyl anesthesia: Randomized comparative study

Background:The composite auditory evoked potentials index (cAAI) was considered a measure of overall balance between noxious stimulation, analgesia, and hypnosis; while bispectral index (BIS) shows only hypnosis, and auditory evoked potentials index (AAI) shows response to stimuli. The present study compared the performance of cAAI, BIS, and AAI in propofol-fentanyl anesthesia.Materials and Methods:Forty-five patients for abdominal surgery aged 30-65 years with ASA physical status I or II were randomly divided into three groups by an envelope method. Anesthesia was induced with midazolam, propofol, and fentanyl alongwith an epidural block. When hemodynamics were stable during surgery, propofol infusion rate was fixed at 4 mg/kg/h for 10 min, then increased to 6 mg/kg/h and kept it for 10 min. AAI (AEP version 1.4), cAAI (AEP version 1.6), or BIS (A-2000) was monitored in each 15 patients, and the performance of three indices was compared.Results:All three indices decreased significantly before intubation. Only the AAI increased significantly by intubation. During anesthesia except for at propofol 6 mg/kg/h, the cAAI was significantly higher than the AAI. Only the AAI was significantly lower at propofol 6 mg/kg/h than at 4 mg/kg/h. The cAAI had the largest and AAI had the smallest inter-individual variations. The cAAI was higher than the manufacturer's recommended range of general anesthesia.Conclusion:In propofol-fentanyl anesthesia, AAI might be better to discriminate anesthetic depth than cAAI and BIS.

Comparison of Sevoflurane versus Propofol under Auditory Evoked Potential Monitoring in Female Patients Undergoing Breast Surgery

General anesthesia is used for most major surgeries, and the most common side effects include headache, nausea, vomiting, and sore throat. Major breast surgery is associated with a high incidence of postoperative nausea and vomiting (PONV). We compared the postoperative nausea and vomiting of propofol-based total intravenous anesthesia (TIVA) and sevoflurane (SEVO) anesthesia under auditory evoked potential (AEP) monitoring in female patients undergoing breast surgery. A total of 84 patients scheduled to undergo elective breast surgery from 1 to 4 h in duration from March 2011 to December 2011 were prospectively included in the study. All participants were randomly assigned to TIVA or SEVO group. The AEP index was maintained at 15-25. After completing the surgery, the duration of surgery, emergence time, and the side effects of PONV were recorded. Patient characteristics, intraoperative and postoperative data, and the amounts of intraoperative analgesic drugs used were not significantly different between the TIVA and SEVO groups. The incidence of PONV was significantly higher in the SEVO group than in the TIVA group (50% and 14.3%, respectively; p < 0.001), and the total cost was significantly lower in the TIVA group than in the SEVO group (648 ± 185 and 850 ± 197, respectively). We observed that when compared with sevoflurane, propofol given for the maintenance of general anesthesia improves the postoperative patient well-being and reduces the incidence of PONV. Furthermore, total intravenous anesthesia with propofol resulted in significant cost reductions.

The sedative effect of dexmedetomidine and the hemodynamic influence of dexmedetomidine on tracheal intubation

Objective To study the influence of dexmedetomidine (Dex) on auditory evoked potential index (AAI) and its hemodynamic influence as tracheal intubation. Methods 60 patients were randomized divided into dexmedetomidine group (D group) or control group(C group).Patients were intravenously pumped into Dex 1 μg/kg with in 20 min in D group,the same volume placebo was administered in C group.Tracheal intubation was done 2 min after medication.Systolic blood pressure (SBP),mean arterial pressure(MAP),diastolic blood pressure(DBP),heart rates(HR),pulse oxygen saturation(SpO2) and AAI were recorded at the following time points (before medication,before induction,before intubation,the time after intubation,3 min after intubation,5 min after intubation and 10 min after intubation). Results Before medication,the general conditions have no difference in two groups.The values of AAI before medication and before induction were (62±5) and (35±6)(P＜0.05) respectively,decreased by 53％,and there were no difference in C group.The SBP,MAP,DBP and HR at the time after intubation in D group were (112±18),(90±19),(80±19) mm Hg(1 mmHg=0.133 kPa) and (81±14) beat/min respectively,while in C group were (140±21),(109±16),(97±17) mm Hg,(95±10) beat/min respectively,there were significant difference between the two groups(P＜0.05). Conclusions Dex has good sedative effects before surgery,and it can also depress the stress responses of tracheal intubation effectively. Key words: Dexmedetomidine; Tracheal intubation; Hemodynamics; Auditory evoked potential index

Auditory evoked potential index does not correlate with observer assessment of alertness and sedation score during 0.5% bupivacaine spinal anesthesia with nitrous oxide sedation alone

The aim of this study was to evaluate the auditory evoked potential (AEP) index as a hypnosis monitor during nitrous oxide (N(2)O) sedation added to spinal analgesia. Forty-five patients scheduled to undergo surgery under spinal anesthesia were recruited after giving informed consent. Adequate anesthesia levels were confirmed, and a disposable AEP index sensor (aepEX, Medical Device Management) was placed. A tight facemask was fitted, and a fresh gas flow of 100% oxygen 10L/min was provided. AEP index monitoring was then initiated, and measurements and observer assessment of alertness/sedation (OAA/S) scores were recorded manually. N(2)O was administered in stepwise increases in the end-tidal concentration of 33%, 50%, and 67%. Paired AEP index and OAA/S scores were obtained immediately before each change in N(2)O concentration. Sixteen patients were excluded from final analysis because of nausea, vomiting, or abnormal excitatory behaviors. The increases in N(2)O concentration induced significant decreases in OAA/S scores and no substantial AEP index changes. Although OAA/S scores of 1 and 2 were observed in only two and five patients, respectively, a reduction in the OAA/S score from 5 to 1 was associated with a significant decrease in AEP index to the level indicative of moderate sedation. The AEP index might not be a suitable indicator of light hypnosis as defined by an OAA/S score of ≥3 during sedation with N(2)O alone.

AepEX monitor for the measurement of hypnotic depth in patients undergoing balanced xenon anaesthesia

Previously, we showed a significant difference in the measurements of hypnotic depth by the bispectral index (BIS) and auditory-evoked potentials (AEPs) using the A-line autoregressive index during xenon anaesthesia. In the present study, we evaluate the alternative AEP-based auditory-evoked potential index (aepEX) for the measurement of hypnotic depth in patients undergoing general anaesthesia with xenon. Forty-two patients undergoing elective abdominal surgery were enrolled in this controlled, double-blinded, randomized, clinical study. Patients were randomized to receive either xenon (n=21) or sevoflurane anaesthesia (n=21). During anaesthesia, BIS values were recorded simultaneously with the aepEX monitoring. The anaesthetist performing the anaesthesia was blinded to the hypnotic depth monitors. After surgery, the incidence of recalls and awareness was evaluated. Patients' characteristics such as gender, age, and weight did not differ between the groups. The aepEX and BIS values behaved similarly during anaesthesia. The comparison of aepEX values during xenon and sevoflurane anaesthesia revealed significantly lower aepEX values in the xenon group after 25 min [xenon: 32.9 (4.8) vs sevoflurane: 39.3 (9.0); P=0.008] and after 35 min [xenon: 31.4 (6.6) vs sevoflurane: 37.0 (6.8); P=0.012]. During anaesthesia, aepEX values correlated with the clinical evaluation of depth of anaesthesia (e.g. >20% changes of the baseline arterial pressure or heart rate, spontaneous breathing and/or intolerance of mechanical ventilation, coughing, abdominal pressing, sweating, eye tearing). We found the aepEX monitor to provide index in the range of adequate depth of xenon anaesthesia, when combined with remifentanil infusion in intubated patients undergoing elective abdominal surgery.

Comparison of auditory evoked potential index and clinical signs as indicator for laryngeal mask airway insertion

Objective Auditory evoked potential (AEP) index is one of the several physiological parameters for assessing the depth of anesthesia. The purpose of this study was to investigate whether the AEP monitoring could provide a better information for assessment of anesthesia level in classic laryngeal mask airway (C-LMA) insertion than the use of clinical signs in general anesthesia with single standard dose of intravenous propofol and fentanyl. Methods One hundred and seventy adult patients requiring general anesthesia for minor surgery were recruited and randomized to receive AEP monitoring (group A) or judgment of clinical signs (group B) for assessment of anesthesia depth and optimal condition to insert the C-LMA. The insertion conditions, including jaw relaxation, movements, presence of airway trauma and airway reflex, successful insertion rate and induction time were recorded and compared. Results The two groups were demographically similar. In group A, baseline heart rate was slower than group B (74 ± 14 vs. 78 ± 14 beats/min, p = 0.0267) and persisted throughout the whole study period. There was no significant difference in the change of heart rate during induction of general anesthesia between both groups. The incidence of movement was reduced in group A patients with AEP monitoring in comparison with group B patients (2.4% vs. 28.2%, p < 0.0001); of the unwanted events, swallowing was 0% versus 7.1%, p = 0.0126; laryngospasm was 0% versus 4.7%, p = 0.0430 and emergence of airway reflex was 1.2% versus 11.8%, p = 0.0050; the successful insertion rate was 100% versus 94.1%, p = 0.0232; and jaw relaxation was 83.5% versus 70.6%, p = 0.0448. There were no differences between both groups in trauma and induction time. Conclusion This study demonstrated that AEP index provided better information for C-LMA insertion with higher successful rate, less emergence of airway reflex and lower incidence of movement during induction of general anesthesia with single dose of intravenous propofol and fentanyl.

Effect of Auditory Evoked Potential-Guided Anaesthesia on Consumption of Anaesthetics and Early Postoperative Cognitive Dysfunction: a randomised controlled trial

Post-operative cognitive dysfunction (POCD) after non-cardiac surgery is a well known problem in some categories of patients. This study aims to evaluate the influence of auditory evoked potential (AEP)-guided anaesthesia on the requirement for anaesthetic drugs and their influence on POCD. Four hundred and fifty patients aged between 18 and 92 years scheduled for ophthalmic surgery under general anaesthesia were assigned randomly to one of two groups. In group A (AEP group), the depth of anaesthesia (DoA) was aimed at an AEP index (AAI) between 15 and 25. In group C (control group), DoA was guided by clinical signs. Hypotension was treated with fluids and vasopressors using a standardised algorithm. A mini-mental test and the Cognitive Failure Questionnaire were used to evaluate cognitive function. Anaesthetic drug requirements were significantly lower in group A than in group C: propofol 92.5 ± 26.5 vs. 103.8 ± 39.5 mg (P = <0.001) and desflurane end-tidal concentration 2.5 ± 0.58 vs. 3.3 ± 0.79% (P < 0.001). In group A, 36 patients (16%) received additional fluids and vasopressors compared to 65 patients (29%) in group C (P < 0.01). AAI values differed significantly between the groups: 18 (11-21) in group A vs. 12 (10-19) in group C (P < 0.001). The number of patients with POCD was 16 in group C compared to two in group A (P < 0.001) at day 1 post-operation. AEP monitoring allows dose reduction of anaesthetic agents, leading to better cardiovascular stability and decreased requirements for intra-operative fluids and vasopressors. Cognitive decline seen following minor ophthalmic surgery, even when anaesthesia is assessed clinically, is short-lived with no long-term sequelae.

Changes in auditory evoked potential index and bispectral index produced by treatment of hypotension with ephedrine or phenylephrine during induction of general anesthesia

Objective To investigate the changes in auditory evoked potential index(AAI)value and bispectral index(BIS)value produced by treatment of hypotension with ephedrine or phenylephrine during induction of general anesthesia.Methods Seventy-five ASA Ⅰ or Ⅱ patients of both sexes aged 30-50 yr with body mass index ＜ 30 kg/m2 underwent elective abdominal surgery under general anesthesia.Anesthesia was induced with 8%sevoflurane,midazolam 0.1 mg/kg and fentanyl 3 μg/kg.Tracheal intubation was facilitated with succinylcholine 2 mg/kg.Anesthesia was maintained with sevoflurane inhalation.BIS value was maintained at 40-50 and AAI value at 20-30 by adjusting the concentration of sevoflurane.When the desired level of BIS value and AAI value was reached during induction of anesthesia,hypotension(MAP ＜ 80 % of the baseline)was treated with intravenous ephedrine 0.1 mg/kg(group E,n = 25)or phenylephrine 2 mg/kg(group P,n = 25)or 6% HES(130/0.4)10 ml/kg(group C,n = 25)at random.MAP,HR,BIS value and AAI value value were recorded before(T0)and at 2,5,7,10 min after fluid or vasoactive agent administration(T1-4).Results MAP significantly increased after treatment at T1-4 as compared with MAP at To in all 3 groups.BIS and AAI values were significantly increased after administration of ephedrine at T3,4 as compared with MAP at To in group E.There were no significant differences in BIS and AAI values before and after administration of phenylephrine and 6% HES in group P and C.Con-clusion Treatment of hypotension with ephedrine during induction of general anesthesia can increase BIS and AAI and decrease the depth of anesthesia but phenylephrine cannot. Key words: Ephedrine; Deoxyepinephrine; Electroencephalography; Evoked potentials,auditory; Anesthesia,general

Continuous auditory evoked potential index (AEPI) monitoring during cardiopulmonary arrest patients’ resuscitation in an emergency department

Continuous auditory evoked potential index (AEPI) monitoring during cardiopulmonary arrest patients’ resuscitation in an emergency department