Journal of Anaesthesiology Clinical Pharmacology

ORIGINAL ARTICLE
Year
: 2013  |  Volume : 29  |  Issue : 3  |  Page : 333--336

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


Tomoki Nishiyama 
 Department of Anesthesiology and Critical Care, New Tokyo Hospital, Wanagaya, Matsudo, Chiba, Japan

Correspondence Address:
Tomoki Nishiyama
Kishi-cho, Urawa-ku, Saitama, 330-0064
Japan

Abstract

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«SQ»s recommended range of general anesthesia. Conclusion: In propofol-fentanyl anesthesia, AAI might be better to discriminate anesthetic depth than cAAI and BIS.



How to cite this article:
Nishiyama T. Composite auditory evoked potentials index is not a good indicator of depth of anesthesia in propofol-fentanyl anesthesia: Randomized comparative study.J Anaesthesiol Clin Pharmacol 2013;29:333-336


How to cite this URL:
Nishiyama T. Composite auditory evoked potentials index is not a good indicator of depth of anesthesia in propofol-fentanyl anesthesia: Randomized comparative study. J Anaesthesiol Clin Pharmacol [serial online] 2013 [cited 2019 Sep 16 ];29:333-336
Available from: http://www.joacp.org/text.asp?2013/29/3/333/117087


Full Text

 Introduction



During anesthesia, electroencephalographic (EEG) index is now one of the routine monitoring. Mainly, there are two kinds of EEG indices available in anesthesia, one uses cortical EEG such as bispectral index (BIS), and another uses subcortical EEG response to stimuli, in which only the auditory evoked potentials (AEP) index (AAI) is available. The BIS and AAI measure different aspects of brain activity. BIS measures hypnotic component of anesthesia, while AAI shows the information of both analgesia and hypnosis. [1] Recently, a new index has been developed, a composite AAI (cAAI), which uses both cortical EEG and AEP. In the cAAI, active measurement is based on the AEP, and passive measurement during deep anesthesia is based on spontaneous EEG. In case of low AEP signal quality, cAAI is calculated from the spontaneous EEG activity. This prevents mis-interpreting low cAAI values. [2] The cAAI is considered to be a measure of total balance between analgesia and hypnosis. [3] Therefore, cAAI might be better than BIS and AAI as a monitor of anesthetic depth. The present study compared the performance of cAAI, BIS, and AAI in propofol-fentanyl anesthesia with an epidural block.

 Materials and Methods



Ethical approval for this randomized controlled non-blind study (No. 1573) was provided by the Institutional Ethical Committee. After informed consent from patients, 45 patients for abdominal surgery aged 30-65 years were equally allocated to one of the three groups (AAI, cAAI, or BIS group) randomly by an envelope method. Those who had neurological disorders, hearing disturbance, liver or renal disease, mental impairment, alcohol abuse, or taking any drugs affecting cerebral function such as hypnotics, antidepressants, etc., before surgery were excluded.

As a premedication, midazolam 0.05 mg/kg was intramuscularly administered 30 min before entering the operation room as a routine practice. An epidural catheter was inserted in an appropriate interspinal space. Besides usual noninvasive blood pressure, heart rate, and percutaneous oxygen saturation; AAI (AEP version 1.4, Danmeter, Odense, Denmark), cAAI (AEP version 1.6, Danmeter, Odense, Denmark), or BIS (A-2000, Aspect Medical Systems, Newton, MA, USA) was monitored (15 patients each). Anesthesia was induced with midazolam 0.05 mg/kg, propofol 2 mg/kg, and fentanyl 4-5 μg/kg; and endotracheal intubation was facilitated with vecuronium 0.15 mg/kg. Anesthesia was maintained with propofol infusion, fentanyl, and intermittent epidural administration of 1.5% mepivacaine 4-6 mL. 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 for 10 min. During this period, epidural mepivacaine was not administered. The AAI, cAAI, and BIS as well as blood pressure and heart rate were compared before induction, just before and after intubation, 10 min after fixed propofol infusion rate at 4 and 6 mg/kg/h, and just after extubation.

Power analysis was performed to detect power of 0.95 for the indices analyzed by repeatedly measuring analysis of variance (ANOVA) using the G Power TM (ver. 3.03, University Mannheim, Germany), and showed that a total of 36 patients were necessary. Therefore, 15 patients in each group were enrolled considering some patients with protocol failure. Statistical analysis was performed with factorial ANOVA and chi-square test for demographic data; and factorial and repeated measures ANOVA for blood pressure, heart rate, and electroencephalographic indices. A P-value less than 0.05 were considered to be statistically significant.

 Results



Demographic data were not different among the three groups [Table 1]. Blood pressure and heart rate significantly decreased by anesthesia induction, returned to the baseline (before surgery) after intubation, decreased at propofol 4 and 6 mg/kg/h, and increased after extubation. However, no significant differences were observed among the three groups (data is not shown).{Table 1}

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 showed significantly higher values than the AAI. The AAI at propofol 6 mg/kg/h was significantly lower than that at 4 mg/kg/h, while the cAAI and BIS were not different. The cAAI had the largest and AAI had the smallest interindividual variations [Figure 1]. The cAAI was higher than the manufacturer's recommended range of general anesthesia.{Figure 1}

 Discussion



The present study compared the performance of AAI, cAAI, and BIS in propofol-fentanyl anesthesia with an epidural block. The AAI had the smallest inter-individual variation, and only the AAI increased by intubation and was significantly different between different propofol infusion rates. The cAAI had the largest inter-individual variation without any difference between different propofol infusion rates.

To compare different indices, it is better to measure all in the same patient simultaneously. However, it is impossible to measure cAAI and AAI simultaneously in the same patient, and we already showed that the click sound of the AEP affects the BIS, [4] therefore we used only one monitor in one patient. All indices are simple numbers, therefore, it might not have introduced any bias. In addition, it would be better to include only one type of surgery with the same site of epidural catheter insertion to avoid the effects of surgical stimuli and epidural anesthesia. We included two types of surgery and different epidural catheter insertion sites. However, there were no differences among the groups in the type of surgery, site of epidural catheter insertion, blood pressure, and heart rate. Therefore, three groups were comparable.

We kept propofol infusion rate for 10 min before measurements. We could not find any studies describing how long it takes to stabilize anesthetic condition if we change the infusion rate. However, in 10 min all indices became constant, which suggested that three indices might be comparable.

The cAAI greater than 50-60 indicated fully awake or under minimal sedation, 40-50 or 60 were suggestive of moderate sedation, 30-40 were associated with moderate to deep sedation, and less than 30 showed deep sedation like general anesthesia in the studies by Huang et al., [5] and by Lu et al. [6]

However, present study showed that cAAI was between 20 and 80 when patients were fully anesthetized with propofol and fentanyl. Our study was performed during surgery in general anesthesia with an epidural block, while the study by Huang et al., [5] was in sedation during endoscopy and that by Lu et al., [6] was in sedation and an epidural block in intensive care unit. Epidural lidocaine produced a reduction of cAAI. [7] Therefore, cAAI in the study by Lu et al., [6] and ours should be lower than that in the study by Huang et al., [5] at similar hypnotic level. However, the cAAI in our study showed higher values than the other two studies. [5],[6] The reason of this discrepancy was not known. In our previous study, [8] manufacturer's recommended range of general anesthesia fitted better with the AAI than with the BIS. [8] The present study showed both BIS and AAI fitted well, but cAAI did not fit at all.

The AEP measures output of the central nervous system to a controlled input. AEP provides information about the function of the brainstem and subcortical and cortical components, showing the overall anesthetic state. [9] Because BIS measures cortical function, it is only able to monitor hypnotic state and is a poor indicator of the sensitiveness to pain. [10] Therefore, the AAI and not the BIS increased by intubation in the present study as in our previous studies. [8],[11] The cAAI uses AEP as a base measurement and add cortical EEG in deep hypnosis, which seems better than the AAI or BIS. The cAAI had a better correlation with calculated propofol effect site concentration than AAI in the previous study. [12] However, our present study showed that the AAI and neither cAAI nor BIS was significantly different between different propofol infusion rates.

During induction of anesthesia by propofol-remifentanil, BIS performed better than cAAI, but cAAI was statistically a better discriminator of the consciousness during the wake-up test and emergence, although these differences did not appear to be clinically meaningful. [13] Rehberg et al., [14] reported that lightening of anesthesia before recovery could be noticed earlier with BIS than cAAI, although consciousness was detected with a significantly higher pK values by cAAI. These results suggest that in light hypnosis, cAAI is better than BIS probably due to the factor of AEP. The AAI followed rapid changes from awake to sleep, [15] and showed no overlap between awake and asleep values. [16]

The variability of cAAI was higher than the BIS in comparison with the difference between median index values during anesthesia and the threshold recommended by the manufacturer. [14] The cAAI was higher and had larger inter-individual variation than AAI and BIS during propofol-fentanyl anesthesia, especially in deep anesthesia in the present study. Hadzidiakos et al., [17] showed that the EEG components of cAAI may obscure slight changes in consciousness at light sedation level. Therefore, adding cortical EEG might obscure the fine changes of AAI.

In conclusion, in propofol-fentanyl anesthesia with an epidural block, AAI might be better to discriminate anesthetic depth than cAAI and the BIS.

References

1Musialowicz T, Niskanen M, Ypparila-Woltres H, Poyhonen M, Pitkanen O, Hynynen M. Auditory-evoked potentials in bispectral index-guided anesthesia for cardiac surgery. Eur J Anaesthesiol 2007;24:571-9.
2Weber F, Zimmermann M, Bein T. The impact of acoustic stimulation on the AEP monitor/2 derived composite auditory evoked potential index under awake and anesthetized conditions. Anesth Analg 2005;101:435-9.
3Gajraj RJ, Doi M, Mantzaridis H, Kenny GN. Comparison of bispectral EEG analysis and auditory evoked potentials for monitoring depth of anesthesia during propofol anesthesia. Br J Anaesth 1999;82:672-8.
4Nishiyama T. The effects of auditory evoked potential click sounds on bispectral index and entropy. Anesth Analg 2008;107:545-8.
5Huang YY, Chu YC, Chang KY, Wang YC, Chan KH, Tsou MY. Performance of AEP Monitor/2-derived composite index as an indicator for depth of sedation with midazolam and alfentanil during gastrointestinal endoscopy. Eur J Anaesthesiol 2007;24:252-7.
6Lu CH, Ou-Yang HY, Man KM, Hsiao PC, Ho ST, Wong CS, et al. Relative reliability of the auditory evoked potential and bispectral index for monitoring sedation level in surgical intensive care patients. Anaesth Intensive Care 2008;36:553-9.
7Lu CH, Chen JL, Wu CT, Liaw WJ, Yeh CC, Cherng CH, et al. Effect of epidural neuraxial blockade-dependent sedation on the Ramsay sedation scale and the composite auditory evoked potentials index in surgical intensive care patients. J Formos Med Assoc 2010;109:589-95.
8Nishiyama T, Matsukawa T, Hanaoka K. A comparison of the clinical usefulness of three different electroencephalogram monitors: Bispectral index, processed electroencephalogram, and Alaris auditory evoked potentials. Anesth Analg 2004;98:1341-5.
9Bonhomme V, Llabres V, Dewandre PY, Brichant JF, Hans P. Combined use of bispectral index and A-line autoregressive index to assess anti-nociceptive component of balanced anesthesia during lumbar arthrodesis. Br J Anaesth 2006;93:353-60.
10Mi WD, Sakai T, Takahashi S, Matsuki A. Haemodynamic and electroencephalograph responses to intubation during induction with propofol and propofol/fentanyl. Can J Anaesth 1998;45:19-22.
11Nishiyama T, Hanaoka K. The A-line ARX index may be a more sensitive detector of arousal than the bispectral index during propofol-fentanyl-nitrous oxide anesthesia: A preliminary investigation. Can J Anesth 2004;51:539-44.
12Vereecke HE, Vasquez PM, Jensen EW, Thas O, Vandenbroecke R, Mortier EP, et al. New composite index based on midlatency auditory evoked potential and electroencephalographic parameters to optimize correlation with propofol effect site concentration: Comparison with bispectral index and solitary used fast extracting auditory evoked potential index. Anesthesiology 2005;103:500-7.
13Blussé van Oud-Alblas HJ, Peters JW, de Leeuw TG, Vermeylen KT, de Klerk LW, Tibboel D, et al. A comparison in adolescents of composite auditory evoked potential index and bispectral index during propofol-remifentanil anesthesia for scoliosis surgery with intraoperative wake-up test. Anesth Analg 2008;107:1683-8.
14Rehberg B, Ryll C, Hadzidiakos D, Dincklage FV, Baars JH. Variability comparison of the composite auditory evoked potential index and the bispectrtal index during propofol-fentanyl anesthesia. Anesth Analg 2008;107:117-24.
15Jones JG. Awareness under anesthesia. Anaesth Rounds 1988;21:1-28.
16Litvan H, Jensen EW, Revuelta M, Henneberg SW, Paniagua P, Campos JM, et al. Comparison of auditory evoked potentials and the A-line ARX index for monitoring the hypnotic level during sevoflurane and propofol induction. Acta Anaesthesiol Scand 2002;46:245-51.
17Hadzidiakos D, Petersen S, Baars J, Herold K, Rehberg B. Comparison of a new composite index based on midlatency auditory evoked potentials and electroencephalographic parameters with bispectral index (BIS) during moderate propofol sedation. Eur J Anaesthesiol 2006;23:931-6.