Anesth Analg 2003;97:1206
© 2003 International Anesthesia Research Society
LETTERS TO THE EDITOR
BIS Monitoring Requires Proper Electrode Placement for Optimum Performance
Paul J. Manberg, PhD
Aspect Medical Systems, Inc., Newton, MA
To the Editor:
The recent study by Muncaster et al. (1) attempted to compare the performance of several electroencephalogram (EEG) measures during recovery from an opioid-based anesthetic. Unfortunately, this study used an obsolete monitor and Bispectral Index (BIS) version, and the improper electrode placement (Fp1-F7 and Fp2-F8) was not the montage utilized in previous BIS validation studies and, equally importantly, is not the montage specified by the manufacturer for derivation of the BIS calculation (2–4). Since artifact processing, feature estimation, and suppression detection methods are sensitive to electrode placement, different values may be obtained when incorrect electrode placements are used (5). In this case, the short interelectrode distance used by these investigators resulted in the very small amplitude signal resembling suppression observed in some patients. The misplacement of EEG electrodes for BIS calculation is akin to misplacing ECG electrodes for a device that estimates ST-elevation/depression within a specified ECG lead. To address this improper electrode placement issue, in 1998—5 full years ago—Aspect Medical Systems introduced specific BIS sensors to facilitate proper signal acquisition. The comparative results presented in this paper do not accurately reflect the performance of the current commercially available BIS products.
References
- Muncaster ARG, Sleigh JW, Williams M. Changes in consciousness, conceptual memory, and quantitative EEG measures during recovery from sevoflurane- and remifentanil-based anesthesia. Anesth Analg 2003; 96: 720–5.[Abstract/Free Full Text]
- Johansen JW, Sebel PS. Development and clinical application of electroencephalographic bispectrum monitoring. Anesthesiology 2000; 93: 1336–44.[Web of Science][Medline]
- Glass PS, Bloom M, Kearse L, et al. Bispectral analysis measures sedation and memory effects of propofol, midazolam, isoflurane, and alfentanil in healthy volunteers. Anesthesiology 1997; 86: 836–47.[Web of Science][Medline]
- Gan TJ, Glass PS, Windsor A, et al., and the BIS Utility Study Group. Bispectral index monitoring allows faster emergence and improved recovery from propofol, alfentanil, and nitrous oxide anesthesia. Anesthesiology 1997; 87: 808–15.[Web of Science][Medline]
- Hall JD, Lockwood GG. Bispectral Index: comparison of two montages. Br J Anaesth 1998; 80: 342–4.[Abstract/Free Full Text]
Response
Andrew Ronald Gordon Muncaster, MBChB,
James Wallace Sleigh, MD, and
Murray Williams, FANZCA
Waikato Clinical School, Waikato Hospital, Hamilton, New Zealand
In Response:
We thank Dr. Manberg for his interest in our paper. We agree that close placement of scalp EEG electrodes will tend to result in smaller observed voltages. We had used a bipolar montage because we were interested in interhemispheric EEG correlations. However (as we had already mentioned in the discussion in our article), we commonly see the same phenomenon when using the more modern Aspect A-2000 monitor; with the recommended placement of the commercially-available, disposal, EEG electrode strip. We conclude that the phenomenon is not purely the result of the montage, and that practicing anesthesiologists should be cognizant of potential inaccuracies when using the BIS to titrate remifentanil-based general anaesthesia.
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