BIS-vista occipital montage in patients undergoing neurosurgical procedures during propofol-remifentanil anesthesia.

Background: Neurosurgical procedures that require a frontal approach could be an impediment for a successful Bispectral Index ® (BIS ® ) frontal sensor placement. The aim of this study was to explore the utility of using the new BIS-Vista™ monitor (Aspect Medical Systems, Newton, MA) for occipital sensor placement in the patients undergoing brain neurosurgical procedures during propofolremifentanil anesthesia. Methods: Two BIS ® Quatro sensors (Aspect Medical Systems, Newton, MA) mounted on the occipital and frontal regions were connected to two BIS-Vista™ monitors at three anesthesia states: before induction, during anesthesia maintenance, and recovery. Results: There were significant differences before induction (P = 0.0002) and at anesthesia maintenance (P = 0.0014) between mean ± SD occipital (83.4 ± 4.8, 66.7 ± 7.2) and frontal (93.1 ± 3.4, 56.9 ± 9.1) BIS-Vista™ values. During anesthesia recovery, there was no difference (P = 0.7421 ) between occipital (54.6 ± 9.3) and frontal (53.1 ± 7.3) BIS-Vista™ values. Bland and Altman analysis revealed a BIS-Vista negative-bias (limits of agreement) of -9.7 (+1.1, -20.5) before anesthesia induction, +9.8 positive-bias (+22.8, -1.7) during anesthesia maintenance, and -0.9 bias (+10.9, -12.8) during anesthesia recovery. Conclusion: We demonstrated that not only the regional limits of agreement are too wide to allow data of the two montages to be used interchangeably but also the variation is a function of anesthetic depth. However, keeping in mind a relatively consistent BIS-Vista™ -10 bias before induction and +10 bias during anesthesia maintenance with limits of agreement of approximately ±11 BIS units, approximately double the clinically acceptable less than 10 BIS units level of agreement, BIS-Vista™ off-label occipital montage might be helpful in following a trend of propofol-remifentanil anesthesia in individual cases where frontal access is particularly difficult.