BIS-Vista™ Occipital Montage in Patients Undergoing Neurosurgical Procedures during Propofol–Remifentanil Anesthesia

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Abstract
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 propofol-remifentanil 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.