PREDICTION OF MOVEMENT USING BISPECTRAL ELECTROENCEPHALOGRAPHIC ANALYSIS DURING PROPOFOL ALFENTANIL OR ISOFLURANE ALFENTANIL ANESTHESIA

Conventional electroencephalographic (EEG) analysis techniques do not use the phase information from the Fourier analysis. This study used a new technique of EEG analysis, bispectral analysis, which measures in terfrequency phase relationships in the EEG. Using a reference databas e, and a process of multivariate discriminant analysis, we developed a univariate bispectral variable, the bispectral index (BIS). This stud y was designed to test the efficacy of BIS in predicting movement to i ncision during either an isoflurane/alfentanil anesthetic or a propofo l/alfentanil anesthetic technique. Fifty consenting patients were rand omized to two groups; one received isoflurane/alfentanil and the other , propofol/alfentanil for anesthesia. EEG was recorded using a microco mputer system and the data were analyzed off-line. Hemodynamic variabl es were also recorded. After skin incision, each patient was observed carefully for 2 min to detect purposeful movement. A significant diffe rence was found between the BIS values for movers versus nonmovers wit hin each of the two treatment groups (P less than or equal to 0.002). However, isoflurane/alfentanil nonmovers could not be distinguished fr om propofol/alfentanil movers (P less than or equal to 0.180), suggest ing a treatment group effect independent of response classification. P reincision hemodynamic variables did not predict patient movement in r esponse to skin incision. These findings suggest the possibility that different anesthetics have different effects on BIS, and thus BIS may not be independent of the anesthetic. Interfrequency phase coupling, a nonlinear feature of the EEG which is measured with bispectral analys is, may contain clinically useful information for the assessment of an esthetic adequacy. In this study, BIS was a better predictor of patien t response than other currently available variables including hemodyna mic status.