BISPECTRAL ANALYSIS OF THE ELECTROENCEPHALOGRAM CORRELATES WITH PATIENT MOVEMENT TO SKIN INCISION DURING PROPOFOL NITROUS-OXIDE ANESTHESIA

Background: Bispectral analysis is a signal-processing technique that determines the harmonic and phase relations among the various frequenc ies in the electroencephalogram. Our purpose was to compare the accura cy of a bispectral descriptor, the bispectral index, with that of thre e power spectral variables (95% spectral edge, median frequency, and r elative delta power) in predicting patient movement in response to ski n incision during propofol-nitrous oxide anesthesia. Methods: Forty-fo ur adult patients scheduled for elective noncranial surgery were studi ed. Gold cup electroencephalographic electrodes were placed on each pa tient in a frontoparietal montage (F-p1, F-p2, P-3, and P-4) referred to C-2, and the electroencephalogram was recorded continuously and pro cessed off-line. Conventional frequency bands were used to describe po wer spectrum variables. Anesthesia was induced with propofol (1.5-3.0 mg(-1).kg(-1)) and maintained with 60% nitrous oxide in oxygen and wit h propofol at one of three randomized infusion rates (100, 200, or 300 mu g.kg(-1).min(-1)). Inadequate anesthetic depth was defined as pati ent movement in response to a 2-cm skin incision at the planned site o f surgery. Plasma propofol concentrations were measured within 2 min a fter skin incision. Results: Complete data were available for 38 patie nts, of whom 17 moved in response to skin incision. Analysis of the ar ea under the receiver operating characteristic curves showed that only for bispectral index and drug dose group was there a significant pred ictive relation (area > 0.5). Furthermore, the bispectrum was signific antly predictive even after stratification by dose group. Conclusions: The bispectral index of the electroencephalogram is a more accurate p redictor of patient movement in response to skin incision during propo fol-nitrous oxide anesthesia than are standard power spectrum paramete rs or plasma propofol concentrations.