EEG BISPECTRUM PREDICTS MOVEMENT DURING THIOPENTAL ISOFLURANE ANESTHESIA

Objective. The objective of our study was to test the efficacy of the bispectral index (BIS) compared with spectral edge frequency (SEF), relative delta power, median frequency, and a combined univariate power spectral derivative in predicting movement to incision during isoflurane/oxygen anesthesia. Methods, A total of 42 consenting patients were assigned to 3 groups, isoflurane 0.75, 1.0, and 1.25 minimal alveolar concentration (MAC). Anesthesia was induced with thiopental and maintained with the appropriate end-tidal concentration of isoflurane. The electroencephalogram (EEG) was recorded using a microcomputer system, and data were analyzed off-line. The EEG during the 2 min before incision was analyzed. Following skin incision, each patient was carefully observed for 60 sec to detect occurrence of purposeful movement. Results, For all groups combined, there was a statistically significant difference for BIS (p < 0.0001) and also for relative delta power (p < 0.016) between movers and nonmovers. There was a statistically significant difference between movers and nonmovers at 1.25 MAC isoflurane for BIS (p < 0.01). There were no other significant differences for any other EEG variable at any concentration of isoflurane. No EEG variable showed a relationship to isoflurane concentration. Conclusions, When bispectral analysis of the EEG was used to develop a retrospectively determined index, there was an association of the index with movement. Thus, it may be a useful predictor of whether patients will move in response to skin incision during anesthesia with isoflurane/oxygen.