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), re lative delta power, median frequency, and a combined univariate power spectral derivative in predicting movement to incision during isoflura ne/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 mainta ined with the appropriate end-tidal concentration of isoflurane. The e lectroencephalogram (EEG) was recorded using a microcomputer system, a nd data were analyzed off-line. The EEG during the 2 min before incisi on was analyzed. Following skin incision, each patient was carefully o bserved for 60 sec to detect occurrence of purposeful movement. Result s, For all groups combined, there was a statistically significant diff erence for BIS (p < 0.0001) and also for relative delta power (p < 0.0 16) between movers and nonmovers. There was a statistically significan t difference between movers and nonmovers at 1.25 MAC isoflurane for B IS (p < 0.01). There were no other significant differences for any oth er EEG variable at any concentration of isoflurane. No EEG variable sh owed a relationship to isoflurane concentration. Conclusions, When bis pectral analysis of the EEG was used to develop a retrospectively dete rmined index, there was an association of the index with movement. Thu s, it may be a useful predictor of whether patients will move in respo nse to skin incision during anesthesia with isoflurane/oxygen.