Abnormally low bispectral index and isoelectric electroencephalogram observed after administration of small doses of propofol during induction of anesthesia.

We describe a case in which an unexpectedly, abnormally low bispectral index value (BIS = 4) and an almost isoelectric electroencephalogram (EEG) pattern were observed during typical induction of anesthesia with propofol. Starting 2 min after the beginning of propofol administration (1.26 mg kg(-1)), the EEG recordings showed burst and suppression pattern for the next 12 min. The EEG during this period was characterized by gradual prolongation of suppression periods until the appearance of the isoelectric line. After that, burst activity returned and eventually the burst suppression pattern disappeared. We excluded the possibility of ischemic brain damage, and the evidence increasingly points toward a greater sensitivity to propofol. The findings described in this case report support the thesis that there is a wide variability in the responses of patients to propofol that cannot be detected without continuous monitoring of cortical electrical activity.