[Mid-latency auditory evoked potentials during induction of intravenous anesthesia using midazolam, diazepam and...

Since intraoperative awareness is not infrequently observed under balanced anaesthetic regimens employing benzodiazepines for suppression of consciousness, we studied the effect of intravenous induction of general anaesthesia using the benzodiazepines midazolam, diazepam and flunitrazepam on mid-latency auditory evoked potentials and auditory evoked neuronal 30-40 Hz oscillation. Following informed consent in 30 patients scheduled for minor gynaecological procedures, anaesthesia was induced with midazolam (0.2-0.3 mg/kg b.w. i.v., group I n = 10), diazepam (0.3-0,4 mg/kg b.w., i.v., group II n = 10) or flunitrazepam (0.03-0.04 mg/kg b.w., i.v., group III n = 10). Auditory evoked potentials were recorded before, during and after induction of general anaesthesia on vertex (positive) and mastoides on both sides (negative). Auditory clicks were presented binaurally at 70 dBnHL with a frequency of 9.3 Hz. Using the electrodiagnostic system Pathfinder I (Nicolet), 1000 successive stimuli were averaged over a 100 ms poststimulus period and analysed off-line. Latencies of the peak V, Na, Pa were measured. By means of Fast-Fourier transformation-analysis corresponding power spectra were calculated to analyse energy portions of the AEP frequency components. In the awake state AEP showed an oscillatory component between 20 and 100 ms poststimulus latency. Corresponding power spectra indicated a predominant 30-40 Hz frequency. After induction of general anaesthesia using midazolam, diazepam and flunitrazepam, there was no increase in latencies of the peaks V, Na, Pa, but only a small decrease in amplitudes Na/Pa without statistical significance. The auditory evoked mid-latency neuronal oscillation persisted under induction of general anaesthesia with midazolam, diazepam, flunitrazepam.(ABSTRACT TRUNCATED AT 250 WORDS)