EFFECTS OF BENZODIAZEPINES ON MIDLATENCY AUDITORY-EVOKED POTENTIALS

Midlatency auditory evoked potentials (MLAEP) reflect primary cortical processing of auditory stimuli. The effects of benzodiazepines on MLA EP have not yet been studied. We examined the effects of intravenous i nduction of general anaesthesia using the benzodiazepines midazolam, d iazepam and flunitrazepam on MLAEP in 30 patients scheduled for minor gynaecological procedures. Anaesthesia was induced with midazolam (0.2 -0.3 mg . kg-1, Group I, n = 10), diazepam (0.3-0.4 mg . kg-1, Group I I n = 10) or flunitrazepam (0.03-0.04 mg . kg-1, Group III, n = 10). A uditory-evoked potentials were recorded before and five to ten minutes after induction of general anaesthesia. Latencies of the peak V, Na, Pa, Nb and P1 (ms) and amplitudes Na/Pa, Pa/Nb and Nb/P1 (muV) were me asured. In the awake state, MLAEP had high peak to peak amplitudes and a periodic waveform. After induction of anaesthesia there was no or o nly a small increase in latencies of the peaks Na, Pa, Nb and P1, whic h was significant only for P1 in the midazolam group. Amplitudes Na/Pa , Pa/Nb and Nb/P1 decreased only slightly and which reached statistica l significance only for Na/Pa in the flunitrazepam group. The MLAEPs d o not change markedly in amplitude or latency during induction of gene ral anaesthesia with benzodiazepines. Primary cortical processing of a uditory stimuli seem to be preserved under benzodiazepines This may be seen in connection with cases of intraoperative awareness and especia lly the perception of auditory stimuli during anaesthetic regimens whe re benzodiazepines are used to suppress consciousness.