MIDLATENCY AUDITORY-EVOKED POTENTIALS DURING KETAMINE ANESTHESIA IN HUMANS

We studied mid-latency auditory evoked potentials (MLAEP) during induc tion of general anaesthesia with ketamine 2 mg kg-1. MLAEP were record ed before, during and after induction of general anaesthesia on the ve rtex (positive) and mastoid (negative) positions. Latencies of the pea k V, Na, Pa, Nb, P1 and amplitudes Na/Pa, Pa/Nb and Nb/P1 were measure d. Fast-Fourier transformation was used to calculate power spectra of the MLAEP. In the awake state, MLAEP had large peak-to-peak amplitudes and a periodic waveform. Peak latencies remained within the normal ra nge. Power spectra indicated high energy in the 30-40 Hz frequency ran ge. After induction of general anaesthesia with ketamine, there was no change in latency of peaks V, Na, Pa, Nb, P1 and no apparent reductio n in amplitudes Na/Pa, Pa/Nb and Nb/P1. In the power spectra, frequenc ies in the range of 30-40 Hz retained high energy. Amplitudes and late ncies of MLAEP did not change during induction of general anaesthesia with ketamine. Primary processing of auditory stimuli in the primary a uditory cortex seemed to be preserved under ketamine. Suppression of s ensory (auditory) information processing must take place at a higher c ortical level in a dissociative manner.