[Acoustic evoked potentials mid-latency following anesthesia with sufentanil]

We have studied mid-latency auditory evoked potentials (MLAEP) during general anaesthesia with sufentanil in ten patients scheduled for elective major urological surgery. Anaesthesia was induced with sufentanil 2-3 micrograms/kg; for maintenance of anaesthesia a further bolus of sufentanil (1-2 micrograms/kg) 10 min before the start of surgery (skin incision) was given. MLAEP were recorded before and 10 min after the last sufentanil bolus on the vertex (positive) and mastoids on both sides (negative). Latencies of the peaks V, Na, Pa, Nb, and Pl (ms) and amplitudes Na/Pa, Pa/Nb, and Nb/Pl (microV) were measured.

In the awake state, MLAEP had high peak-to-peak amplitudes and a periodic wave form. During general anaesthesia with sufentanil the brainstem response V was stable. There was a marked increase in latency and a decrease in the amplitude of Nb and Pl. In contrast, for the early cortical potentials Na and Pa only small increases in latencies and decreases in amplitudes were observed. Na and Pa showed a similar pattern to that in awake patients.

There is no substantial difference of sufentanil's effect on MLAEP compared with the opioids alfentanil, fentanyl, and morphine. Because Na, Pa, and Nb are generated in the primary auditory cortex of the temporal lobe, it must be concluded that during general anaesthesia with sufentanil primary cortical processing of auditory stimuli may be preserved.