MIDLATENCY AUDITORY-EVOKED POTENTIALS DUR ING SUFENTANIL ANESTHESIA

Patients and methods. We have studied mid-latency auditory evoked pote ntials (MLAEP) during general anaesthesia with sufentanil in ten patie nts scheduled for elective major urological surgery. Anaesthesia was i nduced with sufentanil 2-3 mu g/kg; for maintenance of anaesthesia a f urther bolus of sufentanil (1-2 mu g/kg) 10 min before the start of su rgery (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 P 1 (ms) and amplitudes Na/Pa, Pa/Nb, and Nb/P1 (mu V) were measured. Re sults. In the awake state, MLAEP had high peak-to-peak amplitudes and a periodic wave form. During general anaesthesia with sufentanil the b rainstem response V was stable. There was a marked increase in latency and a decrease in the amplitude of Nb and P1. In contrast, for the ea rly cortical potentials Na and Pa only small increases in latencies an d decreases in amplitudes were observed. Na and Pa showed a similar pa ttern to that in awake patients. Conclusions. There is no substantial difference of sufentanil's effect on MLAEP compared with the opioids a lfentanil, fentanyl, and morphine. Because Na, Pa, and Nb are generate d in the primary auditory cortex of the temporal lobe, it must be conc luded that during general anaesthesia with sufentanil primary cortical processing of auditory stimuli may be preserved.