[The effect of thiopental on mid-latency auditory evoked potentials and their frequency analysis]

The effect of Thiopentone on mid-latency auditory evoked potentials has not yet been examined sufficiently. Therefore, mid-latency auditory evoked potentials during induction of general anaesthesia with thiopentone were studied. Following informed consent in 10 patients scheduled for elective surgery, anaesthesia was induced with thiopentone (5 mg/kg b.w. i.v.). Assisted ventilation via face mask with 100% O2 was performed until the first purposeful movement of the limbs appeared. Then a second bolus of thiopentone (2 mg/kg b.w. i.v.) was given and general anaesthesia was maintained according to anaesthesiological and operative necessities. Auditory evoked potentials were recorded in the awake and on-line when thiopentone was injected up to 9 min after the onset of general anaesthesia. Latencies of the peaks V, Na, Pa were measured. Using Fast-Fourier-Transform-Analysis, corresponding power spectra were calculated to analyse energy portions of the AEP frequency components. In the awake state peak latencies were in the normal range. Corresponding power spectra indicated energy maxima in the 30-40 Hz frequency range. After induction of general anaesthesia an increase in latencies of the peaks Na, Pa could be observed. The energy in the 30-40 Hz range became suppressed, the AEP energy maxima shifted to the low frequency range. These effects were observable until 3 min after injection. When the first purposeful movement of a limb occurred, Na, Pa latencies returned to normal values and most part of the AEP-energy was in the 30-40 Hz range as in the awake.(ABSTRACT TRUNCATED AT 250 WORDS)