[Sensory information processing during general anesthesia-- acoustic-evoked 30-40 Hz oscillations and intraoperative...

Neuropsychological and neurophysiological investigations indicate that the underlying framework of adequate sensory information processing is a 30-40 Hz oscillatory brain mechanism, which also can be observed in mid-latency auditory evoked potentials (MLA-EP). Since high incidence of stimuli perception and wakefulness is a phenomenon during Caesarean section under general anaesthesia it was studied if auditory evoked 30-40 Hz oscillation correlate with intraoperative wakefulness during this surgical procedure. Following informed consent, 21 patients were selected for elective Caesarean section. Anaesthesia was induced with thiopentone (5 mg/kg b.w. i.v.) and maintained with thiopentone bolus injection (1-2 mg/kg b.w.i.v). and O2/N2O 1:1 according to clinical signs of adequate anaesthesia. After delivery, a balanced anaesthetic technique using fentanyl, enflurane and N2O in O2 1:1 was employed. Clinical signs of intraoperative wakefulness were spontaneous movements of the limbs, mimics, eye-opening, wakefulness after auditory stimulation (tape A: crying baby, tape B: classical music), one hour and 24 hours postoperatively reported dreams, hallucinations and detailed reports about intraoperative events. Auditory evoked potentials were recorded on-line before and during general anaesthesia, during the entire surgical procedure. Latencies of the peaks V, Na, Pa were measured. Employing Fast-Fourier transformation analysis, corresponding power spectra were calculated to analyse energy portions of AEP's frequency components. Spontaneous motoric movements occurred in 60% of the patients and did not correlate with heart rate, blood pressure or other clinical signs of inadequate anaesthesia. Provoked motoric reactions were 4 times as often after presentation of tape A as after tape B.(ABSTRACT TRUNCATED AT 250 WORDS)