Motor signs of wakefulness during general anaesthesia with propofol, isoflurane and flunitrazepam/fentanyl and midlatency auditory evoked potentials

Auditory evoked potentials have been used as an indicator of awareness. In the present study we combined epidural analgesia with three techniques of general anaesthesia. Motor signs of intra‐operative wakefulness were documented and assessed along with cardiovascular changes and with midlatency auditory evoked potentials. Thirty patients undergoing elective laparotomy were studied as follows: first continuous epidural analgesia was used in all patients to block painful sensation to the level of T5. Intravenous general anaesthesia was induced with propofol (2.5 mg.kg‐1 b.w., group 1, n = 10), thiopentone (5 mg.kg‐1 b.w., group 2, n = 10) or etomidate (0.2 mg.kg‐1 b.w., group 3, n = 10) and maintained with a propofol (3–5 mg.kg‐1, group 1), isoflurane (0.4‐0.8 Vol%, group 2), flunitrazepam and fentanyl (0.005 mg.kg‐1 b.w.) bolus injection every 20 to 30 s (group 3). Heart rate and arterial pressure were recorded continuously. Purposeful movements of the limbs, eye‐opening or other movements as well as coughing were documented as motor signs of intra‐operative wakefulness. Auditory evoked potentials were recorded in the awake state, after induction and during maintenance of general anaesthesia. Motor signs of intra‐operative wakefulness occurred statistically significantly more often in the patients of the flunitrazepam/fentanyl group than in those of the propofol and isoflurane group. There was no correlation between wakefulness and cardiocirculatory parameters. In the awake patients midlatency auditory evoked potentials had high peak to peak amplitudes and a periodic waveform. After induction of general anaesthesia with propofol, thiopentone and etomidate as well as during maintenance of general anaesthesia with propofol and isoflurane, midlatency auditory evoked potentials were severely attenuated or abolished. In contrast, during maintenance of general anaesthesia with flunitrazepam/fentanyl midlatency auditory evoked potentials reestablished high peak to peak amplitudes. The persistence of midlatency auditory evoked potentials coincides with a high incidence of motor signs of wakefulness. During the combination of regional and general anaesthesia, isoflurane and propofol seem to provide better suppression of motor signs of wakefulness than the intermittent bolus injection of flunitrazepam/fentanyl.