Auditory steady-state response, upper facial EMG, EEG and heart rate as predictors of movement during isoflurane-nitrous oxide anaesthesia

We have studied the relationship between patient movement andchanges in the auditory steady-state evoked potential, upperfacial muscle electromyogram (FEMG), electroencephalographic-zerocrossing frequency (EEG–ZCF) and heart rate during emergencefrom anaesthesia. Twelve healthy patients underwent surgeryduring stable isoflurane-nitrous oxide-oxygen anaesthesia withoutneuromuscular block. After skin closure, anaesthesia was discontinuedabruptly while mechanical ventilation was continued until thepatient moved. The magnitude of change in each physiologicalsignal was evaluated in decibels (dB). Both the auditory steadystate evoked potential and FEMG showed significant increasesin amplitude during the last 5-min period before movement (6.1and 10.7 dB, respectively). EEG-ZCF increased rapidly afteranaesthesia was discontinued (2.5 dB) but there was no furtherincrease in activity before movement. Heart rate did not changebefore movement. The use of the decibel transformation offersa promising method of displaying and interpreting changes inphysiological variables during anaesthesia.