To determine threshold values, sensitivity and specificity of the spectral edge frequency (SEF) of the electroencephalogram (EEG) that indicate intraoperative movements, we studied 49 patients undergoing, elective laparotomy. Extradural analgesia was used in all patients. To maintain general anaesthesia, patients in group 1 (n = 23) received 0.4-1.2 vol% isoflurane and patients in group 2 (n = 24) propofol 3-5 mg kg-1 h-1 i.v. During operation and emergence from anaesthesia, spontaneous purposeful movements were documented. The EEG was recorded continuously in the awake state until the end of anaesthesia. Power spectral analysis calculated the SEF and power in the delta, theta, alpha and beta bands and the delta ratio. Adequate anaesthesia caused a statistically significant decrease in SEF from 16 to 12 Hz. Power in the beta band decreased and power in the theta band and total power increased compared with the awake state. Before and during movements observed in the intraoperative period or during emergence from general anaesthesia, SEF increased from 12 to 18 Hz, the power in beta band increased and theta power decreased compared with the state of adequate anaesthesia. A threshold value of SEF 14 Hz to predict movements during anaesthesia had a sensitivity of 72% and specificity of 82%.

SummaryWe studied the effects of increasing end-expiratory concentrations of isoflurane (0.3, 0.6, 0.9, 1.2 vol.%) (n ¼ 12 patients), desflurane (1.5, 3.0, 4.5, 6.0 vol.%) (n ¼ 12 patients) and sevoflurane (0.5, 1.0, 1.5, 2.0 vol.%) (n ¼ 12 patients) on power spectral analysis of the electroencephalogram (EEG). Spectral edge frequency (SEF), total power (TP) and relative power in the delta, theta, alpha and beta band were calculated. EEG changes were very similar within the three groups. SEF decreased, TP and relative power in the delta and theta band increased, power in the beta band decreased in a dose-dependent fashion with comparable regression lines. This indicates that MAC equivalent administration of isoflurane, desflurane and sevoflurane in clinically applied dose ranges is associated with equipotent EEG suppression.

The results of this study imply that MLAEP can successfully be recorded during anaesthesia in children above the age of 2 yr. Further studies are necessary before MLAEP might be applicable for monitoring purposes in paediatric anaesthesia.

MLAEP latencies increase at the influence of sevoflurane in a dose-dependent manner and in relation to age. These results imply that MLAEP detection is a reasonable tool for monitoring hypnotic effects at all ages. Further studies are required to standardize MLAEP alterations related to effects of medication used for general anaesthesia at all different ages.

To determine threshold values, sensitivity, and specificity of midlatency auditory evoked potentials (MLAEP) for prediction of spontaneous intraoperative movements, 40 patients undergoing elective laparotomy were studied. Continuous epidural analgesia was used in all patients. To maintain general anesthesia, the patients in Group 1 (n = 20) received isoflurane (0.4-1.2 vol%), and the patients in Group 2 (n = 20) received propofol (3-5 mg x kg(-1) x h(-1) intravenously). Spontaneous movements were documented intraoperatively. Auditory evoked potentials were recorded continuously until the end of anesthesia. Latencies of the peaks V, Na, Pa, Nb, and P1 (ms) and amplitudes Na/Pa, Pa/Nb, and Nb/P1 (microV) were measured. Changes of MLAEP latencies and amplitudes during anesthesia were similar in both groups. Anesthesia led to statistically significant increases in the latencies of Na, Pa, Nb, and P1 and decreases in the amplitudes of Na/Pa, Pa/Nb, and Nb/P1 compared with the awake state. Before and during spontaneous movement observed intraoperatively or during emergence from anesthesia, the latencies of the peaks Na, Pa, Nb, and P1 decreased, and the amplitudes Na/Pa, Pa/Nb, Nb/P1 increased significantly. A threshold value of 60 ms of Nb proved to be most predictive of movement during anesthesia. MLAEP recording seems to be a promising method to monitor the level of anesthesia as defined by spontaneous movement during anesthesia.

Propofol affects MLAEP latencies and amplitudes in children in a dose-dependent manner. MLAEP measurement might therefore be a useful tool for monitoring depth of propofol anaesthesia in children.

Spontaneous or evoked electrical brain activity is increasingly used to monitor general anesthesia. Previous studies investigated the variables from spontaneous electroencephalogram (EEG), acoustic (AEP), or somatosensory evoked potentials (SSEP). But, by monitoring them separately, the available information from simultaneous gathering could be missed. We investigated whether the combination of simultaneous information from EEG, AEP, and SSEP shows a more discriminant power to differentiate between anesthesia states than from information derived from each measurement alone. Therefore, we assessed changes of 30 EEG, 21 SSEP, and 29 AEP variables recorded from 59 patients during four clinical states of general anesthesia: "awake," "light anesthesia," "surgical anesthesia," and "deep surgical anesthesia." The single and combined discriminant powers of EEG, AEP, and SSEP variables as predictors of these states were investigated by discriminant analysis. EEG variables showed a higher discriminant power than AEP or SSEP variables: 85%, 46%, and 32% correctly classified cases, respectively. The frequency of correctly classified cases increased to 90% and 91% with information from EEG + AEP and EEG + AEP + SSEP, respectively. Thus, future anesthesia monitoring should consider combined information simultaneously distributed on different electrophysiological measurements, rather than single variables or their combination from EEG or AEP or SSEP.

We have studied midlatency auditory evoked potentials (MLAEP) and motor signs of wakefulness during anaesthesia with midazolam in 10 patients undergoing elective laparotomy under continuous extradural analgesia. Anaesthesia was induced with midazolam 0.3 mg kg-1 and maintained with midazolam 0.3-0.9 mg kg-1 h-1. Motor signs of wakefulness were documented as spontaneous movements and movements after simple commands (open eyes or move arms). MLAEP were recorded continuously awake, and during anaesthesia until the end of anaesthesia. Latencies of the peaks V, Na, Pa, Nb and P1 (ms) and amplitudes of the peaks Na/Pa, Pa/Nb and Nb/P1 (microV) were measured. Twenty-five movements were observed during anaesthesia; 15 movements in six patients were in response to commands. In two patients supplementary isoflurane was given. Latencies of the MLAEP peaks Pa, Nb and P1 increased slightly during anaesthesia. Amplitudes for Na/Pa, Pa/Nb and Nb/P1 did not change significantly. The high incidence of motor signs of wakefulness associated with preserved MLAEP indicated a high level of cortical neural activity and none of the MLAEP variables predicted movement during anaesthesia with midazolam.