SPECTRAL EDGE FREQUENCY OF THE ELECTROENCEPHALOGRAM TO MONITOR DEPTH OF ANESTHESIA WITH ISOFLURANE OR PROPOFOL

To determine threshold values, sensitivity and specificity of the spec tral edge frequency (SEF) of the electroencephalogram (EEG) that indic ate intraoperative movements, we studied 49 patients undergoing electi ve laparotomy. Extradural analgesia was used in all patients. To maint ain 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, spontan eous purposeful movements were documented. The EEG was recorded contin uously 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 statisti cally 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 c ompared 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 anaesthes ia had a sensitivity of 72% and specificity of 82%.