QUANTITATIVE EEG IN ASSESSMENT OF ANESTHETIC DEPTH - COMPARATIVE-STUDY OF METHODOLOGY

Methodology for assessment of depth of anaesthesia based on analysis o f the electroencephalogram (EEG) is controversial. Techniques range fr om display of single measures,for example median value of the frequenc y spectrum, to dedicated pattern recognition systems based on measures of several EEG features. We have compared the performance of four tec hniques using tape-recorded data from 23 patients anaesthetized with e ither halothane or isoflurane using standardized regimens. The techniq ues were: (1) median frequency, (2) spectral edge frequency, (3) the c erebral function analysing monitor (CFAMI) and (4) a depth of anaesthe sia monitor based on EEG pattern recognition (ADAM). Dose-response cur ves are presented for stepwise increases in stable end-tidal concentra tions of each agent. Results indicated considerable inter-patient vari ability and the limitations of single EEG measures, particularly with deeper anaesthesia producing a burst suppression pattern in the EEG. P attern recognition techniques reduced these difficulties and appeared to be promising over a wide range of anaesthetic levels.