Processed electroencephalogram during combined extradural and general anaesthesia

The processed electroencephalogram (pEEG) was monitored in eight patients undergoing gynaecological laparotomy under combined extradural and nitrous oxide-isoflurane anaesthesia. Pre-incisional mean spectral edge frequency 95 percentile (SEF95) and median frequency (MF) were 11.67 (SD 1.63) Hz and 3.74 (0.24) Hz, respectively. After skin incision, both SEF95 and MF decreased to 6.61 (2.04) Hz and 2.72 (0.32) Hz, respectively (P < 0.001). An increase in mean arterial pressure after incision suggested inadequate depth of anaesthesia. After introduction of extradural analgesia, these variables returned to pre-incisional values (SEF95 11.65 (1.73); MF 4.02 (0.41)). Reduction of end-tidal isoflurane from 1.0% to 0.5% after extradural analgesia did not cause significant pEEG changes. pEEG may assist anaesthetists to recognize adequacy of combined general-extradural anaesthesia.