[Quantitative electroencephalogram monitoring the depth of anesthesia during skin incision]

We investigated the EEG parameter changes of skin incision during different depth of sevoflurane/nitrous oxide analgesia. 65 ASA physical status I patients (aged 34 +/- 12 yr) scheduled for elective abdominal surgery were studied. The tracheal of each patient was intubated and the lungs were ventilated. Patients were randomly assigned to one of three groups. Anesthesia was maintained with 1% (group I n = 25), 1.5% (group II n = 20) or 2% (group III n = 20) end-tidal sevoflurane concentration in 66% nitrous oxide. Each of the concentration levels was maintained for at least 15 minutes before surgical incision. The EEG electrodes were placed on each patient in a front-oparietal montage (Fp1- A1, Fp2- A2) referred to Cz. EEG was recorded during 3-min period before incision. Hemodynamic variables were also monitored. Inadequate anesthetic depth was defined as patient movement in response to a 5-cm skin incision. The ventilation was controlled to maintain normocapnia (PETCO2 5 +/- 0.04 kPa). The data were analysed using ANOVA, liner correlation analysis and t-test. A significant difference between EEG parameters (SEF, BIS,) and skin incision responsive rate were found among the three concentration groups (P < 0.01). There were no difference of hemodynamics among the three groups. Patients who moved at incision also had significantly higher SEF, BIS leveles compared to non-movers (P < 0.01). Quantitative EEG determinants were correlated well with the end-tidal sevoflurane concentration and were a useful predictor of patient movement in response to skin incision during sevoflurane/nitrous oxide anesthesia.