Skin conductance monitoring compared with Bispectral Index® to assess emergence from total i.v. anaesthesia using propofol and remifentanil

Background. Arousal after sevoflurane anaesthesia has been detectable by monitoring changes in skin conductance (SC) with similar accuracy as monitoring Bispectral Index (BIS (R)). As SC monitoring detects changes in sympathetic tone, the measurements might be confounded by the sympatholytic properties of propofol, a component of total i.v. anaesthesia (TIVA). Therefore in this study, monitoring of SC during emergence from TIVA was compared with the monitoring of BIS (R). Methods. Twenty-five patients undergoing plastic surgery were investigated. The number of fluctuations of SC per second (NFSC), BIS (R) and haemodynamic variables [systolic blood pressure (SBP) and heart rate (HR)] were recorded simultaneously. The performance of the monitoring devices in distinguishing between the clinical states 'steady-state anaesthesia', 'first clinical reaction' and 'extubation' were compared using the method of prediction probability (Pk) calculation. Results. BIS (R) showed the best performance in distinguishing between 'steady-state anaesthesia' and 'first reaction' (Pk BIS (R) 0.99 vs NFSC 0.80; P < 0.01), and 'steady-state anaesthesia' and 'extubation' (Pk BIS (R) 1.00 vs NFSC 0.91; P < 0.05); the time from first change of BIS (R) or NFSC to a first clinical reaction was significantly longer for NFSC (median BIS (R) 135 s vs NFSC 191 s; P < 0.05). BIS (R) and NFSC performed better in distinguishing between the investigated clinical states than SBP and HR. Conclusions. In this study, BIS (R) was found to predict arousal with a higher probability but slower response times than NFSC in patients waking after TIVA.