Objective To compare the prediction probability (Pk) of loss of consciousness (LOC) for the four EEG nonlinear indexes-correlation dimension ( D2), approximate entropy (ApEn) complexity (Cx) and bispectral index (BIS) and their relative accuracy. Methods Twenty ASA Ⅰ-Ⅱ patients aged 22-71 undergoing elective operation on lower limb under epidural anesthesia were studied. The patients were unpremedicated. Epidural catheter was placed at L2,3 or L3,4 interspace. The block height was 95% . Sedation was produced by target-controlled infusion (TCI) of propofol. The target plasma concentration of propofol (Cp) was initially set at 0.5 ?g?ml-1. Cp was gradually increased in increments of 0.3-0.5 ?g?ml-1 every 3 min until LOC. Depth of sedation was assessed using OAA/S scale (5 = alert, 1 = LOC) . LOC was maintained for 12 min. Cp was equal to effect-site concentration (Ce) by the end of 12 minutes. Cp was then gradually decreased in increments of 0.3-0.5 ?g?ml-1 until the patients regained consciousness. The same procedure was repeated 4 times in every patient. BIS, D2 , ApEn and Cx were recorded simultaneously every 3 min. The prediction probability of LOC for D2, ApEn, Cx and BIS was calculated and compared.Results The BIS value was 80.2?6.2 when the patients regained consciousness (T1) and 67.3?7.9 at LOC (T2); D2 was 3.45?0.18 (T1) and3.01?0.16 (T2); ApEn was 0.84?0.05 (T1) and 0.71?0.06 (T2); Cx was 0.55?0.05 (T1) and 0.44?0.05. There was no significant difference in Pk of LOC among the 4 indexes. Conclusion Our results show that all the 4 indexes can be used to monitor the level of sedation produced by propofol.

Objective To analyze the bispectral index (BIS) and the EEG nonlinear index (including Correlation dimension, D2; Approximate entropy, ApEn; Complexity, Cx.) during alternating periods of consciousness and unconsciousness produced by target-controlled infusions (TCI) of propofol. Methods We studied twenty patients (ASA Ⅰ～Ⅱ grades) undergoing the elected leg operations under epidural anesthesia. With TCI consciousness of the patient was controlled by an increase or decrease of concentration of propofol in a range of 0.3～0.5?g/ml for four times. Every target plasma concentration of propofol lasted 12 minutes. BIS, D2, ApEn and Cx were recorded simultaneously during the periods of consciousness and unconsciousness every 3 minutes. Results During consciousness and unconsciousness, the respective mean values for the four measurements were: BIS, 80.2?6.2 and 67.3?7.9; D2, 3.45?0.18 and 3.01?0.16; ApEn, 0.84?0.05 and 0.71?0.06; Cx, 0.55?0.05 and 0.44?0.05. Determined threshold values with 100% specificity during the state of unconsciousness were: BIS, 51 (sensitivity3.8%); D2, 2.90 (sensitivity 30.3%); ApEn, 0.69 (sensitivity42.3%); Cx, 0.41 (sensitivity 25.5%). Conclusion BIS, D2, ApEn and Cx can all reflect the change in consciousness and unconsciousness produced by TCI of propofol. Our findings suggest that of the four EEG variables, ApEn was best in identifying the transition from unconsciousness to consciousness.