Identifying consciousness alterations during intravenous anesthesia with the depth of anesthesia index and bispectral index: a randomized multicenter study

Abstract

Objective To evaluate the validity of the depth of anesthesia index (Ai), based on sample entropy of electroencephalogram, in identifying the status of the consciousness during total intravenous anesthesia. Methods EEG electrode strips for recording Ai and BIS were randomly positioned on the left or right side of each patient′s forehead. Target-controlled infusion of propofol was increased by 0.5 mg/L per minute in a stepwise manner until loss of consciousness (LOC) was achieved. Values of Ai, BIS and estimated effect-site concentration (Ce) of propofol were recorded and analyzed during induction and emergence of general anesthesia. Logistic regression was used to analyze the relationship between consciousness state and values of Ai or BIS. Results One hundred and forty four patients in six medical centers were enrolled and have accomplished this protocol safely. In patients at LOC, the values of Ai and BIS were 61±12 and 62±11, which were respectively reduced by 15.0% and 9.3% one minute after LOC. When patients regained consciousness (ROC), Ai and BIS respectively reached 74±14 and 76±8, and increased by 15.0% and 7.0%, correspondingly, one minute after ROC. The estimated values of Ai and BIS were 48.3 and 52.3 for 95% LOC, and were 55.7 and 63.1 for 5% ROC. Conclusions At LOC, ROC, estimated 50% LOC and 50% ROC, the values of Ai and BIS were close to each other and they are equivalent for clinical monitoring. When consciousness states altered, changes of Ai were significantly greater than those of BIS. It suggests that Ai is a better parameter to estimate alterations of consciousness state. Key words: Loss of consciousness; Recovery of consciousness; Total intravenous anesthesia; Depth of anesthesia index; Bispectral index