Statistical analysis The primary outcome variables are T-BIS80, T-SIMV, and T-extubation. Statistics are performed using the program Sigmastat ver.3.1(Systat Software Inc, San Jose, USA). Continuous variables were analyzed by a t-test, while categorical variables are by a chi-square test between two groups. The data collected are expressed as mean and standard deviation, numbers of patients or absolute numbers. A P value < 0.05 is considered significant.