Figure 10-5 Relationship between the bispectral (BIS) index and the probability of consciousness (i.e., response to verbal command) with the use of logistic regression analysis in volunteers receiving propofol, isoflurane, or midazolam. The probability of response was no different for the three anesthetics used. It can also be noted that 95% of the volunteers were unconscious with a BIS index of 50 or less.