Logistic regression is used to determine the ideal minimum dose of sevoflurane (ED 95) that 95% of patients undergoing anesthesia during CPB in cardiac surgery have no intraoperative awareness. The level of consciousness will be evaluated maintaining the value of the bispectral index (BIS) below 50 during CPB. The probability of BS (p) is modelled in terms of log odds by a linear function of the independent explanatory variable 'measured concentration' X by a logistic regression: