The endtidal sevoflurane concentration was adjusted with starting dose for the first cohort patients 1% and maintained for 10 min to ensure equilibration with the cerebral anesthetic partial pressure followed by a 1-min assessment of BIS taken at 10-s intervals. Briefly, a first dose is given to the first patient and the next doses are given according to the following rule: if the subject responds positively (BIS<50), the dose is decreased one step for the next subject, and conversely, if the subject does not respond (BIS>50), the dose is increased one step. The dose adjustment is 0.2% for sevoflurane. The CRM is used to calculate the dose adjustment for every cohort with the number of patients for every cohort .