[Changes in sedative level during induction of anesthesia using a single volatile anesthetic]

We investigated the changes in sedative level during induction of anesthesia using a single volatile anesthetic, sevoflurane, compared with the changes when propofol and sevoflurane were used. We used a bispectral index (BIS) monitor (Aspect, Newton, USA) to monitor the sedative level. Thirty patients were randomly divided into one group receiving sevoflurane alone (S group, n = 15) and another group receiving propofol and sevoflurane (PS group, n = 15). The S group received 5% sevoflurane with nitrous oxide 6 l.min-1 and oxygen 3 l.min-1 via a face mask, while the PS group received propofol 1.5 mg.kg-1 i.v. followed by step-wise increasing sevoflurane up to 5%. Induction times, as assessed by loss of eyelash reflex, were 32 s in the PS group and 65 s in the S group. The decrease in the BIS value was smooth in the S group, whereas it increased transiently and varied greatly in the PS group. Two patients in the PS group showed body movement during induction of anesthesia, and the BIS values in both cases transiently exceeded 60. BIS monitor is useful for monitoring the sedative level during induction of anesthesia, and induction using a single volatile anesthetic such as sevoflurane is smooth.