Effect-site Concentration of Propofol Necessary for Induction of Anesthesia with a Closed-loop Delivery System for Propofol Using the Bispectral Index

Osamu Nagata, Fumiko Horiuchi, Mika Hiki, Hiroko Isoyama, and Makoto Ozaki

Department of Anesthesiology, Tokyo WomenÕs Medical University, Tokyo, Japan

We evaluated the effect-site concentration of propofol necessary for induction of anesthesia with a closed-loop delivery system for propofol using the Bispectral Index (BIS).

Methods & Materials:

We examined 15 female patients aged from 21 to 51, ASA 1 or 2, who underwent gynecological surgery. The patients were premedicated with atropine 0.5 mg and hydroxyzine 50 mg before admission to the operating room. The anesthesia was induced and maintained with propofol, fentanyl, and vecuronium without nitrous oxide. The propofol delivery was controlled with our original closed-loop delivery system using BIS gathered online from an A-2000 BIS monitor. Five minutes after injection of fentanyl 2 µg/kg, this system started target-controlled infusion (TCI) at the target level of 3 µg/ml and maintained the infusion at the level for three minutes. After the initial 3 minutes of TCI induction, the system calculated the sigmoidal regression curve between BIS and the effect-site concentration of propofol every 5 seconds and changed the target effect-site concentration of propofol to the value suitable for maintaining the BIS value at 50. All the information on the delivery of propofol, fentanyl, and vecuronium was recorded once a minute and saved to a disk.

Results:

The effect-site concentration of propofol was 1.87 ± 0.63 (range : 0.70 - 3.10) µg/ml when the BIS value fell below 60, which indicated that the patient fell asleep. The amount of propofol used for 15 minutes of automated induction was 2.66 ± 0.57 mg/kg, while that used for 15 minutes of TCI induction at the target blood concentration of 4 µg/ml was 4.34 mg/kg.

Conclusion:

The mean effect-site concentration of propofol necessary for induction of anesthesia with our closed-loop delivery system for propofol using BIS was 1.87 µg/ml. The wide range of the effect-site concentrations for induction among patients was considered as individual differences.