Effects of epidural anesthesia on the effect site concentrations of propofol in a target-controlled infusion technique

Tomoko Watanabe, MD, Yoshimi Inagaki, MD, Tae Funakoshi, MD, Yuichi Ishibe, MD, PhD

Dept of Anesthesiology and Rianimatology, Tottori University Faculty of Medicine, Yonago, Tottori 683-8504, Japan

We investigated the effects of epidural anesthesia on the effect site concentration (EC) of propofol in a target-controlled infusion(TCI) technique on middle-aged patients and old-aged patients.

Methods

Fourteen geriatric patients, aged 71~77 yr and 14 middle age patients, aged 27~58 yr who underwent major upper-abdominal operations were randomly allocated to four groups according to age and combination with epidural anesthesia. Anesthesia was induced by a TCI technique using propofol. EC of propofol in the old-aged group was 4 mcg/ml and 6mcg/ml in the middle-aged group. Target concentration of propofol was changed by 0.5 mcg/ml to keep the BIS value within 50±5 and/or keep the mean blood pressure(MBP) within ± 15% of the preoperation value. Fentanyl was initiated 5min before the start of propofol infusion, and maintained EC1.5 mcg/ml for 1 hour after the start of operation. Thereafter, EC of fentanyl was maintained 1.0mcg/ml until the end of operation. The patient’s trachea was intubated with 0.12 mg/kg of vecuronium and 0.04 mg/kg of vecuronium was administered to maintain muscle relaxation under observation of train-of-four as necessary. Epidural anesthesia was established by a bolus injection of 10 ml of 7.5 mg/ml ropivacaine followed by a rate of 7.5 mg/kg/h. In the groups without epidural anesthesia, same volume of saline was administered in the same manner. To assess the median EC of propofol, we compared the percentage of time possession of each EC to anesthesia time (from the start of propofol infusion to the discontinuation) in the four study groups. The data was expressed as median (range) and was analyzed by Kruskal-Wallis test. Statistical significance was taken as p<0.05.

Results

Median age of the old-aged group was 73 years old, and that of middle-aged group was 46 years old. The median effect-site concentration of propofol in the groups with epidural anesthesia was 3.0 (2.0~4.0) mcg/ml and that was 4.5 (3.5~5.0) mcg/ml in the groups without epidural anesthesia. There were no significant differences in the effect-site concentration between middle-aged patients and old-aged patients with/without epidural anesthesia.

Discussion and conclusion

These results suggested epidural blockage could increase the depth of anesthesia level. In conclusion, epidural anesthesia can reduce the effect site concentration of propofol necessary for maintaining anesthesia the same level.