Background and Objectives: Spinal anesthesia and intrathecal clonidine are known to have hypnotic effects. We investigated the effect of spinal anesthesia and intrathecal clonidine on the requirement of propofol for sedation.

Methods: Sixty adult patients scheduled for stripping and ligation of varicose veins under local or spinal anesthesia were enrolled in this study. Group 1 included patients given local anesthesia, group 2 included patients given spinal anesthesia, and group 3 included patients given spinal anesthesia with 75 μg of clonidine. Target-controlled infusion of propofol was started to achieve a target concentration of 1 and 1.5 μg/mL, and the mean bispectral index (BIS) for 1 min was checked after an effect site concentration (Ce) of 1 and 1.5 μg/mL propofol was reached. In addition, the Ce of propofol was documented when the mean BIS for 1 min reached 80 and 70 for the 3 groups, respectively, during the observation period.

Results: The BIS at 1 μg/mL propofol Ce was 87 (group 1), 80 (group 2), and 69 (group 3). The BIS at 1.5 μg/mL propofol Ce was 76, 64, and 51, respectively. The Ce of propofol when the BIS first reached 80 was 1.4, 1.1, and 0.7 μg/mL, respectively. The Ce of propofol when the BIS first reached 70 was 1.7, 1.4, and 0.9 μg/mL, respectively.

Conclusions: Spinal anesthesia and intrathecal clonidine might reduce the requirement of propofol for sedation. Our study showed target concentrations of propofol for sedation of 1.4 to 1.7 using local anesthesia only, 1.1 to 1.4 using spinal anesthesia with bupivacaine, and 0.7 to 0.9 μg/mL using spinal anesthesia with bupivacaine and 75 μg of clonidine.