Effect of bupivacaine-induced spinal block on the hypnotic requirement of propofol

The hypnotic dose-response of propofol was compared with its combination with either bupivacaine-induced spinal block or intramuscular bupivacaine 12.5 mg in 105 men, divided into three groups of 35, undergoing lower abdominal, pelvic or lower limb surgery. Dose-response curves were determined for each group using bootstrap analysis. Bupivacaine-induced spinal block at the level of T8-T9 was found to reduce the ED50 of propofol by 39%. While this enhancement of hypnotic effect by spinal block is mostly attributable to reduced afferent input, differences in its potency between drugs suggest a role for additional factors.