EFFECT OF EPIDURAL BUPIVACAINE BLOCK ON MIDAZOLAM HYPNOTIC REQUIREMENTS

Background and Objectives. The aim of the study was to determine the e ffect of epidural bupivacaine block on midazolam hypnotic requirements . Methods. Sixty unpremedicated, ASA physical status I or II male pati ents, aged 45-65 years and scheduled for elective lower abdominal, pel vic, or lower limb surgery participated in this randomized, double-bli nd, placebo-controlled study. The study population was composed of thr ee groups: Before administration of midazolam, patients in the first g roup received an intramuscular injection of 15 mt saline (M), those in the second group an intramuscular injection of 15 mt 0.5% bupivacaine (MIB), and those in the third group an epidural injection of 15 mt 0. 5% bupivacaine at the L3-L4 level (MEB). Loss of the ability to respon d to verbal command was used as an endpoint for the effect of midazola m injected intravenously in predetermined doses (five patients per dos e) 30 minutes after a bupivacaine (or saline) injection. Midazolam dos e-response curves were obtained by probit analysis. Results. The midaz olam median effective dose values for the hypnotic effect were 0.20 mg /kg (95% confidence limit, 0.10-0.27 mg/kg) in the M group; 0.10 mg/kg (0.06-0.22 mg/kg) in the MIB group; and 0.04 mg/kg (0.03-0.07 mg/kg) in the MEB group. The differences between the midazolam median effecti ve dose values had high levels of significance: P <.00001 for MEB vers us M, P <.002 for MEB versus MIB, and P <.01 for MIB versus M. Conclus ions. Epidural bupivacaine block profoundly decreases midazolam hypnot ic requirements. The most likely explanation for this effect is the re duction in afferent input induced by the block.