Minimum effective anesthetic concentration (MEAC) for sciatic nerve block: subgluteus and popliteal approaches.

Background: We tested the hypothesis that using a subgluteus approach to the sciatic nerve requires a lower concentration of mepivacaine to obtain complete anesthesia as compared with the popliteal approach.

Methods: With midazolam premedication (0.05 mg kg(-1) iv), 48 patients undergoing hallux valgus repair were randomly allocated to receive a sciatic nerve block using either a posterior popliteal (group Popliteal, n = 24) or subgluteus (group Subgluteus, n = 24) approach with 30 mL of local anesthetic injected after elicitation of plantar flexion of the foot with a current

Results: The minimum effective anesthetic concentration of mepivacaine resulting in complete block of the sciatic nerve in 50% of cases (ED(50)) was 0.95% +/- 0.014% (95% confidence intervals [CI(95)]: 0.77%-1.12%) in group Subgluteus and 1.53% +/- 0.453% (CI(95): 0.96%-2.00%) in group Popliteal (P = 0.026). The ED(95) for adequate nerve block calculated with probit transformation and logistic regression analysis was 1.12% (CI(95): 0.71%-1.99%) in group Subgluteus and 1.98% (CI(95): 1.39%-2.31%) in group Popliteal.

Conclusions: A subgluteus approach to the sciatic nerve facilitates a reduction of the minimum effective concentration of local anesthetic required to produce an effective surgical block within 30 min after the injection as compared with the posterior popliteal approach.