Effective volumes of 1.5% mepivacaine with different sodium concentration for ultrasound guided popliteal block

Abstract

Study objectiveTo determine if a solution of 1.5% mepivacaine diluted with 5% dextrose, which decreases the sodium concentration by 30%, results in reduced volume requirements for a complete sensory block, in the case of an ultrasound guided popliteal nerve block. DesignA randomized controlled study. SettingOperating room. PatientsWe included seventy ASA 1–3 patients, undergoing unilateral “hallux valgus” repair under ultrasound guided popliteal nerve block. InterventionsAn ultrasound guided popliteal nerve block was performed on all patients, with 1.5% mepivacaine using the normal dilution (ND group, thirty-five patients) or the 5% dextrose dilution (D5 group, thirty-five patients). Starting with 25ml in each group, increasing or decreasing it by 1ml on subsequent patients, depending on the success or failure in the previous one (Dixon's “up-and-down” sequential allocation). MeasurementsEffective dose in 50, 90, and 95% of patients (ED50, ED90, and ED95) of 1.5% mepivacaine in both groups. Onset time and duration of the blocks, side effects, and neurological complications. Main resultsThere were no statistically significant differences between ED50 in ND group (6.2ml; 95% confidence interval, 5.2–7.5), and D5 group (5.8ml; 95% CI, 5.1–7). Also no statistically significant differences in ED90 (7.7ml, 95% CI 6.9–8.1 in the D5 group; 7.8ml, 95% CI 7–8.1 in the ND) or in ED95 (7.9ml, 95% CI 7.1–8.2 in the D5 group; 8ml, 95% CI 7.2–8.2 in the ND) were found. Onset time for a complete sensory block in D5 group was 14min (95% CI, 12–17) and 15min in ND (95% CI, 13–18), p=0.66. Neither severe side effects, nor neurological complications were reported. ConclusionsA dilution of 1.5% mepivacaine with 30% less sodium concentration does not decrease volume requirement for ultrasound guided sciatic nerve block at popliteal level.