• Mercedes López, Miguel Calvo, Azahara Sancho, Nicolas Brogly, Emilia Guasch, and Fernando Gilsanz.
• Department of Anesthesia, "La Paz" University Hospital, Paseo de la Castellana 261, 28046 Madrid, Spain. Electronic address: mercelopezmartinez@yahoo.es.
• J Clin Anesth. 2017 Feb 1; 37: 139-144.

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.Copyright © 2016 Elsevier Inc. All rights reserved.

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