Effect of Local Anesthetic Dilution on the Onset Time and Duration of Double-Injection Sciatic Nerve Block: A Prospective, Randomized, Blinded Evaluation

Cappelleri, Gianluca MD*; Ambrosoli, Andrea Luigi MD; Turconi, Stefania MD; Gemma, Marco MD; Ricci, Erika Basso MD*; Cornaggia, Gabriele MD*

Anesthesia & Analgesia:
doi: 10.1213/ANE.0000000000000293
Regional Anesthesia: Research Report

BACKGROUND: Among the various factors influencing the success rate, onset time, and duration of peripheral nerve blocks, the role of local anesthetics concentration remains uncertain. In this prospective, randomized, single-blinded study, we evaluated whether varying the dilution of a fixed dose of mepivacaine solution influenced onset time and duration of sciatic nerve block.

METHODS: Ninety ASA physical status I to II patients scheduled for foot surgery were randomly allocated to receive a double-injection Labat sciatic nerve block with 12 mL mepivacaine 2% (group concentration I = 45 patients) or 24 mL of mepivacaine 1% (group volume II = 45 patients). The nerve stimulator was initially set at 2 Hz, 0.1 millisecond, 1 mA. The total amount of local anesthetic (240 mg) was kept constant and equally divided between the peroneal and tibial nerves. All patients also received an ultrasound-guided popliteal sciatic nerve catheter for postoperative analgesia. Times to readiness for surgery, performance, and offset of local anesthetic were recorded. Our primary end point was to determine a possible difference in offset time between groups. Continuous variables were expressed as median (IQR) and compared with the Wilcoxon-Mann-Whitney U test; WMWodds are reported together with their 95% confidence interval.

RESULTS: The overall success rate of sciatic nerve block was 99%. Time of performance was shorter in group I, 120 seconds (90–150 seconds), than that in group II, 150 seconds (120–180 seconds) (P = 0.0048; WMWodds 2.26 [1.35–4.34]). The onset time of sensory and motor sciatic nerve block was 4 minutes (2–9 minutes) in group I and 6 minutes (4–10 minutes) in group II (P = 0.41; WMWodds 1.21 [0.77–1.95]), while the duration of sensory block was 235 minutes (203–250 minutes) in group I, and 240 minutes (218–247 minutes) in group II respectively (P = 0.51; WMWodds 1.20 [0.69–2.16]).

CONCLUSIONS: We found no evidence that varying volume and concentration while maintaining a fixed total dose of mepivacaine alters the onset time and duration of double-injection sciatic nerve block. Considering our WMWodds results, possible differences in onset time and duration comparable to differences in the performance time between groups cannot be excluded.

In Brief

Published ahead of print June 10, 2014.

Author Information

From the *Department of Anesthesia, Azienda Ospedaliera Istituto Ortopedico Gaetano Pini, Milano; Department of Anesthesia, Ospedale di Circolo Varese, Varese; and Department of Anesthesia, Irccs San Raffaele, Milano, Italy.

Erika Basso Ricci, MD, is currently affiliated with Department of Anesthesia, Università Degli Studi di Milano, Via Festa del Perdono 7, Milano, Italy.

Accepted for publication March 14, 2014.

Published ahead of print June 10, 2014.

Funding: No fund was received.

The authors declare no conflicts of interest.

Reprints will not be available from the authors.

Address correspondence to Gianluca Cappelleri, MD, Department of Anesthesia, Azienda Ospedaliera Istituto Ortopedico Gaetano Pini, Piazza cardinal Ferrari 1, 20122 Milano, Italy. Address e-mail to kappe@hotmail.com.

© 2014 International Anesthesia Research Society