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Anesth Analg. 2014 Aug;119(2):489-93. doi: 10.1213/ANE.0000000000000293.

Effect of local anesthetic dilution on the onset time and duration of double-injection sciatic nerve block: a prospective, randomized, blinded evaluation.

Author information

1
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.

Abstract

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.

PMID:
24914630
DOI:
10.1213/ANE.0000000000000293
[Indexed for MEDLINE]

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