Subparaneural injection for popliteal sciatic nerve block shows faster onset and longer duration than circumferential extraneural injection.

pearl

• Olivier Choquet, Guillaume Brault Noble, Bertrand Abbal, Didier Morau, Sophie Bringuier, and Xavier Capdevila.
• From the *Department of Anesthesiology and Critical Care, Montpellier University Hospital; †Department of Anesthesiology and Critical Care Medicine, Lapeyronie University Hospital; ‡Epidemiology and Clinical Research Department, Arnaud de Villeneuve University Hospital; and §Institut National de la Sante et de la Recherche Médicale U1046, UM1, Montpellier, France.
• Reg Anesth Pain Med. 2014 Jul 1;39(4):306-11.

BackgroundThe ideal spread of local anesthetic for effective, rapid, and safe sciatic nerve block is debated. We hypothesized that subparaneural ultrasound-guided injection results in faster onset and has a better success rate than extraneural circumferential spread.MethodsPatients undergoing elective tibial, foot, and ankle surgery with popliteal sciatic nerve blocks were prospectively enrolled. After randomization, the needle tip position was adjusted to ensure circumferential extraneural or subparaneural spread; 0.3 mL/kg of mepivacaine 10 mg/mL was injected. Post hoc video analysis was used to group the patients according to extraneural, subparaneural, and unintentional intraepineural spread.ResultsThere were 26 (43.3%) patients in the subparaneural group and 22 (36.7%) in the extraneural group. Block onset time was shorter in the subparaneural group than in the extraneural group (11 [3-21] minutes; mean [95% confidence interval], 11 [8.97-13.02] minutes and 17 [6-30] minutes; mean [95% confidence interval] 18.37 [14.17-22.57] minutes, respectively; P = 0.002). The duration of sensory blockade increased (397 [178-505] minutes vs 265 [113-525] minutes; P = 0.04). The success rate of the block also increased. Unintentional intraepineural injection occurred in 8% of patients (3 patients in the subparaneural group and 1 patient in the extraneural group; NS). Block onset time was shorter than for the subparaneural and extraneural groups (6 [3-12] minutes, 12 [3-21] minutes, and 18 [6-30] minutes; P = 0.01).ConclusionsA subparaneural injection accelerated the onset time and increased the duration of tibial nerve sensory blockade compared with circumferential extraneural injection. With unintentional intraepineural spread, the onset time was significantly shorter than for the other groups.

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