• Ban C H Tsui, Jennifer J Pillay, Kinny T Chu, and Derek Dillane.
• Department of Anesthesiology and Pain Medicine, 8-120 Clinical Sciences Building, University of Alberta, Edmonton, Alberta, Canada. btsui@ualberta.ca
• Anesthesiology. 2008 Sep 1;109(3):479-83.

BackgroundIntraneural injection during peripheral nerve blockade can cause neurologic injury. Current approaches to prevent or detect intraneural injection lack reliability and consistency, or only signal intraneural injection upon the event. A change in electrical impedance (EI) could be indicative of intraneural needle placement before injection.MethodsAfter animal care committee approval, eight pigs were anesthetized and kept spontaneously breathing. In four pigs (part 1), the sciatic nerves were exposed bilaterally for direct needle placement; in a further four pigs (part 2), the tissue was kept intact for ultrasound-guided needle placement. An insulated needle (Sprotte 24 gauge; Pajunk GmbH Medizintechnologie, Geisingen, Germany), attached to a nerve stimulator displaying EI (Braun Stimuplex HNS 12; B. Braun Medical, Bethlehem, PA), was placed extraneurally and then advanced to puncture the nerve sheath. Five punctures within approximately a 1-cm length of each nerve were performed. For each Part, overall EI at each compartment and EI after individual punctures were compared using a general linear model, with post hoc analysis using the Duncan multiple range test.ResultsThe EI was lower extraneurally compared with intraneurally during open dissection (12.1 +/- 1.8 vs. 23.2 +/- 4.4 kOmega; P < 0.0001; n = 8) and when using ultrasound guidance (10.8 +/- 2.9 vs. 18.2 +/- 6.1 kOmega; P < 0.0001; n = 7 nerves were visualized adequately). The EI difference was maintained despite performing five sequential punctures.ConclusionsWith further study, EI could prove to be a quantifiable warning signal to alert clinicians to intraneural needle placement, preventing local anesthetic injection and subsequent nerve injury.

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