Continuous Popliteal Sciatic Blocks: Does Varying Perineural Catheter Location Relative to the Sciatic Bifurcation Influence Block Effects? A Dual-Center, Randomized, Subject-Masked, Controlled Clinical Trial.

Continuous Popliteal Sciatic Blocks: Does Varying Perineural Catheter Location Relative to the Sciatic Bifurcation Influence Block Effects? A Dual-Center, Randomized, Subject-Masked, Controlled Clinical Trial Amanda M. Monahan, MD,* Sarah J. Madison, MD,* Vanessa J. Loland, MD,* Jacklynn F. Sztain, MD,* Michael L. Bishop, MD,* NavParkash S. Sandhu, MD,* Richard H. Bellars, MD,* Bahareh Khatibi, MD,* Alexandra K. Schwartz, MD,† Sonya S. Ahmed, MD,† Michael C. Donohue, PhD,‡ Scott T. Nomura, BS,§ Cindy H. Wen, BS,‖ and Brian M. Ilfeld, MD, MS*¶ BACKGROUND: Multiple studies have demonstrated that, for single-injection popliteal sciatic nerve blocks, block characteristics are dependent upon local anesthetic injection relative to the sciatic nerve bifurcation. In contrast, this relation remains unexamined for continuous pop- liteal sciatic nerve blocks. We, therefore, tested the hypothesis that postoperative analgesia is improved with the perineural catheter tip at the level of the bifurcation compared with 5 cm proximal to the bifurcation. METHODS: Preoperatively, subjects having moderately painful foot or ankle surgery were randomly assigned to receive an ultrasound-guided subepimyseal perineural catheter inserted either at or 5 cm proximal to the sciatic nerve bifurcation. Subjects received a single injection of mepivacaine 1.5% either via the insertion needle preoperatively or the perineural catheter postoperatively, fol- lowed by an infusion of ropivacaine 0.2% (6 mL/h basal, 4 mL bolus, and 30-min lockout) for the study duration. The primary end point was the average pain measured on a numeric rating scale (0–10) in the 3 hours before a data collection telephone call the morning after surgery. RESULTS: The average numeric rating scale of subjects with a catheter inserted at the sciatic nerve bifurcation (n = 64) was a median (10th, 25th to 75th, and 90th quartiles) of 3.0 (0.0, 2.4–5.0, and 7.0) vs 2.0 (0.0, 1.0–4.0, and 5.0) for subjects with a catheter inserted proximal to the bifurcation (n = 64; P = 0.008). Similarly, maximum pain scores were greater in the group at the bifurcation: 6.0 (3.0, 4.4–8.0, and 9.0) vs 5.0 (0.0, 3.0–8.0, and 10.0) (P = 0.019). Differences between the groups for catheter insertion time, opioid rescue dose, degree of numbness in the foot/toes, catheter dislodgement, and fluid leakage did not reach statistical significance. CONCLUSIONS: For continuous popliteal sciatic nerve blocks, a catheter inserted 5 cm proximal to the sciatic nerve bifurcation provides superior postoperative analgesia in subjects having moderately painful foot or ankle surgery compared with catheters located at the bifurcation. This is in marked contrast with single-injection popliteal sciatic nerve blocks for which benefits are afforded to local anesthetic injection distal, rather than proximal, to the bifurcation. (Anesth Analg 2016;122:1689–95) C ontinuous popliteal sciatic nerve blocks provide postoperative analgesia after surgical procedures of the foot and ankle. 1 The sciatic nerve courses down From the *Department of Anesthesiology, University of California San Diego, San Diego, California; †Department of Orthopedics, University of California San Diego, San Diego, California; ‡Division of Biostatistics and Bioinformat- ics, University of California San Diego, San Diego, ­California; §School of Med- icine, University of California San Diego, San Diego, C ­ alifornia; ‖Department of Ophthalmology, University of California San Diego, San Diego, California; and ¶Outcomes Research Consortium, Cleveland, Ohio. Accepted for publication December 28, 2015. Funding: Funding for this project was provided by the National Institutes of Health grant GM077026 (Principal Investigator: Dr. Ilfeld) from the National Institute of General Medical Sciences (Bethesda, Maryland); and the Department of Anesthesiology, University California San Diego (San Diego, California). The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the funding entities. The authors declare no conflicts of interest. Reprints will not be available from the authors. Address correspondence to Brian M. Ilfeld, MD, MS, Department of ­Anesthesiology, University of California San Diego, 200 West Arbor Dr., MC 8770, San Diego, CA 92103. Address e-mail to bilfeld@ucsd.edu. Copyright © 2016 International Anesthesia Research Society DOI: 10.1213/ANE.0000000000001211 May 2016 • Volume 122 • Number 5 the posterior thigh and bifurcates just above or within the popliteal fossa into 2 branches: the tibial and common peroneal nerves. Cadaver studies have confirmed the location of this bifurcation to range from approximately 0 to 11 cm proximal to popliteal crease, most commonly 5 to 7 cm above the crease. 2,3 Using ultrasound guidance, practitioners can target a precise location along the sciatic nerve relative to the sciatic bifurcation for deposition of local anesthetic. 4–6 Previous randomized studies document that depositing an initial bolus of local anesthetic via a needle distal to the sciatic bifurcation—compared with proximal to the bifur- cation—results in decreased time to onset of sensory and motor block and at times an increased surgical-quality block success rate. 4–6 This suggests that deposition of local anes- thetic at various locations along the sciatic nerve can influ- ence block characteristics. However, findings from studies involving single-injection nerve blocks have not always been replicated when investigated in relation to continuous peripheral nerve blocks. 7–12 Whether the perineural catheter location relative to the sciatic nerve bifurcation influences www.anesthesia-analgesia.org 1689 Copyright © 2016 International Anesthesia Research Society. Unauthorized reproduction of this article is prohibited.