Continuous Adductor Canal Blocks: Does Varying Local Anesthetic Delivery Method (Automatic Repeated Bolus Doses Versus Continuous Basal Infusion) Influence Cutaneous Analgesia and Quadriceps Femoris Strength? A Randomized, Double-Masked, Controlled, Split-Body Volunteer Study.

Continuous Adductor Canal Blocks: Does Varying Local Anesthetic Delivery Method (Automatic Repeated Bolus Doses Versus Continuous Basal Infusion) Influence Cutaneous Analgesia and Quadriceps Femoris Strength? A Randomized, Double-Masked, Controlled, Split-Body Volunteer Study Amanda M. Monahan, MD,* Jacklynn F. Sztain, MD,* Bahareh Khatibi, MD,* Timothy J. Furnish, MD,* Pia Jaeger, MD, PhD,†‡ Daniel I. Sessler, MD,‡§ Edward J. Mascha, PhD,‡∥¶ Jing You, MS,‡ Cindy H. Wen, BS,# Ken A. Nakanote, BA,** and Brian M. Ilfeld, MD, MS*‡ BACKGROUND: It remains unknown whether continuous or scheduled intermittent bolus local anesthetic administration is preferable for adductor canal perineural catheters. Therefore, we tested the hypothesis that scheduled bolus administration is superior or noninferior to a con- tinuous infusion on cutaneous knee sensation in volunteers. METHODS: Bilateral adductor canal catheters were inserted in 24 volunteers followed by ropi- vacaine 0.2% administration for 8 hours. One limb of each subject was assigned randomly to a continuous infusion (8 mL/h) or automated hourly boluses (8 mL/bolus), with the alternate treatment in the contralateral limb. The primary end point was the tolerance to electrical current applied through cutaneous electrodes in the distribution of the anterior branch of the medial femoral cutaneous nerve after 8 hours (noninferiority delta: −10 mA). Secondary end points included tolerance of electrical current and quadriceps femoris maximum voluntary isometric contraction strength at baseline, hourly for 14 hours, and again after 22 hours. RESULTS: The 2 administration techniques provided equivalent cutaneous analgesia at 8 hours because noninferiority was found in both directions, with estimated difference on tolerance to cutaneous current of −0.6 mA (95% confidence interval, −5.4 to 4.3). Equivalence also was found on all but 2 secondary time points. CONCLUSIONS: No evidence was found to support the hypothesis that changing the local anes- thetic administration technique (continuous basal versus hourly bolus) when using an adductor canal perineural catheter at 8 mL/h decreases cutaneous sensation in the distribution of the anterior branch of the medial femoral cutaneous nerve. (Anesth Analg 2016;122:1681–8) From the *Department of Anesthesiology, University of California San ­Diego, San Diego, California; †Department of Anesthesiology, Rigshospi- talet, ­Copenhagen University Hospital, Copenhagen, Denmark; ‡Outcomes Research Consortium, Cleveland, Ohio; §Department of Outcomes Research, Anesthesiology Institute, The Cleveland Clinic, Cleveland, Ohio; Depart- ments of ∥Quantitative Health Sciences and ¶Outcomes Research, The Cleve- land Clinic, Cleveland, Ohio; #­Department of Ophthalmology, University of California San Diego, San Diego, California; and **School of Medicine, University of California San D ­ iego, San Diego, California. Accepted for publication November 25, 2015. Funding: This study was supported by the University of California San Diego Clinical and Translational Research Institute (San Diego, CA); the National Institutes of Health National Center for Research Resources grant UL1RR031980; Department of Anesthesiology, University California of San Diego (San Diego, CA); and Smiths Medical (St. Paul, MN). In addition, Smiths Medical provided the portable infusion pumps, and Teleflex Medical (Research Triangle Park, NC) provided the perineural catheters used in this investigation. Neither company had input into any aspect of study concep- tualization, design, and implementation; data collection, analysis and inter- pretation; or manuscript preparation. The content of this article is solely the responsibility of the authors and does not necessarily represent the official views of the funding entities. The authors declare no conflicts of interest. Presented, in part, as a scientific abstract at the Annual Meeting of the American Society of Anesthesiologists in San Diego, CA, October 26, 2015. Reprints will not be available from the authors. Address correspondence to Brian M. Ilfeld, MD, MS, Department of Anesthe- siology, 200 West Arbor Dr., MC 8770, San Diego, CA 8770. Address e-mail to bilfeld@ucsd.edu. Copyright © 2016 International Anesthesia Research Society DOI: 10.1213/ANE.0000000000001182 May 2016 • Volume 122 • Number 5 C ontinuous adductor canal blocks provide pain con- trol after surgical procedures of the knee, but there is growing evidence that they provide less-potent analgesia, at times, than continuous femoral nerve blocks. 1,2 Because perineural adductor canal infusions induce far less quadriceps femoris muscle weakness than their femoral counterparts, they may be preferable if the cause(s) of the inferior analgesia can be identified and corrected. A poten- tial cause of inferior analgesia is due to the neuroanatomy of the adductor canal (an intermuscular space within the anterior thigh). 3–5 The saphenous nerve enters the adduc- tor canal at the apex of the femoral triangle, contributes to the innervation of the knee, and then innervates the medial leg below the knee and the ankle capsule. 6,7 Because adduc- tor canal perineural catheters are located within the canal itself, local anesthetic introduced through the catheter pre- sumably reaches the saphenous and other nerves passing through the canal, which is deep to the sartorius muscle. In contrast, nerves that innervate much of the skin around the knee do not pass through the adductor canal: the medial femoral cutaneous nerve branches from the anterior branch of the femoral nerve approximately 4 cm distal to the ingui- nal ligament, crosses anterior to the femoral artery, and then further divides into posterior and anterior branches. 6,8 The anterior branch runs close to the deep fascia superficial to www.anesthesia-analgesia.org 1681 Copyright © 2016 International Anesthesia Research Society. Unauthorized reproduction of this article is prohibited.