Background and Objectives: It is currently unknown if the primary determinant of continuous peripheral nerve block effects is simply total drug dose, or whether local anesthetic concentration and/or volume have an influence. We therefore tested the null hypothesis that providing ropivacaine at different concentrations and rates — but at an equal total basal dose — produces similar effects when used in a continuous interscalene nerve block.
Methods: Preoperatively, an anterolateral interscalene perineural catheter was inserted using the anterolateral approach in patients undergoing moderately painful shoulder surgery. Subjects were randomly assigned to receive a postoperative perineural infusion of either 0.2% ropivacaine (basal 8 mL/h, bolus 4 mL) or 0.4% ropivacaine (basal 4 mL/h, bolus 2 mL) through the second postoperative day. Our primary endpoint was the incidence of an insensate hand/finger during the 24 hours beginning the morning following surgery.
Results: The incidence of an insensate hand/finger did not differ between the treatment groups (n = 50) to a statistically significant degree (0.2% ropivacaine, mean [SD] of 0.8 [1.3] times; 0.4% ropivacaine, mean 0.3 [0.6] times; estimated difference = 0.5 episodes, 95% confidence interval, −0.1 to 1.1 episodes; P = .080). However, this is statistically inconclusive given the confidence interval. In contrast, pain (P = .020) and dissatisfaction (P = .011) were greater in patients given 0.4% ropivacaine.
Conclusions: For continuous interscalene nerve blocks, given the statistically inconclusive primary endpoint results and design limitations of the current study, further research on this topic is warranted. In contrast, providing a lower concentration of local anesthetic at a higher basal rate provided superior analgesia.
- Continuous peripheral nerve block
- Continuous interscalene nerve block
- Patient-controlled regional analgesia
- Perineural local anesthetic infusion
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Funding for this project provided by NIH grant GM077026 (Principal Investigator: Dr. Ilfeld) from the National Institute of General Medical Sciences (Bethesda, MD); NIH grant RR00082 from the National Center for Research Resources (Bethesda, MD); the Departments of Anesthesiology, University of Florida (Gainesville, FL), University of California San Diego (San Diego, CA), Wake Forest Medical Center (Winston-Salem, NC), University of Louisville (Louisville, KY), University of Ottawa (Ottawa, Ontario, Canada), and the Cleveland Clinic (Cleveland, OH); and Sorenson Medical (West Jordan, UT). Dr. Sessler is supported by the Joseph Drown Foundation (Los Angeles, CA). The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of these entities. A portion of the results of this investigation was submitted in abstract form for the Annual Meeting of the American Society of Anesthesiologists, Orlando, Florida, October 18-22, 2008. Sorenson Medical (West Jordan, UT) provided funding and donated portable infusion pumps for this investigation. This company had no input into any aspect of study conceptualization, design, and implementation; data collection, analysis and interpretation; or manuscript preparation. None of the authors has a personal financial interest in this research.