• Linda T Le, Vanessa J Loland, Edward R Mariano, J C Gerancher, Anupama N Wadhwa, Elizabeth M Renehan, Daniel I Sessler, Jonathan J Shuster, Douglas W Theriaque, Rosalita C Maldonado, Brian M Ilfeld, and PAINfRE Investigators.
• Department of Anesthesiology, University of Florida, Gainesville, FL, USA.
• Reg Anesth Pain Med. 2008 Nov 1; 33 (6): 518-25.

Background And ObjectivesIt 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.MethodsPreoperatively, 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.ResultsThe 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.ConclusionsFor 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.

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