Clonidine added to a continuous interscalene ropivacaine perineural infusion to improve postoperative analgesia: a randomized, double-blind, controlled study.

Although clonidine has been shown to increase the duration of local anesthetic action and prolong postoperative analgesia when included in single-injection nerve blocks, the only controlled investigation of the efficacy of this practice to improve analgesia for continuous perineural local anesthetic infusion failed to discern any clinically relevant benefits. For this study, we used a larger dose of clonidine in an attempt to improve analgesia. Patients (n = 20) undergoing moderately painful orthopedic surgery of the shoulder received an interscalene brachial plexus block (40 mL of mepivacaine 1.5%, epinephrine 2.5 microg/mL, and clonidine 50 microg) and a perineural catheter before surgery. After surgery, ropivacaine 0.2% or ropivacaine 0.2% plus clonidine 2 microg/mL was delivered via the catheter for 3 days (basal rate, 5 mL/h; patient-controlled bolus, 5 mL; lockout, 1 h). Investigators and patients were blind to random group assignment. The primary outcome variable was designated as the most intense pain during the day after surgery. Secondary end-points included additional pain scores, patient-controlled bolus doses, oral analgesic use, sleep quality, and catheter- or infusion-related complications. There were no statistically significant differences between groups for any of the variables investigated. We conclude that adding clonidine 2 microg/mL to a ropivacaine interscalene perineural infusion does not decrease breakthrough pain intensity the day after surgery. For the additional end-points, our negative findings are only suggestive of a lack of effect and require further study for verification.