Postoperative analgesia after peripheral nerve block for podiatric surgery: clinical efficacy and chemical stability of lidocaine alone versus lidocaine plus clonidine.

Abstract

Postoperative analgesia may be prolonged by the addition of clonidine to local anesthetic solutions used for regional anesthesia. The purpose of this study was to test this hypothesis in a clinical trial of patients undergoing podiatric surgery. The study design was prospective, double-blinded, and randomized. Ninety ASA physical status I or II patients scheduled for bunionectomy or hammer toe repair were randomized to receive ankle or metatarsal blocks with plain 1.73% lidocaine (Group L), 1.73% lidocaine with 10 micrograms/mL of clonidine added (Group C10), or 1.73% lidocaine with 20 micrograms/mL clonidine (Group C20). Time from the performance of the block to 1) loss of sensation to pinprick, 2) return of sensation to pinprick, 3) onset of postsurgical pain, and 4) time of first oral pain medication intake were recorded. Beginning at 1 h after the completion of the block, visual analog scale (VAS) and verbal pain scores were recorded every 30 min. Additional postoperative oral pain medication required in the first 9 h after the block was also recorded. Analysis of variance (ANOVA) was used to analyze intergroup differences in the VAS and verbal pain scores, the time to first reported pain, the time to first oral pain medication, and the total amount of oral pain medications required. Repeated-measures ANOVA was used to analyze the VAS and verbal pain scores overall and integrated assessment of pain scores and rescue medication was per-formed. Adverse events were also recorded for each group. There were no differences among the three groups with regard to overall VAS pain scores although Group C10 had significantly better verbal pain scores after the first 3 h (P < 0.05). There was also no difference in time to loss or return of pinprick sensation. Group C10 had a longer time to first reported pain (P < 0.01), a longer time to first oral pain medication (P < 0.01), a lower average total dose of oral pain medication required (P < 0.05), and a lower integrated assessment of pain and medication (P < 0.01) than Group L. More patients in Group C10 reported no pain postoperatively (P < 0.01) and no pain medication taken (P < 0.01) than Group L. Group C20 results suggested no statistically significant improvement over plain lidocaine. One patient in Group C20 experienced significant hypotension postoperatively. pH determinations and chemical analysis by capillary electrophoresis showed no significant change in composition of the solutions when clonidine was mixed with lidocaine and stored at 4 degrees C for 1 wk. Compared to 1.73% lidocaine, combining clonidine (10 micrograms/mL) with lidocaine for local anesthetic block for foot surgery significantly increases the duration and quality of postoperative analgesia.