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

Abstract

Background and objectives: The purpose of this study was to determine whether the addition of ketorolac tromethamine to local anesthesia for ankle block alters the quality or duration of analgesia after podiatric surgery. The second aim was to determine the chemical stability of ketorolac tromethamine when added to local anesthetic solutions.

Methods: The study design was double-blinded, placebo-controlled, and randomized. Seventy-nine American Society of Anesthesiologists (ASA) class I or II patients scheduled for bunionectomy or hammer toe repair, or both were randomized to 1 of 4 groups. Group L received plain 1.73% lidocaine for their ankle block. Group K received 1.73% lidocaine with ketorolac (4 mg/mL) added to the local solution. Group Kiv received 1.73% plain lidocaine for ankle block and 20 mg of ketorolac intravenously. Group E received 1.73% lidocaine with .67% ethanol added. The final concentration of lidocaine for all groups was 1.73%. The block performed in each patient was a 5-point ankle block. Beginning at 1 hour after the completion of the block and every 30 minutes thereafter, visual analogue scale (VAS) and verbal pain scores were recorded. The time from performance of the block to the initial pain and time to the first oral pain medication intake were also recorded. The time and amount of postoperative oral analgesics in the first 9 hours after the block were recorded. Adverse events were also recorded for each group.

Results: There were significantly lower overall VAS and verbal pain scores for group K compared with groups E and L and group Kiv compared with group E. Group K also had a significantly longer time to the first reported pain and first oral pain medications than groups E and L, but not with Group Kiv. The same group had significantly fewer average doses of pain medications postoperatively than Groups E and L. Group E had significantly shorter times to first report of pain and first pain medications and higher mean dose of postoperative oral analgesics than group K and Group Kiv. There were no untoward side effects reported from any group. Chemical analysis by gas chromatography (GC) and capillary electrophoresis (CE) showed no significant change in composition of the solutions when ketorolac was mixed with lidocaine and/or bupivacaine and stored at 37 degrees C for 1 week.

Conclusions: The addition of ketorolac to lidocaine for ankle block contributed to longer duration and better quality analgesia after foot surgery compared with plain 1.73% lidocaine or 1.73% lidocaine plus intravenous ketorolac. The ethanol vehicle is unlikely responsible for the analgesic effects of ketorolac. Ketorolac retains its chemical stability when placed in local solutions of lidocaine or bupivacaine.