Onset and duration of anesthesia for local anesthetic combinations commonly used in forefoot surgery; surprise results with sequential blocks

Abstract

Local anesthetic nerve blocks are frequently used for postoperative analgesia and to the best of our knowledge no studies have evaluated the effects of injecting bupivacaine into an area previously injected with lidocaine. Sensation was tested in three groups of subjects receiving local anesthetic digital blocks. Group A received bupivacaine 0.25% plain. Group B received a 1:1 mixture of lidocaine 1% plain and bupivacaine 0.25%. Group C received an initial block of lidocaine 1% plain sequentially followed by bupivacaine 0.25% 1h later. Bupivacaine exhibited a delayed onset and the longest duration when compared to the other two groups. The group receiving the 1:1 mixture showed a rapid onset that resembled that of lidocaine and a shortened duration that did not resemble bupivacaine. The group receiving the sequential injections showed that even after a 1h interval following the lidocaine infiltration, there was a deleterious effect on duration of action of the bupivacaine. Using bupivacaine as a post-surgical block in the presence of residual lidocaine from a preoperative block is not warranted as once again, the extended duration of bupivacaine is mitigated. Bupivacaine alone as an initial operative block affords clinically acceptable onset of anesthesia while also providing extended duration of action.