Introduction In an effort to shorten onset time, a common practice is to add lidocaine to bupivacaine. In the setting of infraclavicular block, it is unclear what the block characteristics of this practice are compared with bupivacaine alone. We hypothesized that bupivacaine alone increases the duration of motor block, sensory block, and postoperative analgesia while resulting in a slower onset time compared with a bupivacaine and lidocaine mixture.

Methods 40 patients receiving ultrasound-guided infraclavicular brachial plexus block were randomly assigned to receive either 35 mL of 0.25% bupivacaine and 1% lidocaine or 0.5% bupivacaine, both associated with perineural adjuvants (epinephrine 5 µg/mL and dexamethasone 4 mg). After the block was performed, a blinded observer evaluated the success of the block, the onset time, and the incidence of surgical anesthesia. Postoperatively, a blinded observer contacted patients who had successful blocks to inquire about the duration of motor block, sensory block, postoperative analgesia, and the presence of rebound pain.

Results When comparing patients having bupivacaine alone versus bupivacaine and lidocaine, the mean (SD) motor block duration was 28.4 (5.2) vs 18.9 (3.1) hours, respectively; the mean difference 9.5 hours (95% CI 6.5 to 12.4; p<0.001); the mean (SD) sensory block duration was 29.3 (5.8) vs 18.7 (4.0) hours, respectively; the mean difference 10.6 hours (95% CI 7.1 to 14.0; p<0.001); the mean (SD) postoperative analgesia duration was 38.3 (7.4) vs 24.3 (6.6) hours, respectively; the mean difference 14 hours (95% CI 9.2 to 18.8; p<0.001); and the median (IQR) onset time was 35 (15) vs 20 (10) min, respectively; p<0.001. No other significant differences were detected.

Conclusions Compared with mixed bupivacaine–lidocaine, 0.5% bupivacaine significantly prolongs sensorimotor block and postoperative analgesia at the expense of a delayed onset time.

Trial registration number NCT05834023.