Triple-blind randomized clinical trial of time until sensory change using 1.5% mepivacaine with epinephrine, 0.5% bupivacaine, or an equal mixture of both for infraclavicular block.

Abstract

Practitioners mix faster-onset, intermediate-duration local anesthetics (LAs) with slower-onset, long-duration LAs to get fast peripheral nerve block (PNB) onset and long duration. We hypothesized that 1.5% mepivacaine (with epinephrine) (mepivacaine) or 1.5% mepivacaine (with epinephrine) mixed with 0.5% bupivacaine (mixed) would reduce PNB sensory onset by 20% or more versus 0.5% bupivacaine alone (bupivacaine). Patients (n = 93) having arm surgery were randomized to 1 of the 3 LA groups. Infraclavicular PNB was administered using 1 of 3 LAs; afterward, PNB sensory (motor) onset, duration, and other outcomes were assessed. Subjects, physicians, and the biostatistician were blinded until study completion. Median (interquartile range) PNB sensory onset (in minutes) was as follows: mepivacaine, 3 (3-6); mixed, 6 (3-6); and bupivacaine, 6 (3-12) (P = 0.0085). Mepivacaine PNB sensory onset was not faster than mixed (P = 0.57), but mixed was faster than bupivacaine (P = 0.0035). More mixed group patients achieved PNB sensory onset (0.81) versus the bupivacaine group (0.54) at 6 mins. Median (interquartile range) PNB motor onset (in minutes) was as follows: mepivacaine, 15 (12-18); mixed, 17 (12-21); and bupivacaine, 21 (12-24) (P < 0.0001). Median sensory and motor PNB duration (in minutes) was as follows: mepivacaine, 281 and 320; mixed, 439 and 556; and bupivacaine, 850 and 1109. Sensory (motor) PNB duration was shorter with mepivacaine versus mixed (P < 0.0001, P = 0.034), and mixed was shorter versus bupivacaine (P = 0.0243, P = 0.034). Mixing 1.5% mepivacaine (with epinephrine) with 0.5% bupivacaine speeds up PNB sensory (motor) onset compared with 0.5% bupivacaine alone.