The sequence of administration of 1.5% mepivacaine and 0.5% bupivacaine does not affect latency of block onset or duration of analgesia in ultrasound-guided interscalene block.

BACKGROUND: During peripheral nerve blockade, different local anesthetics may be sequentially administered. Typically, a short- or intermediate-acting local anesthetic is administered before a long-acting local anesthetic to achieve a block with rapid onset and long duration. However, there is a paucity of data on advantages of such sequencing. We hypothesized that when using a sequential mixture of mepivacaine and bupivacaine for ultrasound-guided interscalene block, the order of injection of the drugs does not influence the clinical characteristics of the block achieved. METHODS: Sixty-four patients undergoing arthroscopic shoulder surgery (aged 18-65 years; ASA physical status I-II) with a single-injection ultrasound-guided interscalene brachial plexus block as sole anesthetic were studied. The subjects were randomized to receive 1 of 2 local anesthetic sequences: 15 mL of mepivacaine 1.5% followed by 15 mL of bupivacaine 0.5% (group A), or the same local anesthetics in the reverse order (group B). The durations of sensory and motor block were the primary outcomes. Block onset was also assessed. RESULTS: Duration of motor block was similar between group A and group B (10.1 ± 4.7 hours vs 10.3 ± 5.1 hours, mean difference 0.2 hours, 95% confidence interval [CI] -3.3 to 2.9, P = 0.9). Duration of analgesia was also similar between group A and group B (9.5 ± 5.6 hours vs 10.2 ± 4.5 hours, mean difference 0.7 hours, 95% CI -3.2 to 1.9, P = 0.42). Onset of sensory block was similar between the 2 groups (15.9 ± 7.1 minutes for group A, 13.9 ± 7.0 minutes for group B, mean difference 1.9 minutes, 95% CI -1.4 to 5.2, P = 0.25). CONCLUSIONS: The sequence in which 15 mL mepivacaine 1.5% and 15 mL bupivacaine 0.5% are administered does not seem to have a clinically meaningful effect on duration or onset of ultrasound-guided interscalene brachial plexus block.

The effect of stimulating versus conventional perineural catheters on postoperative analgesia following ultrasound-guided femoral nerve localization.

STUDY OBJECTIVE: To test the hypothesis that, if the femoral nerve is correctly localized using ultrasound (US) guidance, the type of perineural catheter used has no effect on catheter success. DESIGN: Randomized controlled trial. SETTING: Post-anesthesia care unit of an academic teaching hospital. PATIENTS: 40 ASA physical status 1, 2, and 3 patients, ages 55-85 years, undergoing elective total knee arthroplasty. INTERVENTIONS: All patients received postoperative continuous femoral nerve blocks and a single injection sciatic nerve block. Nerve localization was accomplished using US guidance and electrical nerve stimulation so that the needle tip was visualized deep to the femoral nerve. Patients were randomized to receive either stimulating (Group SC) or nonstimulating catheters (Group NSC) in the usual manner for each device. Catheters were bolused with ropivacaine and an infusion commenced. MEASUREMENTS: The primary outcome was quality of analgesia (as measured by a numerical rating scale). Other outcomes included sensory block success rate, number of attempts and time required to localize the needle tip correctly, number of attempts and time required to place the perineural catheter, amount of local anesthetic and opioid use postoperatively, and degree of completion of preset postoperative rehabilitation goals. MAIN RESULTS: Quality of analgesia was similar at all time intervals. Rates of successful femoral block (95% vs 80%; P = 0.34) were similar between groups. Time required to position the catheter was greater in Group SC than Group NSC (3.45 ± 2.05 min vs 1.72 ± 0.88 min; P < 0.01). CONCLUSIONS: Ultrasound guidance for needle localization prior to catheter insertion for femoral nerve block results in similar block characteristics between stimulating and nonstimulating catheters. The use of nonstimulating catheters avoids the technical challenges of stimulating catheters and does not require additional helpers.

The effect of mixing 1.5% mepivacaine and 0.5% bupivacaine on duration of analgesia and latency of block onset in ultrasound-guided interscalene block.

BACKGROUND: Short- and long-acting local anesthetics are commonly mixed to achieve nerve blocks with short onset and long duration. However, there is a paucity of data on advantages of such mixtures. We hypothesized that a mixture of mepivacaine and bupivacaine results in a faster onset than does bupivacaine and in a longer duration of blockade than does mepivacaine. METHODS: Sixty-four patients undergoing arthroscopic shoulder surgery (ages 18 to 65 years; ASA physical status I-II) with ultrasound-guided interscalene brachial plexus block as the sole anesthetic were studied. The subjects were randomized to receive 1 of 3 study solutions: 30 mL of mepivacaine 1.5%, 30 mL of bupivacaine 0.5%, or a mixture of 15 mL each of bupivacaine 0.5% and mepivacaine 1.5%. The block onset time and duration of motor and sensory block were assessed. RESULTS: Onset of sensory block in the axillary nerve distribution (superior trunk) was similar among the 3 groups (8.7 ± 4.3 minutes for mepivacaine, 10.0 ± 5.1 minutes for bupivacaine, and 11.3 ± 5.3 minutes for the combination group; P = 0.21 between all groups). The duration of motor block for the combination group (11.5 ± 4.7 hours) was between that of the bupivacaine (16.4 ± 9.4 hours) and mepivacaine (6.0 ± 4.2 hours) groups (P = 0.03 between bupivacaine and combination groups; P = 0.01 between mepivacaine and combination groups). Duration of analgesia was the shortest with mepivacaine (4.9 ± 2.4 hours), longest with bupivacaine (14.0 ± 6.2 hours), and intermediate with the combination group (10.3 ± 4.9 hours) (P < 0.001 for mepivacaine vs. combination group; P = 0.01 for bupivacaine vs. combination group). CONCLUSIONS: For ultrasound-guided interscalene block, a combination of mepivacaine 1.5% and bupivacaine 0.5% results in a block onset similar to either local anesthetic alone. The mean duration of blockade with a mepivacaine-bupivacaine mixture was significantly longer than block with mepivacaine 1.5% alone but significantly shorter than the block with bupivacaine 0.5% alone.