Volume of ropivacaine 0.2% and sciatic nerve block duration: A randomized, blinded trial in healthy volunteers.

BACKGROUND: Sciatic nerve blocks are used for many orthopaedic procedures on the knee, lower leg, foot and ankle. However, as nerve block durations vary considerably, the timing of supplemental analgesia is challenging. Therefore, knowledge on the effect of local anaesthetic (LA) dose on block duration is important to outweigh the benefits of increasing LA dose against the risk of LA systemic toxicity. In this randomized, double-blind trial, we aimed to explore the relationship between the volume of ropivacaine 0.2% and sciatic nerve block duration. We hypothesized that increasing LA volume would prolong block duration. METHODS: We randomized 60 healthy volunteers to receive one of five volumes of ropivacaine 0.2%: 5, 10, 15, 20, or 30 mL. We used an ultrasound-guided, catheter-based technique targeting the sciatic nerve in the infragluteal region. The primary outcome was sensory block duration defined as the time of insensitivity to a cold stimulus. Intergroup differences were tested using one-way ANOVA. RESULTS: Mean (SD) sensory block durations for the tibial nerve (TN) with increasing volume were: 9.3 hours (1.7), 10.4 hours (1.6), 9.7 hours (2.9), 10.7 hours (2.8) and 9.9 hours (2.6). Mean (SD) sensory block durations for the common peroneal nerve (CPN) were: 10.6 hours (2.7), 11.9 hours (1.5), 11.0 hours (3.3), 13.2 hours (3.7), and 13.5 hours (6.1). There were no intergroup differences (P = .67 [TN]; P = .25 [CPN]). CONCLUSION: We found no effect of increasing the volume of ropivacaine 0.2% from 5 to 30 mL on sensory sciatic nerve block duration.

Local Anesthetic Injection Speed and Common Peroneal Nerve Block Duration: A Randomized Controlled Trial in Healthy Volunteers.

BACKGROUND AND OBJECTIVES: The speed of local anesthetic (LA) injections in peripheral regional anesthesia ranges from slow continuous infusions (3-12 mL/h) to rapid manual injections (>7500 mL/h). Optimizing injection speed could augment the spread of LA toward the targeted nerves and influence nerve block characteristics. The objective of this study was to investigate whether injection speed of a single dose of LA affects peripheral nerve block duration. METHODS: After approval from the Danish Regional Scientific Ethics Committee, we enrolled 60 healthy adult volunteers. We used an ultrasound-guided catheter-based technique to perform a common peroneal nerve block. Participants were randomized to receive 4.0 mL of ropivacaine 0.2% with 1 of 5 injection speeds: 12, 60, 300, 600, or 1800 mL/h. Investigators and participants were blinded to group assignment and intervention. Primary outcome was duration of sensory nerve block defined by insensitivity toward cold. Secondary outcomes were duration of motor nerve block, time to onset of sensory nerve block, and grades of sensory and motor nerve block.Intergroup differences were tested by one-way analysis of variance. RESULTS: We found no differences in sensory block duration between the 5 groups. Durations were median [range]: 11 [6-14], 12 [9-14], 10.5 [2-15], 11 [8-17], and 12 [9-18] hours, respectively (P = 0.294). In addition, we found no differences in secondary outcomes. CONCLUSIONS: Injection speed of LA in the range of 12 to 1800 mL/h did not affect common peroneal nerve block duration. CLINICAL TRIAL REGISTRATION: This study was registered at ClinicalTrials.gov, identifier NCT02801799.

"Eyeball test" of thermographic patterns for predicting a successful lateral infraclavicular block.

PURPOSE: Increased distal skin temperature can be used to predict the success of lateral infraclavicular (LIC) block. We hypothesized that an "eyeball test" of specific infrared thermographic patterns after LIC block could be used to determine block success. METHODS: In this observational study, five observers trained in four distinct thermographic patterns independently evaluated thermographic images of the hands of 40 patients at baseline and at one-minute intervals for 30 min after a LIC block. Sensitivity, specificity, and predictive values of a positive and a negative test were estimated to evaluate the validity of specific thermographic patterns for predicting a successful block. Sensory and motor block of the musculocutaneous, radial, ulnar, and median nerves defined block success. Fleiss' kappa statistics of multiple interobserver agreements were used to evaluate reliability. RESULTS: As a diagnostic test, the defined specific thermographic patterns of the hand predicted a successful block with increasing accuracy over the 30-min observation period. Block success was predicted with a sensitivity of 92.4% (95% confidence interval [CI], 86.8 to 96.2) and with a specificity of 84.0% (95% CI, 70.3 to 92.4) at min 30. The Fleiss' kappa for the five observers was 0.87 (95% CI, 0.77 to 0.96). CONCLUSION: We conclude that visual evaluation by an eyeball test of specific thermographic patterns of the blocked hands may be useful as a valid and reliable diagnostic test for predicting a successful LIC block.