Brachial plexus block of the posterior and the lateral cord using ropivacaine 7.5 mg/mL

BACKGROUND We recently showed that the novel combination of a superficial cervical plexus block, a suprascapular nerve block, and the lateral sagittal infraclavicular brachial plexus block (LSIB) provides an alternative anaesthetic method for arthroscopic shoulder surgery. In this study, we hypothesised that the LSIB dose for this shoulder block could be significantly reduced by injecting only towards the shoulder relevant posterior and lateral cords. Our aim was to determine the minimum effective volume in 50% of the patients (MEV50 ) and to estimate the MEV95, when using ropivacaine 7.5 mg/mL to block these cords. METHODS Twenty-three adult patients scheduled for hand surgery participated in the study. Considering the artery as a clock face with 12 o'clock ventral, the designated volume was injected immediately outside the arterial wall and between 8 and 9 o´clock. The in-plane technique was used. Block success was assessed 30 minutes after withdrawal of the needle. Successful posterior cord block was defined as anaesthesia or analgesia of the axillary nerve. Successful lateral cord block was defined as either anaesthesia or analgesia, or >50% motor block of the musculocutaneous nerve. MEV50 was determined by the staircase up-and-down method. Logistic regression and probit transformation were applied to estimate MEV95 . RESULTS MEV50 and MEV95 were 7.8 mL [95% confidence interval (CI), 7.3-8.4] and 9.0 mL (95% CI, 7.8-10.3), respectively. CONCLUSION For single-deposit infraclavicular posterior and lateral cord block, the MEV95 of ropivacaine 7.5 mg/mL was estimated to 9.0 mL.