Minimum effective volume of 0.5% ropivacaine for ultrasound-guided costoclavicular brachial plexus block A dose finding study

BACKGROUND Costoclavicular brachial plexus block (CC-BPB) is a relatively new regional anaesthetic technique and there are no data on the minimum effective volume 90 (MEV90) of 0.5% ropivacaine required for an ultrasound-guided CC-BPB. OBJECTIVE To determine the MEV90 of 0.5% ropivacaine required to produce surgical anaesthesia with an ultrasound-guided CC-BPB. DESIGN Prospective up-down sequential allocation study design. SETTING University teaching hospital in Hong Kong from March 2016 to December 2017. PATIENTS Forty-eight, ASA physical status I to III patients, aged 70 years or less and scheduled for elective forearm or hand surgery under an ultrasound-guided CC-BPB, were recruited. INTERVENTION Ultrasound-guided CC-BPB was performed with the assigned volume of 0.5% ropivacaine. The Dixon 'up-and-down' sequential allocation method using the biased coin design was used to determine the MEV90 of 0.5% ropivacaine. The assigned volume of ropivacaine was based on the outcome of the previous patient. After a block failure the next patient received a volume increase of 2 ml. If the block was a success, the next patient was allocated, with a probability of b = 0.11, to receive 2 ml less, or, with a probability of 1 - b = 0.89, the same volume. MAIN OUTCOME MEASURES A successful block was defined as a minimum score of 14 of 16 points, using a composite sensory and motor block score at 45 min after the injection. The study was stopped when 45 successful blocks were achieved. MEV90 with 95% confidence interval was calculated using the centred isotonic regression for point and interval dose response studies. RESULTS The MEV90 of 0.5% ropivacaine for ultrasound-guided CC-BPB was 20.9 (95% confidence interval, 20.7 to 21.8) ml. The mean +/- SD time to readiness for surgery was 31.4 +/- 12.60 min. CONCLUSION The MEV90 of 0.5% ropivacaine required to produce surgical anaesthesia with an ultrasound-guided CC-BPB is 20.9 ml.