A Randomized Comparison of Minimum Effective Volume With 0.5% Ropivacaine Between Costoclavicular and Paracoracoid Ultrasound-guided Infraclavicular Block for Forearm Surgery

The costoclavicular space block technique is a new developed approach of ultrasound-guided infraclavicular brachial plexus block(USG-ICB) in last two years and has not been studied much yet. USG-ICB represents an attractive option for upper-limb surgery at or below the elbow joint with similar success rate and fewer adverse effects compared with ultrasound-guided supraclavicular block. The paracoracoid approach serves as a standard and traditional method for USG-ICB in clinical practice, easy to learn and perform. However, the minimum effective volume(MEV)of this approach has been studied by different investigators with different regional anesthetics or its mixture, and specially, the 95% MEV result of this approach is more than 30ml in all related researches which is still a large volume. According to the investigators' experience in using the costoclavicular space technique for forearm surgery, it usually can get a comparable sensation and motor block effect by no more than 25ml. Recently, there was a clinical randomized control study which compared the costoclavicular and paracoracoid USG-ICB for upper limb surgery using a 35ml-mixture of 1% lidocaine-0.25% bupivacaine with epinephrine 5 ug/ml and came to the conclusions: two groups resulted in similar onset times and no intergroup difference were found in terms of performance time and success rate. However, 35ml is a much larger regional anesthetic volume than what we used in routine brachial plexus block. So, we set this parallel controlled dose-finding trial to work out the MEV with 0.5% ropivacaine of both approaches above for forearm surgery and compare the performance time between them, providing reasonable evidence for clinical choice. Patients enrolled in this study will be assigned to costoclavicular group and paracoracoid group and in each group, the volume of local anesthetic applied to patients start with 30ml, and then decreased by 2.5ml for next patient when the previous block is successful, otherwise increased by 2.5ml when failed,which is also called a staircase up-and-down method usually applied in dose-finding research of nerve block. After certain reflections of the local anesthetic volume sequential line graph, the minimum effective volume could be calculated.