Minimum Effective Volume of Local Anaesthetic in 50% Patients Using Dixon’s Up-And-Down Method for Ultrasound Guided Supraclavicular Brachial Plexus Block: One Year Hospital Based Clinical Study

Abstract

Background: Supraclavicular approach is commonly used for brachial plexus block in upper limb surgeries. This study aimed to determine the minimum dose of local. anaesthetic for a successful ultrasound guided-supraclavicular brachial plexus block in 50% of patients, undergoing upper limb surgeries.

Materials and Methods: This prospective hospital-based study included 40 patients aged 20 to 60 years, posted for elective upper limb surgery receiving a supraclavicular brachial plexus block under ultrasound guidance. The first patient in the study was administered with a volume of 30 mL. Equal volume of injection 0.5% bupivacaine and 2% lidocaine with 1:200,000 adrenaline was administrated (ratio 1:1). Depending on whether the block in the preceding patient was successful or unsuccessful, the subsequent patients received an increase or decrease in 2 mL using Dixon’s up. or down method, after 30 mins of local anaesthetic injection. Sensory block and motor block were assessed.

Results: The mean volume of anesthetic used in the present study for performance of block was 18.6±5.7 mL. Successful block was observed in 77.5% of patients. The minimum effective local anesthetic volume for a successful block in 50% of patients was 16.22 ml and effective volume in 95% of patients (ED₉₅) was calculated to be 46.64 mL (95% CI 35.69-84.31 mL). Conclusion: The minimum effective volume in 50% patients (MEAV50) for ultrasound guided supraclavicular brachial plexus block was 16.22 mL. Lower volumes of local anaesthetic lead to reduced incidence of local anesthetic toxicity at the cost of duration of sensory and motor blockade.