The retrograde infraclavicular brachial plexus block has been proved an effective and safe approach. Realtime ultrasound guide will facilitate a successful peripheral nerve block. The purpose of this study was to determine the medium effective volume required to produce an effective retrograde infraclavicular block using an ultrasound (US)-guided technique.

Thirty adults undergoing elective upper limb surgery received an US-guided retrograde infraclavicular block. The initial concentration of 0.5% ropivacaine injected was 30 ml, which was subsequently varied at a ratio of 1: 1.2 for each consecutive patient according to the response of the previous patient. The medium effective volume (EV50) was determined using the Dixon and Massey up-and-down method. The effective volume in 95% of patients (EV95) was calculated using probit regression.

Inclusion Criteria:

• Elected upper extremity operations
• BMI 17~30kg/m2
• ASA I/II

Exclusion Criteria:

• Infection at injection site
• Sepsis
• Coagulation Dysfunction
• Phrenic nerve palsy
• Pneumothorax
• Recurrent laryngeal nerve palsy
• Clavicle fracture combined with nerve damage