• Edel Duggan, Hossam El Beheiry, Anahi Perlas, Mario Lupu, Alina Nuica, Vincent W S Chan, and Richard Brull.
• Department of Anesthesia and Pain Management, Toronto Western Hospital University Health Network, Ontario, Canada.
• Reg Anesth Pain Med. 2009 May 1;34(3):215-8.

Background And ObjectivesThe aim of this study was to determine the minimum effective anesthetic volume required to produce an effective supraclavicular block for surgical anesthesia using an ultrasound (US)-guided technique.MethodsTwenty-one adults undergoing elective upper limb surgery received a US-guided supraclavicular block. The initial volume of local anesthetic (LA; 50:50 mixture of lidocaine 2% and bupivacaine 0.5% with epinephrine) injected was 30 mL, which was subsequently varied by 5 mL for each consecutive patient according to the response of the previous patient. The minimum effective anesthetic volume in 50% of patients was determined using the Dixon and Massey up-and-down method. The effective volume in 95% of patients (ED95) was calculated using probit transformation and logistic regression.ResultsThe minimum effective anesthetic volume in 50% and calculated effective volume in 95% of patients were 23 mL (95% confidence interval, 13-39 mL) and 42 mL (95% confidence interval, 19-65 mL), respectively. Seven patients received supplemental LA, with no patient requiring a general anesthetic.ConclusionIn this study, the minimum volume required for US-guided supraclavicular block in 50% of patients was 23 mL, and in 95% of patients was 42 mL. Under the present study conditions, the calculated volume of LA required for US-guided supraclavicular block does not seem to differ from the conventionally recommended volume required for supraclavicular blocks using non-US-based nerve localization techniques.

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