• A Choyce, V W Chan, W J Middleton, P R Knight, P Peng, and C J McCartney.
• Department of Anesthesia, University of Toronto, University Health Network, Toronto Western Hospital, Toronto, Ontario, Canada.
• Reg Anesth Pain Med. 2001 Mar 1;26(2):100-4.

Background And ObjectivesTo quantify the motor threshold current of a needle following elicitation of paresthesia during axillary brachial plexus block (ABPB).MethodsThis is a prospective, observational study of ABPB in 72 patients. Having elicited paresthesia, the minimum current required to produce a motor response was noted. The development and success of the block were subsequently followed.ResultsNineteen blocks were excluded (18 because of arterial puncture and 1 blocked needle). Of the remaining 53 blocks, 41 (77%) produced a motor response at 0.5 mA or less. The median current was 0.17 mA (range, 0.03 to 3.3 mA). The site of initial paresthesia and subsequent motor response were related in 43 (81%) of cases.ConclusionsA needle position causing paresthesia produced a motor response at 0.5 mA or less in 77% of cases studied. This current may, therefore, be a reasonable threshold to aim for when performing an ABPB.

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