What is the relationship between paresthesia and nerve stimulation for axillary brachial plexus block?

Background and Objectives: To quantify the motor threshold current of a nee dle following elicitation of paresthesia during axillary brachial plexus bl ock (ABPB). Methods: This is a prospective, observational study of ABPB in 72 patients. Having elicited paresthesia, the minimum current required to produce a mot or response was noted. The development and success of the block were subseq uently followed. Results: Nineteen blocks were excluded (18 because of arterial puncture and 1 blocked needle). Of the remaining 53 blocks, 41 (77%) produced a motor r esponse at 0.5 mA or less. The median current was 0.17 mA (ran,ae, 0.03 to 3.3 mA). The site of initial paresthesia and subsequent motor response were related in 43 (81%) of cases. Conclusions: A needle position causing paresthesia produced a motor respons e at 0.5 mA or less in 77% of cases studied. This current may, therefore, b e a reasonable threshold to aim for when performing an ABPB.