• Anahi Perlas, Ahtsham Niazi, Colin McCartney, Vincent Chan, Daquan Xu, and Sherif Abbas.
• Department of Anesthesia and Pain Medicine, Toronto Western Hospital, Toronto, Ontario, Canada. anahi.perlas@uhn.on.ca
• Reg Anesth Pain Med. 2006 Sep 1;31(5):445-50.

Background And ObjectiveSeeking paresthesia and obtaining a motor response to an electrical stimulus are the two most common methods of nerve localization for the performance of peripheral-nerve blocks. However, these two endpoints do not always correlate, and the actual sensitivity and specificity of either method remains unknown. The objective of this study is to determine the sensitivity of paresthesia and motor response to electrical nerve stimulation as tools for nerve localization when a 22-gauge insulated needle is used for the performance of axillary-nerve block.MethodsAfter IRB approval and informed consent, 103 patients were enrolled. Real-time ultrasonography was used as the reference test. After needle-to-nerve contact was confirmed by ultrasonography, the patient was requested to report the presence of paresthesia, and a nerve stimulator was used to seek a motor response, with a stimulating current of 0.5 mA or less.ResultsOne patient was excluded from analysis because of protocol violation. Paresthesia was found to be 38.2% sensitive and motor response was 74.5% sensitive for detection of needle-to-nerve contact.ConclusionThe very different and relatively low sensitivity of either technique may explain, in part, the lack of correlation previously reported between the 2 endpoints.

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