title: The sensitivity of motor response to nerve stimulation and paresthesia for nerve localization as evaluated by ultrasound.
abstract: OBJECTIVE
  Seeking 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.
  
  
  METHODS
  After 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.
  
  
  RESULTS
  One 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.
  
  
  CONCLUSIONS
  The very different and relatively low sensitivity of either technique may explain, in part, the lack of correlation previously reported between the 2 endpoints.
authors.affiliation: Department of Anesthesia and Pain Medicine, Toronto Western Hospital, Toronto, Ontario, Canada. anahi.perlas@uhn.on.ca
authors.forename: Anahi
authors.initials: A
authors.lastname: Perlas
authors.forename: Ahtsham
authors.initials: A
authors.lastname: Niazi
authors.forename: Colin
authors.initials: C
authors.lastname: McCartney
authors.forename: Vincent
authors.initials: V
authors.lastname: Chan
authors.forename: Daquan
authors.initials: D
authors.lastname: Xu
authors.forename: Sherif
authors.initials: S
authors.lastname: Abbas
mesh_terms: D000328:Adult; D000368:Aged; D001365:Axilla / Q000000981:diagnostic imaging; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009407:Nerve Block; D010292:Paresthesia / Q000503:physiopathology*; D014459:Ulnar Nerve / Q000000981:diagnostic imaging; D014463:Ultrasonography