Article Text

Download PDFPDF
The Sensitivity of Motor Response to Needle Nerve Stimulation During Ultrasound Guided Interscalene Catheter Placement
  1. Michael J. Fredrickson, M.D.*
  1. Department of Anaesthesiology, Faculty of Medical and Health Sciences, The University of Auckland, and Auckland City Hospital, Auckland, New Zealand.
  2. *Reprint requests: Michael Fredrickson, M.D., Anaesthesia Institute, PO Box 109 199, Newmarket, Auckland, New Zealand. E-mail: fredrickson{at}


Background and Objectives: Neurostimulation during single shot interscalene block has a significant false negative motor response rate. Compared with tangential needle approaches for single shot block, interscalene catheter (ISC) placement commonly involves Tuohy needles inserted longitudinally to the brachial plexus. This study aimed to determine the sensitivity of neurostimulation during ultrasound-guided ISC needle placement, and the feasibility of an ultrasound-guided ISC needle endpoint.

Methods: One hundred fifty-five consecutive nonstimulating ISCs were placed with the needle tip position confirmed by the sonographic spread of 5 mL dextrose 5%. Catheter advancement was then blind 2 to 3 cm past the needle tip. A 0.8 mA electrical stimulus at 2 Hz was applied throughout. When a satisfactory image was obtained, neurostimulation was ignored and the minimum motor response amplitude noted. If imaging was equivocal, a brief appropriate motor response at 0.8 mA was sought. A sustained response at <0.5 mA was only sought if imaging was suboptimal. Prior to surgery conducted under general anesthesia, 30 mL ropivacaine 0.5% was administered through the ISC. Catheter success was defined as a recovery room numerical rating pain score of ≤2 (scale, 0-10).

Results: In 57% of patients, a muscle response was not elicited. An ultrasound needle endpoint was used in 92% of ISC placements, of which 96% were successful. Sustained twitches at <0.5 mA were obtained in 12 (8%) patients, 6 (4%) of these deliberately sought because of suboptimal imaging. Catheter success overall was 95%.

Conclusions: This study suggests that the false negative motor response rate for longitudinal ISC needle placement is higher than the false negative response rate associated with tangential needle approach interscalene block. An ultrasound guided ISC needle endpoint is a feasible alternative to a neurostimulation endpoint.

  • Ultrasound
  • Interscalene
  • Catheter
  • Continuous
  • Perineural

Statistics from

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.


  • Funding Sources: None. This work was presented, in part, at the New Zealand Society of Anaesthetists Annual Scientific Meeting, November 9, 2007 (Ritchie Prize Session).