Article Text

Download PDFPDF
An Ultrasound Study of the Phrenic Nerve in the Posterior Cervical Triangle: Implications for the Interscalene Brachial Plexus Block
  1. Jens Kessler, M.D.a,
  2. Ingeborg Schafhalter-Zoppoth, M.D.b and
  3. Andrew T. Gray, M.D., Ph.D.b
  1. aDepartment of Anaesthesiology, University of Heidelberg, Heidelberg, Germany
  2. bDepartment of Anesthesia and Perioperative Care, University of California, San Francisco, and the San Francisco General Hospital, San Francisco, CA


Background and Objectives: Concomitant phrenic nerve block frequently occurs after brachial plexus block procedures in the neck and can result in substantial morbidity. In this study we sought to establish the anatomic basis using ultrasound imaging.

Methods: We scanned the neck region of 23 volunteers with high resolution ultrasonography and identified the phrenic nerve in 93.5% of scans.

Results: The phrenic nerve was monofascicular with a mean diameter of 0.76 mm. The phrenic nerve position was nearly indistinguishable from the C5 ventral ramus at the level of the cricoid cartilage (mean distance 1.8 mm). Separation between the phrenic nerve and the brachial plexus increased substantially at more caudal levels in the neck. Phrenic nerve identification was confirmed by percutaneous injection of methylene blue followed by open dissection in a cadaver. Furthermore its identity was confirmed by ultrasound-guided transcutaneous nerve stimulation.

Conclusions: This descriptive study found that the phrenic nerve and brachial plexus are within 2 mm of each other at the cricoid cartilage level, with additional 3 mm separation for every cm more caudal in the neck. Clinical trials with imaging guidance are needed to establish whether brachial plexus selective blocks can be consistently achieved above the clavicle.

  • Phrenic nerve
  • Interscalene block
  • Supraclavicular block
  • Ultrasound guidance

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.


  • Reprint requests: Andrew T. Gray, M.D., Ph.D., Department of Anesthesia and Perioperative Care, Room 3C-38, San Francisco General Hospital, University of California, San Francisco, CA 94110. E-mail: graya{at}

  • This work was supported by a gift from the Beckman Foundation.