EFSUMB EUROPEAN FEDERATION OF SOCIETIES FOR ULTRASOUND IN MEDICINE AND BIOLOGY ‘Building a European Ultrasound Community’ Young Investigator’s Award WFUMB 2011 VIENNA AUSTRIA 28 August 2011 13.50 – 15.45 10 minutes each for presentation plus 3 minutes discussion An Ultrasound Study of the Phrenic Nerve in the Posterior Cervical Triangle: Implications for the Interscalene Brachial Plexus Block

Jens Kessler University Hospital Heidelberg

ABSTRACT The interscalene block of the brachial plexus is one of the most important regional anaesthesia techniques in the world. In the first description of this invasive procedure it was recommended to choose the cricoid cartilage as the reference point for insertion of the needle. More than 40 years later avoidance of the interscalene plexus block is suggested in patients with chronic respiratory disease, chronic obstructive lung disease, bronchial asthma, and advanced pregnancy, or in patients with a high body mass index because of phrenic paralysis resulting from this kind of nerve block. The aim of the study was ultrasonographic description of the shape, size, and course of the phrenic nerve along the neck, and its relationship to the brachial plexus, to educate regional anaesthesiologists about the ultrasonic appearance of the phrenic nerve during interscalene or supraclavicular block. In this prospective observational study, 23 volunteers underwent phrenic nerve examination on both sides of the neck by use of a linear 14-MHz ultrasound probe. The phrenic nerve could be identified in 93.5% of all scans.

Sonogram of (A) the interscalene groove in the neck obtained 1cm caudal to the cricoid cartilage, and (B) corresponding labeled image. The phrenic nerve (PN) is identified medial to the brachial plexus and superficial to the anterior scalene muscle (ASM), shown with approximate probe location in the inset. Large tick marks are spaced 10mm. SCM, sternocleidomastoid muscle. The borders of the sternocleidomastoid, anterior scalene and middle scalene muscles are shown in red.

The phrenic nerve was monofascicular with a mean diameter of 0.76mm. The phrenic nerve position was nearly indistinguishable from the C5 ventral ramus at the level of the cricoid cartilage (mean distance 1.8mm). 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.

Phrenic nerve exposed after dissection of the cadaver. The phrenic nerve is seen over the anterior scalene muscle adjacent to the brachial plexus. Methylene blue dye surrounds the nerve.

Furthermore its identity was confirmed by functional examination data using ultrasoundguided transcutaneous nerve stimulation.

(A) Transcutaneous stimulation of the phrenic nerve, and corresponding (B) M-mode, and (C) B-mode sonograms of the moving ipsilateral hemidiaphragm. (A) One ultrasound system guides transcutaneous nerve stimulation while a second system simultaneously monitors diaphragm contraction.

This descriptive study found that the phrenic nerve and brachial plexus are within 2mm of each other at the cricoid cartilage level, with additional 3mm separation for every cm more caudal in the neck. This knowledge might be useful in further development of new approaches for brachial plexus block in the interscalene and supraclavicular region. Meanwhile the knowledge from this study is also used for ultrasound-guided phrenic nerve block in cases of intractable chronic hiccup therapy.