Clinical And Anatomic Study Of An Ultrasound-Guided Selective Block Of The Superior Trunk Of The Brachial Plexus. Description Of A New Approach

Introduction

Interscalene brachial plexus block is the most commonly performed regional anesthesia technique to promote analgesia for shoulder surgeries. However, one of limitations is the risk of phrenic nerve palsy despite injection of low volumes, being contraindicated in patients with limited pulmonary reserve.

Burckett-St.Laurent et al described an alternative approach to avoid phrenic block - the superior trunk approach.

In this case series, the investigators suggest a modification of Burckett-St.Laurent's technique. The objective of this study is to evaluate efficacy, phrenic nerve function and contrast dispersion in cadavers after performing this new approach.

Materials and methods

The study was approved by Institutional Review Board of our institution. To perform the superior trunk approach described by Burckett-St.Laurent, C5 and C6 nerve roots are identified within the interscalene groove and traced distally to where they coalesce into the superior trunk, proximal to the takeoff of the suprascapular nerve. Burckett-St.Laurent et al suggest spreading local anesthetic around superior trunk at this point.

The investigators suggest an injection more distally, where superior trunk is in costoclavicular space below omohyoid muscle, proximal to the suprascapular outlet. The needle is advanced below the prevertebral layer of deep cervical fascia, avoiding that the tip of the needle lies in the fascial plane between investing layer of deep vertebral fascia and prevertebral layer, a loose fascial plane where lymph node chain is located and may allow postero-anterior dispersion toward phrenic. To guarentee right position of the tip the investigators suggest an intracluster pattern of spread.

Patients scheduled for rotator cuff surgery will receive 6 mL of 0,5% bupivacaine in this new approach. Successful block is defined as motor score of ≤ 2 on modified Bromage scale in the deltoid and bíceps; absent sensation to cold and pinprick sensation in C5 and C6 dermatomes within 30 minutes of injection.

To evaluate phrenic nerve, diaphragmatic excursion will be assessed by ultrasonography of ipsilateral hemidiaphragm and impedance tomography. Pain scores and analgesic consumption will be assessed in PACU.

Moreover, 6 mL of methylene blue will be injected into cadavers to evaluate if dispersion is restricted to fibers of the superior trunk and don't reach phrenic nerve.