Effects of C8 nerve root block during interscalene brachial plexus block on anesthesia of the posterior shoulder in patients undergoing arthroscopic shoulder surgery: study protocol for a prospective randomized parallel-group controlled trial

Abstract

Background: A classical approach to produce interscalene brachial plexus block (ISBPB) consistently spares the posterior aspect of the shoulder and ulnar sides of the elbow, forearm, and hand, which are innervated by the lower trunk of the brachial plexus (C8-T1). As an alternative to the classical approach, a caudal approach to ISBPB successfully produces anesthesia of the ulnar sides of the elbow, forearm, and hand. However, its beneficial effects on anesthesia in the posterior aspect of the shoulder have not been investigated. In addition, the C8 nerve root is not routinely selectively blocked during ISBPB. Therefore, we will compare the C5 to C7 and C5 to C8 nerve root blocks during a caudal approach to ISBPB to assess the clinical benefit of C8 nerve blocks for the surgical anesthesia of the posterior aspect of the shoulder.

Methods/design: In this prospective parallel-group single-blind randomized controlled trial, 74 patients scheduled to undergo arthroscopic shoulder surgery under ISBPB are randomly allocated to receive the C5 to C7 or C5 to C8 nerve root block at a 1:1 ratio. The primary outcome is pain intensity, which is rated as 0 (no pain), 1 (mild pain), or 2 (severe pain), during the introduction of a posterior portal into the glenohumeral joint. The secondary outcomes are (1) the extent of the ipsilateral sensory, motor, hemidiaphragmatic, and stellate ganglion blockade, (2) changes in the results of a pulmonary function test, (3) incidence of complications related to ISBPB, (4) postoperative numerical pain rating scale scores, (5) patients' satisfaction with the ISBPB, (6) dose and frequency of analgesic use, and (7) incidence of conversion to general anesthesia.

Discussion: This study is the first to evaluate the beneficial effects of the C8 nerve root block during ISBPB, which has rarely been performed due to the technical challenge in visualizing and blocking the C8 nerve root. It is expected that a C8 nerve root block performed during ISBPB will provide sufficient surgical anesthesia of the posterior aspect of the shoulder, which cannot be achieved by a classical approach to ISBPB.

Trial registration: ClicnicalTrials.gov, NCT03487874 . Registered on 4 April 2018.

Keywords: Arthroscopic shoulder surgery; Cervical nerve root; Interscalene brachial plexus block; Lower trunk of the brachial plexus.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

The SPIRIT flow diagram: the schedule of enrolment, interventions, and assessments. t1 is before the placement of the interscalene brachial plexus block. t2 is when the interscalene brachial plexus block is placed. t3 is 30 min after the placement of the interscalene brachial plexus block. t4 is during surgery. t5 is on admission to the postanesthetic care unit. t6 is on discharge from the postanesthetic care unit. t7 is between 6 and 12 h after surgery. t8 is 24 h after surgery. * Forced expiratory volume at 1 s (FEV1) and FEV1/forced vital capacity. † Including worst numerical pain rating score.

Fig. 2

CONSORT flow chart

Fig. 3

Ultrasound-guided C5 to C8 nerve root block for interscalene brachial plexus block. a The C5 to C8 nerve roots located between the anterior and middle scalene muscles. The C8 nerve root lies on the first rib, and the C5 and C6 nerve roots are fused into the upper trunk of the brachial plexus. b Spread of local anesthetic around the C8 nerve root. c The separated C5 and C6 nerve roots visualized by the oblique rotation of the medial side of the ultrasonography transducer. d Spread of local anesthetic around the C5 and C6 nerve roots