Interscalene vs Phrenic-sparing Blocks in Obesity and Effect of Maximum Inspiratory Pressure

Summary

The goal of this clinical trial is to learn whether a phrenic-sparing nerve block can lower early breathing problems after shoulder surgery in adults with obesity, and whether a simple breathing-strength test (maximum inspiratory pressure, MIP) helps identify who is at higher risk. The main questions are:

Does the phrenic-sparing approach reduce breathlessness or oxygen need in the recovery room (30-60 minutes after arrival)? Do patients have similar pain control and opioid use compared with the standard interscalene block (ISB)? Are there any breathing-related complications or unplanned admissions within 24 hours? Researchers will compare the phrenic-sparing block (infraclavicular + distal suprascapular) to the standard ISB, both commonly used at UNC.

Participants will:

Have a quick MIP breath test before surgery (and, if age ≥65, a brief thigh muscle ultrasound).

Be randomly assigned to receive either the standard ISB or the phrenic-sparing block (both ultrasound-guided and part of routine care).

Receive usual anesthesia/surgery; have a brief recovery check at 30-60 minutes (breathlessness score, oxygen use, oxygen level).

Have pain medicines recorded from anesthesia start to PACU discharge; the team may review the chart up to 24 hours and make a short follow-up call (24-48 hours).

Conditions

• Shoulder Surgery
• Obesity

Interventions

PROCEDURE

Ultrasound-Guided Interscalene Brachial Plexus Block

Single 16 mL injection (15 mL 0.5 % bupivacaine + 1 mL dexamethasone 4 mg) at the C5-C6 root level under ultrasound guidance. Performed pre-operatively as standard care for shoulder surgery. Arm Cross-Reference: Standard Interscalene Block (Control)

PROCEDURE

Phrenic-Sparing Block Combination (Experimental)

Infraclavicular: 15 mL (75 mg) 0.5 % bupivacaine + 1 mL dexamethasone (4 mg) injected around the cords of the brachial plexus beneath the clavicle under ultrasound guidance. Distal Suprascapular: 12 mL (60 mg) 0.5 % bupivacaine + 1 mL (4 mg) dexamethasone injected at the suprascapular notch under ultrasound guidance to provide complete shoulder coverage while minimizing phrenic nerve involvement. Total local anesthetic dose = 135 mg bupivacaine + 8 mg dexamethasone. Arm Cross-Reference: Phrenic-Sparing Block Combination (Experimental)

DRUG

Bupivacaine HCl 0.5% Injectable Solution

Infraclavicular: Adminstered as 15 mL (75 mg) injection (together with dexamethasone). Distal Suprascapular: Adminstered as 12 mL (60 mg) injection (together with dexamethasone).

DRUG

Dexamethasone 4mg

Adminstered as applicable for infraclavicular and distal suprascapular: as 1 mL (4 mg) injection (together with bupicacaine 0.5%).

Sponsors & Collaborators

• American Society of Regional Anesthesia

  collaborator OTHER

• University of North Carolina, Chapel Hill

  lead OTHER

Principal Investigators

• Monika Nanda · University of North Carollina at Chapel Hill

Study Design

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

SINGLE

Model

PARALLEL

Eligibility

Min Age

18 Years

Sex

ALL

Healthy Volunteers

No

Timeline & Regulatory

Start

2026-01-21

Primary Completion

2027-11-01

Completion

2027-11-15

Countries

• United States

Study Locations