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

NCT ID: NCT07216820

Last Updated: 2025-10-20

Basic Information

• Recruitment Status: NOT_YET_RECRUITING
• Clinical Phase: NA
• Total Enrollment: 68 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2025-11-01
• Study Completion Date: 2027-11-15

Brief 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

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: PARALLEL
• Primary Study Purpose: TREATMENT
• Blinding Strategy: SINGLE

Study Groups

Arm 1: Standard Interscalene Block

Standard Interscalene Brachial Plexus Block (Control)

Description:

Participants receive a single 16 mL interscalene block at the C5-C6 level under ultrasound guidance. The injectate contains 15 mL of 0.5% bupivacaine HCl (75 mg) mixed with 1 mL preservative-free dexamethasone (4 mg).

Group Type: ACTIVE_COMPARATOR

Ultrasound-Guided Interscalene Brachial Plexus Block

Intervention Type: PROCEDURE

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)

Bupivacaine HCl 0.5% Injectable Solution

Intervention Type: DRUG

Infraclavicular: Adminstered as 15 mL (75 mg) injection (together with dexamethasone).

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

Dexamethasone 4mg

Intervention Type: DRUG

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

Arm 2: Phrenic-Sparing Block Combination

Combined Infraclavicular + Distal Suprascapular Block (Phrenic-Sparing Technique)

Description:

Participants receive two ultrasound-guided peripheral nerve blocks designed to minimize phrenic nerve involvement:

Infraclavicular block: 15 mL 0.5% bupivacaine + 1 mL dexamethasone (total 16 mL) Distal suprascapular block: 12 mL 0.5% bupivacaine + 1 mL dexamethasone (total 13 mL) Total local-anesthetic dose = 135 mg bupivacaine + 8 mg dexamethasone, within accepted safety limits.

Group Type: EXPERIMENTAL

Phrenic-Sparing Block Combination (Experimental)

Intervention Type: PROCEDURE

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)

Bupivacaine HCl 0.5% Injectable Solution

Intervention Type: DRUG

Infraclavicular: Adminstered as 15 mL (75 mg) injection (together with dexamethasone).

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

Dexamethasone 4mg

Intervention Type: DRUG

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

Interventions

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)

Intervention Type: 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)

Intervention Type: PROCEDURE

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).

Intervention Type: DRUG

Dexamethasone 4mg

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

Intervention Type: DRUG

Other Intervention Names

Bupivacaine Hydrochloride Injection; Decadron, Dexamethasone Intensol, De-Sone LA, Dxevo, Dexacorten

Eligibility Criteria

Inclusion Criteria

• Age ≥ 18 years (self-report, confirmed on chart).
• Body-mass index ≥ 35 kg m^2 at the pre-operative clinic visit (chart).
• Scheduled for elective unilateral shoulder surgery (arthroscopy, arthroplasty, rotator cuff repair, reverse arthroplasty) under general anesthesia at UNC Hospitals
• Planned use of a single-injection regional brachial-plexus block for postoperative analgesia (anesthesia record).
• Able to perform a maximal-inspiratory-pressure (MIP) maneuver at screening, producing two reproducible efforts (bedside test)
• Able to read or understand English and provide written informed consent (consent discussion).

Exclusion Criteria

• Emergent or trauma shoulder procedure or case converted to open surgery (schedule/chart).
• Pregnancy confirmed by point-of-care urine test on day of surgery (POC test). Prisoner status or legal incapacity to consent (chart/interview).
• Severe pulmonary disease: GOLD stage 3-4 COPD, restrictive lung disease unrelated to obesity with FVC < 50 % predicted, baseline dyspnea Borg ≥ 3, or home oxygen therapy (pulmonary clinic notes, patient interview).
• Severe heart disease- Severe valvular heart disease, Congestive Heart Failure NYHA Class III or IV, Obstructive Coronary Artery Disease with Angina
• Neuromuscular disorders affecting respiratory muscles (e.g., ALS, myasthenia gravis) or known diaphragmatic paralysis (chart).
• Coagulopathy (platelets < 100 × 10/ L or INR > 1.5) or local infection at block sites (pre-op labs/assessment).
• Anemia and hemoglobinopathies: Hgb <10 g/dl, clinically significant hemoglobinopathy.
• Allergy to bupivacaine, dexamethasone, or ultrasound gel (self-report).
• Chronic opioid use > 100 mg oral-morphine equivalents per day in the three months preceding surgery (medication history, PDMP query).
• Prior enrolment in this trial or planned participation in another interventional study that might confound outcomes (research registry).
• Anticipated inability to comply with postoperative assessments (e.g., profound cognitive impairment, expected early transfer to outside facility) as judged by the investigator

• Minimum Eligible Age: 18 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: No

Sponsors

American Society of Regional Anesthesia

OTHER

Sponsor Role: collaborator

University of North Carolina, Chapel Hill

OTHER

Sponsor Role: lead

Responsible Party

Responsibility Role: SPONSOR

Principal Investigators

Monika Nanda

Role: PRINCIPAL_INVESTIGATOR

University of North Carollina at Chapel Hill

Locations

University of North Carolina Hospitals

Chapel Hill, North Carolina, United States

Countries

United States

Central Contacts

Monika Nanda

Role: CONTACT

mnanda@aims.unc.edu

919-966-5136

Facility Contacts

Monika Nanda

Role: primary

mnanda@aims.unc.edu

919-966-5136

Other Identifiers

23-3332

Identifier Type: -

Identifier Source: org_study_id