Interscalene vs Phrenic-sparing Blocks in Obesity and Effect of Maximum Inspiratory Pressure
Interscalene vs Phrenic-sparing Blocks in Obesity: Effect of Pre-operative Maximum Inspiratory Pressure in a Randomized Trial
University of North Carolina, Chapel Hill
68 participants
Jan 21, 2026
INTERVENTIONAL
Conditions
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).
Eligibility
Inclusion Criteria6
- 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 Criteria11
- 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
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Interventions
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)
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)
Infraclavicular: Adminstered as 15 mL (75 mg) injection (together with dexamethasone). Distal Suprascapular: Adminstered as 12 mL (60 mg) injection (together with dexamethasone).
Adminstered as applicable for infraclavicular and distal suprascapular: as 1 mL (4 mg) injection (together with bupicacaine 0.5%).
Locations(1)
View Full Details on ClinicalTrials.gov
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NCT07216820