Interscalene vs Phrenic-sparing Blocks in Obesity and Effect of Maximum Inspiratory Pressure
Trial statusRecruiting
Trial phaseNot applicable
Trial typeInterventional
Biological sexAll
Age18+
SponsorUniversity of North Carolina, Chapel Hill
About this trial
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 criteria
This trial does not accept healthy volunteersQualifiers
Age ≥ 18 years (self-report, confirmed on chart).
Body-mass index ≥ 35 kg m² 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).
Disqualifiers
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
Trial design
Design model
Parallel
Treatments tested in this trial
Ultrasound-Guided Interscalene Brachial Plexus Block
Procedure/SurgerySingle 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)
Phrenic-Sparing Block Combination (Experimental)
Procedure/SurgeryInfraclavicular: 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
DrugInfraclavicular: Adminstered as 15 mL (75 mg) injection (together with dexamethasone). Distal Suprascapular: Adminstered as 12 mL (60 mg) injection (together with dexamethasone).
Dexamethasone 4mg
DrugAdminstered as applicable for infraclavicular and distal suprascapular: as 1 mL (4 mg) injection (together with bupicacaine 0.5%).
Treatment groups
68 Participants
are divided into 2 treatment groupsGroup A: Arm 1: Standard Interscalene BlockActive comparator 3 interventions
Group B: Arm 2: Phrenic-Sparing Block CombinationExperimental treatment 3 interventions
Trial outcomes
Primary outcomes
1
Incidence of Early Postoperative Respiratory Compromise
Composite outcome defined as either (a) a Modified Borg Dyspnea Score ≥ 3 in the post-anesthesia care unit (PACU, 30-60 minutes after surgery) or (b) continued need for supplemental oxygen at the PACU assessment. Outcome Type: Primary Unit of Measure: Percentage of participants meeting composite endpoint.
Time frame
Within 60 minutes after arrival to PACU2
Effect Modification by Preoperative Maximum Inspiratory Pressure (MIP)
Assess whether the magnitude of treatment benefit from the phrenic-sparing block varies by baseline inspiratory-muscle strength. The effect is modeled as the interaction between block type and continuous MIP (cm H₂O) on the composite respiratory-compromise endpoint. Unit of Measure: Interaction odds ratio (per 10 cm H₂O decrement in MIP).
Time frame
Baseline (preoperative MIP test) and PACU assessment (30-60 minutes post-surgery).Secondary outcomes
1
Lowest Oxygen Saturation (SpO₂) in PACU
Minimum oxygen saturation recorded by pulse oximetry during the PACU stay Unit of Measure: Percent (%)
Time frame
From PACU arrival to discharge (typically 60-120 minutes)2
Total Duration of Supplemental Oxygen Use
Total number of hours on oxygen from PACU arrival until hospital discharge (maximum 24 hours). Unit of Measure: Hours.
Time frame
0-24 hours post-surgery.3
Post-Induction Opioid Consumption
Total opioid dose administered from anesthesia induction to PACU discharge, converted to oral morphine milligram equivalents (OMME). Unit of Measure: mg OMME.
Time frame
0-6 hours post-surgery.4
Diaphragmatic Excursion Change from Baseline
Percent change in diaphragmatic excursion (ultrasound-measured) from baseline to PACU. Unit of Measure: Percent change (%).
Time frame
Baseline (pre-block) and 30-60 minutes post-surgery in PACU.Other outcomes
1
Exploratory: Association of Frailty and Sarcopenia Measures With Respiratory Outcomes
Explore whether rectus femoris index (cm/height²) or Clinical Frailty Scale (CFS) scores predict postoperative respiratory compromise in participants ≥ 65 years. Unit of Measure: Correlation coefficient or adjusted risk ratio.
Time frame
Baseline preoperative assessment; outcome analyzed at PACU.Sponsors and contacts
Click on the lead sponsor to view all of their trials.
University of North Carolina, Chapel Hill
Lead sponsor
American Society of Regional Anesthesia
Collaborator
Source ClinicalTrials.gov