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

Official title

Interscalene vs Phrenic-sparing Blocks in Obesity: Effect of Pre-operative Maximum Inspiratory Pressure in a Randomized Trial

Overview

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).

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: Phreni
• 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%).

Primary outcome measures

• Incidence of Early Postoperative Respiratory Compromise [Time frame: Within 60 minutes after arrival to PACU]
• Effect Modification by Preoperative Maximum Inspiratory Pressure (MIP) [Time frame: Baseline (preoperative MIP test) and PACU assessment (30-60 minutes post-surgery).]

Secondary outcome measures (5)

• Lowest Oxygen Saturation (SpO₂) in PACU [Time frame: From PACU arrival to discharge (typically 60-120 minutes)]
• Total Duration of Supplemental Oxygen Use [Time frame: 0-24 hours post-surgery.]
• Post-Induction Opioid Consumption [Time frame: 0-6 hours post-surgery.]
• Diaphragmatic Excursion Change from Baseline [Time frame: Baseline (pre-block) and 30-60 minutes post-surgery in PACU.]
• PACU Pain Score [Time frame: Within 1 hour after PACU arrival.]

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

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Single blind

Primary purpose

Treatment

Study locations

United States · 1 center

• University of North Carolina Hospitals — Chapel Hill

Identifiers

NCT: NCT07216820 · 23-3332

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗