Effect of Local Anesthetic Concentration (0.2% Ropivacaine vs 0.1% Ropivacaine) on Phrenic Nerve Function, Pulmonary Function, and Analgesia After Ultrasound-guided Interscalene Brachial Plexus Block for Shoulder Arthroscopy

Abstract Brief abstract (250 words or less) describing the study in language understandable to a lay person. Include brief description of the purpose, target disease/condition if applicable, key eligibility criteria, and main study interventions.

The interscalene brachial plexus block is well-suited for surgical procedures of the shoulder and proximal humerus. A well-established hazard of the interscalene block is ipsilateral hemidiaphragm paresis in nearly 100% of patients secondary to phrenic nerve blockade. This side effect is well-tolerated in most patients; however, extreme caution should be employed in patients with pulmonary disease, who may experience acute pulmonary failure from unilateral phrenic nerve blockade and resulting hemidiaphragm paresis. This study seeks to determine if using a lower concentration of ropivacaine will result in less diaphragm dysfunction and reduction in pulmonary function than a higher concentration of the local anesthetic. Patients will be randomized to one of two groups--Group A and Group B. Group A will receive ultrasound-guided interscalene block with 20mL 0.1% ropivacaine in the preoperative holding area prior to induction of general anesthesia. Group B will receive ultrasound-guided interscalene block with 20mL 0.2% ropivacaine in the preoperative holding area prior to induction of general anesthesia. The primary outcome variable is the degree of phrenic nerve blockade as assessed by ultrasonographic evaluation of diaphragm function and bedside spirometry (lung function testing). Secondary outcome variables will be assessed at various time intervals. They include oxygen saturation measurements, oxygen requirements, motor strength and sensation of blocked extremity, pain scores, opioid requirements, PACU (Post-Anesthesia Care Unit)length of stay, and patient satisfaction and quality of recovery scores. We hypothesize that interscalene brachial plexus blocks performed with a lower concentration of ropivacaine will result in less pulmonary dysfunction without compromising analgesia.

Objectives Overall objectives

1. Primary Objective: Compare the degree of phrenic nerve blockade after ultrasound-guided interscalene block using either 0.1% ropivacaine or 0.2% ropivacaine
2. Hypothesis: Using a lower concentration of local anesthetic will result in lesser degree of phrenic nerve blockade. Specifically, we hypothesize that outcome measures will be as follows for patients receiving lower concentrations of ropivacaine: 1. Less dysfunction of diaphragm movement, 2. PFT (Pulmonary Function Test) values drop less in lower concentration groups, 3. Less oxygen desaturation in PACU, 4. Less symptomatic shortness of breath post-block, 5. Less need for supplemental oxygen in PACU, 6. Less unplanned hospital admission
3. Secondary Objective: Compare the analgesia efficacy as well as block duration between 0.1% and 0.2% ropivacaine. Assess the quality of recovery as well as overall satisfaction of patients undergoing arthroscopic shoulder surgery under combined regional/ general anesthesia. Also compare and evaluate the presence of other complications that arise in the two groups Primary outcome variable(s) The primary outcome variable is the degree of phrenic nerve blockade as assessed by ultrasonographic evaluation of diaphragm function and bedside spirometry.

Secondary outcome variable(s) Secondary outcome variables include oxygen saturation measurements and oxygen requirements before block performance, 20 minutes after block performance, and in the PACU; motor strength and sensation of affected extremity before block performance, 20 minutes after block performance, and in the PACU; pain scores and opioid requirements in the PACU and up to 72 hours post-operatively, PACU length of stay, patient satisfaction and quality of recovery scores 24 hours post-operatively.