Comparison of Interscalene Catheter to Single Injection Interscalene Blocks for Total Shoulder Arthroplasties

Regional anesthesia in the ambulatory surgery center venue has been shown to decrease unwanted side effects of anesthesia and improve patient satisfaction with their operative care. Total shoulder arthroscopy is noted to be a surgery that has high pain post-operatively. Patients generally utilize narcotics for up to two weeks post-operatively for pain control. Interscalene nerve blocks are widely utilized to help with better recovery and less post-operative opioid use. This may enhance patient satisfaction and make for fewer unwanted post-operative side effects from anesthesia such as nausea and vomiting. Single injection interscalene blocks with ropivacaine have been shown to last 12-18 hours. Unfortunately, with this shorter duration patients can experience rebound pain or intense pain after the nerve block has worn off. One way to prolong regional anesthesia for patients is to provide peripheral nerve catheter and run an infusion for these patients for 24-48 hours. However, there can be multiple interventions associated with these. Catheter adverse conditions include infection, local anesthetic toxicity, catheter failure or dislodgement, infusion leakage, difficulty for the patient to remove their own catheter, and inadequate access to medical resources.

Liposomal bupivacaine is a newer agent approved by the FDA in 2018 for interscalene nerve blocks. The administration of medication via liposomal technology is not a new concept. The basic principle relies on an outer layer of phospholipids, cholesterol, and surfactants with a core that carries the principal medication to the primary source, which is encapsulated so that it is unaltered. The core can carry hydrophilic or hydrophobic substances due to this structure. Bupivacaine is the active component in liposomal bupivacaine. It is an amide local anesthetic that interferes with generation of nerve cell action potentials by increasing the cell electrical excitation. The action of liposomal bupivacaine released into tissues is twofold. Primarily it is released through systemic absorption of the bupivacaine from the liposome model. Secondly, the bupivacaine is slowly released from the core of the phospholipid vesicle. This explains the long duration up, to 96 h of analgesia reported in literature. After the bupivacaine has been released from the liposomal component, its pharmacokinetic profile is like that of bupivacaine. Thus, the rate of systemic absorption depends on the amount of drug administered, route of administration, and vascularity of the site administration. These factors influence the onset of action of the drug. After systemic absorption, the distribution the drug follows are that for any bupivacaine formulation, with the highest concentration found in blood-rich organs such as the liver, lungs, heart, and brain. Like other amide local anesthetics, bupivacaine is primarily metabolized by the liver and then is excreted by the kidneys. Bupivacaine has one of the longer half-lives of the local anesthetics.

Shoulder outcome is not only related to pain, but also to functionality and patient satisfaction. Orthopedic surgeries have been doing outcome scoring on this element for some time. There are general health surveys as well as joint specific surveys. Patient-Reported Outcomes Measurement Information System (PROMIS) is the most popular general health measure in the field of orthopedics and reviewed extensively in orthopedic literature. It is believed that studies that include a general health measure and a disease-specific measure to allow broad comparison across patient populations and allow better adaption of results in institutions. PROMIS allows for general assessment and is used widely for shoulder pathology.

Both options proposed have some concerns. Interscalene catheter placement requires higher skill level of the regional anesthesiologist. It also requires increased nursing time due to the infusion on a pump that must be maintained. Liposomal bupivacaine, while it can be placed as a single injection, does have a high cost associated with the medication at around $200 for a single vial needed of 133 mg (dosage used for single injection interscalene block for shoulder arthroscopy). This will be a randomized control feasibility trial where total shoulder patients will be randomized to either interscalene catheter and infusion or liposomal bupivacaine single interscalene block. Both practices are accepted as standard of care for shoulder surgery at this institution and nationally. In addition, liposomal bupivacaine is FDA approved for use with interscalene nerve blocks. However, research on superior method is not well studied. In addition, this institution's acute pain service has been utilizing liposomal bupivacaine for about 6 months. The plan is to look at which method has better pain control by looking at Visual Analog Scores (VAS) for pain as well as opioid use in morphine milligram equivalents (MME). The investigators also want to look at cost with each (liposomal bupivacaine is a higher cost medication than plain bupivacaine.). The investigators will look at total cost (supplies, medication and nursing time), needed for each. The investigators will also look at the environmental cost of this in regard to waste for each process. Finally, the investigators will look at post-operative pain scores up to 3 mos. to look at any difference in chronic pain scores for each. Pre-operatively patients already complete in clinic American Shoulder and Elbow (ASES) questionnaire (which has VAS Pain and ADL), Patient Reported Outcomes Measurement Information System (PROMIS) Pain Interference, and PROMIS Global Health (both CAT versions) at pre-op, and then at 2-weeks and 6-weeks postop and 3 months postop. These look at disability and health-related quality of life. Pertinent demographics will also be collected from EPIC. All patients will have general anesthesia induced and recovery in the Post-operative Care Unit (PACU) prior to admission for 23 hours. Total opioid consumption intra-operatively, post-operatively and after discharge will be recorded. Functional Pain scores will also be recorded (and patient will be educated about this scale) to report post-discharge. Surveys at 7 days, 14 days and 30 days to follow-up on functional pain scores and to look at opioid use and complication rates.