Analgesic Duration of Interscalene Block After Outpatient Arthroscopic Shoulder Surgery With Intravenous Dexamethasone, Dexmedetomidine or Their Combination: A Randomized Controlled Trial

BACKGROUND & RATIONALE Optimal postoperative analgesia is very important in the ambulatory arthroscopic shoulder surgery patient population; interscalene blocks are used for this surgery because they reduce acute pain and have opioid sparing effects postoperatively. While older patients, higher ASA grades and more complex arthroscopic procedures are risk factors for unplanned overnight admissions, in the ambulatory surgery setting, poor analgesia is one of the most common reasons a patient visits a health care provider after their surgery. Approximately 30 % of patients undergoing arthroscopic surgery globally experience significant postoperative pain within the first 24 hours post surgery. In light of this, interscalene brachial plexus blockade (ISB) has been found to be the most effective and preferred method of analgesia for arthroscopic shoulder surgeries when compared to subacromial/intra-articular injections, cryotherapy and oral pain medications. ISB usually consists of a single injection of local anesthetic, anywhere from 5 to 30 minutes prior to shoulder surgery. Although ISB reduces postoperative pain in arthroscopic shoulder surgeries, the length of analgesia from a single injection of local anesthetic is limited to 6 to 15 hours after surgery. Due to the limited duration of analgesia, interscalene catheters have been studied for prolongation of analgesia via continuous infusion of local anesthetics. Although continuous catheter infusions are effective and feasible, there exist several complications such as dyspnea, peripheral neuropathies, nausea, and practical challenges that limit their wider application in an ambulatory setting. Recently, different adjuncts given in combination with local anesthetics have been used to prolong the analgesic duration of a single injection ISB. These adjuncts have been given by both the intravenous and by the perineural routes, where perineural means the adjunct is injected with the local anesthetic around the brachial plexus.

Dexamethasone, a potent glucocorticoid, has been shown in multiple studies to prolong the duration of analgesia of the ISB compared to placebo when administered either perineurally or intravenously. A recently completed large trial (in press) at our centre showed that the duration of analgesia (mean (standard deviation), in hours (h)) with 4mg of intravenous dexamethasone (24.0 (4.6)h) is not significantly different from 8mg (24.8 (6.4)h) and only slightly shorter than perineural dexamethasone doses of 4mg (25.4 (6.6)h) or 8mg (27.2 (8.5)h). The 4mg intravenous dose was favored given the established safety of the intravenous route, its approximately equivalent effectiveness compared to the higher 8mg dose and the absence of differences in adverse effects between groups.

Dexmedetomidine, a highly selective α2 adrenergic agonist with sedative and analgesic properties, has also been shown to potentiate peripheral nerve blockade and prolong the duration of analgesia versus placebo when used as an adjunct to local anesthetic for regional anesthesia, including interscalene block. Most studies have compared perineural dexmedetomidine to placebo, as is the case for other adjuncts such as dexamethasone, even though there is less experience with the perineural route for dexmedetomidine compared to dexamethasone. Interestingly, a recent study found both intravenous and perineural dexmedetomidine reduced the 24 hour opioid consumption and comparably prolonged the duration of ISB analgesia compared to placebo. In a recent meta-analysis, a 50-60ug Dexmedetomidine perineural or intravenous dose maximized sensory block duration while minimizing hemodynamic side effects.

To our knowledge, there are no published studies comparing the analgesic duration of ISB between dexamethasone and dexmedetomidine, and no studies have evaluated whether there is additional benefit to administering these widely available medications in combination. Three ongoing studies are comparing dexamethasone and dexmedetomidine as single adjuncts, without a combination. All three of these studies are using the perineural route, despite the established safety and effectiveness of the intravenous route for both drugs. With this study we are seeking to improve our patients' postoperative experience with superior analgesia by better defining the relative analgesic effectiveness of dexamethasone and dexmedetomidine when given alone or in combination as intravenous adjuncts to ISB.

OBJECTIVES AND HYPOTHESES