The Effect of Systemic or Perineural Dexamethasone on the Duration of Interscalene Nerve Blocks With Ropivacaine

Patients undergoing rotator cuff repair or subacromial decompression at the investigators institution are frequently hospitalized overnight due to inadequate pain relief after resolution of interscalene brachial plexus blocks. For ropivacaine 0.5%, the investigators usual local anesthetic, previous studies report an analgesic duration of 11.1 ± 5 hours without epinephrine and approximately 12 hours with epinephrine. Consequently, a method of prolonging analgesia from a brachial plexus block without the extra equipment and logistical difficulties of indwelling catheters would benefit both patients and caregivers. A potential approach is use of adjuvant drugs that prolong block duration when added to the local anesthetic. In addition to the usual adjuvant anesthetic drugs, investigators have begun to evaluate glucocorticoids as adjuvants for regional anesthesia. Known for their anti-inflammatory, analgesic, immunosuppressive, and antiemetic properties, these corticosteroids exert their effects by inhibition of phospholipase A2 as well as changes in cell function induced by glucocorticoid receptor activation. Although associated with significant toxicity when administered in large doses for long periods, emerging literature suggests that a single perioperative dose of glucocorticoid is safe. Several studies, including a recent trial at the investigators institution, have demonstrated the efficacy of dexamethasone in prolonging regional anesthetics. Available data thus suggest that combining glucocorticoids with local anesthetics prolongs block duration. However, systemic glucocorticoids have also been shown to reduce postoperative pain. This raises the question whether the beneficial effects of adding glucocorticoid to a regional anesthetic is solely due to local effect or is mediated at least in part by systemic action. Previous trials, however, have not addressed this important issue. If this beneficial effect of analgesic duration is mediated by systemic action, adding dexamethasone to the local anesthetic mixture may be unnecessary. Although no study has reported neurotoxicity from perineural dexamethasone and laboratory data appear to confirm the safety of this route, achieving similar results with more conventional administration would be desirable for two reasons. First, conventional intravenous dosing is convenient, useful for other reasons (for example, postoperative nausea prophylaxis), and well-studied. Second, equivalent (or not equivalent) results from systemic dosing would provide valuable information about the mechanism behind dexamethasone's effect on block duration.