Safety and efficacy of supplementing interscalene blocks

OBJECTIVES: Interscalene brachial plexus block is widely used for shoulder surgery. The benefits of this technique include excellent postoperative analgesia, decreased postoperative nausea, and early ambulation. However, these advantages may be lost if the block fails and general anesthesia is employed. Finucane et al. (1) demonstrated the safety of supplementing axillary blocks within 31 minutes of initial injection. The purpose of this study was to evaluate the safety and efficacy of early supplementation of interscalene blocks after an initial dose of local anesthetic. METHODS: 148 patients scheduled for shoulder surgery received premedication with midazolam 1-5 mg IV and fentanyl 50-250 meg IV. Patients were prepared for an interscalene block in the usual fashion. Nerve stimulation using a 22-gauge 2-inch Stimuplex needle (B. Braun Medical Inc., Bethlehem, PA) identified the brachial plexus. Motor response below 0.5 mA current distal to the elbow or in the deltoid muscle was accepted for an end point. 40 ml of 0.5% bupivacaine with 1:200,000 epinephrine was injected in divided doses. Patients with a negative deltoid sign (inability to abduct the upper arm) (2), fifteen minutes after initial injection, received a second interscalene block. Motor response below 1.S mA current was accepted as an end point for repeat block. 40 ml of 1.5% mepivacaine with 1:200,000 epinephrine and 4 meq sodium bicarbonate was injected in divided doses. Patients with a negative deltoid sign fifteen minutes after repeat injection were converted to a general anesthetic. RESULTS: 25 of 148 patients (16.9%) had a negative deltoid sign and required supplementation. Following repeat interscalene block, only 4 patients (2.7%) had inadequate regional anesthesia and required general anesthesia. There were no central or peripheral nervous system, cardiovascular, or local anesthetic toxicity complications. All patients were discharged home within 23 hours of surgery. DISCUSSION: This study indicates that interscalene brachial plexus block can be safely redosed with 1.5% mepivacaine as early as 15 minutes after an initial injection with 0.5% bupivacaine. While further studies are necessary to determine local anesthetic blood levels when supplementation is required, this technique appears to be a safe way to salvage interscalene blocks.

Duke Scholars

Author Stephen Matthew Klein Anesthesiology, Ambulatory