Continuous interscalene brachial plexus block for postoperative analgesia following shoulder surgery

Background: Severe postoperative pain is a well-known problem following shoulder surgery. This study evaluates the clinical efficacy of continuous interscalene brachial plexus block, patient-controlled analgesia, and morphine (i.v. and i.m.) for postoperative analgesia in this setting. Methods: Thirty patients, scheduled for acromioplasty during general anesthesia, were randomly allocated to one of three different postoperative pain management groups. Group MO received morphine (5 mg i.m. and 2 mg i.v.) when visual analogue pain score (VAS) >3, group PL received a continuous interscalene brachial plexus block with bupivacaine (1.25 mg kg(-1)+0.25 mg kg(-1) h(-1)) and group PCA received patient-controlled analgesia with morphine (bolus 1 mg). Postoperative pain relief was assessed (24 h) by VAS, circulatory and respiratory stress parameters (heart rate, systemic arterial pressure and respiratory rate) and stress metabolites (glucose, lactate, glycerol by abdominal subcutaneous microdialysis). Results: Pain relief in the PL group was effective (VAS <3) and significantly more potent than in groups MO and PCA, except at 16 and 20 h. Lactate was significantly increased in the PL group, glucose was significantly increased in all groups, while glycerol showed a variable pattern. There were no significant stress metabolite differences among groups. VAS showed no statistical correlation with microdialysate, respiratory or circulatory data. Conclusion: Successful continuous interscalene brachial plexus block provides very good pain relief following shoulder surgery and is superior to tho other methods studied. However, we were unable to demonstrate a correlation between VAS pain scores and stress indicators in metabolic, circulatory and respiratory parameters.