Dose-response relationship of perineural dexamethasone for interscalene brachial plexus block: a randomised, controlled, triple-blind trial.

Abstract

Perineural dexamethasone has a ceiling dose of 4mg for prolongation of analgesia duration after injection of long-acting local anaesthetic for peripheral nerve block, but evidence for doses <4mg is lacking. This randomised controlled triple-blind trial tested the hypothesis that increasing doses of perineural dexamethasone between 1mg and 4mg would prolong the duration of analgesia in a dose-dependent manner. Eighty ASA physical status 1-2 patients scheduled for shoulder arthroscopy under general anaesthesia with ultrasound-guided interscalene brachial plexus block were randomly allocated to receive saline (control), dexamethasone 1mg, 2mg, 3mg and 4mg, together with 20ml ropivacaine 0.5%. Postoperative analgesia consisted of paracetamol, diclofenac and oxycodone on request, using a pre-defined protocol. The primary outcome was the duration of analgesia, defined as the time between the block procedure and the first analgesic request. Secondary outcomes included rest and dynamic pain scores, and analgesic consumption at 2h, 24h and 48h postoperatively. An analysis of the dose-response relationship was performed using multiple comparison procedure-modelling. The median (IQR [range]) duration of analgesia was significantly prolonged in a dose-dependent manner: control 685 (590-860 [453-1272]) min; 1mg 835 (740-1110 [450-1375]) min; 2mg 904 (710-1130 [525-1365]) min; 3mg 965 (875-1025 [730-1390]) min; 4mg 1023 (838-1239 [518-1500]) min (p=0.03). There were no significant differences between the secondary outcomes. Perineural administration of dexamethasone with doses between 1mg and 4mg, combined with ropivacaine for interscalene brachial plexus block, prolongs duration of analgesia in a dose-dependent manner.