Background: Shoulder arthroscopy can be very painful and interscalene brachial plexus block (ISB) provides excellent, but time-limited analgesia. Dexamethasone added perineural prolongs the duration of ISB and intravenous (i.v.) glucocorticoids also improve postoperative analgesia. 
Aim: 
To compare the effect of i.v. dexamethasone with that of perineural dexamethasone on the prolongation of analgesic duration of ISB for shoulder arthroscopy.
Methods: 
This is a prospective double-blind randomized placebo-controlled study in patients undergoing elective arthroscopic shoulder surgery under regional anesthesia with a single-shot ISB (ropivacaine 0.5% 30 mL). Patients were randomized in three groups: ropivacaine 0.5% (G1); ropivacaine 0.5% and dexamethasone 8 mg perineural (G2); and ropivacaine 0.5% with dexamethasone 8 mg i.v. (G3). Patients were assessed during first 24 hours after surgery for the duration of analgesia, defined as the time from the onset of sensory blockade to the first analgesic request, motor block duration, satisfaction score with pain control and total analgesic use. 
Results: 
Between 1/2015-5/2016, 129 patients were randomized. 120 patients (51F/69M) with a mean age of 57.6 years (range, 18-79 years) completed the study (forty patients in each group). The median duration of analgesia was significantly different between the three groups (G1, 12,65 [12.1-13.1] h; G2, 21,09 [19.9-22.2] h; and G3, 22,5 [21.2-23.6] h; p = 0.0001). Patients experienced significantly longer pain free interval when dexamethasone was added to ISB. Total analgesic use presented a significant lower consumption comparing G1 group to G2 and G3 respectively (p<0,0001). In both dexamethasone groups (G2 and G3) patient satisfaction was significantly higher in comparison with G1 group (p<0.001).
Conclusion:   
Dexamethasone significantly prolongs the duration of analgesia for ISB when added perineural and even more when administrated i.v.
Analysis showed significantly lower median consume of analgesics in G2 and G3 comparing with G1.
Dexamethasone added perineural and mostly i.v. have evidence supporting for decreased postoperative pain and increased patient satisfaction.

FIRS DO NOT HARM: HOW THE DEXAMETHASONE CAN IMPROVE POSTOPERATIVE ANALGESIA AFTER SHOULDER ARTHROSCOPY