Consistent analgesic effect of intravenous dexamethasone on rebound pain after brachial plexus block: a causal...

Rebound pain, a sudden increase in pain intensity after resolution of regional anesthesia, remains a major challenge in postoperative patient care. Intravenous (IV) dexamethasone has been proposed as a preventive strategy, but whether its effectiveness varies across patient characteristics remains unclear.

This retrospective study included patients who underwent upper extremity orthopedic surgery under brachial plexus block (BPB). Rebound pain was defined as the occurrence of both severe pain (numeric rating scale ≥ 7) and rescue analgesic administration between 4 and 24 hours after BPB. The association between IV dexamethasone and rebound pain was evaluated using multivariable logistic and generalized random forest (GRF) models.

Among the 1,171 patients, 651 (55.6%) received IV dexamethasone. The dexamethasone group had a significantly lower incidence of rebound pain (7.1% vs. 16.9%, P < 0.001) with delayed onset (median 14 vs. 11 hours). IV dexamethasone was an independent protective factor (odds ratio, 0.42; 95% confidence interval [CI], 0.27 to 0.64; P < 0.001). GRF analysis estimated an average treatment effect of -0.09 (95% CI -0.13 to -0.05), corresponding to a 9% absolute risk reduction. Calibration testing demonstrated accurate model (GRF) estimation (mean coefficient, 0.98; P < 0.001) and no statistically detectable heterogeneity in treatment effect (differential coefficient, -0.30; P = 0.713).

IV dexamethasone was associated with reduced rebound pain without evidence of meaningful heterogeneity in treatment effect in patients undergoing upper extremity surgery under BPB. These findings suggest a potential preventive role for dexamethasone as an adjunct to perioperative pain management in this population.