Background Dexmedetomidine is an effective local anesthetic adjunct for peripheral nerve blocks. The intravenous route for administering dexmedetomidine has been suggested to be equally effective to the perineural route; but comparative evidence is conflicting.

Objectives This evidence-based review evaluated trials comparing the effects of intravenous to perineural dexmedetomidine on peripheral nerve block characteristics in adult surgical patients. Our primary aim was to evaluate the durations of sensory and motor blockade. Duration of analgesia, onset times of sensory and motor blockade, analgesic consumption, rest pain, and dexmedetomidine-related adverse events were evaluated as secondary outcomes.

Evidence review We sought randomized trials comparing the effects of intravenous to perineural dexmedetomidine on peripheral nerve block characteristics. The Cochrane Risk of Bias tool and the Grades of Recommendation, Assessment, Development, and Evaluation criteria was used to evaluate the quality of evidence for when an outcome was reported by at least three studies.

Results Ten studies compared intravenous and perineural dexmedetomidine in the setting of upper extremity blocks (seven), lower extremity blocks (two), and truncal block (one). The doses of dexmedetomidine supplementing long-acting local anesthetics varied between a predetermined dose (50 μg) and a weight-based dose (0.5 μg/kg–1.0 μg/kg). Clinical diversity precluded quantitative pooling; and evidence is presented as a systematic review. Compared with the intravenous route, moderate quality evidence found that perineural dexmedetomidine prolonged the duration of sensory blockade in four of six trials and motor blockade in five of seven trials. Perineural dexmedetomidine also hastened the onset of sensory and motor blockade in three of six trials. No differences were reported for the remaining outcomes; and intravenous dexmedetomidine was not superior for any outcome in any of the trials.

Conclusions Moderate quality evidence appears to suggest that intravenous dexmedetomidine is an inferior peripheral nerve block adjunct compared with perineural dexmedetomidine. Perineural dexmedetomidine is associated with longer durations and faster onset of sensory and motor blockade.