Dissociation between Sensory and Motor Blockade Durations in Supraclavicular Brachial Plexus Regional Anesthesia: A Comparative Analysis of Perineural Dexmedetomidine versus Dexamethasone as Adjuvants to Ropivacaine

Abstract

Background: Supraclavicular brachial plexus block is widely used for anesthesia and postoperative analgesia in upper-limb surgeries because of its high success rate and excellent perioperative pain control. The addition of adjuvants to long-acting local anesthetics has become an effective strategy to improve block quality, prolong analgesia, and reduce postoperative opioid consumption. Among the various adjuvants, dexmedetomidine, a highly selective α₂-adrenergic agonist, and dexamethasone, a long-acting corticosteroid, have consistently demonstrated favourable effects on peripheral nerve blockade. However, direct comparisons have largely focused on overall block duration rather than the differential effects on sensory and motor blockade, an outcome that has important implications for postoperative recovery and early mobilization.¹–⁶

The present study aimed to compare the efficacy of perineural dexmedetomidine and dexamethasone as adjuvants to ropivacaine in supraclavicular brachial plexus block, with particular emphasis on the dissociation between sensory and motor blockade durations.

Methods: The current study was conducted in ninety adult patients with American Society of Anesthesiologists (ASA) physical status I and II undergoing elective upper-limb surgery under supraclavicular brachial plexus block. Patients received supraclavicular brachial plexus block using 30 mL of 0.5% ropivacaine combined with either dexmedetomidine 50 μg or dexamethasone 8 mg (total volume 32 mL).

The primary outcome was the duration of sensory blockade. Secondary outcomes included onset of sensory blockade, onset and duration of motor blockade, duration of postoperative analgesiaand sensory–motor dissociation nanalysis.

Results: Baseline demographic characteristics, ASA physical status, body weightand duration of surgery were comparable between the two groups. Dexmedetomidine produced significantly earlier onset of both sensory and motor blockade compared with dexamethasone. Furthermore, sensory block duration, motor block duration, and postoperative analgesia were significantly prolonged in the dexmedetomidine group (P<0.05).⁷–¹²

Although both sensory and motor blockade were prolonged with dexmedetomidine, sensory blockade demonstrated a proportionately greater extension than motor blockade, suggesting a favorable sensory–motor dissociation profile. No serious neurological complications or major adverse events were observed.¹³–¹⁵

Conclusion: Both dexmedetomidine and dexamethasone are effective adjuvants to ropivacaine for supraclavicular brachial plexus block. Dexmedetomidine provides faster block onset, prolonged postoperative analgesia, and superior sensory blockade while maintaining an acceptable safety profile. The observed sensory–motor dissociation may represent an additional clinical advantage by extending analgesia without proportionately delaying motor recovery.