Effect of Intravenous Esketamine on Rebound Pain Following Single-Shot Brachial Plexus Block in Patients Undergoing Shoulder Arthroscopic Surgery: A Prospective, Randomized, Placebo-Controlled Study.

Purpose: Rebound pain (RP) often occurs after the resolution of peripheral nerve blocks. Studies suggest that perineural esketamine prolongs block duration and reduces RP incidence. This study aimed to determine whether intravenous esketamine reduces RP incidence following single-shot interscalene brachial plexus block (ISBPB) in shoulder arthroscopic surgery.

Patients and methods: In this randomized controlled trial, 200 patients scheduled for shoulder arthroscopy received ultrasound-guided single-shot ISBPB preoperatively and were randomized to receive either intravenous esketamine (0.5 mg/kg bolus + 0.25 mg/kg/h infusion) or placebo. Primary outcomes included RP incidence, onset time, duration, and pain scores. Secondary outcomes included block duration, postoperative pain scores, and hemodynamic parameters (heart rate [HR], mean arterial pressure [MAP]).

Results: The incidence rates of rebound pain (RP) were comparable between groups, with no significant differences in RP duration or pain scores (P>0.05). However, the Numeric Rating Scale at rest (NRS-R) scores at 8h, 12h, and 24h postoperatively were significantly higher in the C-group compared to the E-group (P<0.05). Hemodynamic stability was superior in the E-group during immediately post-administration (T4) to skin incision (T8), with higher MAP at T6-T10 (P<0.05). Sensory/motor block onset and duration showed no intergroup differences (P>0.05). Adverse events (dizziness, nausea) were comparable, with one transient hallucination in the E-group.

Conclusion: Patients undergoing arthroscopic rotator cuff repair under combined single-shot interscalene brachial plexus block and general anesthesia exhibit a rebound pain incidence of approximately 25%. Intravenous administration of esketamine (0.5 mg/kg bolus followed by continuous infusion at 0.25 mg/kg/h) during the operation failed to significantly reduce the incidence of rebound pain post-block (P>0.05). However, it demonstrated significant reductions in pain scores at 8h, 12h, and 24h postoperatively (P<0.05), with enhanced hemodynamic stability observed from anesthetic induction to pre-incision periods. No severe adverse events were reported.