Comparison of 10 mL 0.15% vs 20 mL 0.25% bupivacaine boluses for continuous adductor canal block in total knee arthroplasty: a randomized non-inferiority trial.

OBJECTIVES: Different concentrations and volumes of local anesthetic boluses are used for continuous adductor canal block. We hypothesized that a 10 mL 0.15% bupivacaine bolus would provide non-inferior pain relief to a 20 mL 0.25% bupivacaine bolus for continuous adductor canal block as part of comprehensive multimodal analgesia.

METHODS: 140 patients undergoing total knee arthroplasty were randomly allocated to receive either a 20 mL bolus of 0.25% bupivacaine (20/0.25 bupi group) or a 10 mL bolus of 0.15% bupivacaine (10/0.15 bupi group). Both groups received continuous adductor canal block with 0.15% bupivacaine (5 mL/hour), local infiltration analgesia, and interspace between the popliteal artery and capsule of the knee block. The primary outcomes were average knee-pain scores 6 and 12 hours postoperatively; the non-inferiority margin was a score difference of 1. Secondary outcomes included rest and movement pain scores, morphine consumption, and time to first rescue analgesia.

RESULTS: The median knee-pain scores for the 20/0.25 and 10/0.15 bupi groups were 0 (0 to 1) and 0 (0 to 2), respectively, after 6 hours and 2 (1 to 2) and 2 (1 to 3), respectively, after 12 hours. The median treatment difference (10/0.15 bupi ̶ 20/0.25 bupi) was 0 (95% CI -0.45 to 0.45) at both time points, with neither interval exceeding the non-inferiority margin. No clinical differences were observed in secondary outcomes.

DISCUSSION: A 10 mL 0.15% bupivacaine bolus in continuous adductor canal block offers comparable average knee-pain relief 6 and 12 hours after total knee arthroplasty to a 20 mL 0.25% bupivacaine bolus.

TRIAL REGISTRATION NUMBER: NCT06179628.