Outcomes of Low-Dose 2% Mepivacaine Spinal for Total Hip and Knee Arthroplasty in an Ambulatory Surgery Center Setting.

Abstract

Background: Optimizing anesthetic duration enhances recovery and efficiency in total joint arthroplasty (TJA). Spinal anesthesia with 2% mepivacaine offers a rapid onset and shorter duration, but optimal dosing strategies remain unclear. We examined (1) the relationship between time to motor function recovery and dose of 2% mepivacaine, (2) procedure- and patient-specific factors associated with differences in motor function recovery and postoperative pain, and (3) the incidence of transient neurological symptoms (TNS), postoperative urinary retention (POUR), and other side effects at various doses.

Methods: This prospective observational study enrolled 212 patients undergoing primary TJA at a single ambulatory surgery center between September 2024 and January 2025. The mepivacaine dose was based on anticipated surgical duration, not on height and weight. The primary outcome, time to motor function recovery (defined as initiation of spinal anesthesia to achievement of Bromage 0),was assessed every 10 minutes upon arrival in the post-anesthesia care unit (PACU). Secondary outcome measures included the incidence of POUR, TNS, pain scores, perioperative durations, milestone achievement, drug administration, and adverse anesthesia effects.

Results: There was a strong positive correlation between dose and motor recovery time (R² = 0.954, P<0.001). Higher doses (1.7 mL) resulted in longer recovery times (99.8 ± 19.4 minutes) than lower doses (1.0 mL, 60.1 ± 7.2 minutes). Multivariate stepwise linear regression analyses revealed that age (β = 0.29, P = 0.011) and weight (β = -0.07, P = 0.007) were significantly associated with recovery time. The NRS pain at discharge was not associated with dose (P = 0.934) or spinal level (P = 0.620). There were no POUR and three cases of TNS were observed.

Conclusion: Basing the spinal mepivacaine dose on anticipated surgical time, rather than solely on demographic factors, appears to be safe and effective in optimizing motor function recovery without increasing adverse events.