The Impact of Spinal Anesthetic Dose on Length-of-Stay in Primary Total Knee Arthroplasty.

Abstract

The implementation of neuraxial anesthesia in total knee arthroplasty (TKA) has been shown to shorten hospital lengths of stay (LOS) compared to general anesthesia. Despite these advances, LOS for TKA in a hospital outpatient department (HOPD) setting remains high. We examined the association between the dose of neuraxial anesthesia and LOS in patients undergoing primary TKA. A retrospective review of internal medical records for patients who underwent primary TKA at a single institution from June 1, 2024, to December 31, 2024, was performed. Demographic data, comorbidities, surgeon, anesthesiologist details, neuraxial anesthetic details, and LOS were collected. For uniformity, only patients who received bupivacaine were included. Univariate and multivariable analyses were conducted. A total of 1,486 primary TKA patients were included in the study. The largest increase in LOS occurred at a dosage greater than 1.6 mL. Patients who received 1.6 mL or less of neuraxial bupivacaine had a six-hour shorter LOS than those who received more than 1.6 mL (P < 0.001). Multivariate regression analyses revealed that the dose of neuraxial anesthetic (β = 8.2, P = 0.03) and age (β = 0.31, P = 0.004) were predictors of increased LOS. Being a man was predictive of lower LOS (β =-6.56, P = 0.003). In this study of primary HOPD TKA, dose of bupivacaine administered for neuraxial anesthesia was a strong predictor for LOS when controlling for provider, procedural, and patient-level factors. A 0.1 mL increase in bupivacaine dosing was associated with an increase in LOS by 49 minutes, and a strong dose-response relationship was noted between anesthetic dose and LOS. This finding suggests that optimized neuraxial anesthesia protocols targeting lower anesthetic doses may be the next important frontier in expedited recovery management in HOPD TKA.