The preventive efficacy of lipid emulsion on the occurrence of local anesthetic systemic toxicity in patients receiving local infiltration analgesia for total joint arthroplasty.

Background: Motor-sparing local infiltration analgesia (LIA) enhances recovery after total hip arthroplasty (THA) and total knee arthroplasty (TKA). However, LIA can induce local anesthetic systemic toxicity (LAST), sometimes necessitating rescue lipid emulsion therapy. Our institute initiated a pilot study to pretreat patients with lipid emulsion (SMOFlipid^®) to test its efficacy in mitigating LIA-induced LAST events.

Methods: This retrospective study enrolled 1,621 adult patients who received LIA with bupivacaine (2-3 mg/kg, maximum 300 mg) for unilateral primary THA or TKA under general anesthesia between January 2020 and April 2022. A total of 439 patients received lipid pretreatment, while 1,182 did not. Demographics, surgical and anesthesia profiles, along with LAST events affecting the neurological, cardiovascular, and respiratory systems, were compared after propensity score matching for age, sex, body mass index (BMI), and surgery type.

Results: The incidence of severe LAST events requiring rescue lipid emulsion slightly decreased after lipid pretreatment (from 2.54 to 2.28 per 1000). Lipid pretreatment significantly reduced the incidence of bradycardia and new-onset arrhythmia (odds ratio: 0.13, adjusted p-value: 0.024) but increased postoperative opioid requirement (odds ratio: 1.71, adjusted p-value: 0.032) after Benjamini-Hochberg correction for multiplicity.

Conclusions: The efficacy of lipid pretreatment (SMOFlipid^® 1.5 ml/kg, maximum 100 ml) in mitigating LIA-induced LAST remains controversial. While lipid pretreatment reduced the incidence of new-onset arrhythmia, it showed no clear benefits for neurologic and respiratory outcomes. Additionally, lipid pretreatment might hinder postoperative recovery by increasing the need for rescue opioid analgesia. Further prospective pharmacokinetic studies are required to assess plasma bupivacaine concentrations following LIA and lipid pretreatment, examine their relationship to LAST events, and establish the efficacy and safety of lipid pretreatment.