Plasma Pharmacokinetics of Ropivacaine in Patients Undergoing Fascia Iliaca Compartment Block

Background: Fascial plane block (FPB) has gained increasing clinical attention for its favorable safety and operational simplicity, yet its pharmacokinetic profiles and the associated risk of local anesthetic systemic toxicity (LAST) remain inadequately elucidated in clinical practice. Methods: A sample size calculation was performed based on the single-sample proportion formula, with a preset expected non-occurrence rate of LAST of 90%, a margin of error of 10%, and a 95% confidence level, determining a minimum sample size of 14 patients. A retrospective analysis was conducted on 14 patients with hip fracture undergoing total hip arthroplasty (THA) who received ultrasound-guided fascia iliaca compartment block (FICB) with 30 mL of 0.33% ropivacaine (100 mg) from July to September 2024. Plasma ropivacaine concentrations were measured at serial time points via high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS, Agilent 1290-6470, USA), and block-related adverse events were closely monitored. Results: No cases of LAST were observed in all patients. The mean peak plasma concentration (Cmax) of ropivacaine was 0.88±1.13 μg/mL, with a median time to peak concentration (Tmax) of 15 (interquartile range, 6–40) minutes; individual Cmax values ranged from 0.22 to 4.63 μg/mL. Statistical analysis revealed a significant negative correlation between Cmax and body mass index (BMI) (P<0.05), while Tmax showed no significant correlation with clinical characteristics including age and BMI (P>0.05). Conclusion: Ultrasound-guided FICB with 30 mL of 0.33% ropivacaine (100 mg) demonstrates good clinical safety in patients undergoing THA. Marked individual variability exists in plasma ropivacaine concentrations, and Cmax is negatively correlated with patient BMI.