Pharmacokinetics of Ropivacaine in elderly Patients with combination of paravertebral nerve and lumbosacral plexus blocks for Hip Surgeries

Objective: This study is to describe the pharmacokinetics of ropivacaine in elderly patients with multiple nerve blocks for hip surgeries. Methods: : The patients aged over 65 years with ASA II-III, BMI50kg, Albumin>25g/L, and creatinine clearance>30ml/min, undergoing unilateral hip surgery were enrolled in this study. All the patients received unilateral hip surgery under combination of paravertebral nerve (T12, L1) and lumbosacral plexus block (CPLSB) with total dose of 245 mg ropivacaine. The total and free plasma concentrations of ropivacaine were measured from arterial sample using ultra-performance liquid chromatography (UPLC). Results: : A total of 40 elderly patients were investigated and analyzed in this study. No signs of LAST were found during the study. The Tmax, Cmax, and t1/2 of free ropivacaine were 23（20.25-26.75）min, 0.1701（0.1201-0.2499）microgram/ml, and 416.2（306.9-618.9）min, respectively. The concentration of free ropivacaine fluctuated significantly within 80 min and presented with multiple peaks on the concentration-time curve. Multiple linear regression analysis found that there were no relationships between Cmax of free ropivacaine and the factors including gender, age, height, weight, dose, incomplete blocks, duration of injection, blood loss, red cell transfusion, infusion fluids, surgery types, and operation time. Conclusion: The serum free concentration of 245 mg ropivacaine in elderly patients with multiple nerve blocks for hip surgery was below the assumed systemic toxic threshold of 0.46microgram/ml. However, the serum ropivacaine free concentration fluctuated significantly and was hard to predict for the first 80 min after local ropivacaine injection.