Effects of age factors on pharmacokinetics of ropivacaine during combined lumbar plexus-sciatic nerve block

Abstract

Objective To evaluate the effects of age factors on the pharmacokinetics of ropivacaine during combined lumbar plexus-sciatic nerve block in patients. Methods Twenty patients of both sexes, aged ≥18 yr, weighing 50-75 kg, of American Society of Anesthesiology physical status Ⅰ or Ⅱ, scheduled for elective lower extremity surgery, were divided into 2 groups (n=10 each) according to age: young and middle-aged group (18-59 yr) and elderly group (≥ 60 yr). Combined lumbar plexus-sciatic never block was performed using an ultrasonic instrument and a nerve stimulator.Lumbar plexus block was performed with 0.5% ropivacaine 30 ml.Sciatic never block was performed with 2% lidocaine 10 ml plus 0.75% ropivacaine 10 ml.Before administration and at 5, 10, 15, 20, 30, 45, 60, 120, 180 and 360 min after administration, blood samples were collected from the radial artery for determination of the blood concentration of ropivacaine by high-performance liquid chromatography.The area under the concentration-time curve, maximum concentration (Cmax), time to Cmax, terminal elimination half-life and clearance were calculated. Results Compared with young and middle-aged group, the blood concentration of ropivacaine was significantly decreased at 5-45 min after administration, the Cmax was significantly decreased, terminal elimination half-life was significantly prolonged (P 0.05). Conclusion Age factors can affect the pharmacokinetics of ropivacaine during combined lumbar plexus-sciatic nerve block, and both absorption and metabolism of ropivacaine are slower in elderly patients than in young and middle-aged patients. Key words: Age factor; Amides; Pharmacokinetics; Lumbosacral plexus; Sciatic nerve; Neuromuscular blockade