106 · DOS Abstracts Pharmacokinetics of high-dose Ropivacaine for local infiltration anesthesia in unilateral and simultaneous bilateral total knee arthroplasty Kirill Gromov, Stanislas Delyle, Nicolai Bang Foss, Lars Møller Pedersen, Christian Skovgaard Nielsen, Elodie Lamy, Anders Troelsen, Saik Urien, Henrik Husted Department of Orthopaedic Surgery, Hvidovre Hospital; Plateforme de Spectrométrie, Université de Versailles Saint-Quentin-en-Yvelines; Department of Anaesthesiology , Hvidovre Hospital Background: Ropivacaine is commonly used in local infiltration anesthesia (LIA) as pain management following total knee arthroplasty (TKA). Systemic toxic thresholds of 4300 ng/mL and 560 ng/mL for total and free plasma Ropivacaine, respectively, have been suggested. Although considered safe, no studies evaluate pharmacokinetic properties and serum concentration of high dose Ropivacaine infiltration in unilateral TKA (uTKA) and bilateral simultaneous TKA (SBTKA). Purpose / Aimof Study: The purpose of this study was to describe Ropivacaine concentrations in patients undergoing uTKA and SBTKA receiving LIA with high dose Ropivacain. Materials and Methods: 16 unilateral and 15 SBTKA patients were included. All patients were operated in a fast-track setup without use of drains or tourni- quet. Standard LIA technique was used with 200mL 0.2% Ropivacaine (400mg) injected periarticular in each knee. Free and bound serum concentrations of Ropivacaine was measured at 9 and 12 time points within 24 hours after first injection for uTKA and SBTKA, respectively, using liquid chronomatography mass spectrometry. Findings / Results: Mean peak free Ropivacaine concentration was 30 ng/mL and 95ng /mL for uTKA and SBTKA, respectively. Mean peak bound Ropivacaine concentration was 756 ng/mL and 1695 ng/mL for uTKA and SBTKA, respec- tively. Peak concentration for both free and bound Ropivacaine was reached between 2 and 4 hours after first injection both for uTKA and SBTKA. There was no difference in the proportion of free Ropivacaine between unilateral TKA and BSTKA at any time points. Conclusions: Peak free and peak bound Ropivacaine concentrations stayed way below previously proposed toxic thresholds in patients undergoing uTKA as well as SBTKA receiving LIA with high dose Ropivacaine 47.