Observation Study of the Pharmacokinetics of Adductor Canal Block

With the aging of the population, osteoarthritis of knees and hips become major orthopedic problems worldwide. Osteoarthritis of the knees and hips is associated with a significant pain problem and functional disability. Total joints replacement is the ultimate surgical procedure to deal with such problems. Multimodal analgesia, including periarticular local infiltration of analgesia (LIA), regional nerve block using adductor canal block (ACB), opioid and non-opioid have been shown to be effective in managing postoperative pain. Regional nerve block using femoral nerve block or adductor canal block (ACB) is also a well-established analgesic technique after total knee replacement. Standard bupivacaine (SB), levobupivacaine, ropivacaine were used in ACB in these studies. Whether combining ACB with periarticular LIA has the additional benefit of prolonging analgesia or with synergistic effect remains controversial, because the number of RCTs conducted is not enough. Liposomal bupivacaine (LB) may further prolong the analgesic effect of ACB, as the therapeutic levels of bupivacaine are below the toxic range and sustained for 72 hours after injection. The purpose of this study is to evaluate the safety and systemic levels of serum bupivacaine following adductor canal block using LB 66.5mg in patients undergoing TKA with LIA over a 72-hour period. This also serves as a pilot study to determine the dose and timing of blood taking for serum bupivacaine level of a previously IRB approved study - "Comparing the efficacy of combining periarticular local infiltration of analgesia and adductor canal block using liposomal bupivacaine and standard bupivacaine- A prospective randomized controlled trial".