Serum bupivacaine levels after peri-articular injection of liposomal bupivacaine (Exparelâ) mixed with 0.25% bupivacaine HCl
Pain control is an important part of post-surgical recovery after total knee arthroplasty. A relatively new technique to reduce post-operative pain is a peri-articular injection of a liposomal and plain bupivacaine mixture during total knee arthroplasty.
At the University of Utah, current practice is to inject a 100ml solution of 266 mg liposomal bupivacaine (Exparelâ), 125 mg bupivacaine HCl, 1:300,000 epinephrine, and saline.
When this mixture does not achieve adequate pain relief, peripheral nerve blocks are requested as a rescue technique. Because of the unique properties of liposomal bupivacaine, the FDA package insert for Exparelâ recommends against using additional bupivacaine within 96 hours after administration of Exparelâ due to concern for the potential of local anesthetic systemic toxicity.
Due to very low levels of serum bupivacaine observed in the early minutes after injection and the lack of a peak at 24 hours, we modified the study to eliminate blood draws at 5 and 10 minutes and added draws at 30 and 48 hours.
Serum bupivacaine levels remained below accepted toxic levels within the first 48 hours with no symptoms of local anesthetic toxicity.
Serum bupivacaine levels continued to rise at 48 hours, therefore we did not capture peak serum concentration.
Data at 48 hours was only completed in 15 subjects due to discharge before 48 hours and patient dropout.
Further studies are needed to characterize serum bupivacaine concentration after 48 hours.