Optimizing Local Anesthetic Concentration for Continuous Femoral Nerve Blocks

This is a randomized, observer-masked, controlled study. Subjects will be patients
undergoing bilateral total knee arthroplasty (TKA). One side (left or right) will be
randomized to one of two treatment groups: a postoperative ropivacaine concentration of 0.1%
or 0.4%. The contralateral side will receive the other possible ropivacaine concentration of
0.1% or 0.4%. The basal rate and patient-controlled bolus volume will depend upon the
treatment group, but the total dose of local anesthetic is the same for each. For the
duration of the study, all patients will receive the current usual and customary analgesics
for bilateral TKA patients. All patients will receive a ropivacaine perineural infusions
initiated in the operating room and continued until at least the afternoon of postoperative
day (POD) 2, as well as oral acetaminophen, a sustained-release oral opioid; and celecoxib.
Rescue opioid and route of administration will be determined by pain severity using a
Numeric Rating Scale of 0-10, with 0 equal to no pain and 10 being the worst imaginable
pain.