Diagnostic 4 ml blood samples will be drawn from 20 liver resection patients sited with an epidural catheter for 3-5 days of bupivacaine infusion to manage their postoperative pain. Blood will be drawn by phlebotomy with standard of care blood blood-work at 4 time points: preoperatively, upon entry to the post-anesthesia care unit, 2 days postoperatively and then immediately before discontinuation bupivacaine infusion. Blood will be immediately centrifuged by the hospital laboratory and plasma divided into 2 aliquots to be stored at -70 until all samples are collected- at which point they will be shipped to collaborators for analysis of AGP as well as bound and unbound bupivacaine.