The purpose of the study is to measure the blood levels of the medicine called ropivacaine (local anesthetic) used to manage pain. Ropivacaine is a widely used medication and is not the subject of this study, but the investigators are studying how much of the drug can be found in the patient's blood, known as the blood level, of this medicine. Too much ropivacaine in a patient's blood can lead to local anesthetic toxicity. Once the nerve catheter is removed, local anesthetic toxicity is no longer a potential problem. However, there is little data on what ropivacaine blood levels are after having the catheter in for a long period of time(up to one month).