Study Measuring Total Plasma Ropivacaine Levels During Continuous Peripheral Nerve Catheter Infusion

Inclusion Criteria: * Males and females 18 years and older, capable of providing informed consent indicating awareness of the investigational nature of the study, in keeping with institutional policy * Written informed consent must be obtained from each patient prior to entering the study * Patients must be scheduled to receive a continuous peripheral nerve catheter Exclusion Criteria: * Refusal to have serial blood drawn * Contraindication for a continuous peripheral nerve catheter (allergy to local anesthetic, infection at site of injection, elevated coagulation times (international normalized ratio (INR)\>1.5, partial thromboplastin time (PTT)\>38; these values are drawn as part of routine standard of care and those values will be checked prior to initial catheter insertion), therapeutic dosing of anticoagulation medication, moderate to severe head injury and moderate to severe traumatic brain injury * Patients with a hematocrit \< 20. Complete Blood Counts (CBCs) are drawn as part of routine standard of care and will be followed by the Acute Pain Service. Although the CBCs and ropivacaine blood draws will not always coincide, we will always check the last hematocrit obtained prior to our blood draw * Severe liver or renal disease (values greater than two times normal range)