The plasma ropivacaine samples will be assayed at the Department of Research Programs Laboratory (DRP) at WRNMMC. Once the whole blood sample has been centrifuged, the plasma will be removed with a glass pipette, placed in a storage container. The blood samples will be labeled with a non sequential serial number and will not include the time of the blood draw. This will blind the DRP laboratory to the patient's identity and timing of the blood draw.