A South Florida federal grand jury has charged Martin County resident Catherine Shannon Dunton, 54, with tampering with vials of liquid fentanyl at an outpatient surgery center where she worked as a licensed registered nurse. Medical providers use a liquid form of fentanyl — fentanyl citrate — to keep patients from moving during surgery and relieve their pain. According to the indictment, while working as a nurse at a Martin County outpatient surgery center, Dunton removed liquid fentanyl from vials, refilled them with saline, and returned the adulterated vials to their location for use during surgeries. If convicted, Dunton faces up to 10 years in prison.