A nurse anesthetist who worked for decades at hospitals in Pulaski and Montgomery County pleaded guilty Thursday to federal charges that he stole the medicine that was supposed to numb patients undergoing surgery.

Alvin Earl Parkes, 62, of Draper admitted in U.S. District Court in Roanoke that between July and September 2008, he removed fentanyl citrate from vials at Pulaski Community Hospital and replaced it with saline solution in an attempt to avoid detection.

A statement released after the hearing by the U.S. attorney's office said Parkes would take the fentanyl himself, self-administering it via injection in a hospital bathroom.

Fentanyl is a synthetic opioid used as an anesthetic and for treating pain. It can be habit-forming, and Parkes told U.S. District Court Judge Samuel Wilson he had been treated for addiction after his actions at the hospital were detected.

After the hearing, both Assistant U.S. Attorney Charlene Day and Parkes said no patients appeared to have been affected by Parkes' actions. Parkes said he knew that the drug was diluted and adjusted dosages accordingly.

U.S. attorney's office spokesman Brian McGinn said Parkes obtained fentanyl for himself by sometimes administering an amount that was less than had been prescribed but still enough to have a painkilling effect. He also sometimes obtained from hospital supplies a greater amount of the drug than had been prescribed, keeping the extra dosage, McGinn said.

For example, when pregnant women requested an epidural, Parkes would get twice as much fentanyl as needed, McGinn said.

Staff at the Pulaski hospital, which is run by HCA Southwest Virginia, became suspicious when Parkes began reporting a much higher rate of broken fentanyl vials. There were no witnesses to the breakages, so staff took a syringe from Parkes' cart, had it tested and discovered it didn't contain fentanyl, Day said.

Parkes began his career as an anesthetist while serving in the U.S. Air Force. Parkes said he came to Pulaski in 1979 and had worked at the hospital there ever since, except for a few years spent at Carilion New River Valley Medical Center. Carilion spokesman Eric Earnhart confirmed Parkes worked at the facility near Radford from 2003 to 2006.

Parkes gave up his registered nurse license in October, the statement from the U.S. attorney's office said.

Parkes said he had been at the Pulaski hospital so long that a sign had been hung there in his honor reading "WWED" for "What Would Earl Do?"

"That's how much I messed up," he said.

Each count of obtaining fentanyl by fraud carries a maximum sentence of four years in prison and a fine of up to $250,000, though federal sentencing guidelines likely will recommend much less.

A sentencing date has not been listed on the federal court schedule.