Updated

A woman poisoned her infant son by repeatedly injecting salt water into his feeding tube at hospitals in Tennessee and Pittsburgh in what she claimed were attempts to hasten the death of a suffering child, authorities said Wednesday.

Four-month-old Noah King is in critical condition with sodium poisoning at Children's Hospital of Pittsburgh, and police said they believe the baby's medical problems were caused entirely by his mother.

Amber Brewington, 21, was charged with attempted homicide and police said she told investigators she had injected her son with salt water five or six times, and that she had severe postpartum depression.

A hospital worker called police late Tuesday after a nurse reported seeing Brewington disconnect the boy's feeding tube. Brewington was carrying a pink camouflage backpack with a container of Morton salt, two bottles filled with salt water and a syringe, police said.

Noah had been a patient at Vanderbilt University Medical Center in Nashville, Tenn., where he had suffered unexplained seizures and possible brain damage, the mother told police.

Vanderbilt hospital spokesman John Howser said Noah was treated there for a documented disease and was transferred to the Pittsburgh hospital due to its expertise in treating the symptoms he was showing. He declined to discuss the boy's care in more detail.

Noah arrived at Children's Hospital of Pittsburgh on July 9. Upon arrival, he had one of the highest recorded levels of sodium, even for an adult, according to a Pittsburgh police affidavit.

Brewington admitted giving Noah another syringe of salt water on Sunday, though she denied she was trying to do it again when she was caught by the nurse Tuesday, police said.

Pittsburgh Police Cmdr. Thomas Stangrecki, however, said Wednesday: "We believe last night was another attempt to deliver more salt water or sodium to her child."

Too much sodium can cause neurological problems and, at its most severe, can cause death. Officials at the Pittsburgh hospital wouldn't discuss specifics of Noah's condition.

Investigators believe all Noah King's illnesses were "related to what she's done," Stangrecki said. "But we have to follow up with all the medical facilities that he's been at ... and try to make that determination of whether he was sick as part of an illness or from ingesting sodium."

Brewington, of Duck River, Tenn., also was charged with aggravated assault and endangering the welfare of a child. She was ordered held on $50,000 bail at an arraignment Wednesday. Police didn't whether she had an attorney.

The boy's father has been questioned, but is not suspected of wrongdoing and faces no charges, Stangrecki said.

Brewington's two other children are being cared for by a relative, said Rob Johnson, a spokesman for the Tennessee Department of Children's Services.