VISTA -- A woman who authorities said deliberately mixed drain cleaner with her toddler's apple juice pleaded not guilty Tuesday to aggravated mayhem, a charge that could send her to prison for life if she is convicted.

Christina Noel Howell's son suffered internal damage so severe he risks choking every time he drinks water, according to the child's doctor, who testified at a key pretrial hearing for Howell on Tuesday.

The accusations against Howell, 22, have qualities of what is commonly known as "Munchausen by proxy," a form of child abuse in which a caregiver, usually the mother, falsely reports that a child is ill or actually causes illness to the child.

That the child drank poison twice in four days was an accident, the child's mother reportedly told authorities. Serving him the poison was deliberate, Deputy District Attorney Keith Watanabe said.

The prosecutor contends Howell poisoned her then-22-month-old son last May, possibly to get attention from the child's father, Christopher Daly, a tow-truck driver who testified that he was at work when the child fell ill.

"This is one of the most appalling cases I have ever seen," Watanabe said during a break in the hearing. "The very person sworn to protect and care for (the child) is the person who was poisoning him."

Howell's attorney, Karsten Boone, declined comment.

A week before the child was first poisoned, Howell, her two young sons and their father had moved to Warner Springs from Temecula. Before that, the couple had lived in Poway and Rancho Penasquitos.

Howell was in a Vista courtroom for her preliminary hearing, at the end of which Superior Court Judge Timothy Casserly will decide if enough evidence exists to send Howell on to face trial. Testimony is expected to wrap up Wednesday morning.

In addition to the mayhem charge, which prosecutors added Tuesday, Howell has pleaded not guilty to two counts of child abuse and two counts of poisoning.

Three times over the course of four days last spring, Howell called 911 to report that her son was sick, according to court testimony.

And two of those times -- on May 25 and again on May 28 -- emergency workers flew him by helicopter to Rady Children's Hospital from his family's mobile home in remote Warner Springs.

The first time, Howell said the child had unscrewed a cap on a bottle of bathroom cleaner and drank it, consuming as much as 32 ounces, according to volunteer firefighter Adam Knight, who responded to Howell's 911 call.

The toddler had caustic burns on his face, according to his pediatrician, Jennifer Davis. But, she said, an endoscopy revealed no internal damage.

Four days later, the child was back in the hospital. And this time, testing revealed internal injuries so severe, tissue was peeling off inside his body, she said.

Watanabe said the mother told authorities that, on that occasion, she had poured drain cleaner into the child's sippy cup so she could dip a toothbrush into it and clean a toilet. She said she forgot the cleaner was in the cup when she later topped it off with apple juice and handed it to the child.

Davis said the child may never recover the ability to drink thin liquids. And, she said, he suffered internal damage so severe, he has a thousand times greater risk for developing cancer.

Davis, who is a member of a team of caregivers at Children's Hospital specializing in child abuse cases, said she and other doctors discussed the possibility that the child's case was Munchausen by proxy.

However, she testified, that is a dated term that takes into account the caregiver's motive, such as seeking attention. She said she and her colleagues prefer to use the term "pediatric condition falsification," which essentially encompasses the same behavior on the part of the caregiver, but does not take into account the caregiver's motive.

Davis testified she was aware of Howell because, in the months leading to the poisoning, Howell had taken another son to the hospital 13 times before he reached 8 months old. Although Howell reportedly claimed the infant had been vomiting and displaying other symptoms, doctors did not observe anything wrong with the younger child, according to testimony.

Howell has not been charged with wrongdoing against the younger son.

Both children are in foster care, according to testimony.

Contact staff writer Teri Figueroa at (760) 740-5442 or tfigueroa@nctimes.com.