A 9-year-old girl died after a dental surgery. Now we know why

The death of a 9-year-old girl who became unresponsive after dental surgery in San Diego County has been ruled an accident resulting from a rare blood disorder, according to autopsy report by the San Diego County Medical Examiner‘s Office.

Silvanna Moreno died from a disorder called methemoglobinemia that could have been triggered by the administration of nitrous oxide and other commonly used anesthetic medications during her dental surgery on March 18, the medical examiner said.

Methemoglobinemia is a rare blood disorder which disrupts how iron in the hemoglobin can deliver oxygen to cells and tissue in the body.

It’s extremely rare for a person to be born with the disorder — there isn’t an exact number of affected people due to its rarity. Experts who have studied the condition say it can, more commonly, be developed by an unusual confluence of events involving the exposure to medication, which may have happened in the case of Moreno.

It’s not clear if Moreno had the congenital form of methemoglobinemia, meaning present at birth, or a form triggered by exposure to certain medications.

The disorder leads to symptoms such as shortness of breath, fatigue and cyanosis, or bluish discoloration of the skin, said Dr. Michael Levine of UCLA Health.

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“Sometimes people have a defect in that system and they get congenital methemoglobinemian as a result,” said Dr. Gentry Wilkerson, associate professor at the University of Maryland School of Medicine who has authored a study on the condition and ways to treat it. “It‘s so rare, I would be shocked if I ever saw it in my career.”

The San Diego Police Department’s child abuse unit announced in April that it was investigating the girl’s death but the department said Friday it has ceased its investigation and closed the case, said Lt. Travis Easter.

Dreamtime Dentistry, the Vista, Calif., facility where Moreno underwent surgery, responded to the medical examiner’s report by saying the death was “not due to dosage but instead due to her rare but undiagnosed/undetected medical condition.” The dentistry office also said there were no clear signs before the surgery that she had this condition.

“A common cause of exposure that can lead to methemoglobinemia is dental procedures because one of the medicines that they’ll give for patients that have dental pain is benzocaine,” Wilkerson said.

Benzocaine was not listed in the medical examiner’s report as one of the medications administered to Moreno.

Wilkerson said dental procedures are generally very safe. But in other cases, “it’s a medication dose dependent effect where a person can take an excess of quantity or an excess amount of the drug and then subsequently develop methemoglobinemia,” Levine said.

Moreno was referred to Dreamtime Dentistry after complaining about a toothache four months prior, according to the autopsy reviewed by The Times.

The dental office accepted the referral because it offered Moreno “treatment under general anesthesia due to her young age and acute situational anxiety,” the facility stated.

A day before her March 18 surgery, Moreno’s autopsy said that she had a fever but her symptoms resolved after being given children’s Tylenol.

Representatives for Dreamtime Dentistry told The Times they were not aware of her fever and noted that Moreno’s mother, “completed and signed a pre-operative check-in form indicating ‘No’ when asked if the patient was sick.”

The pre-op evaluation included a thorough review of Moreno’s medical and dental history, assessment of vital signs, a physical examination including heart, lung sounds and airway evaluation, among other procedures, according to a statement from Dreamtime Dentistry.

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“All medications were administered according to manufacturer guidelines based on Moreno’s age and weight,” according to the statement from the facility.

Throughout the procedure, anesthesiologist Dr. Ryan Watkins observed Moreno and noted no complications, the dental office stated. Once the procedure was completed, the child was monitored in the facility’s recovery area until she awoke with stable vital signs.

After the procedure, she was discharged into the care of her mother and sent home, according to the County of San Diego Medical Examiner’s Office.

Moreno fell asleep on the car ride home, and when she arrived home she stayed asleep and was transitioned into her bed, according to the medical examiner’s office. Her family checked on her throughout the day and called 911 when it was discovered later that she was unresponsive.

First responders transported Moreno to Rady Children’s Hospital while performing life saving measures.

When the child arrived at the hospital medical staff assumed life saving measures to no avail and she was pronounced dead, according to the medical examiner.