The death of a 9-year-old girl just hours after a March visit to a Vista dentist was an accident and caused by a rare medical condition after she was given nitrous oxide and other medications when under anesthesia, according to the county medical examiner’s office.
Silvanna Moreno’s death on March 18 was caused by “methemoglobinemia in the setting of recent nitrous oxide istration” at the dental office, Deputy Medical Examiner Debra Berry said in a report issued last week. Methemoglobinemia is a rare blood condition that affects how red blood cells deliver oxygen to the body.
Silvanna was put under general anesthesia and underwent a three-hour procedure that involved a root canal, placement of crowns and fillings and extraction of teeth. After time in the recovery room, she was helped from a wheelchair into her mother’s car. The girl fell asleep on the drive to her San Diego home, the report said. Once there, she was carried to bed.
About 90 minutes later, her mother called 911 after she noticed her breathing was “quieting and slowing” and used a blood pressure cuff to check her heart rate, the report said. The girl was rushed to Rady Children’s Hospital, but doctors were unable to resuscitate her.
Silvanna was a third grader at Sherman Elementary School in the Sherman Heights neighborhood and had three siblings. She was described as “kind, caring, and always happy, a true friend to everyone she met” in a GoFundMe fundraiser.
Berry’s report said a “significant” contributing condition was the istration of other medications, including dexamethasone, glycopyrrolate, hydromorphone, isoflurane, ketorolac, midazolam, ondansetron, propofol and sevoflurane. “Of the anesthetic and inhalational agents istered intraoperatively, only nitrous oxide has a known association with methemoglobinemia; however, the possibility of a synergistic contribution by the combined effects of the additional drugs istered cannot be definitively excluded,” the report said.
The dental office called the listed medications “standard anesthesia drugs commonly used in pediatric dental sedation procedures.”
Experts say methemoglobinemia can be a congenital condition that may or may not cause symptoms, such as bluish-tinted skin, or can be triggered by certain chemicals or substances, including some local/topical anesthetics and antibiotics.
When asked if the patient had a congenital condition or acquired methemoglobinemia, a spokesperson for the office told the Union-Tribune the investigation did not definitively determine the “causative issue.”
The dentist anesthesiologist involved in the case said he followed pediatric dental sedation procedures and istered the proper dosage for the patient’s age and weight. “Any interactions or negative side effects were not due to dosage but instead due to her rare but undiagnosed/undetected medical condition,” Dr. Ryan Watkins said in a statement.
The day before the appointment, Silvanna had a fever. The morning of the appointment, she had a headache but did not appear “distressed,” the child’s mother told a medical examiner’s investigator.
Watkins, who owns Dreamtime Dentistry, said he was unaware his patient had a fever the day before the procedure and said if he had known of a recent fever or illness, the office would have rescheduled the procedure.
He said the patient’s temperature and breathing were monitored during the procedure, and no problems were seen. Patients experiencing methemoglobinemia typically will show abnormally low pulse oximetry readings in the 80s.
“Importantly, Silvanna never exhibited these warning signs during her procedure,” Watkins said. If they had observed any indication of methemoglobinemia, he said, “we would have immediately discontinued the procedure and transported her to the hospital for emergency treatment.”
He said his office plans to conduct a thorough internal review of the case and will implement additional safety measures if they can help prevent future occurrences.
A San Diego police spokesperson said the investigation into the death remains open.
Online records with the Dental Board of California indicate Watkins faced discipline after another patient’s heart stopped beating while under anesthesia under Watkins’ care during surgery in 2016. The patient was hospitalized for two days before being released. According to the accusation, the patient continued to suffer from mild neurocognitive disorder a year after the incident. In 2020, Watkins and the dental board reached a settlement that placed Watkins on probation for 35 months.
The medical examiner’s report has raised serious concerns among some who work with pediatric patients. They worry the finding could undermine confidence in the use of nitrous oxide, which is frequently used to manage anxiety and pain in pediatric patients.
“Nitrous oxide is extremely safe. It is the safest sedative agent that pediatric dentists have at our disposal,” said Mitchell Poiset, a San Diego dentist who is past president of the California Society of Pediatric Dentistry. “It is very effective and it is widely, widely used throughout adult and pediatric dentistry.”
Poiset said he has requested to meet with Berry to discuss the report’s findings.
“If this becomes the narrative, if this report gives the impression to parents that nitrous oxide is unsafe, and parents start refusing to use it, it is going to have a very negative impact on pediatric dentistry,” he said.
Several dentists and anesthesiologists consulted by the Union-Tribune said they had never heard of nitrous oxide leading to methemoglobinemia.
Toxicology tests showed a high level of methemoglobin detected in the girl’s blood, which was taken after she died. NMS Labs, which tested the blood, noted in its report that methemoglobin levels can begin increasing several hours following the collection of a blood specimen and warned “postmortem methemoglobin saturation levels must be interpreted with extreme caution.”
Pediatric anesthesiologist Stephen Long, who works in the Bay Area and who has lectured on anesthesia safety for the California Society of Pediatric Dentistry, said he’s concerned that people will overlook the caution about interpreting the blood test results when they hear of the child’s death. There could be “a ripple effect” of dental patients and parents of pediatric patients becoming scared of using nitrous oxide, he said.
“If you’re going to read the conclusion, you have to understand that it must be interpreted with extreme caution,” he said.
