A nine-year-old was left dead after a freak accident occurred while she was at a routine dentist appointment.
Silvanna Moreno, 9, from San Diego, California, was at the dentist getting a root canal and several cavities filled. There were no complications and afterward Moreno was moved to the recovery room in a wheelchair before being taken to her mother’s car.
On the drive home she was described as ‘out of it’, and fell asleep snoring loudly. She was taken to her bedroom, but then her snoring slowed and began to quieten — prompting her mother to call 911.
She was rushed to the hospital after her heart stopped, reports said, where doctors tried to resuscitate her without success.
The San Diego Medical Examiner’s Office has now discovered in a report, viewed by DailyMail.com, that she was suffering from methemoglobinemia — a condition in which blood cannot carry adequate oxygen through the body.
The condition can be genetic, but can also be triggered by prolonged exposure to nitrous oxide, known as laughing gas, which is often used in dental procedures for mild sedation and to reduce anxiety.
Nitrous oxide normally diffuses directly into the brain after being breathed in through the nose, but can also enter the blood where it can bind to hemoglobin, the protein that carries oxygen, and leave it unable to carry out its function.
Moreno was receiving nitrous oxide during her appointment but it’s not known if she had been previously diagnosed methemoglobinemia — which estimates suggest may affect up to one in 3,000 Americans.
Silvanna Moreno (pictured), 9, died after having dental surgery under anesthesia at Dreamtime Dentistry in March this year
Warning signs of methemoglobinemia caused by nitrous oxide exposure can appear in minutes to hours later, and include a bluish tinge to the lips, difficulty breathing and struggling to stay awake.
No foul play is suspected in the girl’s death, which was stated as methemoglobinemia in the setting of recent nitrous oxide administration and ruled an accident by the medical examiner. There is no suspicion that anyone at the dentist’s office acted improperly.
Read More
Young mum died after making a deadly mistake while doing laughing gas, inquest hears
In methemoglobinemia, blood cells contain a higher level of methemoglobin — a form of hemoglobin that cannot carry oxygen.
Normally, the blood contains about zero to two percent methemoglobin, but in methemoglobinemia these levels rise to anywhere between 15 and 70 percent.
Doctors say that levels below 20 percent generally trigger no symptoms, while levels above 70 percent can prove fatal if someone is exposed to a gas like nitrous oxide.
A 2024 study from Toxicology Reports estimates that exposure to nitrous oxide as a medical therapy is the second most common cause of methemoglobinemia — accounting for about 18 percent of cases in children and 13 percent of cases in adults among the nearly 300 cases surveyed.
The genetic form of methemoglobinemia is rare, doctors say, with there being few reliable estimates on how many people have the condition.
In Moreno’s autopsy, carried out a day after her death, examiners found her blood’s methemoglobin levels were 75 percent.
They cautioned, however, that this may have been a significantly higher figure than that when she died, saying these levels can rise significantly in the hours after death.
Dreamtime Dentistry (pictured), led by Dr. Ryan Watkins, said in a statement that the girl was awake at the time of her release
The report also notes that she received other drugs while at the dental office, which they said could also have contributed to the death.
Moreno had received a root canal, placement of crowns and fillings and extraction of teeth at Dreamtime Dentistry in Vista, run by Dr Ryan Watkins, who has 20 years of experience in the field.
In a previous incident in 2016, however — revealed by online records with the Dental Board of California — he faced disciplinary action after a patient's heart stopped beating while under anesthetic.
The individual, who has not been named, was hospitalized for two days and allegedly continued to suffer from a mild cognitive disorder for a year afterward.
Dr Watkins was placed on probation for 35 months by state dental regulators over the issue in 2020, meaning he could continue to practice — but only with enhanced observations.
In a statement, Dr Watkins told People that methemoglobinemia is 'an extremely rare condition that can occur with nitrous oxide administration'.
He insisted that Moreno 'never exhibited' any warning signs and that her oxygen saturation levels remained normal. He said he also undertook a 'thorough review' of her medical records before the procedure, which raised no concerns.
According to the practice website, Watkins (pictured) is the only dentist listed who is trained in anesthesiology. There is no evidence of wrong doing and the dentist has not been charged
He added: 'We are committed to learning from this tragic event and will implement any additional safety measures that may help prevent such occurrences in the future.
'We extend our deepest condolences to Silvanna's family and ask for continued respect for their privacy during this time of grief.'
The day before the procedure Moreno had a fever and received Tylenol, but her symptoms resolved afterward — the Medical Examiner's report also noted.
On the day of the surgery, she also complained of a headache 'without appearing distressed', her mother said.
The dental office said if staff were aware of this they would not have carried out the procedure.