A nine-year-old girl tragically passed away after a dental appointment took a fatal turn. Silvanna Moreno, from San Diego, California, was undergoing a routine root canal and cavity fillings when complications arose after the procedure.
Initially, Moreno was moved to the recovery room in a wheelchair but exhibited no immediate issues. During the ride home, her mother described her as being ‘out of it’ before she fell asleep, snoring loudly. However, when her snoring became faint, her mother alerted emergency services.
Emergency responders rushed her to a local hospital, but efforts to resuscitate her were unsuccessful after her heart stopped. According to a report from the San Diego Medical Examiner’s Office, Silvanna was suffering from methemoglobinemia, a serious condition that impairs the blood’s ability to transport oxygen throughout the body.
Methemoglobinemia can be hereditary but may also result from prolonged exposure to nitrous oxide, a common sedative used in dental procedures. While nitrous oxide typically enters the brain quickly, it can also bind to hemoglobin in the blood, rendering it ineffective in oxygen transport.
Moreno received nitrous oxide during her appointment, but it remains unclear if she had a prior diagnosis of methemoglobinemia, which affects an estimated one in 3,000 Americans. Symptoms of the condition can manifest shortly after exposure, including a bluish tint to the lips, difficulty breathing, and extreme drowsiness.
Authorities have ruled that no foul play was involved in Moreno’s death, which has been classified as an accident attributed to methemoglobinemia following recent nitrous oxide administration. The dental office staff is not suspected of any wrongdoing.
Under normal conditions, blood contains between zero and two percent methemoglobin; however, those with methemoglobinemia have levels ranging from 15 to 70 percent. Medical professionals warn that levels above 70 percent can be life-threatening, especially with exposure to nitrous oxide.
A 2024 study suggested that nitrous oxide use in medical settings is the second most common cause of methemoglobinemia, representing 18 percent of cases in children and 13 percent in adults among nearly 300 cases reviewed. The genetic form of the condition is rare, limiting reliable statistics.
An autopsy conducted the day after her death revealed that Moreno’s methemoglobin level was alarmingly high at 75 percent. However, experts caution that this reading could have escalated post-mortem.
Silvanna had received an extensive range of dental work at Dreamtime Dentistry in Vista, operated by Dr. Ryan Watkins, who has two decades of experience. The dental practice noted that Moreno was fully conscious when released. However, records from the Dental Board of California indicated that Dr. Watkins faced disciplinary measures in 2016 when another patient’s heart stopped during a procedure.
In that case, the patient was hospitalized for two days and experienced lingering cognitive effects. As a result, Dr. Watkins was placed on probation for 35 months, allowing him to continue his practice under increased scrutiny.
In a statement to People, Dr. Watkins expressed that methemoglobinemia is ‘an extremely rare condition’ and confirmed that Moreno showed no immediate warning signs. He emphasized that her oxygen saturation levels were normal and that he had thoroughly reviewed her medical history prior to the procedure.
The day before her dental work, Silvanna had a fever treated with Tylenol, but the Medical Examiner indicated that her symptoms had resolved. On the day of the surgery, she complained of a headache but did not appear distressed.
The dental office stated that had their staff been aware of her prior symptoms, the procedure would have likely been postponed.