The cause of death has been revealed for a 9-year-old girl who underwent anesthesia for a dental procedure earlier this year.
Silvanna Moreno, a Southern California third-grader, died on March 18 hours after surgery at Dreamtime Dentistry in Vista, Calif., according to a new San Diego County Medical Examiner’s Office (SDCME) autopsy report obtained by PEOPLE.
Silvanna’s cause of death was listed as methemoglobinemia in the setting of recent nitrous oxide administration.
Methemoglobinemia can occur when excessive amounts of nitrous oxide get into someone’s hemoglobin (the protein contained in red blood cells that delivers oxygen to the tissues) and cause hypoxia, so tissues do not receive enough oxygen.
Nitrous oxide was among the anesthetics Silvanna was administered during her procedure, according to the autopsy report.
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Silvanna’s autopsy states she had surgery after she complained of tooth pain in October 2024, She was referred to Dreamtime Dentistry, which booked her for a March procedure.
The day before, she had a fever but her symptoms resolved after being given children’s Tylenol, according to the autopsy report.
The day of her surgery, she complained of a headache “without appearing distressed,” according to the report. She was administered anesthesia at 10 a.m. for a three-hour procedure.
Once she woke up, she was moved to a recovery room and then discharged, the autopsy states. On the way home, she was described as being “out of it” and later was snoring heavily but was also initially able to open her eyes and stand.
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Once Silvanna arrived home, she was carried inside and remained asleep for around 90 minutes before her snoring got noticeably quieter and slower, according to the autopsy.
Her grandmother then administered two separate readings of her heart rate. After the second reading, she remained unresponsive and 911 was called at 4:46 p.m. local time — about six hours after her getting anesthesia.
A dispatcher instructed the grandmother to administer chest compressions while they waited for emergency personnel to arrive.
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She was taken to Rady Children’s Hospital Emergency Department, where she was in asystole — a condition in which the heart’s electrical system fails, causing the heart to stop pumping, according to the Cleveland Clinic.
Silvanna was administered several life-saving tactics but was pronounced dead at 5:44 p.m.
In a new statement, Dr. Ryan Watkins — a board-certified dental anesthesiologist at Dreamtime Dentistry with over 20 years of experience in pediatric anesthesia — said, in part, that methemoglobinemia is an “extremely rare condition that can occur with nitrous oxide administration,” and that typically, when patients experience this condition, their “pulse oximetry readings will show abnormally low levels in the 80s.”
Watkins insisted that Silvanna “never exhibited” any warning signs throughout the procedure and that her oxygen saturation levels continued to remain normal throughout her recovery.
Ahead of the procedure, they took a “thorough review of her medical and dental history” and Watkins said that during the procedure, they “maintained our standard of care with continuous monitoring by me.”
Watkins went on to say that while the manner of Silvanna’s death was ruled accidental, Dreamtime Dentistry is conducting a thorough internal review.
“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,” Watkins added. “We extend our deepest condolences to Silvanna’s family and ask for continued respect for their privacy during this time of grief.”
