The cause of death for a 9-year-old who received anesthesia for a dental procedure was disclosed

A 9-year-old girl who had anesthesia for a dental operation earlier this year has had her cause of death disclosed.

According to a recent autopsy report from the San Diego County Medical Examiner’s Office (SDCME) that PEOPLE was able to obtain, Silvanna Moreno, a third-grader from Southern California, passed away on March 18 hours following surgery at Dreamtime Dentistry in Vista, California.

Given the recent nitrous oxide treatment, methemoglobinemia was indicated as Silvanna’s cause of death. Methemoglobinemia can happen when too much nitrous oxide enters a person’s hemoglobin, which is the protein in red blood cells that carries oxygen to the tissues. This results in hypoxia, which means that tissues don’t get enough oxygen. The autopsy report states that one of the anesthetics Silvanna received during the operation was nitrous oxide.

According to Silvanna’s autopsy, she complained of dental ache in October and underwent surgery. After referring her, Dreamtime Dentistry scheduled a treatment for March.

According to the autopsy report, she had a fever the day before, but after taking children’s Tylenol, her symptoms went away. According to the report, she complained of a headache “without appearing distressed” on the day of her surgery. At 10 a.m., she was put under anesthesia for a three-hour procedure.

According to the autopsy, she was sent to a recovery room after waking up and then released. She was said to be “out of it” on the trip home and subsequently started snoring loudly, but at first she was able to stand and open her eyes.

According to the autopsy, Silvanna was brought inside her house after arriving and slept for about ninety minutes before her snoring became notably slower and quieter. After then, her grandmother took two different heart rate readings. At 4:46 p.m. local time, approximately six hours after she had received anesthesia, 911 was contacted because she was still not responding after the second reading.

While they awaited the arrival of emergency responders, a dispatcher gave the grandmother instructions to perform chest compressions.

When she was brought to the emergency room of Rady Children’s Hospital, the Cleveland Clinic states that she was in asystole, a condition in which the heart’s electrical system malfunctions and the heart stops beating. Despite receiving multiple life-saving measures, Silvanna was declared dead at 5:44 p.m. Dr. Ryan Watkins recently told PEOPLE that methemoglobinemia is a “extremely rare condition that can occur with nitrous oxide administration” and that patients usually have “pulse oximetry readings that show abnormally low levels in the 80s” when they have it.

Silvanna “never exhibited” any warning indications during her treatment, according to Watkins, and her oxygen saturation levels remained normal during her recuperation. They conducted a “thorough review of her medical and dental history” prior to the treatment, and Watkins stated that they “maintained our standard of care with continuous monitoring by me” throughout.

Although Silvanna’s death was determined to be an accident, Watkins continued, Dreamtime Dentistry is carrying out a comprehensive internal investigation. “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 said. “We extend our deepest condolences to Silvanna’s family and ask for continued respect for their privacy during this time of grief.”