The tragic death of 9-year-old Silvanna Moreno, a third-grade student from Southern California, has been attributed to a rare medical condition known as methemoglobinemia, according to an autopsy report released by the San Diego County Medical Examiner’s Office.

Silvanna passed away on March 18, just hours after undergoing a dental procedure at Dreamtime Dentistry in Vista, California. The young girl had been given nitrous oxide—commonly known as laughing gas—as part of her anesthesia during the surgery. The report concluded that her death was caused by methemoglobinemia in the context of the recent nitrous oxide administration.

Methemoglobinemia occurs when an abnormal amount of methemoglobin—a form of hemoglobin—is produced, which can prevent oxygen from being properly delivered to the body’s tissues. In severe cases, it can lead to life-threatening oxygen deprivation.

Silvanna had first complained of tooth pain back in October 2024 and was eventually referred to Dreamtime Dentistry for treatment. Her procedure was scheduled for March. The day before the surgery, she had a mild fever that subsided after taking children’s Tylenol. On the morning of the procedure, she mentioned having a headache, though she didn’t appear distressed.

At 10 a.m., Silvanna was placed under anesthesia for what would be a three-hour procedure. According to the autopsy, she appeared to recover from the anesthesia, was monitored, and then discharged from the office.

But something didn’t feel right.

On the ride home, her family noticed she seemed groggy and “out of it.” She was snoring heavily and, although initially able to open her eyes and stand, her condition soon worsened.

Back at home, Silvanna was carried inside and continued sleeping. Her family became alarmed when her breathing slowed and her snoring faded. Her grandmother checked her heart rate twice. After the second reading, Silvanna remained unresponsive. At 4:46 p.m.—roughly six hours after she was given anesthesia—her family called 911.

The emergency dispatcher guided her grandmother through chest compressions as they waited for help to arrive.

Silvanna was rushed to Rady Children’s Hospital, but by the time she arrived, her heart had already stopped. Despite life-saving efforts, she was pronounced dead at 5:44 p.m.

Dreamtime Dentistry has not publicly responded to the autopsy findings. In a statement released earlier, Dr. Ryan Watkins, who operates the clinic, expressed deep sorrow over Silvanna’s passing.

“We are deeply saddened by the tragic passing of our young patient, which occurred several hours after her completed dental procedure,” the statement read. The clinic noted that Silvanna had been closely monitored during the procedure by a dentist anesthesiologist with more than 20 years of experience, and that she had been discharged in stable condition.

“Our hearts break for the family during this unimaginable time of grief,” Dr. Watkins added. “We extend our deepest condolences and remain committed to supporting the family and cooperating fully with the medical investigation.”

As Silvanna’s family grieves this devastating and unexpected loss, they are left with questions no parent should have to face—and memories of a young girl whose life was cut far too short.