Joan Rivers died of complications from low blood oxygen during a routine medical procedure to assess voice changes and reflux she underwent at a Manhattan clinic over the summer, the medical examiner's office said Thursday.
The medical examiner said Rivers suffered brain damage when her oxygen supply was cut off and classified the legendary comedian's death as a "therapeutic complication," meaning it resulted from a "predictable complication of medical therapy" -- or a known risk of the procedure.
The findings come nearly two months after Rivers went into hypoxic arrest, which is when the brain lacks oxygen, while undergoing the procedure at Yorkville Endoscopy on 93rd Street Aug. 28.
The 81-year-old Rivers was taken to the hospital, where she was put on life support. She died Sept. 4.
According to the medical examiner, Rivers was undergoing a largyngoscopy -- a medical procedure used to obtain a view of the vocal folds and the glottis -- and upper gastrointestinal endoscopy, which uses a flexible tube with a light to see the lining of the upper GI tract, while being evaluated for voice changes and gastroesophageal reflux disease, when she went into hypoxic arrest.
Rivers was being sedated by the drug propofol during the procedure. A plastic surgeon not connected to the Rivers case said hypoxia is a potential side effect of the drug.
NBC News' Dr. Nancy Snyderman said the type of procedure Rivers was undergoing can only be done in a medical office while the patient is awake or under general anesthesia in a hospital operating room.
No one at Yorkville Endoscopy picked up the phone or answered the office door when NBC 4 New York rang seeking comment on the medical examiner's findings.
In an email, a spokesperson for the facility wrote, "HIPAA laws prevent us from disclosing any information regarding patients."
Rivers' daughter and TV partner, Melissa Rivers, said in a statement after the report was released that, "We continue to be saddened by our tragic loss and grateful for the enormous outpouring of love and support from around the world."
Shortly after Rivers died, a leading gastroenterologist at the clinic where she was being treated stepped down as medical director of the facility.
Yorkville Endoscopy is accredited by the the American Association for Accreditation of Ambulatory Surgery Facilities. The association said it was investigating the facility's accreditation.
The state health department, which had been investigating the clinic, said Thursday it had completed the probe and referred questions to the Federal Centers for Medicare and Medicaid Services. The center could not immediately be reached.