Joan Rivers' Cause of Death Revealed

— -- Joan Rivers died in a New York City hospital Sept. 4 at the age of 81. Now, there are some answers for what happened.

Rivers was sedated with propofol before she died of low blood oxygen during a procedure to treat voice changes and acid reflux, according to the New York City medical examiner.

Rivers lacked sufficient oxygen to her brain for a prolonged period of time, which caused brain damage, the medical examiner said. Her heart had stopped after she was sedated with propofol and undergoing procedures to examine her condition.

Joan Rivers Dies at 81

5 Things You Never Knew About Joan Rivers

Joan Rivers' Doctor's Office, Yorkville Endoscopy, Under Investigation - But Wrongdoing Not Suspected

The medical examiner’s office said it found no obvious medical error and that the manner of death was “therapeutic complication,” indicating that death is an accepted possibility of the procedure she was undergoing.

Her daughter, Melissa Rivers, told ABC News, "We continue to be saddened by our tragic loss and grateful for the enormous outpouring of love and support from around the world. We have no further comment at this time."

A person briefed on the Rivers investigation said an autopsy was not performed on Joan Rivers at the instruction of the family and in accordance with Jewish law. Instead, the report was based on a noninvasive physical examination and a thorough review of her charts from Yorkville Endoscopy, where she was undergoing her procedure, as well as her medical history.

As a result, the report from the medical examiner's office does not explain what caused the sudden lack of oxygen. No additional information will be released by the Office of the Chief Medical Examiner, citing New York state law.

Rivers was being treated at Yorkville Endoscopy in Manhattan Aug. 28 when she suffered cardiac arrest. She was taken to a nearby hospital, where she arrived unconscious and was kept sedated by her doctors.

Her daughter confirmed a few days later that her mother was on life support.

The comic legend died "surrounded by family and close friends," Melissa Rivers said.

"My mother’s greatest joy in life was to make people laugh," she said in a statement. "Although that is difficult to do right now, I know her final wish would be that we return to laughing soon."

Meanwhile, the New York State Health Department recently completed its "full investigation" of the clinic where Rivers was being treated, according to a DOH representative, and results will be released soon. A source said initially there was no suspicion of wrongdoing and the investigation was routine.