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The exact cause of Joan Rivers' death likely will never be determined because her daughter ruled out an autopsy. Rivers died Sept. 4. Reuters

Joan Rivers' daughter Melissa ruled out an autopsy on her mother, the New York medical examiner's office said. Radar Online reported the medical examiner's office concluded the comedian died of "anoxic encephalopathy due to hypoxic arrest during laryngoscopy and upper gastrointestinal endoscopy." Rivers had been given propofol, the same anesthetic that killed Michael Jackson.

Exactly why Rivers' suffered low blood oxygen during the procedure is unclear and the question likely never will be answered because no autopsy was performed, Radar Online said. During the Aug. 28 procedure at the Yorkville Endoscopy clinic in Manhattan, Dr. Gwen Korovin began a biopsy that had not previously been planned.

Joan Rivers, 81, died Sept. 4 at Mount Sinai Hospital where she had been rushed after she stopped breathing.

As a result of Rivers' death, Yorkville Endoscopy has been under investigation and could be closed in January unless it can correct deficiencies in meeting Centers for Medicare and Medicaid Services standards, reported.