Joan Rivers remains in serious condition, daughter says

NEW YORK CITY (KABC) -- Joan Rivers remains in serious condition, one day after going into cardiac arrest at her doctor's office in New York's Upper East Side.

The 81-year-old has been unconscious since she arrived at Mount Sinai Hospital in New York City Thursday morning, a source familiar with the situation told ABC News.

Doctors are intentionally keeping her sedated and under close supervision until they are more comfortable with her condition, the source said.

Rivers was reportedly undergoing a minor throat surgery when her heart stopped.

Her daughter, Melissa Rivers, issued a statement Friday saying her mother was "receiving the best treatment and care possible."

"My mother would be so touched by the tributes and prayers that we have received from around the world," Melissa Rivers said. "Her condition remains serious ... We ask that you continue to keep her in your thoughts as we pray for her recovery."

Rivers co-hosts the E! TV show, "Fashion Police," and continues to do stand-up comedy. Rivers was scheduled to perform Friday in New Jersey.

That show has since been postponed. According to Ticketmaster, she has seven shows planned across the U.S. for November.