Legendary comedienne Joan Rivers remains hospitalized after going into cardiac arrest yesterday. The 81-year-old, who is at Mount Sinai Hospital, was put in a medically-induced coma.

Rivers had been undergoing either a "routine endoscopy" or a procedure to look at her throat at Yorkville Endoscopy.

Her daughter Melissa flew from L.A. yesterday to be with her and released a statement, "I want to thank everyone for the overwhelming love and support for my mother. She is resting comfortably and is with our family. We ask that you continue to keep her in your thoughts and prayers."

A family source told the Daily News, "We are scared. This is not looking good." The News adds, "Rivers, who was in critical condition late Thursday, will remain in a coma until the weekend, when doctors will discuss with her daughter the damage caused when her mother fell unconscious during a routine visit. 'They don’t know how long she was starved of oxygen,' a source said."

According to WCBS 2, "CBS 2’s Dr. Max Gomez said even if Rivers’ throat procedure was promised to be routine and outpatient, risks of serious complications are always present. 'There could be heart arrhythmias. Breathing can stop. You never know,' Gomez said. 'And also, the elderly tend to metabolize medications a little bit differently.'"

Rivers had performed at a Manhattan club on Wednesday; attendee Shade Rupe said,

"She did a joke onstage, she goes, ‘I’m 81 — I could go at any moment.'

The family source told the News, "She would want us all to laugh. But at the moment, we are all praying."